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biology year 2 > Genetics > Flashcards

Genetics Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

define gene?

A

sequence of bases on a DNA molecule that codes for a polypeptide which results in a characteristic

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2
Q

define allele?

A

different forms of the same gene

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3
Q

define genotype?

A

genetic constitution of an organism - alleles an organism has

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4
Q

define phenotype?

A

expression of the genetic constitution DUE TO ENVIRONMENT

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5
Q

define dominant?

A

an allele whose characteristic appears in the phenotype even when theres only one copy

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6
Q

define recessive?

A

an allele whose characteristic only appears in the phenotype if 2 copies are present

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7
Q

define codominant?

A

alleles that are both expressed in the phenotype - neither one is recessive

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8
Q

define locus?

A

the fixed position of a gene on a chromosome

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9
Q

define homozygote?

A

an organism that carries 2 copies of the same allele e.g. BB or bb

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10
Q

define heterozygote?

A

an organism that carries 2 different alleles e.g. Bb

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11
Q

define carrier?

A

a person carrying an allele which is not expressed in the phenotype but that can be passed onto offspring

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12
Q

are humans diploid/haploid?

A

diploid organisms

we have 2 alleles for each gene

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13
Q

what are gametes?

how many alleles do they have for each gene?

A

sex cells

1

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14
Q

what can genetic diagrams be used to predict?

A

genotypes and phenotypes of offspring poduced if 2 parents crossed

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15
Q

what is monohybrid inheritance?

A

inheritance of a characteristic controlled by a single gene

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16
Q

what do monohybrid crosses show?

A

likelihood of diff alleles of that gene being inherited by offspring of certain parents

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17
Q

what is the first set of offspring known as?

A

F1 generation

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18
Q

what is another way of showing a genetic diagram?

A

punnett square

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19
Q

example of codominance?

A

in humans allele for sickle cell anaemia

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20
Q

what do dihybrid crosses show?

A

how 2 different genes inherited at same time

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21
Q

predict the phenotypic ratio of F1 gen for :

  • monohybrid cross
  • homo dom X homo recess
A

all hetero offspring

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22
Q

predict the phenotypic ratio of F2 gen for:

  • monohybrid
  • homo dom X homo recess
A

3: 1
dom: recess

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23
Q

predict the phenotypic ratio of F1 and F2 gen for:

  • dihybrid cross
  • homo dom X homo recess
A

F1 = all hetero offspring

F2 = 9:3:3:1

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24
Q

predict the phenotypic ratio of F1 and F2 gen for:

  • codominant cross
  • Homo dom X homo recess
A
  • F1 - all hetero
  • F2 - 1:2:1
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25
Q

the genetic info for gender is carried where?

A

on 2 sex chromosomes

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26
Q

when is a characteristic said to be sex linked?

A

when allele that codes for it is on a sex chromosome

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27
Q

difference between Y and X chromosome?

A
  • Y = smaller
  • carries fewer genes
  • most genes carried on X chromosome
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28
Q

define X-linked disorders?

A

genetic disorders caused by faulty alleles on sex chromosomes

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29
Q

examples of X-linked disorders?

A
  • colour blindness
  • haemophilia
30
Q

define autosome?

A

any chromsome that isnt a sex chromosome

31
Q

what are autosomal genes?

A

genes located on autosomes

32
Q

genes on the same autosome are said to be linked.

why?

A
  • on same autosome so stay together during independent segregation
  • alleles passed onto offspring together
33
Q

what is the only reason genes from same autosome wont be inerited together?

A

if crossing over splits them up first

34
Q

define backcross?

A

crossing offspring with one of parents

35
Q

what ratio would you not expect if genes were linked?

A

1:1:1:1

36
Q

define epistasis?

A

allele of one gene masks the expression of alleles of other genes

37
Q

examples of epistasis?

A
  • baldness gene is epistatic to widows peak gene
38
Q

predict the phenotypic ratio of a dihybrid cross involvoing recessive epistatic allele?

A

9:3:4

39
Q

predict the phenotypic ratio of dihybrid cross involing dominant epistatic allele?

A

12:3:1

40
Q

what is the chi-squared test?

A

statistical test used to see if results of experiment support a theory

41
Q

what is the expected result?

A

when theory used to predict result

42
Q

what is the observed result?

A

experiment carried out and actual result recorded

43
Q

what is the null hypothesis always for chi-squared?

A

there is no significant difference between observed and expected results

44
Q

when the chi-squared test is carried out, what is it carried out to compare?

A

how well observed and expected match results

45
Q

to find out if there is a significant difference between your observed and expected results, what do you need to compare your chi-squared value to?

A

critical value

46
Q

what is the critical value?

A

value of chi squared that corresponds to 0.05 probability level that the difference between observed and expected results is DUE TO CHANCE

47
Q

if chi squared value is larger than / equal to critical value then…

A
  • is significant difference
  • between observed and expected
  • null rejected
48
Q

if chi-squared value smaller than critical value then…

A
  • no sig difference
  • between observed and expected
  • null NOT rejected
49
Q

male cats with tortoiseshell phenotypes dont occur.

why?

A
  • Y chromsome doesnt carry allele
  • cannot be hetero
50
Q

the allele for polydactyly is dominant.

some cat breeders select for polydactyly.

describe how this would affect the frequences of the homozygous genotypes for this gene in their breeding populations over time?

A
  • homo dominant inc
  • homo recessive dec
51
Q

in birds, males are XX and females are XY.

use this info to explain why recessive, sex linked characteristics are more common in female birds than male birds?

A
  • females have one allele
  • recessive allele always expressed
52
Q

explain the advantage of presenting results as a ratio?

A
  • able compare (valid)
  • number / sample size may vary
53
Q
A

gene/loci on same chromosome

54
Q

how many antigen determining alleles will be present in a white blood cells?

give a reason for your answer?

A
  • 2
  • white blood cells = diploid
55
Q

explain 2 reasons why the fruit fly is a useful organism for studying genetic crosses?

A
  • large number of eggs - reduces sampling error
  • simple nutrient medium - reduces cost
56
Q

suggest why observed ratios are often not the same as expected ratios?

A
  • fertilisation is random
  • population sample small
57
Q

male fruit flies are more likely than female fruit flies to show a phenotype produced by a recessive allele carried on the X chromosome.

explain why?

A
  • males have one allele - only need 1 recessive allele
  • females ned 2 recessive alleles
58
Q

in an investigation, the numbers for tongue rolling and thumb characteristics do not add up to 200.

for each characteristic suggest one reason why the numbers do not add up to 200?

A
  • tongue rolling - some people not willing to tell
  • thumb - thumb bending subjective
59
Q
A
  • 4 and 3
  • both 4 and 3 are carries / hetero
60
Q

explain one piece of evidence from the diagram which proves that the allele for Tay-Sachs disease is not on the X chromosome?

A
  • 11 affected, 3 not
  • 3 doesnt have recessive allele on his chromsome
61
Q

suggest why the actual percentage of heterozygotes is likely to be lower in future generations than the answer you would have calc?

A

affected individuals usually dont reproduce

62
Q

suggest advantages of using island populations?

A
  • can record all individuals on small islands
  • less sampling error
  • diff rates of mutation
  • inbreeding more likely
  • little gene flow
63
Q

the geneticist concluded that arm-folding is NOT determined by a single gene with a dominant allele and a recessive allele.

use info from figure 2 to explain why she reached this conclusion?

A
  • if R recessive, R x R parents cant produce L offpsring
  • if L recessive, L x L parents cant produce R offspring
  • R x R and L x L parents produce both types of offspring
64
Q
A

both twins folded arms differently

65
Q
A
  • 1,2 and 5
  • 1 must pass on recessive allele to 5
66
Q

explain why scientists used the same restriction endonuclease enzyme on each DNA sample?

A
  • cut DNA at same base sequence
  • so get fragments with required gene
67
Q

explain why cells in mitosis were used?

A
  • chromosomes visible
  • can see which chromosome DNA probe attaches to
68
Q
A
  • 2 is not colour blind and 4 is colour blind
  • so 2 must be hetero
69
Q
A

gene/loci on same chromsome

70
Q

use your knowledge of gene linkage to explain these results?

A
  • GgNn individuals produce mainly GN and gn gametes
  • crossing over produces some Gn and gN gametes
  • fewer Ggnn and ggNn individuals
  • GN linked with gn
71
Q

explain why the number of people showing LP would rapidly increase once selection for this condition had been established?

A
  • domiant allele
  • always expressed in phenotype
72
Q

lactase persistence is caused by a mutation in DNA.

this mutation doesnt occur in the gene coding for lactase.

suggest and explain how this mutation causes LP?

A
  • mutation in promoter gene for TF
  • lactase gene continues to be transcribed

biology year 2 (29 decks)

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