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# Use of Twin Information to Calculate Heritability

GENES-7DUIAP

Monozygotic (MZ), or identical, twins result from the splitting of a zygote following a single fertilization event, whereas dizygotic (DZ) twins result from two fertilization events of two different oocytes (they would be referred to as litter-mates in many animal species).

Heritability estimates can be made from twin data when comparing concordance rates between MZ and DZ twins. In a pair of twins, if both have the same phenotype, they are said to be concordant (as opposed to discordant when they do not share the same phenotype). The phenotypes here refer to traits that are qualitative, not quantitative. Consider the twin information below about a particular trait in people.

Type of relationship Genetic considerations Environmental considerations Concordance rates (%)
Monozygotic twins reared together Share all genetic influences Share all environmental influences 90
Monozygotic twins reared apart Share all genetic influences Share only uterine environmental influences 85
Dizygotic twins reared together Share 50% of genetic influences Share all environmental influences 40
Dizygotic twins reared apart Share 50% of genetic influences Share only uterine environmental influences 30


The broad sense heritability is the proportion of the phenotypic variation that is accounted for by all of the genetic variation, and can be determined by comparing differences in discordance rates (1 - concordance rate) between MZ and DZ twins as:

$${ H }^{ 2 }{ =(\text{DZ discordance rate - MZ discordance rate}) }/{ \text{DZ discordance rate} }$$

Based on the information provided, the broad sense heritability here is calculated to be which of the following?

Select ALL that apply.

A

0.75

B

0.79

C

0.83

D

0.86