Human MZ and DZ are the twin pairs of the same sex reared together are studied and the following concordance values are identified for various traits. Depending on the values shown in the table, explain the relative importance of genes versus the influence of environmental factors for each trait. Trait Concordance MZ DZ Blood type 100 65 Chicken pox 89 87 Manic depression 67 13 Schizophrenia 72 12 Diabetes 62 15 Cleft lip 51 6 Club foot 40 4 Introduction: Monozygotic twins (MZ) are the ones who prepared from one zygote, which splits and forms two embryos. In dizygotic twins (DZ), each twin develops from each egg is fertilized by a dissimilar sperm and a separate egg. To estimate the influence of genes on phenotypic variation, the study of identical twins reared together can be carried out. In such studies, concordance is measured. Concordance is the percentage of twin pairs in which both members of the pair have the same phenotype for a trait. Concordance frequency gives a general picture of the overall influence of genes on phenotypes.

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Chapter 19, Problem 18P

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Human MZ and DZ are the twin pairs of the same sex reared together are studied and the following concordance values are identified for various traits. Depending on the values shown in the table, explain the relative importance of genes versus the influence of environmental factors for each trait.

Trait Concordance

MZ DZ

Blood type 100 65

Chicken pox 89 87

Manic depression 67 13

Schizophrenia 72 12

Diabetes 62 15

Cleft lip 51 6

Club foot 40 4

Introduction:

Monozygotic twins (MZ) are the ones who prepared from one zygote, which splits and forms two embryos. In dizygotic twins (DZ), each twin develops from each egg is fertilized by a dissimilar sperm and a separate egg. To estimate the influence of genes on phenotypic variation, the study of identical twins reared together can be carried out. In such studies, concordance is measured. Concordance is the percentage of twin pairs in which both members of the pair have the same phenotype for a trait. Concordance frequency gives a general picture of the overall influence of genes on phenotypes.

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The following table gives the percentage of twin pairs studied in which both twins expressed the same phenotype 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? 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

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