7- Inheritance

Question 1

What is a locus?

Answer 1

fixed location of each allele on each chromosome

Question 2

What is monohybrid inheritance?

Answer 2

characteristics controlled by a single gene

Question 3

Possible reasons that expected phenotypic ratios are not observed in actual offspring

Answer 3

1. random fertilisation/ fusion of gametes- (any sperm could meet any egg)
2. co-dominance
3. sex-linkage
4. samples taken from small pops
5. meiosis- crossing over (diff combo of alleles) + independent assortment (diff combo of maternal & paternal alleles)

Question 4

What is codominance?

Answer 4

• alleles both expressed in phenotype
• neither is recessive
• both appear/ blend (eg. Cᴿ + Cᵂ)

Question 5

Dihybrid inheritance

Answer 5

inheritance of 2 pairs of alleles
- 2 characteristics inherited from 2 diff genes w/ diff alleles

Question 6

Inheritance of immunoglobulin gene

Answer 6

Iᴬ, Iᴮ, Iᴼ
- Iᴬ & Iᴮ- codominant
- Iᴼ/ i- recessive to both
- Iᴮ i x Iᴮ i –> B:O 3:1
- Iᴬ Iᴮ x Iᴮ i –> AB:B:A:O 1:1:1:1

Question 7

Why aren’t expected ratio ratios always observed in dihybrid crosses?

Answer 7

expected pheotypic ratio = 9:3:3:1
1. linkage
2. epistasis