A LEVEL BIOLOGY (year 2)

What is a gene

A sequence of bases on a DNA molecule for protein ( polypeptide)which results in a characteristic

What is an allele

Version of a gene

What is codominance

Both alleles are expressed in the phenotype when present

What is dihybrid inheritance

Patterns of inheritance of 2 different genes on a different pair of autosomes

What are autosomes

Normal non sex chromosome pair

Ratio of dihybrid inheritance for two heterozygous individuals

9:3:3:1

What is autosomal linkage

The loci of two different genes are on the same pair of autosomes so are extremely likely to be inherited together unless crossing over occurs

What is the hardy - Weinberg principle (equations)

• P+q=1

• P2 + 2pm + q2 = 1

What is a gene pool

All alleles of all genes within a population

What does the hardy - Weinberg principle predict

Frequency of specific alleles within each population gene pool

According to the Hardy-Weinberg principle the frequency of alleles will remain constant from one generation to the next provided…

• No mutations occur

• All individual are likely to pass on their alleles

• Mating is random

• No immigration/emigration/migration

• No selection of alleles

• Population is large

What is a sex linked gene

Only present on X (or Y) chromosome

What is epistasis

The interaction between two non linked genes which causes one gene to mask the expression of the other n the phenotype

What is evolution

The gradual change in a species over time (changes to the allele frequency in the gene pool )

What is speciation

When enough difference is accumulated that members of a population are no longer able to breed with the original population / species

What causes the production of new alleles

Mutations

What causes genetic variation between individuals

Meiosis + random fertilisation

Stages of evolution and speciation

1. Isolation

2. Variation caused by mutations

3. Different selection pressures

4. Breed and pass on advantageous alleles

5. Allele increases in frequency

6. Speciation

What are the three types of selection

1. Directional

2. Stabilising

3. Disruptive

What is directional selection

Selection for 1 extreme phenotype e.g giraffe neck length

What is stabalising selection

Average phenotype is preserved eg birth weight

What is disruptive selection

Favours individuals with extreme phenotypes in both directions as both extremes confer to an advantage

Directional selection graph

Shifts left or right

Stabilising selection graph

Narrows

Disruptive selection graph

Splits in two

Two types of speciation

Allopatric and sympatric

What is allopatric speciation

Geographical physical barrier

What is sympatric speciation

Same area however reproductively isolated e.g different mating times

Types of sympatric speciation

1. Ecological

2. Temporal

3. Behavioral

4. Mechanical

5. Gametic

6. Hybrid

Why does anaerobic respiration produce far less ATP than aerobic respiration?

• Anaerobic respiration relies on substrate level phosphorylation in the glycolytic pathway to produce a net 2 ATP per glucose.

• Aerobic respiration produces 2 ATP from substrate-level phosphorylation in glycolysis, 2 ATP from substrate-level phosphorylation in the Krebs cycle and around 32 ATP from oxidative phosphorylation.