Unlinked Genes And Epistasis

Question 1

What are the 2 differences between unlinked and linked genes?

Answer 1

1. Unlinked genes are found on different chromosomes but linked genes are found on the same chromosomes.
2. Unlinked genes are segragated independently of other genes but linked genes are inherited together.

Question 2

What are the offspring ratios like in linked genes?

Answer 2

Offspring ratios are not as expected.

Question 3

What is autosomal linkage?

Answer 3

When the genes that are linked are found on one of the other pairs of chromosomes and linked genes are inherited as one unit.

Question 4

What are 3 factors of homologous chromosomes?

Answer 4

1. Same centromere positions.
2. Same length as one another.
3. Same order.

Question 5

What does linkage do to genetic variation?

Answer 5

Linkage reduces the variety of gametes that can be produced, so reduces the genetic variation in offspring.

Question 6

How are linked genes separated in meiosis?

Answer 6

In prophase 1 in meiosis, crossing over occurs at the chiasmata between non-sister chromatids and swap alleles to separate the linked genes and so creates recombinant genotypes.

Question 7

What are recombinant chromosomes? Genetic variation?

Answer 7

2 new allele combinations that were not possible before crossing over in meiosis, it increases genetic variation.

Question 8

Why are results from genetic crosses different from the expected?

Answer 8

The genes for a particular characteristic must be linked on the same chromosome, so are therefore inherited together.

Question 9

What will the ratio be if there is no linkage?

Answer 9

The expected ratio.

Question 10

What is the recombination frequency? Equation?

Answer 10

• A measure of the amount of crossing over that has happened in meiosis.
• Equation:
  Number of recombinant offspring/total number of offspring.

Question 11

What happens to the recombination frequency as the degree of crossing over reduces?

Answer 11

It decreases.

Question 12

How is the degree of crossing over determined (to help find out the recombination frequency)?

Answer 12

Determined by how close genes are on a chromosome:
- if they are closer together, they are less likely to be separated in meiosis.

Question 13

What is epistasis? Variation?

Answer 13

The interaction between 2 non-linked genes which causes one gene to mask the expression of the other in the phenotype, reduces variation.

Question 14

What ratios does epistasis give?

Answer 14

Unusual ratios.

Question 15

What does hypostatic mean in epistasis?

Answer 15

A gene that is affected by another gene, so is being controlled.

Question 16

What does epistatic mean in epistasis?

Answer 16

A gene that affects the expression of another gene, so is doing the controlling.

Question 17

What are the 2 types of epistasis?

Answer 17

Dominant and recessive.

Question 18

What is dominant epistasis?

Answer 18

If the first gene is homozygous recessive, it will prevent the expression of the next gene.

Question 19

What is recessive epistasis?

Answer 19

When the presence of dominant alleles are the first gene locus masks the expression of alleles at the second gene locus.

Question 20

How can you work out an unknown genotype?

Answer 20

Start with the homozygous recessive genitype and then you can work out the unknown genotype.