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H2 Biology > Inheritance > Flashcards

Inheritance Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

define genotype

A

genetic makeup / allelic composition of an organism

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2
Q

define phenotype

A

physical manifestation of genetic trait that results from a specific genotype and its interaction with the environment

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3
Q

define wild-type allele

A

the most common allele in nature

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4
Q

define true-breeding

A

an organism that gives rise to all offspring o the same phenotype (fully homozygous, dominant or recessive)

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5
Q

describe the general steps of a genetic diagram

A

define alleles (let ? represent ?)
parental phenotype parental genotype
parental gametes
random fertilisation (punnett’s square)
offspring genotypic ratio
offspring phenotypic ratio

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6
Q

what is Mendel’s First Law of Segregation?

A

during the formation of gametes, the paired alleles segregate randomly so that each gamete receives one or the other with equal likelihood

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7
Q

what are reciprocal crosses, and what do they show?

A

crosses where parents “swap” genes yield same pattern of inheritance (eg. round male x square female VS square male x round female)
to see if genes are sex-dependent (if both crosses yield the same thing then they aren’t)

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8
Q

what occurs during a test cross, and what do the two results mean?

A

organism with dominant phenotype but unknown genotype crossed with homozygous recessive

all dominant offspring: homozygous dominant
1:1 dominant and recessive offspring: heterozygous

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9
Q

what are the four possible reasons for non-mendelian inheritance, and what offspring phenotypic ratio does each yield?

A

incomplete dominance (1:2:1)
codominance (1:2:1)
multiple alleles
lethal genes (2:1)

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10
Q

define incomplete dominance

A

neither of the two alleles is completely dominant to the other, heterozygote has an intermediate phenotype

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11
Q

define codominance

A

both alleles are equally expressed in heterozygotes (not an intermediate, that’s incomplete)

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12
Q

what is the similarity in phenotypic ratio and difference between incomplete dominance and codominance?

A

similarity is both are 1:2:1

in heterozygotes–
incomplete dominance: intermediate, new phenotype produced
codominance: not intermediate, both dom and rec phenotypes expressed tgth

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13
Q

what are lethal genes, and how does it affect the offspring phenotypic ratio?

A

arise from mutations

if lethal gene is…
recessive– 2:1 (homo dom : hetero; all homozygous recessive die)
dominant– only homozygous recessive survive lol

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14
Q

what is Mendel’s Second Law of Independent Assortment?

A

The segregation of one pair of alleles is independent of the segregation of other pairs

(during metaphase I)

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15
Q

what types of genes does Mendel’s Second Law not apply to?

A

linked genes

they do not assort independently bc they are linked on the same chromosome

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16
Q

what were the advantages of Mendel using garden peas to learn about inheritance?

A

distinct characteristics (discontinuous variation)
easy to cultivate
short life cycle of one year
large number of seeds produced
pollination easily controlled
pure breeds available

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17
Q

what is the phenotypic ratio of a dihybrid cross between two double heterozygotes?

A

9:3:3:1

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18
Q

what is the phenotypic ratio of a dihybrid cross test cross, between a double heterozygote and double homozygous recessive?

A

1:1:1:1

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19
Q

what are homogametic and heterogametic, and how do males and females call into this category?

A

homogametic females: only one type of gamete (egg with X chromosome)

heterogametic males: two types of gametes (sperm with X or Y chromosome, determines zygote’s gender)

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20
Q

what is sex / X- linkage in inheritance?

A

carrying of genes on sex chromosomes (more likely on larger X chromosome)

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21
Q

what are three examples of human X-linked disorders?

A

haemophilia, colour blindness, Duchenne muscular dystrophy

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22
Q

why do X-linked inheritance mainly affect males?

A

males only have 1 X while females have 2: neither homozygous nor heterozygous
hemizygous: only one copy of allele, will be directly expressed

females need two copies for recessive X-linked

23
Q

what are the effects of Duchenne Muscular Dystrophy?

A

codes for enzyme that induces replacement of muscle by fibre, progressive weakness that affects muscle development

24
Q

what is the purpose of a reciprocal cross, and what do its results show?

A

to tell if a trait is carried on a sex or autosomal chromosome, by reversing the traits of two parents

phenotype regardless of gender: autosomal
phenotype dependent on gender: sex-linked

25
Q

list the four main mode of inheritance

A

autosomal dominant
autosomal recessive
sex-linked dominant
sex-linked recessive

26
Q

what are the characteristics of a recessive inheritance?

A

if both parents are affected, all children should be affected
unaffected parents can produce affected individuals
trait often skips generations

x-linked: unaffected fathers only produce unaffected or carrier daughters

27
Q

what are the characteristics of a dominant inheritance?

A

unaffected parents will not have affected children
trait should not skip generations

28
Q

what is the difference between an autosomal and x-linked inheritance?

A

autosomal: males and females affected with equal probaility

x-linked inheritance:
most affected individuals are male
affected mothers = affected sons (always)

29
Q

define linked genes

A

genes that control different characters and are situated on the same chromosome at different loci

30
Q

if two genes are linked, what is not observed?

A

Mendel’s Second Law of Independent Segregation (9:3:3:1 and 1:1:1:1)

31
Q

what is the difference between complete and incomplete linkage?

A

complete: no crossing over occurs between genes, only parental gametes

incomplete: some crossing over occurs, new combination of alleles in gametes

32
Q

what test cross can be performed to detect gene linkage?

A

double heterozygous individual x double homozygous recessive
AaBb x aabb (expected; 1:1:1:1)

33
Q

what are the three results of a gene linkage test cross, and what do they show?

A

diff chromosomes– 4 phenotypes 1:1:1:1
complete linkage: 2 parental phenotypes 1:1, no recombinants
incomplete linkage: 4 phenotypes, 2 parental 2 recombinant, more parental than recombinant (no fixed ratio)

34
Q

what determines the linkage of linked genes?

A

relative distance between genes, probability of crossing over occurring between 2 gene loci increases with increasing distance between the 2 gene loci

35
Q

in heterozygotes, what is a coupling or repulsion arrangement for linked genes?

A

coupling: AB/ab
repulsion: Ab/aB

36
Q

what is the formula for crossover value (COV) or recombination frequency (RF)?

A

number of individuals with recombination OVER total number of offspring (in percentage)

37
Q

what is cM, and what does it represent?

A

centiMorgan, distance between genes is equal to COV/RF (eg. 10% COV = genes are 10 cM apart)

38
Q

what are the two components of phenotypic variance (Vp)?

A

Vp=Vg+Ve

Vg: genotypic variance
Ve: environmental variance

39
Q

what are gene interactions?

A

two or more genes influence one particular character

commonly: metabolic pathway that controls development of one particular phenotype

40
Q

define non-epistatic gene interactions

A

two unlinked, independently-assorting genes may interact to influence a single character

41
Q

what is the difference between dihybrid inheritance and gene interaction?

A

dihybrid inheritance studies two characteristics controlled by two genes
gene interaction studies one characteristic controlled by two or more genes

42
Q

define epistatic gene expressions

A

when the expression of an allele of one gene suppresses / inhibits the expression of alleles of a different gene

43
Q

what are epistatic and hypostatic genes?

A

epistatic genes suppress / inhibit the effect of a different gene, recessively or dominantly

hypostatic genes are suppressed by epistatic genes

44
Q

define recessive epistasis

A

two recessive alleles at the epistatic gene locus will suppress / inhibit the effect of either allele of the hypostatic gene at a different locus

45
Q

how is recessive epistasis shown? (phenotypic ratio, what type of cross)

A

double heterozygous cross
9:3:4 phenotypic ratio

46
Q

define dominant epistasis

A

one dominant allele at the epistatic gene locus will suppress / inhibit the effects of both alleles of the hypostatic gene at a different locus

47
Q

how is dominant epistasis shown? (phenotypic ratio, type of cross)

A

12:3:1

double heterozygote

48
Q

define duplicate recessive epistasis

A

two recessive alleles at either of the two gene loci will suppress / inhibit the effect of the dominant allele at the other locus

two epistatic genes, one hypostatic gene

49
Q

how is duplicate recessive epistasis shown? (phenotypic ratio, type of cross)

A

9:7

double heterozygote

50
Q

what are two types of variation?

A

continuous and discontinuous

51
Q

compare continuous and discontinuous variation

A

discontinuous has discrete phenotypic classes without intermediates, continuous has range of phenotypes with intermediates

discontinuous controlled by single / a few genes, continuous controlled by multiple additive genes (polygenic inheritance), combined effect

discontinuous unaffected by envt, continuous affected by envt

52
Q

what are the causes of genetic variation in a population (sexual and asexual)?

A

asexual: environmental

sexual:
crossing over between non-sister chromatids of homologous chromosomes during prophase I of meiosis
indep assortment of bivalents at metaphase plate during metaphase I of meiosis
random fertilisation

new alleles from mutations

53
Q

give an example of how the environment affects the phenotype expressed

A

temp on himalayan rabbit colour
- homozygous for the ch allele of the tyrosinase gene
- which codes for a heat-sensitive form of the enzyme tyrosinase: needed for melanin production for black fur;
- heat-sensitive tyrosinase active only below 33°C
- black fur only on cool body parts eg extremities like ears

H2 Biology (24 decks)

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