BY5.5 - Variation And Evolution

Question 0

What is Continuous Variation?

Answer 0

A characteristic controlled by MANY GENES (POLYGENIC EFFECT) shows GRADUAL CHANGE in the population from one extreme to another E.g Height

Question 1

What is discontinuous variation?

Answer 1

A characteristic controlled by ONE OR TWO GENES which shows CLEAR CUT DIFFERENCES in the POPULATION Eg tongue rolling

Question 2

What is Non- heritable variation caused by and what is it responsible for?

Answer 2

The ENVIRONMENTAL FACTORS that cause CONTINUOUS VARIATION

Question 3

How does Inherited Variation cause genetic changes?

Answer 3

Crossing over - during prophase 1 Random Assortment - metaphase 1 Random fusion of haploid gametes Mutation

Question 4

What is the gene pool?

Answer 4

All of the alleles within a population

Question 5

What is Population Genetics?

Answer 5

The relative proportions of the various genotype a or allele frequency present in a population

Question 6

what is the Gene Pool?

Answer 6

All of the alleles within a population within a population

Question 7

What is evolution?

Answer 7

the process by which new species are formed from pre-existing ones over a period of time

Question 8

How did Darwin develop his theory of natural selection?

Answer 8

He recognised the species changed

Organisms overproduce offspring

there is a large variation of genotypes due to gene mutation

However, numbers in the population remain constant

therefore there is a high mortality rate

changes to environmental conditions bring new selection pressures

e.g competition,predatation, disease

Individuals with beneficial alleles have a selective advantage and are more likely to survive

they then reproduce

offspring inherit beneficial alleles –> characteristics,

repeat generation after generation

beneficial allele frequency increases within the gene pool/

Question 9

What is adaptive radiation?

Answer 9

the evolutionary diversification of many species

from a single common ancestor

Question 10

why has antibiotic resistance arisen?

Answer 10

Random mutations produce recessive alleles coding for antibiotic resistance and are not expressed when in combination with a dominant allele

repeated exposure to antibiotics causes more bacteria to survive and pass on recessive alleles

some bacteria have developed a gene codes for penicillinase synthesis, which causes penicillin to be ineffective

in the presence of penicillin non resistant bacteria are destroyed, therefore there is a selective advantage favouring resistant bacteria.

Question 11

What are populations?

Answer 11

Groups of interbreeding individuals of the same species

occupying the same habitat

Question 12

What is a species?

Answer 12

A group of organisms that can interbreed to produce fertile offspring

And do not normally interbreed with any other group of organisms

Question 13

Why are hybrids infertile?

Answer 13

different diploid no. of chromosomes

not homologous chromosomes

cannot form bivalents during meiosis prophase 1

Meiosis does not take place - no gametes produced

Question 14

what name is given to breeding sub-units within populations?

Answer 14

Demes

Question 15

When do new species arise?

Answer 15

when a barrier to reproduction occurs

called the isolating mechanism

Which prevents genes being exchanged between two demes

Question 16

What is Allopatric isolation?

Answer 16

The population is physically split

preventing interbreeding between 2 demes

e.g. river

Question 17

what is sympatric isolation?

Answer 17

when organisms inhabiting the same area are unable to reproduce

Question 18

Name and describe the 4 types of sympatric isolating mechanisms:

Answer 18

1) reproductive isolation - different flowering times
2) Mechanical isolation - Incompatible genetalia
3) Behavioural isolation - courtship behaviour not attracting other deme
4) Hybrid inviability - development of embryo does not occur

Question 19

How do new 2 new species arise from 1 old one?

Answer 19

1) populations become isolated
2) different mutations arise in each population –> different alleles
3) different environmental conditions in each population
4) different selection pressures
5) different gene pools develop
6) causes changes in phenotype

Question 20

What are the different factors which can alter the frequency of genes in a population?

Answer 20

1) Mutation
2) Natural Selection
3) Genetic Drift

Question 21

what is genetic drift?

Answer 21

variation occurring in the gene pool due to chance

Question 22

How is genetic drift different to Natural Selection?

Answer 22

In Natural Selection, allele frequency changes due to a selective advantage,

whereas genetic drift occurs due to chance

Question 23

What is the Founder Effect?

Answer 23

a type of genetic drift occurs when a small group from a populations colonises a new area

because the genotype of the individuals in the colony is random it can lead to reduction in genetic diversity

reduces the size of the new populations gene pool

result = genetic bottleneck