9 Molecular Basis of Gene Interactions

Question 1

Polygenic inheritance - interaction between genes

Answer 1

Genes cooperate in the production of a trait —> formation of molecule complexes / molecular pathways (eg. Cell signalling)

Function of 1 gene can mask / modify function of another cooperating gene (Epistasis) —> protein of 1 gene may stimulate or repress another gene and its protein / Absence of a functional gene often affects the function of another gene and its protein

Question 2

Epistasis

Answer 2

1 gene can mask / modify function of another cooperating gene

Question 3

gene that is doing the masking…

Answer 3

Epistatic

Question 4

masked gene

Answer 4

hypostatic to the other

Question 5

Epistatic rations may allow a geneticist to determine…

Answer 5

the order of genes in a particulatar pathway

Question 6

Dominant Epistasis ratio

Answer 6

12:3:1

dominant allele of 1 gene masks the effect of both alleles on the other gene

Question 7

Complementary gene action ratio

Answer 7

9:7

2 genes needed to produce characteristics (eg. Snapdragon colour)

DIAGRAMS ON ONENOTE

Question 8

Duplicate gene action ratios

Answer 8

15:1 ratio of phenotypes

double dominant alleles, 2 genes working on same part of pathway

DIAGRAM ON ONENOTE

Question 9

Dominant suppression Epistasis RATIO

Answer 9

13:3

certain genes can suppress the expression of a gene at a second locus

DIAGRAM ON ONENOTE

Question 10

Why is the 9:3:3:1 ratio not always seen

Answer 10

Recombination

Question 11

Recombination during meiosis - what did Morgan observe

Answer 11

Prophase 1

Chias at a mark on site of recombination

Recombination occurs at random positions along the chromosome

Question 12

Recombination during meiosis - What Morgan Predicted

Answer 12

Genetic recombination - mixing of genes during gametogensis produces gametes with combinations of genes that are different from the combinations received from parents

Genes on non-homologous chromosomes (unlinked) assort independently - as predicted by Mendel

Genes of same chromosome can co-segregate

Cross overs result in recombination between linked genes

Question 13

The basis of those ratios

Answer 13

Cross over frequency is a function of the distance between 2 loci - the closer the 2 loci the less chance of a cross over event

Question 14

Odd number of crossovers between 2 loci

Answer 14

recombinant chromosome can be detected

Question 15

Even number of crossovers between 2 loci

Answer 15

no recombination is detected

Question 16

Mapping Genes + Recombination

Answer 16

Recombination frequency of 2 genes can tell us how far apart they are on the chromosome, by comparing multiple pairs of genes we shoukd be able to tell the order of genes along the chromosome

Question 17

Recombination frequency equation

Answer 17

Number of recombinant / number of test cross progeny X 100

Question 18

Recombination frequency can be used as a measure of distance

Answer 18

genetic distance is measured in units called mu (Map unit)
Eg. cM (centiMorgan)

Example questions on Lecture Slides

Question 19

What does 40% recombination frequnecy really mean

Answer 19

Cross over occurred in 40% of the population BUT this means that each recombinant chromosome will be present in the population 20% of the time

Question 20

The maximum Rf is 50, when Rf = 50 genes are unlinked

Answer 20

If recombination occurs 50% of the time there are an equal number of parental and recombinants, so its impossible to know which is which - similar to Punnett square

Therefore Rf >50 is impossible to calculate

Question 21

How to identify whether genes are on separate chromosomes or far apart on same chromosome

Answer 21

• Identify more genes in the linkage group

Question 22

SUMMARY AND QUESTIONS

Answer 22

ONENOTE AND LECTURE SLIDES