Lecture 7

Question 1

what is complete recessiveness?

Answer 1

mutations in haplosufficient genes –> require LOF in both alleles to be non-functional

Question 2

what is complete dominance?

Answer 2

mutations in haploinsufficient genes –> GOF/LOF in 1 allele is enough to be non-functional

Question 3

what is dominant negative?

Answer 3

a subunit of a dimer is mutated, binds to the other WT subunit and interferes with its function

Question 4

example of gene that is dominant negative

Answer 4

p53 binds DNA as homotetramer –> dominant mutation in DNA binding domain in 1 allele allows it to form the tetramer but unable to bind DNA –> cannot perform normal function

Question 5

what is incomplete dominance?

Answer 5

heterozygous has phenotype between dominant and recessive

Question 6

what do we see on a gel of gene with incomplete dominance?

Answer 6

band is between dominant and recessive

Question 7

when is incomplete dominance common?

Answer 7

common with mutations in enzymes that make pigments

Question 8

what is codominance?

Answer 8

heterozygous has both dominant and recessive alleles expressed

Question 9

example of codominance

Answer 9

blood types

A –> genotype A/A or A/i
B –> genotype B/B or B/i
AB –> genotype A/B
O –> genotype i/i

Question 10

describe the dominance and codominance found in blood types

Answer 10

A and B are dominant over O but codominant with each other

Question 11

what does the type of dominance depend on?

Answer 11

the phenotype you are looking at and the method of detection

Question 12

what is recessive lethal?

Answer 12

heterozygous appears normal bc haplosufficient but if homozygous individual will die

Question 13

how are recessive lethal mutations maintained in diploids?

Answer 13

heterozygotes will carry the recessive lethal mutations

Question 14

how are recessive lethal mutations maintained in haploids?

Answer 14

not maintained –> only 1 copy is ever present

Question 15

describe recessive lethal in regards to mouse colour

Answer 15

heterozygous yellow x normal
- half yellow, half normal

heterozygous yellow x heterozygous yellow
- 2 yellow, 1 normal, 1 dead

Question 16

in recessive lethal, why is the gene considered dominant and recessive?

Answer 16

gene is dominant in regards to phenotype

gene is recessive in regards to survival

Question 17

what are conditional alleles?

Answer 17

depend on external factor

Question 18

example of conditional allele?

Answer 18

a specific tyrosine kinase is only active at low temp

Question 19

what is penetrance?

Answer 19

% of ppl with given allele who express the phenotype of that allele –> i.e. even with same genotype, may not have same phenotype

Question 20

3 things that determine penetrance

Answer 20

1. environment
2. surrounding genes
3. subtlety of mutant phenotype / how it is diagnosed

Question 21

what happens to pedigree with incomplete penetrance?

Answer 21

may appear like it skips generation but may just be undetected bc of phenotype or detection method for ex.

Question 22

what is expressivity?

Answer 22

degree to which a given allele is expressed at phenotype level –> i.e. intensity of a phenotype

Question 23

3 things that determine expressivity

Answer 23

1. environment
2. surrounding genes
3. subtlety of mutant phenotype / how it is diagnosed