In dogs, there is a hereditary deafness caused by an autosomal recessive Gene,"d". A kennel owner has a male dog that she wants to use for breeding purposes if possible. The dog can hear. If the dog's genotype is Dd, the owner does not wish to use him for breeding so that the deafness gene will not be passed on. This can be tested by breeding the dog to a deaf female. Draw the Punnett squares to illustrate these two possible crosses. In each case, what percentage/ how many of the offspring would be expected to be hearing? deaf? How could you tell the genotype of this male dog? Also, using Punnett square (s) show how two hearing dogs could produce deaf offspring.

An autosomal recessive gene disorders are a disease that gets passed from the parent to the child when the progeny accumulates the mutated copy of genes from normal parents.

50% of the offspring will be deaf with cross Dd × dd and the other 50% will not be deaf.

The two possible genotypes for dog = DD or Dd

Here a test cross that is a cross between the possible genotype and a recessive allele is done.

To see the cross between the cross 1: DD × dd and cross 2: Dd × dd refer to the attached image below.

Hearing (100%) : Deaf (0%)

Hearing (50%) : Deaf (50%)

To see the cross 3 between the two hearing dogs producing deaf offspring see the attached image 2 below.

Therefore, 50% are genotypically heterozygous while 50% is purebred and 2 without deafness: 2 deaf in the cross between Dd and dd.

Learn more about autosomal recessive genes here:

link

Answer and Explanation:

Deafness is a physiological disorder where hearing is impaired. Apart from genetics, this may be caused by infections of the inner or middle ear, toxins and noise exposure. In genetic cases, this may be caused by a mutation in a recessive autosomal gene.

Punnett squares are diagrams  that show the product of hybrid trait crosses by genetic breeding.

For this cross...

Assuming deafness= recessive

Parent generation or P generation:

gametes: Dd → Not deaf i.e. normal dominant (D), deafness recessive (d)

Heterozygousity describes the allelic makeup; these traits comprise two varying forms of a  gene. However, homozygous traits comprise identical forms of the gene.

Male: An  →  without deafness Dd

Female: dd → deaf

genotypes and phenotypes for parent and offspring...

Assuming heterozygousity of the male , for the cross

P generation:                                Dd × dd

                                          Not Deaf   × Deaf

F1 generation:

genotype:                                       Dd × dd      ...(from punnet square)

phenotype:          2 without deafness : 2 deaf

                                                           1 : 1

∴ 50% are genotypically heterozygous while 50% is homozygous ,    2 without deafness ; 2 deaf

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