Showing posts with label chromosomes. Show all posts
Showing posts with label chromosomes. Show all posts
Wednesday, December 17, 2008
Chromosomes
Chromosomes are organized structures of DNA and proteins that are found in cells. A chromosome is a continuous piece of DNA, which contains many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. The word chromosome comes from the Greek χρῶμα (chroma, color) and σῶμα (soma, body) due to their property of being stained very strongly by some dyes.
Chromosomes vary extensively between different organisms. The DNA molecule may be circular or linear, and can contain anything from tens of kilobase pairs to hundreds of megabase pairs. Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Furthermore, cells may contain more than one type of chromosome; for example mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.
In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called chromatin. This allows the massively-long DNA molecules to fit into the cell nucleus. The structure of chromosomes and chromatin varies through the cell cycle. Chromosomes may exist as either duplicated or unduplicated—unduplicated chromosomes are single linear strands, while duplicated chromosomes (copied during S phase) contain two copies joined by a centromere. Compaction of the duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure (pictured to the right).
"Chromosome" is a rather loosely defined term. In prokaryotes, a small circular DNA molecule may be called either a plasmid or a small chromosome. These small circular genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origins. The simplest chromosomes are found in viruses: these DNA or RNA molecules are short linear or circular chromosomes that often lack any structural proteins.
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Tuesday, December 16, 2008
Evolutionary significance of Human Chromosome 2
All apes apart from man have 24 pairs of chromosomes. There is therefore a hypothesis that the common ancestor of all great apes had 24 pairs of chromosomes and that the fusion of two of the ancestor's chromosomes created chromosome 2 in humans. The evidence for this hypothesis is very strong.
The Evidence
Evidence for fusing of two ancestral chromosomes to create human chromosome 2 and where there has been no fusion in other Great Apes is:
1) The analogous chromosomes (2p and 2q) in the non-human great apes can be shown, when laid end to end, to create an identical banding structure to the human chromosome 2.
2) The remains of the sequence that the chromosome has on its ends (the telomere) is found in the middle of human chromosome 2 where the ancestral chromosomes fused.
3) the detail of this region (pre-telomeric sequence, telomeric sequence, reversed telomeric sequence, pre-telomeric sequence) is exactly what we would expect from a fusion.
4) this telomeric region is exactly where one would expect to find it if a fusion had occurred in the middle of human chromosome 2.
5) the centromere of human chromosome 2 lines up with the chimp chromosome 2p chromosomal centromere.
6) At the place where we would expect it on the human chromosome we find the remnants of the chimp 2q centromere .
Not only is this strong evidence for a fusion event, but it is also strong evidence for common ancestry; in fact, it is hard to explain by any other mechanism.
Centromere evidence
Let us re-iterate what we find on human chromosome 2. Its centromere is at the same place as the chimpanzee chromosome 2p as determined by sequence similarity. Even more telling is the fact that on the 2q arm of the human chromosome 2 is the unmistakable remains of the original chromosome centromere of the common ancestor of human and chimp 2q chromosome, at the same position as the chimp 2q centromere (this structure in humans no longer acts as a centromere for chromosome 2.
Refered
http://www.evolutionpages.com/chromosome_2.htm
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Email me : help.me.ishan@gmail.com
The Evidence
Evidence for fusing of two ancestral chromosomes to create human chromosome 2 and where there has been no fusion in other Great Apes is:
1) The analogous chromosomes (2p and 2q) in the non-human great apes can be shown, when laid end to end, to create an identical banding structure to the human chromosome 2.
2) The remains of the sequence that the chromosome has on its ends (the telomere) is found in the middle of human chromosome 2 where the ancestral chromosomes fused.
3) the detail of this region (pre-telomeric sequence, telomeric sequence, reversed telomeric sequence, pre-telomeric sequence) is exactly what we would expect from a fusion.
4) this telomeric region is exactly where one would expect to find it if a fusion had occurred in the middle of human chromosome 2.
5) the centromere of human chromosome 2 lines up with the chimp chromosome 2p chromosomal centromere.
6) At the place where we would expect it on the human chromosome we find the remnants of the chimp 2q centromere .
Not only is this strong evidence for a fusion event, but it is also strong evidence for common ancestry; in fact, it is hard to explain by any other mechanism.
Centromere evidence
Let us re-iterate what we find on human chromosome 2. Its centromere is at the same place as the chimpanzee chromosome 2p as determined by sequence similarity. Even more telling is the fact that on the 2q arm of the human chromosome 2 is the unmistakable remains of the original chromosome centromere of the common ancestor of human and chimp 2q chromosome, at the same position as the chimp 2q centromere (this structure in humans no longer acts as a centromere for chromosome 2.
Refered
http://www.evolutionpages.com/chromosome_2.htm
Hope You Like This Post, Let me know what you feel about this blog.
Email me : help.me.ishan@gmail.com
Sunday, December 14, 2008
Chromosomes
Chromosomes are organized structures of DNA and proteins that are found in cells. A chromosome is a continuous piece of DNA, which contains many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. The word chromosome comes from the Greek χρῶμα (chroma, color) and σῶμα (soma, body) due to their property of being stained very strongly by some dyes.
Chromosomes vary extensively between different organisms. The DNA molecule may be circular or linear, and can contain anything from tens of kilobase pairs to hundreds of megabase pairs. Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Furthermore, cells may contain more than one type of chromosome; for example mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.
Blog contains more than 450 videos covering all the aspects of Biological Sciences
Chromosomes
Chromosomes are organized structures of DNA and proteins that are found in cells. A chromosome is a continuous piece of DNA, which contains many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. The word chromosome comes from the Greek χρῶμα (chroma, color) and σῶμα (soma, body) due to their property of being stained very strongly by some dyes.
Chromosomes vary extensively between different organisms. The DNA molecule may be circular or linear, and can contain anything from tens of kilobase pairs to hundreds of megabase pairs. Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Furthermore, cells may contain more than one type of chromosome; for example mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.
In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called chromatin. This allows the massively-long DNA molecules to fit into the cell nucleus. The structure of chromosomes and chromatin varies through the cell cycle. Chromosomes may exist as either duplicated or unduplicated—unduplicated chromosomes are single linear strands, while duplicated chromosomes (copied during S phase) contain two copies joined by a centromere. Compaction of the duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure (pictured to the right).
"Chromosome" is a rather loosely defined term. In prokaryotes, a small circular DNA molecule may be called either a plasmid or a small chromosome. These small circular genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origins. The simplest chromosomes are found in viruses: these DNA or RNA molecules are short linear or circular chromosomes that often lack any structural proteins.
Chromosomes vary extensively between different organisms. The DNA molecule may be circular or linear, and can contain anything from tens of kilobase pairs to hundreds of megabase pairs. Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Furthermore, cells may contain more than one type of chromosome; for example mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.
Blog contains more than 450 videos covering all the aspects of Biological Sciences
Chromosomes
Chromosomes are organized structures of DNA and proteins that are found in cells. A chromosome is a continuous piece of DNA, which contains many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. The word chromosome comes from the Greek χρῶμα (chroma, color) and σῶμα (soma, body) due to their property of being stained very strongly by some dyes.
Chromosomes vary extensively between different organisms. The DNA molecule may be circular or linear, and can contain anything from tens of kilobase pairs to hundreds of megabase pairs. Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Furthermore, cells may contain more than one type of chromosome; for example mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.
In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called chromatin. This allows the massively-long DNA molecules to fit into the cell nucleus. The structure of chromosomes and chromatin varies through the cell cycle. Chromosomes may exist as either duplicated or unduplicated—unduplicated chromosomes are single linear strands, while duplicated chromosomes (copied during S phase) contain two copies joined by a centromere. Compaction of the duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure (pictured to the right).
"Chromosome" is a rather loosely defined term. In prokaryotes, a small circular DNA molecule may be called either a plasmid or a small chromosome. These small circular genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origins. The simplest chromosomes are found in viruses: these DNA or RNA molecules are short linear or circular chromosomes that often lack any structural proteins.
Saturday, December 13, 2008
Genes and Chromosomes lecture
In today's lecture what I want to do is to look at a little bit of detail at how the connection between Genes and chromosomes was forged.
Chromosomes had not been described when Mendel lived and worked, it was only later with the advent of improved microscopes in the second part of the 19th century of biologists began to describe the structure of cells in some detail, and one of the things they noticed was the formation of dark bodies in the nucleus of cells that would appear just before cells divide and furthermore they notice that as cells were dividing these dark bodies would fall peculiar movement. What they were seeing were chromosomes and movements of these chromosomes in mitosis and meiosis.
Part 1
The significance of the movements of these chromosomes wasn't appreciated at first but then in the early 20th century two-cell biologist independently had an insight Walter Sutton and colleague observed that the highly choreographed movements of chromosomes during meiosis reduced by half number of chromosomes that would be found in gametes. When gametes joined the total number of chromosomes would come back up to its full complement. They realize that this reduction in chromosome number in gametes formation and subsequent restoration zygote formation could explain the patterns of trait transmission that Mendel had described with his laws of segregation and independent assortment.
Part 2
Part 3
In 1903 Sutton and Bovary both independently publish their ideas, which become generally known as the chromosomal theory of inheritance. in that sense they provided a hypothetical mechanism whereby chromosome movements could completely explain these two fundamental principles that Mendel had suggested.
The chromosomal theory of inheritance should seem obvious to us at this point in the course because we are to know so much about DNA learn that before but it wasn't clear then that you could establish this relationship specifically it wasn't clear how during the early part of the 20th century you could prove that genes were on chromosomes and thus prove the chromosome theory of inheritance, sutten & Bovary had suggested this connection but it was just a hypothesis. Confirmation of this hypothesis actually can be attributed to one particular scientist and a remarkable lab group and also to the particular organism, the scientist was Thomas Hunt Morgan who was a embryologist studying patterns of development working at Columbia University.
Like most biologist at the time Morgan to became interested in mechanisms of inheritance that as people began to talk again about Mendel's work .Now Morgan was particularly interested as he was studying development in mutations, and he was interested in how new mutations arose in organisms. Many geneticists at the time had begun working on organisms that had more complex patterns of trait transmission than for example the garden peas Mendel worked on including for example small mammals such as guinea pigs and mice because the way that her color patterns of these mammals would be transmitted from parent to offspring sometimes corresponded to what Mendel observed that also led to a lot of interesting exceptions that these geneticists wanted to understand .so Morgan when he got interested in genetics he set out to work on the genetics of coat color in mammals but mammals are expensive.Morgan couldn't actually raise the money to do this work Morgan's inability to get funded to work on coat color in mammals was probably one of the most fortunate grants turndowns in the history of science because it led Morgan by necessity to start working on a different model organism the Fruit fly a small little fly its scientific name is Drosophila Melagoster and commonly known as Drosophila.
As it turns out Drosophila very quickly became and remains to this day the single most important model organism used in both classical and molecular studies of genetics.From Morgan's point of view there are a lot of advantages to working on fruit flies (i) first of all their cheap and (ii)Fruit flies are also very easy to raise in the laboratory . most important in one of the reasons that supplies remain such an important model organism today(iii) they have a very short generation time adult fruit flies will develop from eggs in only a matter of days and what this means is that it's possible to observe the results of genetic crosses in a very short period time you can do a lot of process he didn't have to wait for those garden peas to growup over a matter of months within a few days you know the answer.
There were some serious problems working with fruit flies that fruit flies that you collect from the wild don't have obvious phenotypic variance. if you put out your pineapple and collect fruit flies, to a first approximation they all look the same ,that is the fruit fly didn't offer traits that Morgan could use in particular establish crosses. This seems like the major problem How you going to understand the genetics of trait transmission if there are obvious traits that you can follow in her crosses. but remember that Morgan was interested in mutation so his first goal really when he started working with Drosophila was to see if and how a mutant phenotype might emerge in a natural wild population .
Morgan and his students and the legion of people who followed him studying fruit flies refer to the phenotypes of these fruit flies in particular ways. they referred to the characteristic that you would observe in a wild fruit fly as being the wild type phenotype. because wild fruit flies don't have a lot of visible variation. it means that basically all fruit flies that you collect our basically just composed of wild type phenotype for any particular characteristic you might be interested. now if they observed an unusual phenotype specifically phenotype that they thought was the mutation they call it a mutant phenotype. we have wild type and mutant phenotypes that are what we're really looking at when we look at fruit flies and the assumption here is that the mutant phenotype somehow must be the result of a mutation in allele for the gene responsible for the trait .another detail is that Morgan and the people who have followed up on fruit flies uses slightly different convention for labeling their alleles,the way it is Morgan designated or labeled essentially the kind of mutant alleles and genotypes he was working with was by him labeling the allele according to the phenotypic characteristic of the mutation of the mutant phenotype don't let me make this clear with an example of a well-known mutation in Drosophila which involved a reduction in the size of wings and these guys are just tiny little flies they have wings but one mutation occurs causes those wings do not develop properly that the wings are also small and scrunched up this mutation has been labeled the vestigial wing mutation or just simply vestigial wings we would label the allele responsible for this mutation VG. the interesting thing is that the mutation in are named after the mutant phenotype not the wild type phenotype.the mutant allele would be referred to as VG and the wild type allele for that same gene we would call VG + .
for any particular mutation that Morgan was studying we can safely assume that the typical wild type Drosophila the one that Morgan would just collect out on his pineapple is homozygous for the wild type allele if we were interested in the vestigial wing of trait if we just caught a wild type individual we would assume it's homozygous for VG + VG + that would be a phenotype for that particular trait.
we observe a mutant that mutant must have at least one mutant allele by for example in that case it's got to be at least VG + VG but actually more often than not the mutant alleles that we find in Drosophila are recessive alles. if we find mutation if we find a mutant phenotype of vestigial wing fly then we can be pretty sure that it's homozygous for the recessive mutant allele in other words it would be VG VG a genotype that particular trait.
Chromosomes had not been described when Mendel lived and worked, it was only later with the advent of improved microscopes in the second part of the 19th century of biologists began to describe the structure of cells in some detail, and one of the things they noticed was the formation of dark bodies in the nucleus of cells that would appear just before cells divide and furthermore they notice that as cells were dividing these dark bodies would fall peculiar movement. What they were seeing were chromosomes and movements of these chromosomes in mitosis and meiosis.
Part 1
The significance of the movements of these chromosomes wasn't appreciated at first but then in the early 20th century two-cell biologist independently had an insight Walter Sutton and colleague observed that the highly choreographed movements of chromosomes during meiosis reduced by half number of chromosomes that would be found in gametes. When gametes joined the total number of chromosomes would come back up to its full complement. They realize that this reduction in chromosome number in gametes formation and subsequent restoration zygote formation could explain the patterns of trait transmission that Mendel had described with his laws of segregation and independent assortment.
Part 2
Part 3
In 1903 Sutton and Bovary both independently publish their ideas, which become generally known as the chromosomal theory of inheritance. in that sense they provided a hypothetical mechanism whereby chromosome movements could completely explain these two fundamental principles that Mendel had suggested.
The chromosomal theory of inheritance should seem obvious to us at this point in the course because we are to know so much about DNA learn that before but it wasn't clear then that you could establish this relationship specifically it wasn't clear how during the early part of the 20th century you could prove that genes were on chromosomes and thus prove the chromosome theory of inheritance, sutten & Bovary had suggested this connection but it was just a hypothesis. Confirmation of this hypothesis actually can be attributed to one particular scientist and a remarkable lab group and also to the particular organism, the scientist was Thomas Hunt Morgan who was a embryologist studying patterns of development working at Columbia University.
Like most biologist at the time Morgan to became interested in mechanisms of inheritance that as people began to talk again about Mendel's work .Now Morgan was particularly interested as he was studying development in mutations, and he was interested in how new mutations arose in organisms. Many geneticists at the time had begun working on organisms that had more complex patterns of trait transmission than for example the garden peas Mendel worked on including for example small mammals such as guinea pigs and mice because the way that her color patterns of these mammals would be transmitted from parent to offspring sometimes corresponded to what Mendel observed that also led to a lot of interesting exceptions that these geneticists wanted to understand .so Morgan when he got interested in genetics he set out to work on the genetics of coat color in mammals but mammals are expensive.Morgan couldn't actually raise the money to do this work Morgan's inability to get funded to work on coat color in mammals was probably one of the most fortunate grants turndowns in the history of science because it led Morgan by necessity to start working on a different model organism the Fruit fly a small little fly its scientific name is Drosophila Melagoster and commonly known as Drosophila.
As it turns out Drosophila very quickly became and remains to this day the single most important model organism used in both classical and molecular studies of genetics.From Morgan's point of view there are a lot of advantages to working on fruit flies (i) first of all their cheap and (ii)Fruit flies are also very easy to raise in the laboratory . most important in one of the reasons that supplies remain such an important model organism today(iii) they have a very short generation time adult fruit flies will develop from eggs in only a matter of days and what this means is that it's possible to observe the results of genetic crosses in a very short period time you can do a lot of process he didn't have to wait for those garden peas to growup over a matter of months within a few days you know the answer.
There were some serious problems working with fruit flies that fruit flies that you collect from the wild don't have obvious phenotypic variance. if you put out your pineapple and collect fruit flies, to a first approximation they all look the same ,that is the fruit fly didn't offer traits that Morgan could use in particular establish crosses. This seems like the major problem How you going to understand the genetics of trait transmission if there are obvious traits that you can follow in her crosses. but remember that Morgan was interested in mutation so his first goal really when he started working with Drosophila was to see if and how a mutant phenotype might emerge in a natural wild population .
Morgan and his students and the legion of people who followed him studying fruit flies refer to the phenotypes of these fruit flies in particular ways. they referred to the characteristic that you would observe in a wild fruit fly as being the wild type phenotype. because wild fruit flies don't have a lot of visible variation. it means that basically all fruit flies that you collect our basically just composed of wild type phenotype for any particular characteristic you might be interested. now if they observed an unusual phenotype specifically phenotype that they thought was the mutation they call it a mutant phenotype. we have wild type and mutant phenotypes that are what we're really looking at when we look at fruit flies and the assumption here is that the mutant phenotype somehow must be the result of a mutation in allele for the gene responsible for the trait .another detail is that Morgan and the people who have followed up on fruit flies uses slightly different convention for labeling their alleles,the way it is Morgan designated or labeled essentially the kind of mutant alleles and genotypes he was working with was by him labeling the allele according to the phenotypic characteristic of the mutation of the mutant phenotype don't let me make this clear with an example of a well-known mutation in Drosophila which involved a reduction in the size of wings and these guys are just tiny little flies they have wings but one mutation occurs causes those wings do not develop properly that the wings are also small and scrunched up this mutation has been labeled the vestigial wing mutation or just simply vestigial wings we would label the allele responsible for this mutation VG. the interesting thing is that the mutation in are named after the mutant phenotype not the wild type phenotype.the mutant allele would be referred to as VG and the wild type allele for that same gene we would call VG + .
for any particular mutation that Morgan was studying we can safely assume that the typical wild type Drosophila the one that Morgan would just collect out on his pineapple is homozygous for the wild type allele if we were interested in the vestigial wing of trait if we just caught a wild type individual we would assume it's homozygous for VG + VG + that would be a phenotype for that particular trait.
we observe a mutant that mutant must have at least one mutant allele by for example in that case it's got to be at least VG + VG but actually more often than not the mutant alleles that we find in Drosophila are recessive alles. if we find mutation if we find a mutant phenotype of vestigial wing fly then we can be pretty sure that it's homozygous for the recessive mutant allele in other words it would be VG VG a genotype that particular trait.
How Sex Leads To Variation Lecture
Scope this lecture continues their discretion of mentors contribution to genetics turned and the subsequent experiments in which Mendel looked at the transmission of more than one trait, leading to an of independent assortment. The lecture summarizes in the wind us up and, linkage, and crossover, all of which result from the way chromosome and the gene located on them move during gamete formation and sexual reproduction. The lecture concludes by recapping the sources that contribute to genetic variation that is essential for evolution to occur.
Part 1
Part 2
Part 3
Outline
I. Mendel continued his space experiment by crossing pea plants that are too phenotypic differences instead of one. From these dihybrid crosses, Mendel inferred additional properties of three transmission from the parents to offspring, properties consistent with knowledge gained later the moment of genes on chromosomes.
A. as wit flower color, seed color in pea plants depend on the single gene with two alleles: the Dominant yellow allele(Y) in the recessive gene allele(y).
B. space for example, when crossing the female pea plant with purple flowers and yellow seeds with the male pea plant with white flowers and green seats, we know that females genotype is PPYY in the male genotype is ppyy.
C.F1 individuals will have purple flower and a yellow seeds, because they are all heterozygous for both traits. As in monohybrid cross, the recessive traits disappeared in F1.
D. when F1 individuals makes gametes, do the allels from the original parents stay together or are they separated next?
If parent alleles are linked, an F1 space individual could produce only PY and py gametes;F2 would then contain only two parental phenotypes. Furthermore, these people takes would have the same 3:1 ratio as in monohybrid cross. This would mean that sets of parent alleles acted as a single alleles.
If parental alleles are not linked,F1 individuals would produce for better gamete in equal proportions:PY,py,Py,pY. A punnet Square using these gametes asserting 16 possible combinations and 9 distinctive F2 genotypes. These nine genotypes would produce 4 possible phenotypes, which would occur in 9: 3:3:1 ratio. Two of these phenotypes would not have existed in parent the generation; these so-called recombinant phenotypes.
Mendel observed 4 phenotypes in a 9:3:3:1 ratio in his F2 generation, which he correctly concluded to mean that alleles of inherited independently of each other.
E. from this conclusion, mendel formatted what is known as law of independent assortment, which simply says that Alleles off different genes segregating independently of each other during gamete formation.
II. Integral assortment of genes during meiosis is an important source of genetic variation.
During first meiotic division, homologues chromosomes line up in the cell and separated into two daughter cells. The assortment of Maternal and parent homology’s for1 chromosome has more effect on the assortment of any other chromosome.
In the genes of two different traits are on different chromosomes, they will assort independently of each other, as Mendel saw, and independent assortment produce recombinant phenotypes.
The number of unique combination of alleles on different chromosome can be very. Humans have 23 pairs of chromosomes; the possible number of assortment is 2(23) or about 8.4 million.
Independent assortment is different from mutation as a source of variation.
Mutation essentially generates new alleles-usually dysfunctional but not always.
Independent assortment does not create new alleles but, rather, new assortment of alleles.
However, both mutation and Independent assortment can change their phenotypes of successive generations.
III. if two genes occur on the same chromosome, an obvious conclusion is that they will be transmitted together as a unit during meiosis. Such genes are called linked genes.
During meiosis, however, homologue pairs of chromosomes associated so closely that they can exchange genetic material, which called crossing over. If linked gene crossover to other chromosome, they can assort independently.
Geneticists expanding on Mendel's work found that in the Everett tosses, F2 generation with linked genes would occasionally produce recombinant phenotypes, though a far fewer number than if the genes unlinked. Link genes, however, should not produce any recombinant phenotypes.
The further apart to genes on the chromosome, the more likely crossing over and recombinant phenotypes with be.
IV. Space though essentially established the sciences of genetics, Mendel’s work was ignored for about 40 years, because nothing was then known of the physical basis of mentors heritable factors and because he used advanced probability mathematics to calculate is ratio. Only when biologists began to see the pattern Mendel described did anyone realize that this work might be significant.
Part 1
Part 2
Part 3
Outline
I. Mendel continued his space experiment by crossing pea plants that are too phenotypic differences instead of one. From these dihybrid crosses, Mendel inferred additional properties of three transmission from the parents to offspring, properties consistent with knowledge gained later the moment of genes on chromosomes.
A. as wit flower color, seed color in pea plants depend on the single gene with two alleles: the Dominant yellow allele(Y) in the recessive gene allele(y).
B. space for example, when crossing the female pea plant with purple flowers and yellow seeds with the male pea plant with white flowers and green seats, we know that females genotype is PPYY in the male genotype is ppyy.
C.F1 individuals will have purple flower and a yellow seeds, because they are all heterozygous for both traits. As in monohybrid cross, the recessive traits disappeared in F1.
D. when F1 individuals makes gametes, do the allels from the original parents stay together or are they separated next?
If parent alleles are linked, an F1 space individual could produce only PY and py gametes;F2 would then contain only two parental phenotypes. Furthermore, these people takes would have the same 3:1 ratio as in monohybrid cross. This would mean that sets of parent alleles acted as a single alleles.
If parental alleles are not linked,F1 individuals would produce for better gamete in equal proportions:PY,py,Py,pY. A punnet Square using these gametes asserting 16 possible combinations and 9 distinctive F2 genotypes. These nine genotypes would produce 4 possible phenotypes, which would occur in 9: 3:3:1 ratio. Two of these phenotypes would not have existed in parent the generation; these so-called recombinant phenotypes.
Mendel observed 4 phenotypes in a 9:3:3:1 ratio in his F2 generation, which he correctly concluded to mean that alleles of inherited independently of each other.
E. from this conclusion, mendel formatted what is known as law of independent assortment, which simply says that Alleles off different genes segregating independently of each other during gamete formation.
II. Integral assortment of genes during meiosis is an important source of genetic variation.
During first meiotic division, homologues chromosomes line up in the cell and separated into two daughter cells. The assortment of Maternal and parent homology’s for1 chromosome has more effect on the assortment of any other chromosome.
In the genes of two different traits are on different chromosomes, they will assort independently of each other, as Mendel saw, and independent assortment produce recombinant phenotypes.
The number of unique combination of alleles on different chromosome can be very. Humans have 23 pairs of chromosomes; the possible number of assortment is 2(23) or about 8.4 million.
Independent assortment is different from mutation as a source of variation.
Mutation essentially generates new alleles-usually dysfunctional but not always.
Independent assortment does not create new alleles but, rather, new assortment of alleles.
However, both mutation and Independent assortment can change their phenotypes of successive generations.
III. if two genes occur on the same chromosome, an obvious conclusion is that they will be transmitted together as a unit during meiosis. Such genes are called linked genes.
During meiosis, however, homologue pairs of chromosomes associated so closely that they can exchange genetic material, which called crossing over. If linked gene crossover to other chromosome, they can assort independently.
Geneticists expanding on Mendel's work found that in the Everett tosses, F2 generation with linked genes would occasionally produce recombinant phenotypes, though a far fewer number than if the genes unlinked. Link genes, however, should not produce any recombinant phenotypes.
The further apart to genes on the chromosome, the more likely crossing over and recombinant phenotypes with be.
IV. Space though essentially established the sciences of genetics, Mendel’s work was ignored for about 40 years, because nothing was then known of the physical basis of mentors heritable factors and because he used advanced probability mathematics to calculate is ratio. Only when biologists began to see the pattern Mendel described did anyone realize that this work might be significant.
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