Exam 2 part 3 Flashcards Preview

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Flashcards in Exam 2 part 3 Deck (34)
1

multiple alleles

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

2

calculating number of possible genotypes in a population

Based on number of alleles n=alleles
n(n+1)/2

3

Hierarchy of dominance

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

4

incomplete dominance

phenotpe of heterozygous is intermediate of homozygotes

5

molecular explanation of incomplete dominance

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

6

Haplosufficiency

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

7

Haploinsufficiency

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

8

essential genes

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

9

Lethal allele

presence results in death

10

Recessive lethal

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

11

Dominant lethal

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

12

dominant negative mutation

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

13

codominance

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

14

molecular explanation for codominance

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

15

Pleiotropy

one gene is responsible for multiple phenotypes
ex. PKU - low IQ, seizures, light skin pigments

16

linked alleles

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

17

Selective sweeps

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

18

Polygenetic trait

most traits are not monogenic
most traits result from the action of multiple loci

19

Epistatsis

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

20

modifier gene

alters the expression of a second gene
transcription factors

21

recessive epistasis

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

22

Dominant epistasis

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

23

synthetic lethal -negative epistasis

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

24

Gene expression and the environment

not all individuals with a particular genotype display the expected phenotype

25

internal environment

age, internal signals, genetic factors, sex

26

external environment

temperative, chemicals, nuture, IQ

27

norm of reaction

range of potential phenotypes for a particular genotype

28

penetrance

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

29

Expressivity

degree to which a phenotype is expressed: severity of phenotype

30

explanation for variations in phenotype

environment
epigenetics
Modifier genes

31

Position effects

physical location of a gene can influence expression
ie. CpG islands

32

Modifier genes

can suppress or enhance phenotypic expression

33

extranuclear genes

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

34

maternal effect

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