Pedigrees

Question 1

What 4 things make it difficult to study inheritance in humans?

Answer 1

Incomplete medical records, can’t control crosses, small sample sizes, medical ethics

Question 2

What is a pedigree?

Answer 2

A family tree with a phenotype trait tracked to determine inheritance

Question 3

What are the symbols used to represent males, females, unknown sex, an unaffected individual, an affected individual, a suspected heterozygote, a dead individual, and a miscarriage?

Answer 3

Male: a square
Female: a circle 
Unknown sex: diamond 
Unaffected: white symbol 
Affected: black symbol
Suspected heterozygote: half black and half white symbol
Dead: crossed out symbol 
Miscarriage: a small symbol

Question 4

Why are genetic disorders rare in the general population?

Answer 4

Natural selection

Question 5

Why don’t we usually see Mendelian ratios with pedigrees?

Answer 5

Sample sizes are too small

Question 6

What is assumed to be the genotype of non family members?

Answer 6

Homozygous unaffected

Question 7

What is more common, recessive disorders or dominant disorders?

Answer 7

Recessive

Question 8

What is the evidence seen in a pedigree for an autosomal dominant disorder? What disorders have this inheritance pattern?

Answer 8

Males and females are equally affected, affected individuals have an affected parent, is present in every generation. Achondroplasia and Huntington’s disease

Question 9

What is the evidence seen in a pedigree for an autosomal recessive disorder? What disorders have this inheritance pattern?

Answer 9

Males and females equally affected, affected individuals have unaffected parents. Cystic fibrosis

Question 10

What is the evidence seen in a pedigree for an sex-linked dominant disorder? What disorders have this inheritance pattern?

Answer 10

Both males and females are affected because the disorder is dominant, but there is a gender bias. Affected males will transmit the trait to their daughters but not their sons. Affected females pass the trait to half their sons and half their daughters. Fragile X syndrome

Question 11

What is the evidence seen in a pedigree for an sex-linked recessive disorder? What disorders have this inheritance pattern?

Answer 11

More males affected than females and affected individuals with unaffected parents. Duchenne muscular dystrophy, colourblindness