Eukaryotic Genetics

Question 1

Mendel’s Experiments

Answer 1

Yellow x Green seeds, with yellow dominant

No irreversible mixing, reciprocal cross had no difference

Question 2

Non-Mendelian

Answer 2

Morgan’s experiments: Drosophilia purple-eye gene and vestigial wings gene are linked, so back cross had vast excess of parental type
Drosophilia white-eyed mutant was X-linked, so reciprocal cross had different results

Question 3

Gene mapping in Drosophila

Answer 3

Crossover proportional to distance
RF = recombinants/progeny
Intervening marker to test for double-crossover event

Question 4

Limitations of Gene mapping

Answer 4

Chiasmata not entirely random (less frequent at centromere
Interference: One chiasma reduces occurrence of another in adjacent region
Drosophila have no recombination in males

Question 5

Variable Dominance

Answer 5

Codominance: Both expressed simultaneously (blood group)

Incomplete Dominance: Both expressed partially (petal colour)

Question 6

Genetic Interactions

Answer 6

Epistasy: eg. Eye-absent in Drosophila hides eye colour

Polygenic Inheritance: 4 different loci

Question 7

Cytoplasmic Inheritance

Answer 7

Vegetative Segregation = random partition of one parent (eg. Asexual reproduction in yeast)

Uniparental Inheritance: Eg. leafcolour in 4-o’clock flower

Biparental Inheritance: Both parents contribute, eg. Mitochondria in yeast sexual reproduction