Lecture 2

Question 1

What is linkage?

Answer 1

The association of genes located on the same chromosome.

Question 2

When do segregation ratios depart from Mendel’s law of independent assortment? (P(recomb))

Answer 2

When the recombination rate = 50%

Question 3

What are non-recombinants?

Answer 3

The parental arrangement of alleles on a chromosome, in other words the offspring has the same arrangement of alleles as the parents.

Question 4

What are recombinants?

Answer 4

Non parental arrangement of alleles on a chromosome, in other words the offspring has a different arrangement of alleles than the parents.

Question 5

What does crossing over do for the population?

Answer 5

• Generates and maintains genetic variability

- Increases evolutionary flexibility

Question 6

How many loci do you need (minimum) to do any mapping?

Answer 6

3

Question 7

What do we implicitly assume about recombination?

Answer 7

Recombination occurs randomly on chromosomes

Question 8

What does the frequency of recombination depend on?

Answer 8

The physical distance between loci on a chromosome.

Question 9

Can you genetically control recombination?

Answer 9

There is some evidence for genetic control of recombination and non-randomness of crossing over. But this is not perfect because of hot and cold spots on the chromosomes. That is, there are some areas that have higher control than others.

Question 10

What does it mean when the probability of recombination =0.5?

Answer 10

Then the two loci are said to be independent and not linked.

Question 11

If you already have a cross over are you likely to have another close by? Why?

Answer 11

Not likely, due to interference.

Question 12

What is coupling?

Answer 12

Two alleles of linked loci on the same homologous chromosome are linked in coupling.
AB and ab

Question 13

What is repulsion?

Answer 13

Two alleles of linked loci on different homologous chromosomes are said to be linked in repulsion.
Ab and aB

Question 14

Define linkage phase. What are the two phases?

Answer 14

Linkage phase refers to the arrangements of alleles at two loci on homologous chromosomes. The two phases are coupling and repulsion.

Question 15

What are the 5 idealized conditions for Hardy-Weinberg equilibrium?

Answer 15

Large population size
Random mating population
No selection of animals
No migration of animals
No mutation of genetic material

Question 16

Under the conditions of HW equilibrium, how are genotypic frequencies determined? How do they change over generations?

Answer 16

Under the 5 conditions of HW equilibrium, genotypic frequencies are determined by allelic frequencies and are constant across generations.

Question 17

When is a population in disequilibrium?

Answer 17

The population is in disequilibrium if the frequency of the genotype differ from HW equilibrium expectations. Add D to the end of allele frequency equations, which tells us how much the frequency has deviated from expectation.

Question 18

How does disequilibrium differ between autosomal and sex-linked genes?

Answer 18

Autosomal genes require one generation of random mating to restore HW equilibrium.
Sex-linked genes require more generations of random mating to restore HW equilibrium.

Question 19

What is heterozygosity?

Answer 19

The degree of detectable variation at a locus.

Question 20

What is PIC?

Answer 20

Polymorphism information content
The probability that the genotype of a given offspring will allow deduction, in the absence of a crossover, of which of the two alleles of the parent it received. It depends on the number of alleles and their frequency.

Question 21

What are the 4 example situations in reference to tracing alleles from parents to progeny and informative matings?

Answer 21

1. Fully informative for both parents (offspring = double F2)
2. Fully informative for parent with full information (offspring = backcross)
3. Offspring with parental alleles is not informative (offspring = F2)
4. All offspring are not informative (offspring = F1)