Chapter 9 - Pedigree Analysis and Genetic Testing

Question 1

Know the symbols used in pedigrees and what they mean.

Answer 1

This is covered in lecture 9 slide 4

Question 2

What does the term proband mean?

L9 S9

Answer 2

The person from whom a pedigree is initiated

Question 3

What are characteristics of an autosomal recessive trait on a pedigree?

L9 S12;24

Answer 3

• present equal in both sexes

- can skips generations

Question 4

What are characteristics of an autosomal dominant trait on a pedigree?

L9 S13;24

Answer 4

• present equal in both sexes
• affected people have an affected parent (does not skip generations)
• unaffected people do no transmit the trait (does not skip generations)

Question 5

What are characteristics of an X-linked recessive trait on a pedigree?

L9 S15;24

Answer 5

• appears more frequently in males
• males do not pass the trait on to sons but can pass it onto daughters
• all daughters of affected males will at least be carriers

Question 6

What are characteristics of an X-linked dominant trait on a pedigree?

L9 S18;24

Answer 6

• does not skip generations
• all daughter of affected males are affected
• half the sons of affected, heterozygous females are affected (the other half aren’t carriers)

Question 7

What are characteristics of a Y-linked trait on a pedigree?

L9 S19;24

Answer 7

• only appears in males

- all sons of affected males are affected

Question 8

Autosomal recessive traits often appear in pedigrees in which there have been consanguineous mating, because these traits…

L9 S20-21

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 both to parent who are unaffected
D. Appear equally in males and females

Answer 8

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

Question 9

How could you distinguish between an autosomal recessive trait with higher penetrance in males and an X-linked recessive trait?

Answer 9

A father could pass it to his son

Question 10

Differentiate between monozygotic twins and dizygotic twins.

L9 S25

Answer 10

Monozygotic:

• “identical” twins
• share the same DNA sequence

Dizygotic:

• “fraternal” twins
• as similar DNA as normal siblings

Question 11

Define concordiant trait and concordance.

L9 S25

Answer 11

Concordiant trait:
-trait shared by both members of a twin pair

Concordance:
-percentage of twin pairs that are concordant for a trait