Gene interactions

Question 1

Define gene interaction

Answer 1

Production of novel phenotypes by the interaction of alleles of different genes

Question 2

What’s the independent gene effect?

Answer 2

When genes act independently from each other, each gene contributes to the phenotype without influencing other genes

Question 3

What’s epistasis ?

Answer 3

One gene masks or modifies the effet of another gene

Question 4

What’s complementation?

Answer 4

when two different mutations restore a wild-type phenotype

Question 5

What are modifier genes?

Answer 5

Genes that enhance or supress the effects of another gene

Question 6

Define polygenic inheritance

Answer 6

When multiple genes contribute to the same trait

Question 7

Gene interactions lead to ___ from classical mendelian ratios

Answer 7

Deviations

Question 8

What’s the phenotypic ratio resulting from recessive epistasis ?

Answer 8

9:3:4

Question 9

What’s the phenotypic ratio resulting from Dominance epistasis ?

Answer 9

12:3:1

Question 10

How can we calculate the number of pairwise interactions in epistasis ?

Answer 10

Number = N(N-1)/2

Question 11

Name the 3 types of epistasis

Answer 11

• Genetical epistasis
• Biological epistasis
• Statistical epistasis

Question 12

Define genetical epistasis

Answer 12

Molecular interactions between genes or proteins, wether they belong to the same pathway or interact directly with one another

Question 13

Define biological epistasis

Answer 13

Change in allelic effect because of the interference with an allele at another locus.

Question 14

How can we measure biological epistasis ?

Answer 14

By substituting one allele for another against a standard and fixed genetic background

Question 15

Define statistical epistasis

Answer 15

When the average combined effects of alleles at different loci on a trait differs from what would be expected based on their individual effects, as measured in a population.

Question 16

How can we measure Statistical epistasis ?

Answer 16

By substituting one allele for another against the population average of genetic backgrounds

Question 17

What is it called when an allele is fully expressed in the phenotype pf a heterozygote diploid organism?

Answer 17

Complete dominance

Question 18

Describe incomplete dominance

Answer 18

Expressing a heterozygous phenotype that is distinct from the phenotype of either homozygous parents

Question 19

If we cross a red flower with a white flower and get pink flowers offsprings, what type of inheritance is the gene for the color ?

Answer 19

Incomplete dominance

Question 20

for which type of dominance do we write alleles with numbers instead of lowercase/upper case letters ?

Answer 20

incomplete dominance

Question 21

What’s the phenotypic ratio for incomplete dominance ?

Answer 21

1:2:1

Question 22

Define codominance

Answer 22

A condition in which the phenotypic effects of a gene’s alleles are fully and simultaneously expressed in a heterozygote

Question 23

Name an example of a codominant trait

Answer 23

ABO blood groups in humans

Question 24

Associate the types of domiance with the following blood types :
- A
- B
- AB
- O

Answer 24

A and B = complete dominance
AB = codominance
O = complete recessivity

Question 25

Define overdominance

Answer 25

The heterozygote phenotype lies outside the phenotypic range of both homozygous parents

Question 26

Name one example of overdominance

Answer 26

Overlap between the distribution of malaria and the prevalence of sickle cell anemia : - The sickle cell allele conveys an advantage against malaria

Question 27

Explain how heterozygote advantage results from overdominance

Answer 27

Sickle cell anemia/malaria example: Being heterozygous (for sickle cell allele) gives the best advantage : not affected by sickle cell anemia + less susceptible to malaria (because sickle cell is recessive) -->whereas no sickle cell anemia allele = more susceptible to malaria and being homozygous for sickle cell anemia = affected :(

Question 28

What is haploinsufficiency?

Answer 28

When an individual possesses only one functional allele (the other is inactivated by mutation or absent through monosomy)

Question 29

What are the consquences of haploinsufficiency ?

Answer 29

Causes an insufficient amount of protein to produce a normal phenotype

Question 30

Name one disease caused by haploinsufficiency

Answer 30

Marfan syndrome

Question 31

What is penetrance ?

Answer 31

The frequency (%) with which individuals of a given genotype manifest at least some degree of a specific mutant phenotype associated with a trait

Question 32

What is complete penetrance ?

Answer 32

When all individuals with the genotype express the associated phenotype

Question 33

What is incomplete inheritance ?

Answer 33

When only some individuals with the genotype express the phenotype

Question 34

Name 2 factors contributing to incomplete penetrance ?

Answer 34

- Epistasis - Environmental factors

Question 35

Define expressivity

Answer 35

Degree to which a phenotype for a given trait is expressed

Question 36

What is variable expressivity ?

Answer 36

When individuals with a shared genotype exhibit varying phenotypes (range, size, color, intensity...)

Question 37

Which factors cause variable expressivity ?

Answer 37

- Modifier genes - Epigenetic factors - Environmental factors

Question 38

What are modifier genes ?

Answer 38

Genes that affect the phenotypic and/or molecular expression of other genes.

Question 39

Genetic modifiers can affect what ?

Answer 39

- Penetrance - Dominance - Expressivity - Pleiotropy

Question 40

Name one example where environmental factors cause variable expressivity

Answer 40

Siamese cats: coat color is affected by temperature - The enzyme responsible for melanin is active at lower temperatures (and inactive at higher temperatures) - Causing melanin to only be produced in the cooler parts of the cat : paws, tail, ears

Question 41

What is complementation ?

Answer 41

When two strains of an organism with different homozygous recessive mutations that produce the same mutant phenotype have offspring that express the wild-type phenotype when crossed | 2 mutant phenotypes. When crossed, they restore the wild type phenotype.