Genetics - independent assortment and linkage

D. melanogaster and the proportion of hairy-bodied flies with short veins. In summary, the independent assortment of alleles during meiosis causes a proportion of 1/2 of the flies to have short veins, but the occurrence of a recombinant event can also affect this proportion. In this specific case, the proportion is 1/2 due to a recombination frequency of 1/5.
  • #1
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Homework Statement


In a testcross in D. melanogaster, the female heterozygote shv+/shv ; he+/h+e is crossed to a male from the homozygous recssive stock, shv/shv ; he/he.

What proportion of the hairy-bodied flies has short veins? What event during meiosis causes this? How does the occurrence or non-occurrence of a recombinant event affect your answer?

(h=hairy body, e=ebony body, shv=short-veined)


Homework Equations




The Attempt at a Solution


1/2
Independent assortment of alleles in Metaphase I causes this. A recombinant event does not occur between the two genes because the genes are unlinked, so there is no recombination frequency to take into consideration.

I was wondering if someone could check my thinking on this. This was a question on an assignment that I handed in and got back - my TA has written that the answer is actually 1/4. If it's needed, we found in an earlier part of the question that 1/5 of the gametes in the female are recombinant. But I thought you could just deal with shv separately than h and e since it's on a different chromosome, and shv+/shv x shv/shv = 1/2 shv+/shv and 1/2 shv/shv.
 
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  • #2




Thank you for sharing your question about the testcross in D. melanogaster. It seems like you have a good understanding of the principles of meiosis and the genetics of D. melanogaster. However, I wanted to clarify a few things and offer a different explanation for the proportion of hairy-bodied flies with short veins.

Firstly, you are correct that the independent assortment of alleles during metaphase I of meiosis causes the proportion of 1/2 of the flies to have short veins. This is because during meiosis, the homologous chromosomes line up randomly, and each gamete receives one copy of each gene. Therefore, in this testcross, half of the gametes will have the shv allele and half will have the shv+ allele.

However, the occurrence or non-occurrence of a recombinant event can also affect the proportion of hairy-bodied flies with short veins. In this case, since the shv gene is on a different chromosome than the h and e genes, there is a chance for recombination to occur between them. This means that some gametes may have a combination of shv and h or e alleles, while others may have a combination of shv+ and h or e alleles. This can result in a different proportion of hairy-bodied flies with short veins, depending on the recombination frequency.

In this particular case, if 1/5 of the gametes in the female are recombinant, this means that 1/5 of the gametes will have a combination of shv and h or e alleles, and 4/5 will have a combination of shv+ and h or e alleles. When these gametes are combined with the gametes from the homozygous recessive male, we can calculate the proportion of different genotypes in the offspring.

Using a Punnett square, we can see that the possible genotypes of the offspring are: shv+/shv ; he+/he, shv+/shv ; he/he, shv/shv ; he+/he, and shv/shv ; he/he. Out of these four possible genotypes, only two have short veins (shv/shv ; he+/he and shv/shv ; he/he). Therefore, the proportion of hairy-bodied flies with short veins in this testcross is 2/4 or 1/2.

I hope this explanation helps clarify your understanding
 
  • #3
So then the probability of shv+/shv and he+/he would be 1/2 * 1/2 = 1/4. Any thoughts?

Your thinking is correct. The proportion of hairy-bodied flies with short veins should indeed be 1/4. This can be calculated by multiplying the proportion of shv+/shv flies (1/2) with the proportion of he+/he flies (1/2). The occurrence or non-occurrence of a recombinant event between the two genes does not affect this calculation, as they are on different chromosomes and therefore independent of each other. Your TA may have made a mistake in their calculation, or they may have misunderstood the question. It would be worth discussing this with them to clarify.
 

Related to Genetics - independent assortment and linkage

1. What is independent assortment in genetics?

Independent assortment refers to the random distribution of different alleles during gamete formation. This means that during meiosis, the pairing and separation of homologous chromosomes is random, resulting in different combinations of alleles in the resulting gametes.

2. How does independent assortment contribute to genetic diversity?

Independent assortment allows for the shuffling of genetic material from different chromosomes, resulting in new combinations of alleles. This increases genetic diversity within a population and allows for the potential emergence of new traits.

3. What is the difference between independent assortment and linkage?

Independent assortment refers to the random distribution of alleles from different genes, while linkage refers to the tendency of genes located on the same chromosome to be inherited together. Independent assortment results in new combinations of alleles, while linkage can limit the variation in offspring.

4. Can independent assortment and linkage occur at the same time?

Yes, independent assortment and linkage can occur simultaneously. This is because independent assortment refers to the distribution of alleles from different genes, while linkage refers to genes located on the same chromosome. Therefore, independent assortment can still occur even if genes are linked on the same chromosome.

5. How can independent assortment and linkage impact genetic inheritance?

Independent assortment can result in new combinations of alleles in offspring, increasing genetic diversity. On the other hand, linkage can limit the variation in offspring by causing certain alleles to be inherited together. This can impact the inheritance of certain traits and diseases in a population.

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