Question

n the following table, average differences of birth height, birth weight, and IQ score between monozygotic twins (reared together and apart are compared. Based on the data below, which quantitative trait has the lowest heritability?

Trait	MZ Reared Together	MZ Reared Apart
Height (cm)	0.7	0.8
Weight (kg)	1.9	4.5
IQ	1.7	1.9

Its weight correct?

Answer 1

Heritability indicates what proportion of phenotype is controlled genetically (not affected by environment).

When monozygotic twins are rared together, they experience same genetic as well as environmental conditions.

Monozygotic twins reared apart will have same genetic but different environmental conditions.

Vp= Vg + Ve, where Vp is variation in phenotype, Vg is variation due to genotype, Ve is variation due to environment. Since twins are monozygotic, they will have same genotype.

Heritability (H2) = Vg / Vp

Trait	MZ reared together (Vg)	MZ reared Apart (Vp)	Ve	Vg / Vp	H2 =(Vg / Vp)
Height	0.7	0.8	0.1	0.7/ 0.8 = 0.875	0.875
Weight	1.9	4.5	2.6	1.9 / 4.5 = 0.422	0.422
IQ	1.7	1.9	0.2	1.7 / 1.9 = 0.894	0.894

Heritability (H2) ranges from 0 to 1.

Weight has lowest heritability of 0.422 and phenotype is affected more by environment.