Question

1 A) Cross Rh- man who is heterozygous for cystic fibrosis with a female who is heterozygous for cystic fibrosis and Rh+. What are the phenotypes and phenotypic ratios of the offspring?

B) Cross a Rh- man who is left handed with a female who is heterozygous Rh+ and right handed. What are the expected phenotypes?

C) The parents of two children are normal in respect to cystic fibrosis. One of their children is normal, one has cystic fibrosis. What is the chance of their having another child with cystic fibrosis.

please show work - thanks in advance

Answer 1

A) Rh+ phenotype is dominant, let the alleles be H dominant and h recessive r.

cystic fibrosis is also due to a recessive allele. let the alleles be C- normal and c-cystic fibrosis

genotype of the Rh- man who is heterozygous for cystic fibrosis is hhCc and genotype of the woman who is heterozygous for cystic fibrosis and Rh+ is HhCc.

HhCc * hhCc

	HC	Hc	hC	hc
hC	HhCC ( Rh+, not affected with cystic fibrosis)	HhCc ( Rh+, not affected with cystic fibrosis)	hhCC( Rh-, not affected with cystic fibrosis)	hhCc ( Rh-, not affected with cystic fibrosis)
hc	HhCc ( Rh+, not affected with cystic fibrosis)	Hhcc ( Rh+, affected with cystic fibrosis)	hhCc ( Rh-, not affected with cystic fibrosis)	hhcc ( Rh-, affected with cystic fibrosis)

possible phenotypes are given in the punnet square.

the phenotypic ratio is

Rh+, not affected with cystic fibrosis: Rh+, affected with cystic fibrosis: Rh-, not affected with cystic fibrosis: Rh-, affected with cystic fibrosis =3:1:3:1

b) right handness is dominant to left handedness

let the alleles be R- right handed

r-left handed

genotype of Rh- man who is left handed is hhrr.

genotype of the female who is heterozygous Rh+ and right handed is HhRr

	RH	Rh	rH	rh
rh	RrHh (right handed, Rh+)	Rrhh ( right-handed, Rh-)	rrHh ( left handed, Rh+)	rrhh ( left handed Rh-)

the phenotypes are given in the punnet square

phenotypic ratio is

right handed, Rh+ : right handed, Rh-: left handed, Rh+ : left handed, Rh-=1:1:1:1

C) parents are normal but they have and affected child means the parents are heterozygous.

Cc * Cc

	C	c
C	CC ( normal)	Cc( normal)
c	Cc( normal)	cc ( cystic fibrosis)

having a child is an independent event so the probability of getting an affected child does not depend on the genotype or phenotype of the siblings.

probability of getting affected progeny= number of cc/total number=1/4