4.1 Inheritance, Selection and Speciation

Question 0

Define: Phenotype

Answer 0

The appearance of a characteristic due to the expression of the genotype and its interaction with the environment.

Question 1

What is a genotype?

Answer 1

The genetic makeup of an organism. Refers to alleles present.

Question 2

Define: alleles

Answer 2

Different forms of the same gene.

Question 3

Define: locus

Answer 3

The position of a gene on a chromosome.

Alleles occupy the same locus on each member of a pair of homologous chromosomes.

Question 4

Define: dominant allele

Answer 4

Always expressed in the phenotype.

Question 5

Define: recessive allele

Answer 5

Only expressed when the genotype is homozygous recessive.

Question 6

Define: Codominance

Answer 6

Both alleles are expressed in the phenotype. Both contribute to the appearance.

Question 7

Define: multiple allelism?

Answer 7

More than two alleles of a particular gene. Only two can be present in a genotype.

Question 8

Define: sex linked gene

Answer 8

Where the gene is carried on only one type of sex chromosome, usually the X chromosome.

Question 9

Why is the observed ratio different to the expected ratio?

Answer 9

The fusion of gametes is random.

Question 10

What is a test cross?

Answer 10

The crossing of an organism with a homozygous recessive.

Question 11

Define: gene pool

Answer 11

All the alleles of all the individuals of a population at any one time.

Question 12

Define: allelic frequency

Answer 12

The number of times an allele of a particular gene occurs within a gene pool.

Question 13

What are the principals of the Hardy Weinberg equilibrium?

Answer 13

Population is large
Mating is random
No mutations occur
No selection
Population is isolated

Question 14

What do p and q represent in the Hardy Weinberg equation?

Answer 14

p= frequency of dominant allele

q= frequency of recessive allele

Question 15

What do p^2, q^2 and 2pq represent in the Hardy Weinberg equation?

Answer 15

p^2 = frequency of homozygous dominant genotype

q^2 = frequency of homozygous recessive genotype

2pq = frequency of heterozygous genotype

Question 16

Describe natural selection.

Answer 16

Variation is present in a population due to mutations.
A change in the environment results in some being better adapted.
Organisms with higher differential reproductive success will survive and breed and pass on these alleles to offspring.
The frequency of the beneficial allele increases in the gene pool.

Question 17

When are two organisms considered different species?

Answer 17

When they breed, infertile offspring are produced.

Question 18

Describe speciation.

Answer 18

Variation is present due to mutations and the population is split by geographical isolation.
Different environmental conditions result in different advantageous alleles (selection).
There is no gene flow between gene pools.
Eventually, gene pools become so different they become different species.
Different alleles increase in frequency.

Question 19

What is stabilising selection?

Answer 19

Selection when the environment isnt changing, usually when an allele is advantageous
Favours those in middle of range

Question 20

What is directional selection?

Answer 20

Selection when the environment is changing, selects for those with alleles for a phenotype towards extreme of a range
Results in change in range until new optimum is established