exam 1: relating phenotype to genotype

Question 1

types of inheritance that have traits controlled by 1 gene (locus) but dont show the typical ratios

Answer 1

1. incomplete dominance: one gene mask the other
2. codominance: work tgt, see them equally
3. > 2 alleles

4.pleiotropy:one gene control multiple traits

5. lethality: bad genetics that are lethal

Question 2

type of inheritance that dont show medelian ratios because they are controlled by many loci

Answer 2

multifactorial
-epistasis
-heterogeneous traits

Question 3

incomplete dominance

Answer 3

1 allele DOES NOT completely mask the presence of another

-occurs when 1 allele is functional (expressed), 1 allele is functional but not enough to mask the other
-phenotype is a heterozygous between the two homozygous phenotypes (red is not enough to completely mask the nonfunctional allele

homozygous: red and white
heterozygous: pink
1:2:1
-> true breeding of white is nonfunctional

Question 4

codominance

Answer 4

both alleles at a locus are expressed equally in the phenotype
(both alleles are functional & equally in the phenotype)
-blood types

Question 5

more than 2 alleles

Answer 5

how to multipple alleles arise? mutation (1 in 3 gametes)

*mutant allele: <1% frequency (distinctly rare)
*wild allele:>1% frequency (common)

dominance series:>2 alleles at a locus that varibale dominance relative to each other
ex. coat color in mice
Agouti: wt=A
Black back:mutant=at
black:mutant=a
order of dominance: A>at>a

Question 6

pleiotropy

Answer 6

1 locus affects many traits(1locus affects > 1 phenotypic trait

ex. phenylketonuria
prevents humans from breaking down phenylalanine so it accumulatesf in the brain
=> mental retardation, musty order to skin, blond hair, and light skin

Question 7

lethality
how is it different from fetal?

Answer 7

genetic combinations are bad so embryo stop develop
-embryo never born
*when doing punett square, ross out the genotype that will die (2/3: 66% surviving)

Question 8

multifactorial traits

Answer 8

multiple genes affecting 1 trait

*true breeding lines (coming from diff ancestors)
yields a 9:7 ratio (variation of 9:3:3:1 resulting from complementary gene action)

Question 9

complementary gene action

Answer 9

when crossed, one parent provides what the other is missing and vice versa, genotypes complement each other

Question 10

what can a complementation test tell u?

Answer 10

cross 2 true breeding parents (with same phenotype) from a separate line
-> if all f1’s have phenotype different than parents, you can assume more than 1 gene affect trait and parent carry mutations at diff genes.

Question 11

epistasis

Answer 11

one genetype at 1 locus completely mask the other genotype at a diff locus
**recessive (homozugous recessive) vs. dominant (homozygous/heterozugous-only need one dominant allele)

Question 12

epistasis: recessive vs dominant

Answer 12

homozygous recessive:
when homozygous recessive genotype at 1st locus masks the presence of an allele at 2nd locus

-ex: coat color in retrievers (e is epistasis to b)
if have two ee then the god will be brown no matter what alleles are at the B locus (__ee)

dominant:
when the presence of 1 dominant allele at 1 locus masks the presence of allele at the 2nd locus
ex: summer squash
fruit color controlled by 2 loci: A & B
if a dominant B allele, fruit will be white no matter what alleles present at A locus
- A_bb=yellow
-aabb=green
-_ B=white

Question 13

heterogenous traits

Answer 13

traits controlled by many loci where mutation in any one of the loci can give rise to the same phenotype

ex:deafness in humans
-50 loci in humans control hearing
-mutation (recessive) in any of them can produce same phenptype of deafness
-possible for 2 deaf ppl w mutations at differnt loci to have that are not deaf
->offspring would be heterozygous at loci that are homozugous recessive in parents
=>gene action:complementary gene action

Question 14

not all individuals with same genotype have the same phenotype…why?

Answer 14

1. penetrance
   2.expressivity
   3.modifier genes
2. environmental differences
   5.chance!

Question 15

penetrance

Answer 15

% of individuals in a pop that have a specific genotype and express the corresponding phenotype

ex. retinoblastoma in humans
-dominant mutation in 1 locus
-only 75% of ppl w mutant allele develoop disease so penetrance=75%

(hace dominant allele, only 75% have the phentotype)

Question 16

expressivity

Answer 16

degree with which specific genotype is expressed as a specific phenotype (how intense?)

ex. retinoblastoma in humans
some ppl w mutant allele have disease in 1 eye
, some have it in both eyes

Question 17

modifier genes

Answer 17

alter phenotypes produced by alleles at other loci
-how does this differ from epistasis? mask completely

ex.tail length in mice
-length controlled by single locus
-diff true breeding lines of mice with same genotype for tail length locus have different tail lengths
-linen specific differences due to modifer gene action

Question 18

environment:

Answer 18

any external force (including in utero)
-may affect penetrancen (whether it is expressed/not) and/or expressivity (how intense)

ex: temp and color in Siamese cats
-color produced by enzyme that only function at lower temp
-hve color on extremities because those body parts are colder

Question 19

chance

Answer 19

no 2 calicos have the same phenotype even though color genotype

Question 20

do continuous variations follow mendel laws ? what cause this phenotypic variation?

Answer 20

yes, they do
-continuous varible traits (height,weight, skin color)

*additive gene action

Question 21

additive gene action

Answer 21

presence of specific alleles at loci controlling specific trait increase expression of that trait

ex: height
-height controlled by 1 locus with 2 alleles
-A0 add nothing
-A1 add 2 unit

A0A0=0 unit tall
A0A1=1 unit tall
A1A1=2 units tall