Lecture 3

Question 1

how are chromosomes found in somatic cells?

Answer 1

in HOMOLOGOUS pairs (maternal and paternal)

Question 2

how are chromosomes found in gametes? why?

Answer 2

gametes only have 1 chromosome bc the homologous pair separates during meiosis

Question 3

in the original chromosome theory, how did they describe the separation of chromosomes?

Answer 3

pairs are separated INDEPENDENTLY of how other pairs separate

Question 4

describe Morgan’s first experiment in relation to sex-linked traits
- what was the predicted outcome according to Mendelian genetics?
- what was the actual outcome?

Answer 4

P: red female x white male
F1: red female and red male
(100% of progeny have red eyes –> therefore red is dominant)

PREDICTION:
F1 x F1:
- 25% red R/R
- 50% red R/r
- 25% white r/r

ACTUAL RESULT:
F1 x F1:
- 50% red female
- 25% red male
- 25% white male

Question 5

describe Morgan’s second experiment in relation to sex-linked traits
- does this contradict or support Mendel?

Answer 5

P: white female x red male
F1: 50% red female, 50% white male

contradicts Mendel because we expect all red

Question 6

why does the pattern of red/white inheritance not follow Mendel’s law?

Answer 6

the pattern of red/white inheritance is X-linked

Question 7

in Morgan’s first experiment, why were all the F1 progeny red for male and female?

Answer 7

red female brought all the X chromosomes with dominant R trait

Question 8

explain the results from Morgan’s F1 x F1 cross now that we know the pattern of R inheritance is X-linked

Answer 8

cross F1 female and F1 male:

Question 9

explain the results from Morgan’s second experiment now that we know the pattern of R inheritance is X-linked

Answer 9

Parents were white female and red female
- only way female can be white is having recessive r on both X
- only way male can be red is having dominant R on its X

Question 10

2 things that you will see in pedigree of autosomal recessive

Answer 10

1. skip generation
2. males and females equally affected

Question 11

2 things that you will see in pedigree of autosomal dominant

Answer 11

1. every generation affected
2. males and females equally affected

Question 12

4 things you will see in pedigree of X-linked recessive

Answer 12

1. more males affected
2. affected mothers always have affected son
3. daughter can only be affected if mother and father have allele
4. affected fathers always have heterozygous daughter
5. affected fathers cannot pass trait to son (no male-male transmission)

Question 13

why are males more affected than females in X-linked recessive?

Answer 13

females require both X to be affected but males with only 1 X will be affected so more likely males will be affected

Question 14

2 things you will see in pedigree of X-linked dominant

Answer 14

1. affected males pass disease to daughters but not sons
2. affected heterozygous females mating with unaffected males will pass disease to 50% of offspring