Lecture 23 - "real world" genetics 1

Question 1

can you test for hardy-weinberg equilibrium if you are examining phenotypes with dominant traits?

Answer 1

no

> can’t test for HW because you don’t know the genotype of the heterozygous individual.

Question 2

What happens if the transciption or translation of a gene goes wrong?

Answer 2

>point mutations
> insertion 
>deletion
>loss of function
> change in function
> change in regulation

Question 3

what does incomplete dominance mean?

Answer 3

the heterozygote has an intermediate phenotype

Question 4

what is an example of a co-dominant trait?

Answer 4

blood type. Both alleles affect the phenotype

Question 5

what is an example of overdominance?

Answer 5

extra fruit in tomato plants.

> heterozygote has more extreme phenotype than either homozygote

Question 6

what is important to keep in mind when thinking about the differetn types of dominance?

Answer 6

> incomplete, co-, and over dominance all describe phenotypic traits in relationship to a single locus.
single locus genotypes are either homozygous or heterozygous

Question 7

what happens when you do not just have one locus to one trait?

Answer 7

> pleiotropy - one gene, multiple trait outcomes.
- “mutant” allele transmitted in an autosomal incomplete dominant mode.
- e.g., frizzle gene in chickens, affects feather curling, metabolism, body temp and number of eggs laid
Polygenic traits - a trait is controlled by multiple genes, usually along a continuum
- e.g., skin colour
epistasis - two or more genes interact to yield a trait

Question 8

what is the ratio of dog coat colour ? (epistasis)

Answer 8

9:3:4 black:brown:yellow

Question 9

how can you test for epistasis?

Answer 9

FOR NO EPISTASIS
>di-hybrid cross
> for genes on separate chromosomes
> each allele pair shows independent segreation
>f1 produces 4 gamete genotypes
>F2 shows 9:3:3:1 phenotypes
FOR EPISTASIS
>different ratio then 9:3:3:1

Question 10

what regulatory mechanisms affect how genes are expressed and thus gene expression ?

Answer 10

> environment
time
-seasonality
age

Question 11

what are the key concepts from this lecture?

Answer 11

> although Mendel was right that genes are inherited in a particular manner (independent assortment), relationships between genotypes and phenotypes can be quite complex
Mendel’s “alleles” represent DNA variation in both protein coding genes and regulatory elements