10.3- gene pools and speciation

Question 1

what does a gene pool consist of?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

if some populations are geographically isolated

Question 4

what does evolution require?

Answer 4

that allele frequency’s change with time in populations

Question 5

define evolution

Answer 5

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

Question 6

give 4 reasons for evolution

Answer 6

• 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 7

give 3 types of natural selection

Answer 7

• directional
• stabilising
• disruptive

Question 8

describe stabilising selection

Answer 8

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

Question 9

describe disruptive selection

Answer 9

selection pressures act to remove intermediate varieties, favouring the extremes

Question 10

describe directional selection

Answer 10

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

Question 11

state the 3 categories of reproductive isolation

Answer 11

• temporal
• behavioural
• geographic

Question 12

define speciation

Answer 12

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

Question 13

state the difference between allopatric and sympatric speciation

Answer 13

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 14

give an example of behavioural speciation

Answer 14

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

Question 15

give an example of temporal speciation

Answer 15

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

Question 16

different populations have

Answer 16

different allele frequencies

Question 17

state the 2 theories about the pace of evolutionary change

Answer 17

• gradualism in speciation
• punctuated equilibrium

Question 18

describe gradualism

Answer 18

• 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 19

describe punctuated equilibrium

Answer 19

• 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 20

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

Answer 20

these organisms have short generation times

Question 21

what is polyploidy?

Answer 21

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

Question 22

how does polyploidy lead to sympatric speciation?

Answer 22

• 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 23

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

Answer 23

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 24

give an example of an organism that has frequently encountered polyploidy

Answer 24

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