Lecture 3-5

Question 1

What is complete dominance

Answer 1

one who carries the dominant allele, no matter homo or hetero, will display the dominant trait

(ie. BB=Bb but bb is different)

Question 2

What is incomplete dominance

Answer 2

BB, Bb, and bb all differ phenotypically, where the heterozygote is an intermediate between homo dominant and homo recessive

(ie. BB=red, Bb=pink, bb=white)

Question 3

What is codominance

Answer 3

BB, Bb, and bb all differ phenotypically, but Bb exhibits phenotypes of both homozygotes

(ie. blood type)

Question 4

What is a dominance/allelic series

Answer 4

< and > indicate dominance while = indicates codominance in a series of allele pairs for a given organism or species

Question 5

What is a wild type allele

Answer 5

the “normal”

Question 6

What is a loss of function allele

Answer 6

protein is no longer produced, protein is reduced in fewer proportion, or protein is non functional

Question 7

What is haplosufficiency

Answer 7

if you have one wild type allele and one loss of function allele, there is still a sufficient amount of wild type of produce a normal phenotype

Question 8

What is haploinsufficiency

Answer 8

when the dominant gene causes a loss of function, so half as much protein is synthesized but it is not enough to produce wild type phenotype

Question 9

What is a recessive lethal allele

Answer 9

only lethal in homozygotes

(ie. the ts allele in Tay Sachs is the mutated allele, so tsts is lethal, but TSts isn’t and neither is TSTS)

Question 10

What is a dominant lethal allele

Answer 10

expressed in either the homo or hetero, depending on which allele is dominant

(ie. the B allele in Huntingtons is the mutated allele, so BB is lethal and Bb is lethal)

Question 11

What is penetrance

Answer 11

the proportion of individual organisms having a particular genotype that express the expected phenotype
*in sum; variation in the population

Question 12

What is expressivity

Answer 12

the degree to which a phenotype is expressed in an individual
*in sum; variation in the individual

Question 13

What is complete penetrance

Answer 13

one phenotype is completely penetrant in a population

Question 14

What is incomplete penetrance

Answer 14

identical known genotypes in a population yield less than 100% expected phenotype
ie. in a population of brown fur, a few in the population are white, regardless of same genotype

Question 15

What is constant expressivity

Answer 15

all identical genotypes with no expressivity effect have 100% the same phenotype

Question 16

What is variable expressivity

Answer 16

when identical known genotypes have a variability effect that yield a range of phenotypes
ie. a brown population with a variability effect has different shades of brown regardless of same genotype

Question 17

If long fingers are inherited as a recessive trait with 80% penetrance, what are the chances that two heterozygotes would produce an offspring with long fingers

Answer 17

1/4 chance of being homozygous recessive
1/4 x 80% = 20%

Question 18

What are some environmental affects on expressivity and penetrance

Answer 18

age
sex
temperature
chemicals

Question 19

What is the norm of reaction

Answer 19

the range of phenotypes shown by a single genotype under different environmental conditions

Question 20

What is a phenocopy

Answer 20

a change in phenotype arising from environmental factors that mimic the effects of a mutation

Question 21

What is Mendels law of independent assortment

Answer 21

the inheritance of one trait will not impact the inheritance of another trait
ie. AaBb x AaBb type crosses

Question 22

What is the ratio of offspring in the F2 generation of independent assortment between RRYY and rryy

Answer 22

9:3:3:1

Question 23

What is the Mendalian ratio

Answer 23

9:3:3:1

Question 24

If you have complete dominance in two gene pairs contributing to one singular trait, how many phenotypes are seen

Answer 24

4…
full dominant
heterozygous (dominant in one)
heterozygous (dominant in the other)
full recessive

Question 25

What is complementation

Answer 25

two strains of an organism with DIFFERENT homozygous recessive mutations that produce the same phenotype, mate and produce offspring of the wild type phenotype

Question 26

What is the catch to complementation

Answer 26

the mutations in the two parentals must be in DIFFERENT genes

Question 27

What is the logic behind complementation - how is a wild type produced from two mutated organisms

Answer 27

the other genome supplies the wild-type allele to “complement” the mutated allele

Question 28

When will complementation NOT occur

Answer 28

if the parental mutations are in the same gene

Question 29

Give an example of complementation using genes A and B (theoretic example)

Answer 29

if one parent is AAbb, and the other parent is aaBB, each parent has the recessive mutation, just on a different gene (one in aa and one in bb)
when these parents mate, offspring of AaBb can be produced, to form the wild type phenotype

Question 30

If you see a 9:7 ratio on a test question, what should be investigated

Answer 30

complementation

Question 31

What is a heterogenous trait

Answer 31

a mutation in any one of a number of genes can give rise to the same phenotype

Question 32

For complementation to work, what must occur in the parental genes

Answer 32

each must have a mutation on DIFFERENT genes
each must be dominant in the other gene

Question 33

What is the compliment ratio

Answer 33

9:7

Question 34

What is epistasis

Answer 34

the masking of the expression of one gene by another

Question 35

What does the epistatic gene do and what does the hypostatic gene do

Answer 35

epistatic = does the masking
hypostatic = is masked

Question 36

What is the recessive epistatic ratio

Answer 36

9:3:4

Question 37

What is the dominant epistatic ratio

Answer 37

12:3:1

Question 38

Explain recessive epistasis

Answer 38

the recessive gene of one trait masks the gene of the other trait
ie. if referring to A/a C/c genes, recessive c would mask any phenotype of A/a
- so, any time a recessive c occurs, the phenotype of A/a is masked… c is the epistatic gene and a is the hypostatic gene

Question 39

Explain dominant epistasis

Answer 39

the dominant gene of one trait masks the gene of the other trait
ie. if referring to W/w B/b genes, dominant W would mask the phenotype of B/b regardless of the dominance
- so, any time a dominant W occurs, the phenotype of B/b is masked…W is the epistatic gene and B is the hypostatic gene

Question 40

What are the monohybrid ratios for complete dominance, incomplete dominance, and codominance, as well as recessive lethal alleles

Answer 40

complete: 3:1
incomplete: 1:2:1
codominance 1:2:1
recessive lethal: 2:1

Question 41

What are the dihybrid ratios for complete dominance, recessive epistasis, dominant epistasis, and complementation

Answer 41

complete: 9:3:3:1 (Mendelian ratio)
recessive epistasis: 9:3:4
dominant epistasis: 12:3:1
complementation: 9:7

Question 42

What is pleiotropy

Answer 42

a single mutated gene is responsible for a number of distinct and seemingly unrelated phenotypic effects
ie. sickle cell disease and cystic fibrosis

Question 43

What is consanguineous mating

Answer 43

inbreeding

Question 44

What is heterosis

Answer 44

two different inbred lines are crossed, creating heterozygous products

Question 45

What happens frequently with inbreeding

Answer 45

higher frequency of homozygotes, fewer frequency of heterozygotes