Topic 7 – Genetics, Populations, Evolution & Ecosystems

Question 1

Variation

Answer 1

Differences between individuals due to genetics, the environment or a combination of both

Question 2

Primary source of genetic variation

Answer 2

Mutation

Question 3

Other causes of genetic variation (2)

Answer 3

Meiosis and the random fertilisation of gametes during sexual reproduction produce further genetic variation

Question 4

Continuous Variation

Answer 4

• 2 extremes and a full range of values in between
• most individuals close to the mean rather than at either extreme
• traits that show continuous variation are often regulated by multiple genes and influenced by the environment

Question 5

Discontinuous variation

Answer 5

• distinct categories with no intermediate values
• even distribution of individuals between categories
• traits often regulated by a single gene and not influenced by the environment

Question 6

Allele frequency

Answer 6

The proportion of an allele within a populations gene pool (how often it occurs)

Question 7

Allele

Answer 7

A form of a gene

Question 8

Genotype

Answer 8

The genetic constitution of an organism

Question 9

Phenotype

Answer 9

The expression of the genotype (the genetic constitution of an organism) and its interaction with the environment

Question 10

Species

Answer 10

A group of organisms that can interbreed and produce fertile offspring

Question 11

Population

Answer 11

A group of organisms of the same species occupying a particular space at a particular time

Question 12

Gene pool

Answer 12

All the alleles of all the genes within a population at one time

Question 13

Dominant allele

Answer 13

Allele that will always be expressed in the phenotype
(represented by capital letter)

Question 14

Recessive allele

Answer 14

Allele that will only be expressed if no dominant alleles are present
(Represented by lowercase letter. 2 lowercase letters-recessive allele expressed in phenotype)

Question 15

Homozygous

Answer 15

A pair of homologous chromosomes carrying the same allele for a single gene
(e.g. BB or bb)

Question 16

Heterozygous

Answer 16

A pair of homologous chromosomes carrying two different alleles for a single gene
(E.g. Bb)

Question 17

Codominant

Answer 17

Both alleles are equally dominant and expressed in the phenotype

Question 18

Multiple alleles

Answer 18

More than two alleles for a single gene

Question 19

Sex linkage

Answer 19

A gene located on the sex chromosome: on the X chromosome

Question 20

Autosomal linkage

Answer 20

genes located on the same autosome (a non sex chromosome) . They are unlikely to be separated by crossing over during meiosis so are likely inherited together

Question 21

Autosome

Answer 21

Not a sex chromosome (so not X or Y)

Question 22

Epistasis

Answer 22

One gene affects (modifies or masks) the expression of a different gene

Question 23

Monohybrid

Answer 23

Inheritance of a characteristic determined by ONE GENE

Question 24

Dihybrid

Answer 24

Inheritance of a characteristic determined by TWO GENES

Question 25

What does the hardy weinberg principal predict

Answer 25

the frequencies of an allele in a population will remain the same from one generation to the next if certain conditions are met

Question 26

State the 5 conditions that need to be met for the hardy Weinberg principle to apply

Answer 26

Large population
No immigration/ emigration
No mutation
No natural selection
Random mating

Question 27

Hardy Weinberg equations

Answer 27

p + q = 1

p^2 + 2pq + q^2 = 1

Question 28

How do we know if an external factor is affecting allele frequency

Answer 28

redo calculation
if allele frequency has changed there must be an external factor affecting

Question 29

Selection pressures + how this leads to natural selection

Answer 29

Predation, disease, competition
- results in differential survival and reproduction (better adapted individuals survive and reproduce)

Question 30

Natural selection

Answer 30

certain environmental conditions apply selection pressure (e.g new disease)
- organisms with phenotypes providing selective advantages (better adapted) more likely to survive and reproduce
- and pass on their favourable alleles to the next generation
- frequency of unfavourable allele decreases, frequency of favourable allele increases

Question 31

Stabilising selection

Answer 31

• Occurs when environmental conditions stay the same
• Individuals close to the mean favoured rather than ones at either extreme
  -> survive and reproduce and pass on alleles
• new characteristics selected against

Question 32

Directional selection

Answer 32

Occurs when environmental conditions change
Favours individuals with phenotypes suited to new conditions (one extreme trait > the other extreme)
-> survive and reproduce, pass on alleles
Over time the population moves in this direction

Question 33

Disruptive selection

Answer 33

Occurs when the environment favours more than one phenotype
Favours both extreme phenotypes over the mean (opposite of stabilising selection)
-> survive and reproduce and pass on alleles
so allele frequencies for extreme traits increase

Can lead to speciation

Question 34

Which type of selection results in low genetic diversity

Answer 34

Stabilising selection