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ib biology > topic 10 (10.2, 10.3) > Flashcards

topic 10 (10.2, 10.3) Flashcards

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AP® Biology flashcards
1
Q

unlinked genes ——- ———- as a result of meiosis

A

segregate independently

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2
Q

what is segregation?

A

the separation of the two alleles of every gene that occurs during meiosis

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3
Q

what is independent assortment?

A

the alleles of one gene segregate independently of the alleles of other genes

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4
Q

genes found on different chromosomes are

genes which are on the same chromosome are

the exception is

A

unlinked and segregate independently

linked and do not segregate independently

linked genes that are far apart on the chromosome (due to crossing over)

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4
Q

look at how to form a punnet square for dihybrid traits

A

p446

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5
Q

describe the difference between a monohybrid and a dihybrid trait

A

monohybrid cross: the cross happening in the F1 generation offspring of parents differing in one trait only, ie the inheritance of a single trait.

dihybrid cross: the cross happening in the F1 generation offspring of parents differing in two traits, the simultaneous study of the inheritance of two different traits.

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6
Q

when are gene loci said to be linked?

A

if they are on the same chromosome and hence don’t independently assort (unless synapsis occurs)

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7
Q

define a locus

A

a locus is a specific, fixed position on a chromosome where a particular gene or genetic marker is located.

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8
Q

define homologous chromosomes

A

two chromosomes that have the same sequence of genes.

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9
Q

why are homologous chromosomes not usually identical to each other?

A

for at least some of the genes on them, the alleles will be different

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10
Q

what is the name of non-sex chromosomes?

A

autosomes- these are common to both males and females

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11
Q

what are the two types of linkage?

A

autosomal gene linkage, when the genes are on the same autosome
sex linkage, when the genes are located on the X chromosome

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12
Q

variation can either be

A

discrete - no in-between categories
continuous - eg height

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13
Q

discrete variation

A

Monogenic traits (characteristics controlled by a single gene loci) tend to exhibit discrete variation, with individuals expressing one of a number of distinct phenotypes

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14
Q

continuous variation

A

Polygenic traits (characteristics controlled by more than two gene loci) tend to exhibit continuous variation, with an individual’s phenotype existing somewhere along a continuous spectrum of potential phenotypes

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15
Q

describe how the phenotypes of polygenic characteristics tend to show continuous variation

A

Increasing the number of loci responsible for a particular trait increases the number of possible phenotypes
This results in a phenotypic distribution that follows a normal distribution curve

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16
Q

monohybrid inheritance =

A

linked genes = two potential gamete combinations

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17
Q

dihybrid inheritance =

A

unlinked genes = 4 potential gamete combinations

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18
Q

why do offspring with unlinked genes have an equal possibility of inheriting any potential phenotypic combination?

A

due to the random segregation of alleles via independent assortment

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19
Q

Offspring with linked genes will only express the phenotypic combinations present in either parent unless

Consequently, the ‘unlinked’ recombinant phenotypes occur —– ——- than the ‘linked’ parental phenotypes

A

crossing over occurs

less frequently

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20
Q

revise the use of chi-squared tests

A
21
Q

Null hypothesis (H0):
Alternative hypothesis (H1):

A

There is no significant difference between observed and expected frequencies (i.e. genes are unlinked)
There is a significant difference between observed and expected frequencies (i.e. genes are linked)

22
Q

Morgan’s discovery of non-Mendelian ratios in Drosophila.

A

Breeding experiments involving fruit flies clearly demonstrated that linked genes were not independently assorted
- when cross-breeding red-eyed wild types with white-eyed mutants, he discovered a clear sex bias in phenotypic distribution
- he inferred this was caused by the gene for eye colour being located on a sex chromosome (i.e. X-linked)

Morgan also observed that the amount of crossing over between linked genes differed depending on the combination of traits
- this led to the idea that crossover frequency may be a product of the distance between two genes on a chromosome – genes with a higher crossover frequency are further apart, whereas genes with a lower crossover frequency are closer together

23
Q

Polygenic traits such as human height may also be influenced by

A

environmental factors, such as nutrition, disease, activity

24
Q

How are linked genes often shown?

A

As vertical pairs

25
Q

The frequency of recombinant phenotypes within a population will typically be —– than that of non-recombinant phenotypes; why?

A

lower

crossing over is a random process and chiasmata do not form at the same locations with every meiotic division

26
Q

The relative frequency of recombinant phenotypes will be dependent on; why?

A

the distance between linked genes

  • recombination frequency between two linked genes will be greater when the genes are further apart on the chromosome because there are more possible locations where a chiasma could form between the genes
27
Q

how can recombinant phenotypes be identified?

A

performing a test cross (crossing with a homozygous recessive for both traits); LOOK AT THIS

28
Q

what does a gene pool consist of?

A

all the genes and their different alleles, present in an interbreeding population

29
Q

how does a gene pool fit into the definition for a species?

A

species are groups of potentially interbreeding populations, with a common gene pool that is reproductively isolated from other species.

30
Q

how would it be possible for multiple gene pools to exist for the same species?

A

if some populations are geographically isolated

31
Q

what does evolution require?

A

that allele frequency’s change with time in populations

32
Q

define evolution

A

the cumulative change in the heritable characteristics of a population over time

33
Q

give 4 reasons for evolution

A
  • mutations introducing new alleles
  • barriers to gene flow emerging between different populations
  • if a population is small, random events can significantly impact allele frequency
  • selection pressures favouring the reproduction of some varieties over others
34
Q

give 3 types of natural selection

A
  • directional
  • stabilising
  • disruptive
35
Q

describe stabilising selection

A

selection pressures act to remove extreme varieties
- eg average birth weights of human babies are favoured over low or high birth weight

36
Q

describe disruptive selection

A

selection pressures act to remove intermediate varieties, favouring the extremes

37
Q

describe directional selection

A

the population changes as one extreme of a range of variation is better adapted.

38
Q

state the 3 categories of reproductive isolation

A
  • temporal
  • behavioural
  • geographic
39
Q

define speciation

A

the formation of a new species by the splitting of an existing population

40
Q

state the difference between allopatric and sympatric speciation

A

allopatric; the result of geographic separation of populations//isolation of gene pools

sympatric; when speciation occurs within the same geographic area (either behavioural or temporal)

41
Q

give an example of behavioural speciation

A

when closely related individuals differ in their courtship behaviour, so are only successful in attracting members of their own population

42
Q

give an example of temporal speciation

A

populations may mate or flower at different seasons or times of day

43
Q

different populations have

A

different allele frequencies

44
Q

state the 2 theories about the pace of evolutionary change

A
  • gradualism in speciation
  • punctuated equilibrium
45
Q

describe gradualism

A
  • the idea that species slowly change through a long sequence of continuous intermediate forms
  • confronted by gaps in fossil record- this as explained as imperfections in the fossil record
46
Q

describe punctuated equilibrium

A
  • holds that long periods of relative stability in a species are ‘punctuated’ by periods of rapid, abrupt evolution
  • gaps in fossil record may mot be gaps at all, as there was no sequence of intermediate forms
47
Q

why may rapid change be much more common in prokaryotes and insects?

A

these organisms have short generation times

48
Q

what is polyploidy?

A

a condition whereby an organism has more than two complete sets of homologous chromosomes in all cells (i.e. > diploid)

49
Q

how does polyploidy lead to sympatric speciation?

A
  • chromosomes duplicate in preparation for meiosis but then meiosis doesn’t occur
  • result is a diploid gamete that when fused with a haploid gamete produces a fertile offspring
  • organism is now reproductively isolated from the original population, and can only self-pollinate or mate with other polyploid plants
50
Q

why is polyploidy far more common in plant species than animal species?

A

Polyploidy is far more common in plant species which lack separate sexes and are capable of self-pollination
Polyploidy is very rare in animal species due to the consequences of having extra allele copies of every gene

51
Q

give an example of an organism that has frequently encountered polyploidy

A

species of angiosperms = flowering plants such as the Allium genus

many species of Allium reproduce asexually and polyploidy may confer an advantage over diploidy under certain selection pressures

ib biology (60 decks)

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