CBG12

Question 1

What is an autosome?

Answer 1

chromosome that is not a sex chromosome

Question 2

what is hemizygous

Answer 2

A chromosome in a diploid organism is hemizygous when only one copy is present. Hemizygosity is also observed when one copy of a gene is deleted, or in the heterogametic sex when a gene is located on a sex chromosome.

Question 3

What is a recessive lethal gene? give an example

Answer 3

can cause organism to die only when present in homozygous 1/4 of offspring die in hetergozygous cross eg. manx cat with no tail hetero= tailess homo = normal recessive = die in utero ratio 2:1 not 3:1

Question 4

How many genotypes and phenotypes are there in human blood groups?

Answer 4

6 genotypes 4 phenotypes A B O AB complete and codominance occur

Question 5

What is an example of incomplete/partial dominance

Answer 5

eg. sna drgaon homozygotes are red/white hetero= pink more red than white. red homo partially dominates looks like blending but not often due to haplo insufficiency - 1 copy of red allele not enough for phenotype

Question 6

What is codominance give an example

Answer 6

2 alleles encode different gene products contributions of both alleles are visible in phenotype eg. 2 forms of glycoprotein (M or N) on RBC L^M or L^N alleles at locus chromosome 4 mating between heterozygotes gets 1:2 :1 ratio

Question 7

What is an example of 2 genes effected a single trait? eg. dihybrid cross 9:3:3:1 phenotypes

Answer 7

can be seen in skin pigmentation in corn snakes 2- independent genes 4 phenotypes camoflage, orange, black, albino

Question 8

What is epistasis?

Answer 8

effect of one gene being dependent on presence of another. epistatic gene interferes with phenotypic expression of other - hypostatic gene

Question 9

What is dominant epistasis?

Answer 9

WwYy selfing leadings to mendalin genotype F2 ratio 9:3:3:1 and 12:3:1 phenotype eg. in fruit colour in summer squash presence of W/Y effects and W dom to Y epistatically.

Question 10

What is polygenic inheritance/additive?

Answer 10

when phenotypic effects of alleles and poly genes are additive. eg. kernal colour in wheat 2 genes each with 2 alleles with additive gene action each A/B add oone unit of colour each a/b add 0 phenotypic sum of additive colour eg. AABB =4 darkest.

Question 11

How many phenotypic classes would do polygenes give?

Answer 11

5 classes eg. AABB aaBB Aabb AaBb AABb more genes gives more classes giving continuous distribution

Question 12

What is penetrance?

Answer 12

% of individual in population exhibiting phenotype associated with their allele

Question 13

What is expressivity?

Answer 13

degree to which a given alle is expressed at the phenotypic level

Question 14

What does variable pentetrance, expressivity and penetrance and expressivity look like?

Answer 14

Question 15

What happens in autosomal recessive?

Answer 15

males and females equally effected

skips generation

Question 16

What happens in autosomal dominant?

Answer 16

males and females equally effected

doesnt skip generatoon

afflicted offsping has afflicted parent

Question 17

What is the result of incomplete pentrance of an autosomal dominant trait?

Answer 17

expect to see phenotype in parent but dont as incomplete penetrance

eg. poluactyly - extra toe.

Question 18

Give an example of variable expressivity of an autosomal dominant trait?

Answer 18

eg. type 1 osteogenesis - brittle bone disease.

different levels of disease

Question 19

For a single gene what things can cause deviations from expected mendalian genetics?

Answer 19

1. sex linkage
2. incomplete dominance
3. codominance
4. multiple alleles
5. lethal genes
6. variable expressivity
7. variable penetrance

Question 20

What is implicated when inheritance gives rise to phenotypic classes expressed in 1/16th?

what are deviations from this?

Answer 20

interaction of 2 genes.

deviations from this are epistasis and polygenic inheritance.