topic 10 (10.2, 10.3)

Question 1

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

Answer 1

segregate independently

Question 2

what is segregation?

Answer 2

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

Question 3

what is independent assortment?

Answer 3

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

Question 4

genes found on different chromosomes are

genes which are on the same chromosome are

the exception is

Answer 4

unlinked and segregate independently

linked and do not segregate independently

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

Question 4

look at how to form a punnet square for dihybrid traits

Answer 4

p446

Question 5

describe the difference between a monohybrid and a dihybrid trait

Answer 5

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.

Question 6

when are gene loci said to be linked?

Answer 6

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

Question 7

define a locus

Answer 7

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

Question 8

define homologous chromosomes

Answer 8

two chromosomes that have the same sequence of genes.

Question 9

why are homologous chromosomes not usually identical to each other?

Answer 9

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

Question 10

what is the name of non-sex chromosomes?

Answer 10

autosomes- these are common to both males and females

Question 11

what are the two types of linkage?

Answer 11

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

Question 12

variation can either be

Answer 12

discrete - no in-between categories
continuous - eg height

Question 13

discrete variation

Answer 13

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

Question 14

continuous variation

Answer 14

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

Question 15

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

Answer 15

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

Question 16

monohybrid inheritance =

Answer 16

linked genes = two potential gamete combinations

Question 17

dihybrid inheritance =

Answer 17

unlinked genes = 4 potential gamete combinations

Question 18

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

Answer 18

due to the random segregation of alleles via independent assortment

Question 19

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

Answer 19

crossing over occurs

less frequently

Question 20

revise the use of chi-squared tests

Question 21

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

Answer 21

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)

Question 22

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

Answer 22

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

Question 23

Polygenic traits such as human height may also be influenced by

Answer 23

environmental factors, such as nutrition, disease, activity

Question 24

How are linked genes often shown?

Answer 24

As vertical pairs

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

how can recombinant phenotypes be identified?

Answer 27

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

Question 28

what does a gene pool consist of?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

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

Answer 30

if some populations are geographically isolated

Question 31

what does evolution require?

Answer 31

that allele frequency's change with time in populations

Question 32

define evolution

Answer 32

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

Question 33

give 4 reasons for evolution

Answer 33

- 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

Question 34

give 3 types of natural selection

Answer 34

- directional - stabilising - disruptive

Question 35

describe stabilising selection

Answer 35

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

Question 36

describe disruptive selection

Answer 36

selection pressures act to remove intermediate varieties, favouring the extremes

Question 37

describe directional selection

Answer 37

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

Question 38

state the 3 categories of reproductive isolation

Answer 38

- temporal - behavioural - geographic

Question 39

define speciation

Answer 39

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

Question 40

state the difference between allopatric and sympatric speciation

Answer 40

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)

Question 41

give an example of behavioural speciation

Answer 41

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

Question 42

give an example of temporal speciation

Answer 42

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

Question 43

different populations have

Answer 43

different allele frequencies

Question 44

state the 2 theories about the pace of evolutionary change

Answer 44

- gradualism in speciation - punctuated equilibrium

Question 45

describe gradualism

Answer 45

- 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

Question 46

describe punctuated equilibrium

Answer 46

- 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

Question 47

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

Answer 47

these organisms have short generation times

Question 48

what is polyploidy?

Answer 48

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

Question 49

how does polyploidy lead to sympatric speciation?

Answer 49

- 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

Question 50

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

Answer 50

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

Question 51

give an example of an organism that has frequently encountered polyploidy

Answer 51

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