Deck 5: Pedigree Analysis, Applications, and Genetic Testing

Question 1

Autosomal recessive traits appear with equal frequency in males and females. Affected children are commonly born to unaffected parents who are carriers of the gene for the trait, and the trait tends to skip generations. Recessive traits appear more frequently among the offspring of consanguine matings.

-Autosomal recessive traits often appear in pedigrees in which there have been consanguine matings, because these traits

A) tend to skip generations.
B) appear only when both parents carry a copy of the gene for the trait, which is more likely when the parents are related.
C) usually arise in children born to parents who are unaffected.
D) appear equally in males and females.

Answer 1

appear only when both parents carry a copy of the gene for the trait, which is more likely when the parents are related.

Question 2

Autosomal dominant traits appear in both sexes with equal frequency. An affected person has an affected parent (unless the person carries new mutations), and the trait does not skip generations. Unaffected persons do not transmit the trait.
-When might you see an autosomal dominant trait skip generations?

Answer 2

It might skip generations when a new mutation arises or the trait has reduced penetrance.

Question 3

Rare X-linked recessive traits appear more often in males than in females and are not passed from father to son. Affected sons are usually born to unaffected mothers who are carriers of the gene for the trait; thus X-linked recessive traits tend to skip generations.
-How can you distinguish between an autosomal recessive trait with higher penetrance in males and an X-linked recessive trait?

Answer 3

If X-linked recessive, the trait will not be passed from father to son.

Question 4

X-linked dominant traits affect both males and females. Affected males must have affected mothers (unless the males possess a new mutation), and they pass the trait on to all their daughters.

-A male affected with an X-linked dominant trait will have what proportion of offspring affected with the trait?

A) 1/2 sons and 1/2 daughters
B) All sons and no daughters
C) All daughters and no sons
D) 3/4 daughters and 1/4 sons

Question 5

Y-linked traits appear only in males and are passed from a father to all his sons.
-What features of a pedigree would distinguish between a Y-linked trait and a trait that is rare, autosomal dominant, and sex-limited to males?

Question 6

Dizygotic twins develop from two eggs fertilized by two separate sperm; they have, on average, 50% of their genes in common. Monozygotic twins develop from a single egg, fertilized by a single sperm, that splits into two embryos; they have 100% percent of their genes in common.

-Why are monozygotic twins genetically identical, whereas dizygotic twins have only 1/2 of their genes in common on average?

A) Monozygotic twins tend to look more similar.
B) Monozygotic twins are always the same sex.
C) Dizygotic twins arise more frequently with older mothers.
D) Monozygotic twins develop from a single embryo, whereas dizygotic twins develop from two embryos.

Question 7

Higher concordance for monozygotic twins compared with that for dizygotic twins indicates that genetic factors play a role in determining differences in a trait. Low concordance for monozygotic twins indicates that environmental factors play a significant role.

-A trait exhibits 100% concordance for both monozygotic and dizygotic twins. What conclusion can you draw about the role of genetic factors in determining differences in the trait?

A) Genetic factors are extremely important.
B) Genetic factors are somewhat important.
C) Genetic factors are unimportant.
D) Both genetic and environmental factors are important.

Question 8

Similarities between adopted persons and their genetically unrelated adoptive parents indicate that environmental factors affect a particular characteristic; similarities between adopted persons and their biological parents indicate that genetic factors influence the characteristic.

-What assumptions underlie the use of adoption studies in genetics?

A) Adoptees have no contact with their biological parents after birth.
B) The foster parents and biological parents are not related.
C) The environments of biological and adopted parents are independent.
D) All of the above.

Question 9

Genetic testing is used to screen newborns for genetic diseases, detect persons who are heterozygous for recessive diseases, detect disease-causing alleles in those who have not yet developed symptoms of the disease, and detect defective alleles in unborn babies. Preimplantation genetic diagnosis combined with in vitro fertilization allows for the selection of embryos that are free from specific genetic diseases.
-How does preimplantation genetic diagnosis differ from prenatal genetic testing?