Lecture 15 - The molecular basis of inheritance

Question 1

Mendel’s particulate inheritance theory

Answer 1

Physical substance transmitted from generation to generation controls traits.
Cells called granules are responsible for this transmission

Question 2

Darwin Pangenesis theory

Answer 2

Cells throw off granules or atoms (gemmules) which circulate freely in the system and self-divide/develop when supplied with proper nutrients

Question 3

Roux’s observations: Why chromosomes are good physical substrates for trait inheritance (proposed in 1880) ?

Answer 3

They divide equally

Question 4

Boveri experiment that led to : A correct number of chromosomes is required for development. (2 steps)

Answer 4

1. Manipulate embryos to affect how chromosomes segregate

2. Only embryos with correct number of chromosomes develop

Question 5

Sutton: 3 conclusions made based on Mendel’s work (physical correlation with his results)

Answer 5

1. Chromosomes occur in matched pairs
2. Pairs segregate 1:1 during meiosis
3. Pairs segregate independently (of other pairs)

Question 6

Inheritance of the white eye trait in flies

Answer 6

recessive X-linked

Question 7

Morgan experiment leading him to associate trait inheritance to chromosomes

Answer 7

Observed the X chromosomes in flies and after crossing a red/red female with a white/Y male (P) and crossing F1, noticed white eyes trait = only males in F2

Question 8

Bridges’ (Morgan’s student) work leading to conclusion that chromosome = basis of inheritance

Answer 8

Looked at cases where segregation of traits wasn’t as predicted and noticed that inheritance of chromosomes matched that (non-disjunction)

Question 9

Crossing XX vermilion females (recessive) and XY white type males, what was the weird observation of Bridges? (+2 explanations)

Answer 9

Rare exceptions in progeny : Vermilion females

• Defect in sperm formation/mutation in vermillion gene -> now mutant (on X from the male)
• Female wasn’t virgin

Question 10

What did bridges did with the vermillion females in F1? expectations vs observations in the ‘‘F2’’

Answer 10

Crossed back to WT males. Expectations: Females all red. Males all vermillion. Observed: Females half red half verm. Males half red half verm

Question 11

Conclusion of Bridges’ observation in F2

Answer 11

Ruled out possibility that females had 2 mutant vermillion alleles

Question 12

Explanation for Bridges’ observations

Answer 12

Rare females in F1 were due to non disjunction in P female gamete. These females were XXY.