Question

** Prior, which I forgot to include:

All Vulcans have pointed ears (P) and a right-sided heart (R) which are dominant over Earthling alleles of rounded ears (p) and a left-sided heart (r). Both Vulcans and Earthlings are homozygous for each allele.

Mr. Spock has a Vulcan father and an Earthling mother.

Gametes produced by an individual that are the same as the gametes contributed by each parent to produce that individual are called parental types.

Gametes that have a combination of parental and maternal alleles are called recombinant types.

Recombinant gametes are the result of independent assortment during Metaphase I if genes are on different chromosomes or crossing over during prophase I if genes are on the same chromosome.

In which I got the following: PR, PP, pR,Pr

_______

In Vulcans, the absence of adrenal glands (A) is dominant over the Earthling allele for adrenal glands (a). All Earthlings have adrenal glands.

A gene map of Mr. Spock shows that the genes for ear shape (P/p) and heart sidedness (R/r) are 20 map units apart on chromosome 7 while the gene for adrenal glands (A/a) is on chromosome 3.

If Mr. Spock fathers a child with an Earthling female, what is the chance that the child will have pointed ears and adrenal glands?

Select one:

a. 10%

b. 20%

c. 25%

d. 50%

Can someone please show me how to get the proper answer? I keep getting myself confused on this self-check question, and I don't know where I keep messing up.

Thank you

Answer 1

1) genotype of Mr.Spock is PpRr

parental cross is

genotype of the Vulcan is PPRR and genotype of Earthling is pprr

PPRR * pprr

PR/pr

( P and R alleles comes the Vulcan parent and p and r alleles comes from the Earthling parent so PR and pr gametes produced by Mr.Spock are parental types and Pr and pR gametes are formed by the recombination between the chromosomes in the dihybrid)

gametes produced by Mr.Spock are PR, pr, Pr, pR.

2) considering A locus genotype of Mr.Spock is

PR/pr; A/a ( P and R are on one chromosome and A is on another chromosome)

wife of Mr.Spock is an Earthling so her genotype is pr/pr; a/a

we have to find out the  chance that the child will have pointed ears and adrenal glands, so we have to consider only A and P genes, these genes are on different chromosomes ( P on chromosomes 7 and A on chromosome 3 so these genes are not linked)

so the cross is AaPp * aapp

	AP	Ap	aP	ap
ap	AP/ap ( no adrenal glands, pointed ears)	Ap/ap ( no adrenal glands, rounded ears)	aP/ap ( adrenal glands, pointed ears)	ap/ap (adrenal glands, rounded ears)

chance of getting child with pointed ears and adrenal glands= (number of children with pointed ears and adrenal glands/total number)*100=(1/4)*100=25%

so the answer is c) 25%