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B > inheritance and evolution > Flashcards

inheritance and evolution Flashcards

1
Q

genotype

A

genetic constitution of an organism

e.g BB

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2
Q

phenotype

A

appearance of a characteristic due to

the expression of the genotype

and its interaction w the environment

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3
Q

what are alleles

A

diff forms of the same gene

may be dominant, recessive or codominant

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4
Q

dominant allele

A

allele always expressed in phenotype

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5
Q

recessive allele

A

only expressed in phenotype when genotype is homozygous recessive

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6
Q

codominant alleles

A

both alleles expressed in phenotype

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7
Q

loci

A

position of a gene on a chromosome

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8
Q

homozygous

A

both alleles same e.g BB, bb

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9
Q

heterozygous

A

both alleles different e.g Bb

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10
Q

gene

A

section of DNA that codes for polypeptide

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11
Q

multiple alleles

A

more than 2 alleles of a particular gene

only 2 can be expressed in genotype tho

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12
Q

sex linked gene

A

genes carried on only one type of sex chromosome

usually X chromosome (non-homologous portion)

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13
Q

monohybrid inheritance

A

inheritance of 1 particular characteristic

punnet squares

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14
Q

what is a test cross used for

A

to determine the genotype of an organism with a dominant phenotype

basically using a punnet square to find ratio of a certain phenotype

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15
Q

non sex and sex chromosomes

A

22 pairs of non sex chromosomes - known as autosomes

1 pair sex chromosomes either XX or XY

females= XX
males= XY

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16
Q

key notes on sex linkage

A
  • man CANT pass sex linked trait onto son but can pass it onto daughter
  • usually X linked
  • only mothers can pass on X chromosome to sons
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17
Q

why are recessive sex linked traits more likely to occur in males

A
  • no other allele on Y chromosome
    -so the recessive allele is always expressed
    -only require 1 recessive allele to be expressed whereas females require 2
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18
Q

pedigree charts tips ( the chart with squares and circles)

A
  • give numbers

-dominant allele= 2 parents who have trait and offspring doesnt - parents must be heterozygous and pass on recessive allele

-not sex linked- dominant= 2 parents with trait (due to dominance) but daughter doesnt (has recessive allele) - daughter would be affected if sex linked

-recessive= 2 parents who dont have trait but offspring does - so parents are heterozygous/ carriers

-not sex linked-recessive = 2 parents w/o trait but daughter with the trait - parents must be heterozygous with both dominant and recessive so cant be sex linked - if it was sex linked, the father and daughter would share the same phenotype as he gives his x chromosome to daughter- daughter would be affected/have trait

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19
Q

dihybrid inheritance

A

inheritance of 2 diff characteristics

each characteristic controlled by diff gene

genes are on separate/diff pairs of homologous chromosomes ( so alleles or diff characteristics can combine e.g seed colour and seed shape to produce a gamete )

use FOIL method to find gametes as there are 4 alleles in genotype

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20
Q

why are diff types of gametes produced

A

independent segregation of homolgous chromosomes during meiosis

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21
Q

what is the expected ratio if there are 4x4 diff gametes in a punnet square

A

9:3:3:1

22
Q

why might the observed and expected ratios not be similar

A
  • small sample size- low n.o offspring, sampling error greater
  • random fusion of gametes at fertilisation

-epistasis

23
Q

statistical tests

A
  • chi squared
  • correlation coefficient
  • T test
24
Q

what is the chi squared test used for

A
  • to compare the difference between the expected and observed ratios from results of a genetic cross

-for categoric data e.g hair/eye colour

25
Q

chi squared equation

A

x²= ∑(o-e)² divided by e

o = observed frequencies

e= expected

26
Q

what is correlation coefficient used for

A

if theres a correlation between 2 variables

27
Q

what is T test used for

A

comparing means

28
Q

null hypothesis in genetics

A

there is no significant difference between the phenotype ratio expected of….. and the one observed

any change from expected ratio is due to chance

29
Q

what is the unit to look for in the charts for chi squared

A

0.05

if value greater than 0.05 column: not significant + accept null hypothesis

if less than 0.05 column - significant + reject null hypothesis

30
Q

autosomal linked genes

A

22 pairs of non sex chromosomes

2+ genes present on same chromosome at diff loci

usually inherited together- so fewer genetic combos of alleles in gametes as no independent segregation

leading to reduced variety of gametes and offspring

31
Q

autosomal linked genes example for ur understanding

A

e.g AaBb - if the 2 genes were linked, only 2 gamete would be produced : AB and ab

due to 1 chromosome having both gene A and gene B on them

and another having both gene a and gene b on them

if not linked then 4 diff types of gamete would be produced

32
Q

expected ratio for linked and unlinked genes

A

unlinked = 9:3:3:1
linked : 3:1

expected ratio assumes no crossing over/recombination occurred

33
Q

epistasis

A

2+ genes interact to contribute to a phenotype

one gene influences expression of another

34
Q

species

A

exist as one or more populations
can breed tg to produce fertile offspring

35
Q

population

A

group of organisms of same species occupying a particular space at a particular time that can potentially interbreed

36
Q

gene pool

A

all the alleles of all the genes of all individuals in a population

37
Q

allelic frequency

A

number of times an allele of a particular gene occurs within the gene pool

38
Q

why is Hardy weinberg principle useful

A
  • can determine frequencies of carriers
  • can identify evolution
39
Q

factors causing allele frequencies to not change

A
  • population large and isolated ( no flow of alleles in or out pop)

-mating in populations random

-no mutations of gene

-no selection

40
Q

Hardy weinberg principle

A

remember to always multiply by population size or divide by population size

FREQUENCY OF ALLELES: ( have allele but not genotype)
p+q=1
p= frequency of DOM allele
q= frequency of RECESSIVE allele

FREQUENCY OF GENOTYPES:
p² + 2pq + q² = 1.0

p² = frequency of homozygous dominant genotype e.g AA
q² = frequency of homozygous recessive genotype e.g aa
2pq = frequency of heterozygous genotype e.g Aa

41
Q

genetic factors causing genetic variation/diversity

A
  • gene mutations
    -crossing over
  • independent segregation
    -random fertilisation of gametes
42
Q

characteristics mainly influenced by genetic factors

A
  • controlled by 1-2 genes
  • expressed as distinct phenotypes w no intermediates e.g tongue roller
    -represented as distinct groups
43
Q

characteristics mainly influenced by environment

A
  • controlled by many genes
    -no separate categories but have range of intermediates
    -produce normal distribution curve on graph
44
Q

stabilising selection

A

environment not changing

select for mean within population

organisms w extremes of the range are less likely to survive

e.g fur thickness

45
Q

directional selection

A

when environment changing

selects for alleles for phenotype towards the extreme of a range

more likely to survive and reproduce

change in range of phenotypes

46
Q

disruptive selection

A

opposite of stabilising

dont want mean average

same frequency of phenotypes

selects phenotypes at the 2 extremes at the expense of the intermediate phenotypes

e.g favours extremes of ranges at random points

47
Q

speciation

A

evolution of new species from exisiting ones

48
Q

general speciation mechanism

A
  • evolution occurs as a result of change in allele frequencies in population

-members of same species are reproductively isolated from other species

-new species arise when genetic differences due to gene pools, lead to inability of members of population to interbreed and produce fertile offspring

  • new species arise from existing species
49
Q

types of speciation

A

allopatric
sympatric

50
Q

allopatric speciation

A

new species form from DIFF populations in diff areas

1) variation in population already present due to mutations
2) geographical isolation causes split of groups e.g formation of an island, preventing breeding between 2 pops causing reproductive isolation (cant breed to produce fertile offspring)
3) no gene flow between gene pools (of separated populations)
4) diff selection pressures (e.g predators/food) will occur in diff environments causing a particular different phenotypes to be selected for
5) organisms with selected / beneficial phenotype/allele are more likely to survive and reproduce
6) passing on advantageous allele
7) frequency of selected phenotypes and alleles in pop increases
8) allelic frequency in 2 separate gene pools will change over time due to mutation - diff species develop

51
Q

sympatric speciation

A

new species form from population living in SAME area

1) random mutations cause reproductive isolation as no reproduction between organisms of same species in same habitat

2) involves disruptive selection

3) no gene flow between gene pools

4) allelic frequencies change due to mutations ( diff alleles passed onto offspring)

5) allelic frequencies in separated groups become so different

6) new species arise

52
Q

genetic drift and speciation

A

1) GD leads to speciation
2) occurs by chance, not due to selection
3) allele of particular gene passed onto offspring more often than other alleles of same gene -by chance
4) frequency of this allele increases over generations
5) much greater effect in smaller pops, with small variety in gene pool
6) can lead to rapid speciation

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