6) A long winged male crow with a head ruff mates with a short winged crow witho

Question

6) A long winged male crow with a head ruff mates with a short winged crow without a head ruff. All of their male offspring have long wings, half of them have a head ruff and half lack a head ruff. All of the female offspring have long wings and half have a head ruff and half do not. A) Are either of these genes sex-linked? B) What is your reasoning? C) What is the most likely genotype for each parent and type of offspring? (4 pts)

Received two different answers how to do this

One said genes were sex-linked and one said genes were not sex-linked

One said to use sex genes of birds ZW

Z^lr W x Z^Lr Z^LR

Second one said to use LLRr x llrr

A long-winged male crow with a head ruff = LLRr

short-winged crow without a head ruff = llrr

Which one is correct and can you please answer the question with a simple explanation and do punnett square. Thank you

Explanation / Answer

C. Let us assume that the allele for long wings is denoted by L and the allele for short wings is denoted by l.

Let us assume that allele for head ruff is denoted by R and allele for no head ruff is denoted by r.

Since one parent had short wings but all the children had long wings, it signifies that long wings are the dominant pattern and so, L is the dominant allele over l. Also, this means that the long-winged crow passed on long wings to all his children. that means he has only L alleles. (LL)

Half of the children have head ruffs and half do not. This means that the parent with the head ruff clearly has an allele other than the dominant allele for a head ruff. So we know that the crow with the head ruff is heterozygous for R. that is, Rr. We also get to know that head ruff is the dominant phenotype since head ruff is present even in a heterozygous condition. (H is dominant over h)

Now, the crow with the long wings and the head ruff has genotype: LLRr

The crow with the short wings and no head ruff has genotype: llrr.

we can now do an independent assortment of these genotypes. (just dissociate into the possible pairs)

LLRr will yield LR and Lr.

llrr will yeild lr.

Now we make the punnett square.

This punnett square can also be made with 2 rows and 2 columns, like this:

Both these squares give the same conclusion.

A) Is either of these genes sex-linked?

When an allele is sex-linked, the number of males and the number of females affected varies greatly.

However, the gene could also be Z linked dominant.

the genes discussed here are definitely not linked to the W gene because they are present in both males and females. (Assuming ZZ is male and Zw is female, this is the convention in birds.)

B. We already know that the male crow is homozygous for long wings. Let us assume his genotype is ZLZL . He mates with a female bird of ZlW. Hence, all offspring will have the genotype ZLW or ZLZl , giving them all tall wings.

The male crow is heterozygous for a head ruff. Let us assume his genotype is ZHZh . He is mated with a female who has ZhW.

The progeny will have genotype:

This shows that half the males have a head ruff and half the females do, too.

So this could be a possibility.

However, Z linked dominant cases are very very rare.

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