Natural selection

Question 1

Define phenotype

Answer 1

The observable characteristics of an organism, resulting from its genotype and interaction with the environment

Question 2

Define gene

Answer 2

A length of DNA which codes for a protein or polypeptide

Question 3

Define genotype

Answer 3

The genetic constitution of an organism

Question 4

Define homozygous

Answer 4

The two alleles of a gene are the same

Question 5

Define heterozygous

Answer 5

The two alleles of a gene are different

Question 6

Define alleles

Answer 6

Different forms of a gene

Question 7

Define recessive

Answer 7

The allele which is only expressed in the phenotype, is absence of a dominant allele

Question 8

Define dominate

Answer 8

The allele is always expressed in the phenotype, even if a different allele/ heterozygous for the same gene is present

Question 9

Define loci

Answer 9

The position of a gene on a chromosome

Question 10

Define genetic diversity

Answer 10

Number of different alleles of the same gene

Question 11

Define allele frequency

Answer 11

Number of different times a specific allele appears in a population

Question 12

Define gene pool

Answer 12

Total number of alleles in a particular in a population

Question 13

What two types of factors causes variation

Answer 13

• genetic factors
• environmental factors

Question 14

Define continous variation

Answer 14

-Normal distribution curve showing variation around a mean
- Quantitative data
- Controlled by many genes
- Many intermediates, no discrete groups
- Affected by environment

Question 15

Define discontinuous variation

Answer 15

. Bar chart
. Qualitative data
. Controlled by 1 or 2 genes
. Discrete groups, no intermediates
. Not affected by environment

Question 16

Define selection

Answer 16

Process that results in organisms with the best adaptations in the population surviving to reproduce and pass on favourable alleles to next generation

Question 17

Define selection pressure

Answer 17

Factor which impacts on an organisms ability to survive

Question 18

Define reproductive success

Answer 18

The ability of an organism to pass on its gene to the next generation

Question 19

Define reproductive isolation

Answer 19

The inability of a species to breed successfully with related species due to geographical, behavioural, physiological, or genetic barriers or differences

Question 20

State the process of natural selection

Answer 20

. New allele arises due to random mutation
. Leads to variation in a population
. Populations may be geographical isolated so no interbreeding
. Different selection pressures
. Competition for reasources- intraspecific Competition
. New alleles give a selective advantage so organism survives and reproduces
. Pass on advantageous allele to the next generation
. Frequency of allele in population increases
. Frequency of the phenotype increases

Question 21

What are the three main selection pressures

Answer 21

. Predation
. Disease
. Competition

Question 22

Define stabilising selection

Answer 22

Organism with phenotype in the middle are more favourable than the two extremes within a population. Usally when selection pressures stay constant

Question 23

Define directional selection

Answer 23

Organisms with phenotype are one extreme are more favourable within the population. Usally when selection pressure changes

Question 24

Define disruptive selection

Answer 24

Organisms with phenotypes at both extremes are more favourable within a population. Usually when selection pressures changes leading to speciation

Question 25

Mass of babies at birth can be small, large or in the middle
. Explain the impact of stabilising selection on the gene pool of the human population

Answer 25

. Mutation leads to variation in population
. Baby weights alleles at extreme phenotype- too heavy or light
. Less likely to survive
. Less likely to reproduce
. To pass on advantageous allele to offspring
. Decrease in allele frequency
. Decrease in gene pool

Question 26

Cheetahs are the fastest animals on land. Individuals that are the fastest are more likely to catch their prey.
Explain the impact of directional selection on the gene pool of the cheetah population

Answer 26

. Mutation leads to variation
. Cheetah with faster allele at extreme phenotypes.
. More likely to survive
. More likely to reproduce
. To pass on advantageous allele to offspring
. Increases in allele frequency
. Move towards extreme phenotype away from the mean

Question 27

Birds break can either be big or small depending on the food source they have. Birds that have beaks that are in the middle cannot really eat anything as their beaks won’t be adapted to the food source.
Explain the impact of disruptive selection on the gene pool of the bird population

Answer 27

. Mutation leads to variation in population
. Beaks size alleles at extreme phenotypes
. Different selection pressures at different peak sizes are able to eat different food
. More likely to survive
. More likely to reproduce
. To pass on different advantageous allele to offspring
. Allele frequency splits towards the extreme phenotypes.
. Leads to speciation