Question

1. Three pairs of genes with two alleles each (A1 and A2, B1 and B2, and C1 and C2) influence lifespan in a human population. The alleles of these genes have an additive relationship and add the number of years indicated to the lifespan of the individual.

allele	years
A1	15
A2	4
B1	16
B2	8
C1	13
C2	9

a. If lifespan were entirely genetically determined, what is the minimum possible lifespan and the associated genotype?

b. If lifespan were entirely genetically determined, what is the maximum possible lifespan and the associated genotype.

c. The following is a range of ages from individuals in this population. If the genetic variance is 25.7, measure the broad-sense heritability of lifespan

lifespan
65
77
89
76
99
97
87
81
78
91

d. Explain what this heritability means, and why the measure may be so low.

Answer 1

A. As it is given in the question that the lifespan is additive and we know that a gene consists of 2 alleles which means that alleles lifespan would add. The lowest lifespan of an individual allele given is 4 i.e of A2 allele. This means that the lifespan of an individual with homozygous A2 condition (A2A2) will have a lifespan of 8 years which is the lowest as compared to the others.

Genotype - A2A2

Lifespan-8 years

B. B1 allele has the maximum lifespan i.e 16 years. So an individual with homozygous B1 condition will have a lifespan of 32 years which is the highest among all of them.

Genotype - B1B1

Lifespan-32 years

C. Broad sense heritability

H​​​​​​2= Vg/Vp

Vg- genetic variance (25.7)

Vp-phenotypic variance (given)

So,

1. H​​​​​​2= 25.7/65 = 0.395

2. H2 = 25.7/77 = 0.333

3. 25.7/89 = 0.288

4. 25.7/76 = 0.338

5. 25.7/99 = 0.259

6. 25.7/97 = 0.264

7. 25.7/87 = 0.295

8. 25.7/81=0.317

9. 25.7/78= 0.329

D. Broad sense heritability is a statistical approach which estimates the degree of phenotypic variation caused due to genetic variation. It is simply the measurement of whether the attribution of the phenotypic trait is due to the genetic factors or the environmental factors.

High heritability shows that the variance in the offspring is low i.e their is high resemblence of the offspring and the parent in regard of a particular trait while low heritability implies low resemblence and high variance. The low heritability also implies that the variation in the phenotypic trait may be due to the environmental factors as the Vp= Vg +Ve.