What is another definition for "hemizygous?"

A chromosome in a diploid organism is hemizygous when only one copy is present. The cell or organism is called a hemizygote. Hemizygosity is also observed when one copy of a gene is deleted, or in the heterogametic sex when a gene is located on a sex chromosome.

What if a white eyed male fruit fly (genotype XwY) is crossed with a heterozygous (i.e. with genotype Xw+Xw) female fruit fly? Don't we get a white eyed female fruit fly?

You may get a white female with a XwXw genotype or a red-eyed female with a XwXw+ genotype. Morgan used this to verify his hypothesis further. Open the hidden experiment tab under the "Confirming the model" subheading above. Hope this helped. :)

Hello! I dont understand why the mutant is on the X chromosome if we said that it is defining by the sex chromosome?? if it's only for male (XY) and female has both XX, I would predict that the mutant would be on the Y chromosome, which only the male has. thnks!

If the white eye trait was linked to having the Y chromosome, then you would expect that: a) all male offspring of white-eyed males had white eyes, because they should all inherit their father's Y chromosome. In actual case they had red eyes though. b) It would not be possible to have white eyed females, because they don't have a Y chromosome. However, in the actual case, Morgan performed experiments by crossing females which were offspring of a white-eyed male with another white eyed male, and found you can get white eyed females, so the trait is not linked to the Y chromosome. This suggests the white eyed trait is X-linked but recessive, so females only show this phenotype when they have two copies of it, and no red-eye version. Hope that helped!

It is stated in the second to the last paragraph that Bridges showed more detail about Morgan's findings wherein he showed that rare male or female flies with the unexpected eye colors were produced through nondisjunction of sex chromosomes during meiosis, and since it is meiosis they should bed divided. What then is left in the cell? Does it have both X and Y? If so what about the other cell that was supposed to inherit the other sex chromosome.

Bridges found rare flies with surprising inheritance patterns: daughters that inherited X-linked traits (like eye colour) only from their mother, and sons that inherited their X-linked traits from their father. Due to these inheritance patterns he suggested that these daughters were XXY, and the sons were XO (unlike in humans, in drosophila, sex is determined by how many X chromosomes are present, rather than depending on the Y chromosome). His explanation was that nondisjunction had occurred during meiosis in the mother, producing egg cells with XX or no sex chromosomes. When these rare eggs were fertilized by sperm carrying either X or Y, the offspring were the XXY daughters with 2X chromosomes from the mother, and X0 sons inheriting an X from the father (those with XXX and Y0 combinations died). He also looked under a microscope and saw that these were indeed the chromosome combinations that the flies had. This work provided further evidence that inherited traits, which could be studied using the breeding experiments of genetics, are linked to physical chromosomes, that were being studied for example with dyes and microscopy. There is more information where I read most of this, here: https://embryo.asu.edu/pages/calvin-bridges-experiments-nondisjunction-evidence-chromosome-theory-heredity-1913-1916 And here is another interesting article on the chromosome theory, Bridges' contribution, and its impact http://www.genetics.org/content/202/1/15

where did the first white eyed fly come from? if there were no white eyed flys to begin with where did he get the white genotype? Please help.

The first mutant white allele isolated (called w1) arose spontaneously because of transposon insertion. There are now many strains of flies with different mutations in the white gene (you can find a long list here: http://flybase.org/reports/FBgn0003996.html). Some of these have far smaller mutations, such as just one amino acid change like described here: https://www.sciencedirect.com/science/article/pii/S0005273699000644

Why was the idea initially controversial? What did it initially lack?

Gregor Mendel's work didn't explain co-dominance and so many other factors but was later found out to be the basic building block of genetics.

so whats the role of the cromosome y in the eye color here?

The role of the Y chromosome is to determine the sex. As for eye color, nothing.

I thought it wasn't possible t obtain a white-eyed female because of the differing chromosomes in the two sexes?...

If you breed a homozygous red eyed female with a white eyed male, the female offspring will be heterozygous and have one copy of the mutant allele, even though the eyes are still red. Then if you breed such a female with a white eyed male, some of the female offspring will receive an X chromosome from the mother containing the white mutation, as well as the white mutant allele on the X chromosome from the father. Such females have two mutant copies and no 'normal' alleles to compensate, so would have white eyes.

Couldn't we have a White EYE female fruit fly in the F3 Generation ?? PLEASE HELPP

The previous comment is incorrect, the logic is flawed. If a white eyed female required a white eyed female, you would have an infinite regression. You can have a white eyed female in generation 3, by mixing a red eyed female with the white eyed gene with a white eyed male.

Main content

Course: AP®︎/College Biology > Unit 5

Lesson 5: Chromosomal inheritance

The chromosomal basis of inheritance

Google Classroom

Thomas Hunt Morgan's experiments. The fruit fly (Drosophila melanogaster) as a model system.

Key points:

Boveri and Sutton's chromosome theory of inheritance states that genes are found at specific locations on chromosomes, and that the behavior of chromosomes during meiosis can explain Mendel’s laws of inheritance.
Thomas Hunt Morgan, who studied fruit flies, provided the first strong confirmation of the chromosome theory.
Morgan discovered a mutation that affected fly eye color. He observed that the mutation was inherited differently by male and female flies.
Based on the inheritance pattern, Morgan concluded that the eye color gene must be located on the X chromosome.

Introduction

Where are genes found in a cell? Odds are, you've already heard the punchline: genes lie on chromosomes. You may have even have heard the second punchline, the one that ushered in the modern genetic era: genes are stretches of DNA that specify proteins.

However, these were not always things that you could look up on Khan Academy! When Gregor Mendel began studying heredity in 1843, chromosomes had not yet been observed under a microscope. Only with better microscopes and techniques during the late 1800s could cell biologists begin to stain and observe subcellular structures, seeing what they did during cell divisions (mitosis and meiosis).

Eventually, some scientists began to study Mendel’s long-ignored work and re-evaluate his model in terms of the behavior of chromosomes. Around the turn of the 20th century, the biology community started to make the first tentative connections between chromosomes, meiosis, and the inheritance of genes

^{1}

The chromosome theory of inheritance

Who figured out that genes are on chromosomes? Walter Sutton and Theodor Boveri generally get credit for this insight. Sutton, who was American, studied chromosomes and meiosis in grasshoppers. Boveri, who was German, studied the same things in sea urchins.

In 1902 and 1903, Sutton and Boveri published independent papers proposing what we now call the chromosome theory of inheritance. This theory states that individual genes are found at specific locations on particular chromosomes, and that the behavior of chromosomes during meiosis can explain why genes are inherited according to Mendel’s laws

^{2, 3}

Observations that support the chromosome theory of inheritance include

^{4}

Chromosomes, like Mendel's genes, come in matched (homologous) pairs in an organism. For both genes and chromosomes, one member of the pair comes from the mother and one from the father.
The members of a homologous pair separate in meiosis, so each sperm or egg receives just one member. This process mirrors segregation of alleles into gametes in Mendel's law of segregation.
Diagram comparing:
1) segregation of alleles into gametes: an Aa organism produces A gametes and a gametes
with
2) segregation of chromosomes into gametes during meiosis. One homologous chromosome bears an A allele, while the other bears an a allele at the corresponding location. During meiosis I, the homologous chromosomes separate. During meiosis II, the chromatids of each homologous chromosome separate. Ultimately, four gametes are produced: two containing a chromosome with an A allele, and two containing a chromosome with an a allele.
The members of different chromosome pairs are sorted into gametes independently of one another in meiosis, just like the alleles of different genes in Mendel's law of independent assortment.
Diagram comparing:
1) How an AaBb individual is proposed to make four equally common gamete types, AB, Ab, aB, and ab, in Mendelian genetics
with
2) The independent assortment of chromosomes in meiosis. The diagram depicts the relationship between chromosome configuration at meiosis I and homologue segregation to gametes for two pairs of homologous chromosomes. The larger chromosome pair bears the A gene and the smaller chromosome pair bears the B gene. The organism is heterozygous, so the larger homologous pair consists of one chromosome with an A allele and another with an a allele, while the smaller homologous pair consists of one chromosome with a B allele and another with a b allele.
If the homologues bearing the A and B alleles are positioned on one side of the metaphase plate, the homologues bearing the a and b alleles will be positioned on the other side of the metaphase plate, and AB and ab gametes will ultimately be produced. If, on the other hand, the homologues bearing the A and b alleles are positioned on one side of the metaphase plate (and the homologues bearing the a and B alleles on the other), Ab and aB gametes will ultimately be produced.

The chromosome theory of inheritance was proposed before there was any direct evidence that traits were carried on chromosomes, and it was controversial at first. In the end, it was confirmed through the work of geneticist Thomas Hunt Morgan and his students, who studied the genetics of fruit flies

^{5}

T. H. Morgan: Fun with fruit flies

Morgan chose the fruit fly, Drosophila melanogaster, for his genetic studies. What fruit flies may lack in charisma (depending on your taste in insects), they make up for in practicality: they're cheap, easy, and fast to grow. You can raise hundreds of them in a little bottle with sugar sludge at the bottom, and many geneticists still do this today!

Morgan's crucial, chromosome theory-verifying experiments began when he found a mutation in a gene affecting fly eye color. This mutation made a fly's eyes white, rather than their normal red.

Unexpectedly, Morgan found that the eye color gene was inherited in different patterns by male and female flies

^{6}

. Male flies have an X and a Y chromosome (XY), while female flies have two X chromosomes (XX). It didn't take Morgan long to realize that the eye color gene was being inherited in the same pattern as the X chromosome.

This may have come as a surprise to Morgan, who had been a critic of the chromosome theory

^{7}

A "sex limited" inheritance pattern $^{6}$ ‍

What made Morgan think that the eye color gene was on the X chromosome? Let's look at some of his data. The first white-eyed fly he found was male, and when this fly was crossed with normal, red-eyed female flies, the

F_{1}

offspring were all red-eyed

^{*}

—telling Morgan that the white allele was recessive. So far, so good, no surprises there.

But when the

F_{1}

flies were crossed to each other, something strange happened: all of the female

F_{2}

flies were red-eyed, while about half of the male

F_{2}

flies were white-eyed. Clearly, the male and female flies were inheriting the trait in different patterns. In fact, they were inheriting it in the same pattern as a particular chromosome, the X.

X marks the spot

Let's see how inheritance of the X chromosome can explain what Morgan saw. Earlier, we said that female flies have an XX genotype and male flies have an XY genotype. If we stick the eye color gene on the X chromosome (writing it as a little subscript,

w +

for red and

w

for white), we can use a Punnett square to show Morgan's first cross:

Punnett square for mating of white-eyed male (

X^{w} Y

) with red-eyed wild type female (

X^{w +} X^{w +}

		$X^{w}$ ‍	$Y$ ‍
$X^{w +}$ ‍		$X^{w +} X^{w}$ ‍	$X^{w +} Y$ ‍
$X^{w +}$ ‍		$X^{w +} X^{w}$ ‍	$X^{w +} Y$ ‍

X^{w +} X^{w}

- red-eyed F1 females

X^{w +} Y

- white-eyed F1 males

_Image modified from "Drosophila melanogaster," by Madboy74 (CC0/public domain)._

The predictions match the

F_{1}

phenotypes, but this set of phenotypes could also be explained by a gene that is not on the X chromosome, since all the flies were red-eyed (regardless of sex). So the real test comes when the

F_{1}

flies are mated to make the

F_{2}

generation:

Punnett square for mating of red-eyed F1 male (

X^{w +} Y

) with red-eyed, heterozygous F1 female (

X^{w +} X^{w}

		$X^{w +}$ ‍	$Y$ ‍
$X^{w +}$ ‍		$X^{w +} X^{w +}$ ‍	$X^{w +} Y$ ‍
$X^{w}$ ‍		$X^{w +} X^{w}$ ‍	$X^{w} Y$ ‍

X^{w +} X^{w +}

X^{w +} X^{w}

- red-eyed F2 females

X^{w} Y

- white-eyed F2 males

X^{w +} Y

- white-eyed F2 males

_Image modified from "Drosophila melanogaster," by Madboy74 (CC0/public domain)._

Here is where the X makes the difference. Our Punnett square with the eye color gene on the X chromosomes correctly predicts that all of the female flies will have red eyes, while half of the male flies will have white eyes. The male flies get their only X chromosome from their mother, who is heterozygous (

X^{w +} X^{w}

), leading to the fifty-fifty split of phenotypes.

Confirming the model

Morgan did lots of other experiments to confirm an X chromosome location for the eye color gene. He was careful to rule out alternative possibilities (for instance, that it was simply impossible to get a white-eyed female fruit fly)

^{6}

By mating the

F_{2}

files from the cross above, Morgan was able to obtain white-eyed females, which he then crossed to red-eyed males. All the female offspring of this cross were red-eyed, while all the males were white-eyed

^{8}

Punnett square for mating of red-eyed male (

X^{w +} Y

) with white-eyed female (

X^{w} X^{w}

		$X^{w +}$ ‍	$Y$ ‍
$X^{w}$ ‍		$X^{w +} X^{w}$ ‍	$X^{w} Y$ ‍
$X^{w}$ ‍		$X^{w +} X^{w}$ ‍	$X^{w} Y$ ‍

X^{w +} X^{w}

- red-eyed females

X^{w} Y

- white-eyed males

_Image modified from "Drosophila melanogaster," by Madboy74 (CC0/public domain)._

This result makes sense if the eye color gene is on the X chromosome. The white females (

X^{w} X^{w}

) provide the male offspring with their only X chromosome (leading to

X^{w} Y

, or white, males). Female offspring, in contrast, get an additional X from their red-eyed fathers (

X^{w +} Y

), giving them an

X^{w} X^{w +}

genotype and red eyes.

Pulling together all of his observations, Morgan concluded (correctly) that the gene must lie on, or be very tightly associated with, the X chromosome

^{7, 9}

. A strong confirmation of this conclusion came later, from Morgan's student Calvin Bridges. Bridges showed that rare male or female flies with unexpected eye colors were produced through nondisjunction (failure to separate) of sex chromosomes during meiosis—basically, the exception that proved the rule

^{10, 11}

Morgan also found mutations in other genes that were not inherited in a sex-specific pattern. We now know that genes are borne on both sex and non-sex chromosomes, in species from fruit flies to humans.

Attribution:

This article is a modified derivative of "Chromosomal theory and genetic linkage, by OpenStax College, Biology, CC BY 4.0. Download the original article for free at http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.53.

This article is licensed under a CC BY-NC-SA 4.0 license.

Works cited:

Meiosis. (2015, December 6). Retrieved December 8, 2015 from Wikipedia: https://en.wikipedia.org/wiki/Meiosis.
Hegreness, M. and Meselson, M. (2007). What did Sutton see? Thirty years of confusion over the chromosomal basis of Mendelism. Genetics, 176(4), 1939-1944. http://dx.doi.org/10.1534/genetics.104.79723.
Baltzer, F. (1967). Theodor Boveri: The life of a great biologist 1862-1915. (D. Rudnick, Trans.). In Developmental biology companion website. Retrieved from http://10e.devbio.com/article.php?ch=7&id=75
Boveri-Sutton chromosome theory. (2015, 31 October). Retrieved December 8, 2015 from Wikipedia: https://en.wikipedia.org/wiki/Boveri%E2%80%93Sutton_chromosome_theory.
Bergmann, D. C. (2011). The chromosomal theory of heredity. In Genetics lecture notes. Biosci41, Stanford University, 21.
Morgan, T. H. (1910). Sex-limited inheritance in Drosophila. Science 32, 120-122 (page 1 of reprint). Retrieved from http://www.esp.org/foundations/genetics/classical/thm-10a.pdf.
Robbins, R. J. (2000). Introduction [to ESP edition of "Sex limited inheritance in Drosophila"]. In ESP foundations reprint series, v. Electronic Scholarly Publishing Project. Retrieved from http://www.esp.org/foundations/genetics/classical/thm-10a.pdf.
Morgan, T. H. (1910). Sex-limited inheritance in Drosophila. Science 32, 120-122 (page 4 of reprint). Retrieved from http://www.esp.org/foundations/genetics/classical/thm-10a.pdf.
Morgan, T. H. (1910). Sex-limited inheritance in Drosophila. Science 32, 120-122 (page 6 of reprint). Retrieved from http://www.esp.org/foundations/genetics/classical/thm-10a.pdf.
Robbins, R. J. (2000). Introduction [to ESP edition of "Sex limited inheritance in Drosophila"]. In ESP foundations reprint series, vi. Electronic Scholarly Publishing Project. Retrieved from http://www.esp.org/foundations/genetics/classical/thm-10a.pdf.
Hartwell, L. H., Hood, L., Goldberg, M. L., Reynolds, A. E., Silver, L. M., and Veres, R. C. (2008). Analysis of rare mistakes in meiosis provided further support for the chromosome theory. In Genetics: From genes to genomes (3rd ed., pp. 109-110). Boston, MA: McGraw-Hill.

^{*}

Actually, not 100% true! If you look at reference 6, Morgan's original paper, you'll see that out of

1,

240

F_{1}

flies, there were actually

3

white-eyed males. The original white-eyed male was bred to his sisters to produce the

F_{1}

generation, and there may have been a few other copies of the same mutation running around in the gene pool. This doesn't change Morgan's result, but is a good example of how biology is not always as neat and tidy as it looks in a textbook.

Additional references:

Bergmann, D. C. (2011). The chromosomal theory of heredity. In Genetics lecture notes (pp. 21-26). Biosci41, Stanford University.

Genome News Network. (2004). Theodor Boveri (1862-1915) and Walter Sutton (1877-1916) propose that chromosomes bear hereditary factors in accordance with Mendelian laws. In Genetics and genomics timeline. Retrieved from http://www.genomenewsnetwork.org/resources/timeline/1902_Boveri_Sutton.php.

Genome News Network. (2004). 1910: Thomas Hunt Morgan (1866-1945) establishes the chromosomal theory of heredity. In Genetics and genomics timeline. Retrieved from http://www.genomenewsnetwork.org/resources/timeline/1910_Morgan.php.

Griffiths, A. J. F., Miller, J. H., Suzuki, D. T., Lewontin, R. C., and Gelbart, W. M. (2000). Historical development of the chromosome theory. In An introduction to genetic analysis. New York, NY: W. H. Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK22088/.

Hemizygous. (2015). In The free dictionary. Retrieved from http://medical-dictionary.thefreedictionary.com/hemizygous.

Meiosis. (2010, August 1). In New world encyclopedia. Retrieved from http://www.newworldencyclopedia.org/entry/Meiosis.

Morgan, T. H. (1910). Sex-limited inheritance in Drosophila. Science 32, 120-122. Retrieved from http://www.esp.org/foundations/genetics/classical/thm-10a.pdf.

OpenStax College, Biology. (2015, May 13). Chromosomal theory and genetic linkage. In OpenStax CNX. Retrieved from http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@9.85:64/Chromosomal-Theory-and-Genetic.

Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). The chromosomal basis of inheritance. In Campbell biology (10th ed., pp. 292-311). San Francisco, CA: Pearson.

Robbins, R. J. (2000). Introduction [to ESP edition of "Sex limited inheritance in Drosophila"]. In ESP foundations reprint series, i-vii. Electronic Scholarly Publishing Project. Retrieved from http://www.esp.org/foundations/genetics/classical/thm-10a.pdf.

Thomas Hunt Morgan. (2015, November 18). Retrieved December 8, 2015 from Wikipedia: https://en.wikipedia.org/wiki/Thomas_Hunt_Morgan.

Tobin, A. J. and Dusheck, J. (2005). From meiosis to Mendel. In Asking about life (3rd ed., pp. 162-191). Belmont, CA: Thomson.

X chromosome. (2015, December 1). Retrieved December 8, 2015 from Wikipedia: https://en.wikipedia.org/wiki/X_chromosome.

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Gabby Werner
Posted 8 years ago. Direct link to Gabby Werner's post “What is another definitio...”
What is another definition for "hemizygous?"
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(17 votes)
Answer
- SpinosaurusRex
  Posted 8 years ago. Direct link to SpinosaurusRex's post “A chromosome in a diploid...”
  A chromosome in a diploid organism is hemizygous when only one copy is present. The cell or organism is called a hemizygote. Hemizygosity is also observed when one copy of a gene is deleted, or in the heterogametic sex when a gene is located on a sex chromosome.
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tomcarbone25
Posted 7 years ago. Direct link to tomcarbone25's post “Hello! I dont understand ...”
Hello! I dont understand why the mutant is on the X chromosome if we said that it is defining by the sex chromosome?? if it's only for male (XY) and female has both XX, I would predict that the mutant would be on the Y chromosome, which only the male has.
thnks!
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(8 votes)
Answer
- RowanH
  Posted 6 years ago. Direct link to RowanH's post “If the white eye trait wa...”
  If the white eye trait was linked to having the Y chromosome, then you would expect that:
  a) all male offspring of white-eyed males had white eyes, because they should all inherit their father's Y chromosome. In actual case they had red eyes though.
  b) It would not be possible to have white eyed females, because they don't have a Y chromosome. However, in the actual case, Morgan performed experiments by crossing females which were offspring of a white-eyed male with another white eyed male, and found you can get white eyed females, so the trait is not linked to the Y chromosome. This suggests the white eyed trait is X-linked but recessive, so females only show this phenotype when they have two copies of it, and no red-eye version.
  Hope that helped!
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  (17 votes)
Ankush Moger
Posted 7 years ago. Direct link to Ankush Moger's post “What if a white eyed male...”
What if a white eyed male fruit fly (genotype XwY) is crossed with a heterozygous (i.e. with genotype Xw+Xw) female fruit fly?
Don't we get a white eyed female fruit fly?
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(9 votes)
Answer
- Lakshmi Sriram
  Posted 7 years ago. Direct link to Lakshmi Sriram's post “You may get a white femal...”
  You may get a white female with a XwXw genotype or a red-eyed female with a XwXw+ genotype. Morgan used this to verify his hypothesis further.
  Open the hidden experiment tab under the "Confirming the model" subheading above.
  Hope this helped. :)
  Comment on Lakshmi Sriram's post “You may get a white femal...”
  (14 votes)
Toni
Posted 7 years ago. Direct link to Toni's post “It is stated in the secon...”
It is stated in the second to the last paragraph that Bridges showed more detail about Morgan's findings wherein he showed that rare male or female flies with the unexpected eye colors were produced through nondisjunction of sex chromosomes during meiosis, and since it is meiosis they should bed divided. What then is left in the cell? Does it have both X and Y? If so what about the other cell that was supposed to inherit the other sex chromosome.
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(5 votes)
Answer
- RowanH
  Posted 6 years ago. Direct link to RowanH's post “Bridges found rare flies ...”
  Bridges found rare flies with surprising inheritance patterns: daughters that inherited X-linked traits (like eye colour) only from their mother, and sons that inherited their X-linked traits from their father. Due to these inheritance patterns he suggested that these daughters were XXY, and the sons were XO (unlike in humans, in drosophila, sex is determined by how many X chromosomes are present, rather than depending on the Y chromosome). His explanation was that nondisjunction had occurred during meiosis in the mother, producing egg cells with XX or no sex chromosomes. When these rare eggs were fertilized by sperm carrying either X or Y, the offspring were the XXY daughters with 2X chromosomes from the mother, and X0 sons inheriting an X from the father (those with XXX and Y0 combinations died). He also looked under a microscope and saw that these were indeed the chromosome combinations that the flies had. This work provided further evidence that inherited traits, which could be studied using the breeding experiments of genetics, are linked to physical chromosomes, that were being studied for example with dyes and microscopy.
  
  There is more information where I read most of this, here: https://embryo.asu.edu/pages/calvin-bridges-experiments-nondisjunction-evidence-chromosome-theory-heredity-1913-1916
  And here is another interesting article on the chromosome theory, Bridges' contribution, and its impact http://www.genetics.org/content/202/1/15
  Comment on RowanH's post “Bridges found rare flies ...”
  (7 votes)
7imon7ays
Posted 3 years ago. Direct link to 7imon7ays's post “Is this a mistake in the ...”
Is this a mistake in the text? Emphasis mine.

Morgan did lots of other experiments to confirm an X chromosome location for the eye color gene. He was careful to rule out alternative possibilities (for instance, that it was simply impossible to get a white-eyed female fruit fly).

By mating the F2 files [sic] from the cross above, Morgan was able to obtain white-eyed females, which he then crossed to red-eyed males. All the female offspring of this cross were red-eyed, while all the males were white-eyed.

Other comments suggest readers are getting thrown off by the contradiction. Personally I can see how a white-eyed female can be born to two parents carrying the recessive allele.
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(5 votes)
Answer
- Davin V Jones
  Posted 3 years ago. Direct link to Davin V Jones's post “There is no mistake or co...”
  There is no mistake or contradiction. Note the statement preceding it: "He was careful to rule out alternative possibilities"
  
  He ruled out that it was impossible to get white-eyed females by obtaining white eyed females.
  Comment on Davin V Jones's post “There is no mistake or co...”
  (5 votes)
noel56
Posted 5 years ago. Direct link to noel56's post “where did the first white...”
where did the first white eyed fly come from?
if there were no white eyed flys to begin with where did he get the white genotype? Please help.
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(4 votes)
Answer
- RowanH
  Posted 4 years ago. Direct link to RowanH's post “The first mutant white al...”
  The first mutant white allele isolated (called w1) arose spontaneously because of transposon insertion.
  There are now many strains of flies with different mutations in the white gene (you can find a long list here: http://flybase.org/reports/FBgn0003996.html).
  Some of these have far smaller mutations, such as just one amino acid change like described here: https://www.sciencedirect.com/science/article/pii/S0005273699000644
  Button navigates to signup page
  (3 votes)
Baron rojo
Posted 6 years ago. Direct link to Baron rojo's post “so whats the role of the ...”
so whats the role of the cromosome y in the eye color here?
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(2 votes)
Answer
- Ivana - Science trainee
  Posted 5 years ago. Direct link to Ivana - Science trainee's post “The role of the Y chromos...”
  The role of the Y chromosome is to determine the sex. As for eye color, nothing.
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  (5 votes)
maskarinecs
Posted 4 years ago. Direct link to maskarinecs's post “Why was the idea initiall...”
Why was the idea initially controversial? What did it initially lack?
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- Chukwuma Anayo- Ezikeoha
  Posted 4 years ago. Direct link to Chukwuma Anayo- Ezikeoha's post “Gregor Mendel's work didn...”
  Gregor Mendel's work didn't explain co-dominance and so many other factors but was later found out to be the basic building block of genetics.
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  (2 votes)
Kyla Reburiano
Posted 4 years ago. Direct link to Kyla Reburiano's post “I thought it wasn't possi...”
I thought it wasn't possible t obtain a white-eyed female because of the differing chromosomes in the two sexes?...
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- RowanH
  Posted 4 years ago. Direct link to RowanH's post “If you breed a homozygous...”
  If you breed a homozygous red eyed female with a white eyed male, the female offspring will be heterozygous and have one copy of the mutant allele, even though the eyes are still red. Then if you breed such a female with a white eyed male, some of the female offspring will receive an X chromosome from the mother containing the white mutation, as well as the white mutant allele on the X chromosome from the father. Such females have two mutant copies and no 'normal' alleles to compensate, so would have white eyes.
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Samirjawhar
Posted 8 years ago. Direct link to Samirjawhar's post “Couldn't we have a White ...”
Couldn't we have a White EYE female fruit fly in the F3 Generation ?? PLEASE HELPP
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- Travis Fisher
  Posted 8 years ago. Direct link to Travis Fisher's post “The previous comment is i...”
  The previous comment is incorrect, the logic is flawed. If a white eyed female required a white eyed female, you would have an infinite regression. You can have a white eyed female in generation 3, by mixing a red eyed female with the white eyed gene with a white eyed male.
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AP®︎/College Biology

Course: AP®︎/College Biology > Unit 5

Key points:

Introduction

The chromosome theory of inheritance

T. H. Morgan: Fun with fruit flies

A "sex limited" inheritance pattern6‍

X marks the spot

Confirming the model

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A "sex limited" inheritance pattern $^{6}$ ‍