Lecture 2

Question 1

What 4 processes contribute to genetic variation?

Answer 1

Mutation.
Independent assortment.
Crossing-over.
Random fertilisation.

Question 2

What are the number of possible offspring combinations from one couple?

Answer 2

2^46.

Question 3

What is a recombinant phenotype?

Answer 3

The combination of phenotypes differs from that found in either parent.

Question 4

2 ways recombinant phenotypes can occur?

Answer 4

Independent assortment.

Crossing over.

Question 5

What is crossing over?

Answer 5

Process of genetic recombination that gives rise to new combinations of linked genes.

Question 6

When does crossing over occur?

Answer 6

Pachytene phase of prophase I.

Question 7

Crossing over begins with synapsis. What is this?

Answer 7

Pairing of homologous chromosomes.

Question 8

What is the synaptonemal complex?

Answer 8

Protein zipper that holds homologous chromosomes together in the tetrad.

Question 9

What does the synaptonemal complex lead to?

Answer 9

Crossing over between homologous chromosomes.

Question 10

What is the result of crossing over?

Answer 10

Recombinant chromosomes with new combinations of linked genes.

Question 11

What is recombination frequency?

Answer 11

Percentage of progeny that inherit a combination of alleles that differs from either parent.

Question 12

How do you calculate recombination frequency?

Answer 12

(No. of recombinants/Total no. of progeny)*100.

Question 13

How can recombination frequencies be estimated?

Answer 13

Studying results of a testcross.

Question 14

What does the recombination frequency depend on?

What will the recombinant frequency be for genes on different chromosomes?

Answer 14

Whether the genes are on same or different chromosomes.

50%.

Question 15

Who was the first to observe gene lineage, and in what scenario?

Answer 15

T.H.Morgan.

Vestigial Wing mutant of Drosophila melanogaster.

Question 16

How is a wild type (normal) allele usually represented?

Answer 16

Superscript +.

Question 17

What did A.H. Sturtevant notice in 1913?

Answer 17

Recombination frequency between two genes should be related to distance apart on chromosomes.

Question 18

What does 1% recombination frequency equal when creating recombination maps?

Answer 18

1cM - 1 centimorgan.

Question 19

Why do map distances not add up in multiple crossovers? (3)

Answer 19

Lead to underestimate of distance between two loci.
Mean recombination frequencies >50% are not possible.
Genes far apart on same chromosome appear to assort independently.

Question 20

What do the largest and smallest numbers indicate in a 3 point cross?

Answer 20

Largest = parental types.
Smallest = result of a double crossover.

Question 21

What are the 2 possible arrangements of alleles in a double heterozygote?
Will these affect the outcome of a testcross with the double mutant?

Answer 21

Coupling heterozygote.
Repulsion heterozygote.
Will affect testcross outcome with double mutant.

Question 22

6 instances of deviations from Mendelian ratios?

Answer 22

Sex-linkage,
Incomplete dominance,
Co-dominance.
Pleiotropy,
Polygenic inheritance,
Epistasis.

Question 23

What are autosomes?

Answer 23

Chromosomes that aren’t sex chromosomes.

Question 24

What does the Y chromosome lack in Drosophila, and what does this mean for the amount of alleles required for a male fruit fly to have white eyes?

Answer 24

Only needs one copy of XW.

Question 25

What is incomplete dominance?

Answer 25

Where a dominant allele does not completely mask the effect of a recessive allele at the same locus.

Question 26

What is an example of incomplete dominance in humans?

Answer 26

Familial Hypercholesterolaemia.

Question 27

What is co-dominance? Example?

Answer 27

Where each allele affects the phenotype in separate, distinguishable ways.
ABO blood type in humans. IA and IB co-dominant.

Question 28

What is Pleiotropy?

Answer 28

When a single gene has multiple effects on the phenotype.

Question 29

What is polygenic inheritance?

Answer 29

When a single trait is determined by multiple genes.

Question 30

What is an observable trait of polygenic inheritance?

Answer 30

Trait shows continuous variation in the population.

Question 31

What is epistasis?

Answer 31

When one gene masks or modifies the expression of another gene.