Question

5. In humans, earlobes that are suspended are dominant over those that are attached. If a mother has suspended earlobes (but her mother did not) and the father has attached earlobes, what are the chances that their first child will have attached earlobes? What about the fourth child? 6. A brown-eyed man whose mother was blue-eyed married a brown-eyed woman whose father had blue eyes. Assume brown to be dominant over blue. What is the probability that the couple will have a blue-eyed child?

Answer 1

1. Suspended earlobes being dominant can be given by genotype: SS

Attached earlobes can be shown by genotype: ss

Mother having suspended earlobes (but her mother does not (ss) attached earlobes) means that mother is heterozygous for the gene suspended ear lobes: Ss

Father has attached earlobe: ss

Mother                                                Father

Ss                            x                              ss

                   

X	S	s
s	Ss	ss
s	Ss	ss

                                                                   

Therefore, there is 50% chance that their first child will have attached earlobes and 50% chance is for the fourth child.

2. Brown eyed man has the genotype: Bb

Brown eyed man's mother has the genotype: Bb

Married to brown eyed women who has genotype: Bb

Father of brown eyed women, who has blue eyed has the genotype: bb

Brown eyed man Bb and brown eyed women Bb will give the following

                                              (Man) Bb               x              Bb (women)

X	B	b
B	BB	Bb
b	Bb	bb

                                                                               

From above it is clear that parents have 25% chance that their child will have blue eyes having bb genotype and rest others with 75% chance will have brown eyes with BB and Bb genotypes.