Exam 2 part 3

Question 1

multiple alleles

Answer 1

most genes have >2 alleles in a population
a single diploid can have up to 2 alleles in genome
Arise through changes in DNA sequence by mutation

Question 2

calculating number of possible genotypes in a population

Answer 2

Based on number of alleles n=alleles

n(n+1)/2

Question 3

Hierarchy of dominance

Answer 3

ex. fly eye color

eye color gene has more than 3 alleles with a decreasing order of dominance

Question 4

incomplete dominance

Answer 4

phenotpe of heterozygous is intermediate of homozygotes

Question 5

molecular explanation of incomplete dominance

Answer 5

gene dosage!
homozygosity for functional allele cause 2 doses of gene products
Heterozygosity causes 1 doe
homozygosity for nonfunctional allele causes no dose

Question 6

Haplosufficiency

Answer 6

one does of gene product supports life
Due to threshold effect classified as autosomal recessive
ex. Cystinosis

Question 7

Haploinsufficiency

Answer 7

one does of gene product is not enough to support life
Homozyous wt is healthy
hets and homozygous mutants are dead/sick
ex. BRCA mutations

Question 8

essential genes

Answer 8

gene that encodes a product that is required for life
when mutated, causes a lethal phenotype
no complementary gene

Question 9

Lethal allele

Answer 9

presence results in death

Question 10

Recessive lethal

Answer 10

need 2 copies of lethal allele to exhibit lethal phenotype
most truly recessive lethals are lethal in utero
ex. cystic fibrosis

Question 11

Dominant lethal

Answer 11

both homozygotes for dominate lethal allele and heterozygotes display lethal phenotype
causes by a gain of function mutation or dominant negative mutation

Question 12

dominant negative mutation

Answer 12

loss of function mutation in the mutant allele interferes with function of wt allele

Question 13

codominance

Answer 13

heterozygote shows the phenotypes of both homozygotes simultaneously
ex. AB blood type

Question 14

molecular explanation for codominance

Answer 14

equally strong, expressed gene products that don’t block or interfere with the cellular functions of each other

Question 15

Pleiotropy

Answer 15

one gene is responsible for multiple phenotypes

ex. PKU - low IQ, seizures, light skin pigments

Question 16

linked alleles

Answer 16

when alleles are on the same chromosome, they tend to be inherited together unless separated by recombination

Question 17

Selective sweeps

Answer 17

when 2 or more genes show strong linkage and one gene has an allele that gives a selective advntage, the other allele tends to be inherited with the advantageous allele
Genetic hitchhiking
ex. Crohn’s disease

Question 18

Polygenetic trait

Answer 18

most traits are not monogenic

most traits result from the action of multiple loci

Question 19

Epistatsis

Answer 19

Form of gene interaction in which one gene interferes with the expression of another gene
–one gene (epistatic) masks another gene (hypostatic)

Question 20

modifier gene

Answer 20

alters the expression of a second gene

transcription factors

Question 21

recessive epistasis

Answer 21

homozygous recessive genotype at locus A masks phenotype expression at locus B
aa epistatic to BB, Bb, bb
aa, B- and aabb have same phenotype

Question 22

Dominant epistasis

Answer 22

Presence of dominant allele at locus A masks phenotype expression at locus B
A- is epistatic to BB, Bb, bb
A-,B- and A-bb same phenotype

Question 23

synthetic lethal -negative epistasis

Answer 23

mutation A-alive
mutation B-alive
mutation A and B -dead
B is masking a 
and A is masking b
gene products of A and B wt are involved in complementary pathways

Question 24

Gene expression and the environment

Answer 24

not all individuals with a particular genotype display the expected phenotype

Question 25

internal environment

Answer 25

age, internal signals, genetic factors, sex

Question 26

external environment

Answer 26

temperative, chemicals, nuture, IQ

Question 27

norm of reaction

Answer 27

range of potential phenotypes for a particular genotype

Question 28

penetrance

Answer 28

percentage of individuals with a particular genotype who show the expected phenotype

Question 29

Expressivity

Answer 29

degree to which a phenotype is expressed: severity of phenotype

Question 30

explanation for variations in phenotype

Answer 30

environment
epigenetics
Modifier genes

Question 31

Position effects

Answer 31

physical location of a gene can influence expression

ie. CpG islands

Question 32

Modifier genes

Answer 32

can suppress or enhance phenotypic expression

Question 33

extranuclear genes

Answer 33

DNA found in mitochondria and chloroplasts
circular
mtDNA encodes proteins involved in cell energy production
cpDNA encodes energy production
typically maternal inheritance

Question 34

maternal effect

Answer 34

phenotype of offspring is determined by the nuclear genotype of mother
mRNA and proteins made in oocyte before fertilization