R12 genetic interactions

Question 1

What is the difference of allelic and non-allelic interactions ?

Answer 1

Allelic interactions – alleles of the same gene
Non-allelic interactions – alleles on different genes

Question 2

What is complete dominance?

Answer 2

heterozygote and homozygous dominant have the same phenotype

Question 3

What is haplosufficiency and haploinsufficiency ?

Answer 3

• Haplosufficiency: recessive mutations, one gene copy produces sufficient protein
• Haploinsufficiency: dominant mutations, one gene copy does not produce sufficient protein

they are properties of the gene not of the mutation

Question 4

What is incomplete dominance ?

Answer 4

the phenotype of the offspring is an intermediate of the two parents. Heterozygote has an intermediate. Pink flower from a white and red.
- One parent has 2 doses and one parent has 0 leading to the offspring having 1

Question 5

What is a lethal allele ?

Answer 5

Compromise the function of an essential gene

organisms can tolerate being heterozygous but not homozygous

Question 6

What is a conditional mutation ?

Answer 6

A mutation that exhibits wild phenotype under certain (permissive) environmental conditions, but exhibits a mutant phenotype under other (restrictive) conditions

Question 7

What is an allelic series ?

Answer 7

Different alleles at one locus leading to variation in a population

Question 8

What will a mutation that abolishes gene function do in haplosufficient cases ?

Answer 8

Will be recessive because both gene copies need to be inactivated before a phenotype is observed

Question 9

What will a mutation that abolishes gene function do in haploinsufficient cases ?

Answer 9

dominant because a phenotype will appear in the heterozygote (the other functional copy, on its own, is not enough to sustain for that particular gene function).

Question 10

What is epistasis ?

Answer 10

Expression of one gene masks the expression of another in the same genetic or biochemical pathway

Question 11

What is the epistatic and hypostatic gene ?

Answer 11

• The masking gene is said to be epistatic to the masked
• The masked gene is said to be hypostatic to the masking.

Question 12

What is recessive epistasis ?

Answer 12

recessive phenotype overrides the other phenotype.
- Mutant phenotypes of the upstream gene take precedence, no matter what happens later on in the pathway

Question 13

What is dominant epistasis ?

Answer 13

dominant allele of an upstream gene inhibits the pathway from progressing. The dominant allele is said to be epistatic over the gene later on in the pathway.

Question 14

What is duplicate gene action ?

Answer 14

2 genes of the same biological function led to genetic redundancy

• One dominant allele is sufficient for function so only double homozygous recessive show a different phenotype
• Can be referred to as duplicate dominant epistasis

Question 15

What is complementary gene action ?

Answer 15

phenotype determined by the combination, due to the concurrent action of the genes (enzymes in the same biochemical pathway). Recessive alleles on either gene leads to the same phenotype. Can be called duplicate recessive epistasis.

both genes could code for a subunit of a protein or one gene could code for a transcription factor for another enzymatic gene

Question 16

What is a complementation test?

Answer 16

Homozygotes in 2 genes are crossed leading to a hybrid forming of different phenotypes

AAbb and aaBB being crossed to make a AaBb.

A and B are vital for making the final trait, so recessive in either will form the same phenotype.

Question 17

What are modifiers ?

Answer 17

mutations that modify the expression of a different gene, this may dilute the colour of cat’s fur for example. This means there can be two different phenotypes for the same genotype (black and blue fur colour).

Question 18

What is a suppressor ?

Answer 18

mutation that reverses the effect of another mutation (resorting in the WT phenotype). Can be within the same gene or different genes and can be dominant or recessive.

Question 19

Are non-allelic interactions present in haploid organisms ?

Answer 19

Yes

Question 20

mutation a is -2, mutation b leads to -3 (loss of function), what does -5 in the offspring show and -2, -3 or 0 or -1?

Answer 20

-5 -> additive action
-2, -3 -> shows epistasis
0, -1-> shows full or partial supression

Question 21

Precursor is turned to O antigens with the H enzyme.

O antigen is then turned into A and B antigens using the ABO law.

h is epistatic over A and B antigens

What blood types do these genotypes form ?
BOHh
AOHH or AOHh
BBhh, BOhh, ABhh
ABHh

Answer 21

BOHh - Blood type B
AOHH or AOHh - Blood type A
BBhh, BOhh, ABhh - Blood type O
ABHh - AB blood type

Question 22

If there dominant epistasis in H/h regulation of blood type, what effect would there be?

Answer 22

H would mask the blood type, meaning hh is needed for any blood type to form other than O