Evolution

Question 1

What is a gene pool?

Answer 1

the complete range of alleles in a population

Question 2

What is allele frequency?

Answer 2

how often an allele occurs in a population. it is usually given as a percentage of the total population or a decimal.

Question 3

What happens to the frequency of an allele over time?

Answer 3

it changes. this is evolution.

Question 4

How does evolution by natural selection occur?

Answer 4

1- individuals in a population vary due to diff. alleles. new alleles arise by mutations.
2- predation, disease, and competition (Selection pressures) create a struggle for survival
3- some are better adapted to selection pressures than others. this increases their chance of survival. they are more likely to survive, reproduce and pass on the advantageous allele.
4- a greater proportion of the next generation inherits the advantageous allele
5- they are more likely to survive, reproduce and pass it on. the frequency of the adv. allele increases from generation to generation.

Question 5

What can’t occur without a selection pressure?

Answer 5

natural selection

Question 6

When is an allele advantageous?

Answer 6

with the right selection pressure

Question 7

What happens in a stable environment?

Answer 7

individuals with alleles for characteristics in the middle of the range are more likely to survive and reproduce- this is called stabilising selection. it reduces the range of possible phenotypes.

Question 8

What happens in a changing environment?

Answer 8

individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce. this is called directional selection.

Question 9

What causes evolution by genetic drift?

Answer 9

change dictates which alleles are passed on.

Question 10

Compare evolution by natural selection and genetic drift.

Answer 10

in natural selection, characteristics become more common if they increase an organism’s likelihood of survival. by genetic drift, they become more common by chance.

Question 11

Evolution via genetic drift

Answer 11

1- individuals within a population show variation within their genotypes
2- by chance, the allele for one genotype is passed on to the offspring more often than others. the no. of individuals with this allele increases.
3- if by chance, the same allele is passed on more often, again and again, it can lead to evolution as the allele becomes more common in the population.

Question 12

Which 2 processes work alongside each other to drive evolution?

Answer 12

natural selection and genetic drift, but one drives evolution more depending on the population size.

Question 13

In what type of population does evolution by genetic drift have a greater effect on evolution?

Answer 13

in smaller populations where chance has a greater influence

Question 14

How can genetic drift be a problem?

Answer 14

it decreases genetic diversity. of a population. this may make a species less able to adapt to future changes in their environment, which can be a problem for smaller populations.

Question 15

What is a genetic bottleneck?

Answer 15

an event (like a natural disaster) that causes a big reduction in a population’s size, leading to a reduction in the gene pool.

Question 16

When does evolution by genetic drift have a greater effect?

Answer 16

when there’s a genetic bottleneck.

Question 17

What is the founder effect?

Answer 17

when a few organisms from a population start a new population and there are only a small no. of diff. alleles in the initial gene pool.

Question 18

The founder effect

Answer 18

1- individuals within a population show variation within their genotypes
2- some of these individuals start a new population. by chance, they mostly have one particular genotype.
3- without any further ‘gene flow’, the new population will grow with a reduced genetic variation. as the population is small, it’s more heavily influenced by genetic drift.

Question 19

When can the founder effect occur?

Answer 19

as a result of migration leading to geographical separation or if a new colony is separated from the original population for another reason, such as religion. (the Amish people)

Question 20

What is the Hardy-Weinberg principle?

Answer 20

a mathematical method that predicts the frequencies of alleles in a population won’t change from one generation to the next. it is only true under certain conditions.

Question 21

Hardy-Weinberg conditions

Answer 21

• has to be a large population with no immigration. emigration, mutations, or natural selection
• needs to be random mating so all possible genotypes can breed with all others

Question 22

What are the 2 Hardy Weinberg equations?

Answer 22

one for allele frequency and another for genetic frequency

Question 23

Hardy Weinberg- allele frequency equation

Answer 23

p+q=1
p= frequency of the dominant allele
q= frequency of the recessive allele

Question 24

Hardy Weinberg- genotype frequency equation

Answer 24

p^2 +2pq+q^2=1
p^2= freq. of homo dom genotype
2pq=freq. of hetero genotype
q^2= freq. of homo recessive genotype

Question 25

What is artificial selection?

Answer 25

when humans select individuals in a population to breed together to get desirable traits e.g. modern dairy cattle and bread wheat.

Question 26

How are modern dairy cows produced?

Answer 26

1- farmers select a female with a very high milk yield and a males whose mother had a very high milk yield and breed them 2- they select the offspring with the highest milk yield and breed them too 3- this is continued over several generations until a very high milk-yielding cow is produced

Question 27

What are other characteristics selected for in dairy cows?

Answer 27

high milk quality, long lactation period, large udders, resistance to mastitis (udder inflammation) and other diseases, and a calm temperament

Question 28

What are modern techniques used instead of artificial selection?

Answer 28

- artificial insemination and IVF to give farmers more control over which cows reproduce. - animal cloning allows farmers to produce genetically identical copies of their best cows

Question 29

How is bread wheat produced?

Answer 29

1- wheat plants with a high wheat yield are bred together 2- their offspring with the highest yields are bred together 3- this is continued over several generations to produce a plant with a very high yield

Question 30

What are other characteristics selected for in bread wheat?

Answer 30

higher tolerance of cold, short stalks (don't collapse under the weight of the ears), and uniform stalk heights to make harvesting easier

Question 31

What techniques are useful in the artificial selection of plants?

Answer 31

plant cloning

Question 32

Problems with artificial selection

Answer 32

1- reduced gene pool so can be more affected by a new disease and an increased incidence of genetic disease 2- potentially useful alleles are accidentally lost from the population when other alleles are being selected 3- can exaggerate certain traits, leading to health problems e.g. pedigree dog breed

Question 33

Artificial selection problems- pedigree dog breed example

Answer 33

- modern PDB descended from a single wolf-like ancestor. they went through many generations of AS. ---dogs like pugs and French bulldogs have been bred to -have a flat, squashed up face which has caused them breathing problems. - dogs like dalmatians and English bull terriers have a high incidence of hereditary deafness

Question 34

What is a species?

Answer 34

a group of similar organisms that can reproduce to give fertile offspring

Question 35

What is speciation?

Answer 35

the development of a new species

Question 36

When does speciation occur? W

Answer 36

when populations of the same species become reproductively isolated- changes in allele freq. cause changes in phenotype that mean they can no longer breed together to produce fertile offspring

Question 37

What is allopatric speciation?

Answer 37

when populations become reproductively isolated through a combination of geographical isolation and natural selection

Question 38

When does geographical isolation occur?

Answer 38

when a physical barrier e.g. a flood or earthquake, divides a population of a species, causing some individuals to be separated from the main population

Question 39

What happens to those that are geographically isolated?

Answer 39

they experience slightly diff. conditions e.g. a diff. climate on each side of the physical barrier. since the environment is diff. for each population, diff. characteristics will become more common due to natural selection.

Question 40

Allopatric speciation and natural selection

Answer 40

1- due to diff. characteristics being advantageous on each side, the allele freq. will change in each population 2- mutations will occur independently in each population, also changing the allele freq. 3- changes in the allele freq. will lead to changes in the phenotype freq. Eventually, individuals from diff. populations will change so much that they cant breed to produce fertile offspring. The 2 groups will become separate species.

Question 41

When does reproductive isolation occur?

Answer 41

changes in the alleles and phenotypes of 2 populations prevent them from successfully breeding together

Question 42

How does reproductive isolation occur?

Answer 42

1- Seasonal changes- individuals of the same pop. develop diff. flowering or mating seasons, or become sexually active at diff. times of the year 2- Mechanical changes- changes in genitalia 3- Behavioural changes- a group of individuals develop courtship rituals that aren't attractive to the main population

Question 43

What is sympatric speciation?

Answer 43

Speciation without geographical isolation. Random mutations occur within a pop., resulting in the same changes as mentioned before, preventing members from breeding with other members of the species.

Question 44

Why is sympatric speciation rare?

Answer 44

It's difficult for a section of a pop. to become completely reproductively isolated without being geographically isolated too.

Question 45

An example of sympatric speciation- polyploid organisms

Answer 45

Individuals with diff. no. of chromosomes can't reproduce to give fertile offspring. So if a polyploid organism emerges in a diploid pop. it will be reproductively isolated. If the polyploid organism reproduces asexually, a new species can develop. Polyploidy can lead to speciation if it isn't fatal to the organism and more polyploid organisms can be produced. It's more common in plants than animals.

Question 46

What is polyploidy?

Answer 46

when one possesses more than 2 sets of homologous chromosomes in their cells

Question 47

What is a difference between sympatric and allopatric speciation?

Answer 47

sympatric occurs in the same place and allopatric occurs in populations that are away from each other