3. Mickey the farmer keeps ducks on his farm among his other animals. When he br

Question

3. Mickey the farmer keeps ducks on his farm among his other animals. When he breeds two non-crested ducks together and incubates the eggs, all of them hatch and give rise to non-crested ducklings. When he breeds two crested ducks together and incubates the eggs, he finds that only about ¼ of the eggs hatch. (A) Explain these resuls geneticall. Be sureto define any gene symbols for alleles involved (0.5 pts.) (A) Explain these results genetically (B) What are the genotypes of 1) the non-crested ducks that Mickey breeds as described above; 2) the crested ducks Mickey breeds and gets the lower hatching rate? (0.5 pts.) (C) What phenotypic ratio do you expect among the ducklings that do hatch from the crested x crested cross? Explain (show the Punnett square of the cross if you like) (0.5 pts.). (D) Is it possible for Mickey to establish a true-breeding strain of crested duck? Explain (0.5 pts.)

Explanation / Answer

a. The Crested genotype, Cr’/cr, it is a lethal gene, therefore you will get 25% population that dies in the shell. This gene is called the “lethal gene” because the crest is formed through a hole in the top of the duckling’s skull.

If a duckling receives the crested gene from both parent birds, that duckling will not survive and will die before hatching. Because a double dose of the crested gene (Cr’Cr’) will cause the duckling’s brain to develop improperly and outside of the skull.

Crested ducks are having heterozygous genotypes, hence their cross will give 50% population with Crested Ducks, 25% population with non crested and 25% population with homozygous Cr’ gene that leads to the death of the offsprings.

b. let the Crested gene be 'A' for convinience. then the noncrested ducks will have genotypes 'aa x aa' in the first cross. while at the second cross both crested ducks will have 'Aa' genotypes.

c. genotypic ratio at crested x crested cross

Crested : non crested = 2:1

(though you will get 4 eggs, out of which the fourth one will die during incubation as mentioned above.)

d. True breeding crested ducks are not possible as they have a heterozygous gene. (Cr'/Cr). If they get homozygous gene condition (Cr'/Cr') the ofspring will no longer be born as double dose of the Cr' gene will lead to the death of the offspring.

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