Bio 273 Exam 2 Self Check 6 part1 (Ch.6)

4) How does the pedigree of an autosomal recessive trait differ from eh pedigree of an X-linked recessive trait?

Autosomal recessive- 1) Usually appears in both sexes with equal frequency 2) Tends to skip generations 3) Affected offspring are usually born to unaffected parents 4) When both parents are heterozygous, approximately one-fourth of the offspring will be affected 5) Appears more frequently among children of consanguine marriages X-linked recessive- 1) Usually more males than females are affected 2) Affected sons are usually born to unaffected mothers (the trait skips generations) 3) Approximately half of a carrier (heterozygous) mothers sons are affected. 4) Never passed from father to son 5) All daughters of affected fathers are carriers

3) For each of the following modes of inheritance, describe the features that will be exhibited in a pedigree which the trait is present : autosomal recessive, autosomal dominant, X-linked recessive, X-linked dominant, and Y-linked inheritance.

Autosomal recessive- 1) Usually appears in both sexes with equal frequency 2) Tends to skip generations 3) Affected offspring are usually born to unaffected parents 4) When both parents are heterozygous, approximately one-fourth of the offspring will be affected 5) Appears more frequently among children of consanguine marriages Autosomal dominant- 1) Usually appears in both sexes equal frequency 2) Both sexes transmit the trait to their offspring 3) Does not skip generations 4) Affected offspring must have an affected parent unless they possess a new mutation 5) When one parent is affected (heterozygous) and the other parent is unaffected, approximately half of the offspring will be affected. X-linked recessive- 1) Usually more males than females are affected 2) Affected sons are usually born to unaffected mothers (the trait skips generations) 3) Approximately half of a carrier (heterozygous) mothers sons are affected. 4) Never passed from father to son 5) All daughters of affected fathers are carriers X-linked dominant- 1) Both males and females are usually affected; often more females than males are affected. 2) Does not skip generations. Affected sons must have an affected mother; affected daughters must have either an affected mother or an affected father 3) Affected fathers will pass the trait on to all their daughters 4) Affected mothers (if heterozygous will pass the trait on to half of their sons and half of their daughters Y-linked- 1) Only males affected 2) Passed from father to all sons 3) Doesn't skip generations

7) Explain how a comparison of concordance in monozygotic and dizygotic twins can be used to determine the extend to which the expression of a trait is influenced by genes or by environmental factors.

Monozygotic twins have 100% genetic identity, whereas dizygotic twins have 50% genetic identity. Any trait that is completely genetically determined will therefore be 100% concordant in monozygotic twins and 50% concordant in dizygotic twins. Any trait that is completely environmentally determined will have the same degree of concordance in monozygotic and dizygotic twins. To the extent that a trait has a greater concordance in monozygotic twins than in dizygotic twins, the trait is genetically influenced. Environmental influences will reduce the concordance in monozygotic twins below 100%.

6) What are the 2 types of twins and how do they arise?

Monozygotic- when a single fertilized egg splits into 2 embryos in early embryonic cleavage divisions. (genetically identical) Dizygotic- 2 different eggs fertilized at the same time by 2 different sperm. ( 50% of the same genes).

5) Other than the fact that a Y-linked trait appears only in males, how does the pedigree of a Y-linked trait differ from the pedigree of an autosomal dominant trait?

A Y-linked dominant trait is passed from a father to all his sons, whereas an autosomal dominant trait would be passed to only half of his sons.

8) How are adoption studies used to separate the effects of genes and environment in the study of human characteristics?

Studies of adoptees, their biological parents, and their adoptive parents separate environmental and genetic influences on traits. Adoptees share similar environments with their adoptive parents, but they share 50% of their genes with each of their biological parents. If adoptees have greater similarity for a trait with their adoptive parents then the trait is environmentally influenced. If the adoptees have greater similarity for the trait with their biological parents, then the trait is genetically influenced.