Trait MZ % DZ % Blood types 100 66 Eye color 99 28 Mental retardation 97 37 Measles 95 87 Hair color 89 22 Handedness 79 77 Idiopathic epilepsy 72 15 Schizophrenia 69 10 Diabetes 65 18 Identical allergy 59 5 Cleft lip 42 5 Club foot 32 3 Mammary cancer 6 3
Genetic Variation
Genetic variation refers to the variation in the genome sequences between individual organisms of a species. Individual differences or population differences can both be referred to as genetic variations. It is primarily caused by mutation, but other factors such as genetic drift and sexual reproduction also play a major role.
Quantitative Genetics
Quantitative genetics is the part of genetics that deals with the continuous trait, where the expression of various genes influences the phenotypes. Thus genes are expressed together to produce a trait with continuous variability. This is unlike the classical traits or qualitative traits, where each trait is controlled by the expression of a single or very few genes to produce a discontinuous variation.
The following table gives the percentage of twin
pairs studied in which both twins expressed the same
for a trait (concordance). Percentages listed are
for concordance for each trait in monozygotic (MZ) and
dizygotic (DZ) twins. Assuming that both twins in each
pair were raised together in the same environment, what
do you conclude about the relative importance of genetic
versus environmental factors for each trait?
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