Chapter 20 - Inheritance + Variation

Question 1

What is a Phenotype?

Answer 1

The physical expression of an organism’s genetic consitution

Question 2

How can meiosis bring about genetic variation?

Answer 2

• Random arrangement of chromosomes during lining up (independent assortment)
• Crossing over of chromatids before the first division

Question 3

How does random fertilisation bring about genetic variation

Answer 3

1. Gametes = haploid (only contains half a person’s DNA)
2. Determined by meiosis - every gamete contains different DNA - therefore same 2 organisms can produce genetically different offspring

Question 4

What is Monogenic Inheritance?

Answer 4

Where one phenotypic characteristic is controlled by a single gene

Question 5

What is Dihybrid Inheritance?

Answer 5

Where 2 phenotypic traits are determined by 2 different genes present on two different chromosomes at the same time.

Question 6

What is sex-linkage?

Answer 6

When an allele is located on one of the sex chromosomes, meaning expression depends on the sex of the individual

Question 7

What is multiple alleles?

Answer 7

A gene with more than two alleles

Question 8

What are codominant alleles?

Answer 8

When two dominant alleles both contribute to the phenotype, either by showing a blend of characteristics, or showing both together.

Question 9

What is autosomal linkage?

Answer 9

When two or more alleles are located on the same non-sex chromosome. In this case, only one homologous pair is needed for all four alleles to be present.

Question 10

What is epistasis?

Answer 10

Where two non-linked genes interact, with one gene either masking or supressing the other gene

Question 11

What is the Chi-squared test?

Answer 11

A statistical test to find out whether the difference between observed and expected data is due to chance or real effect.

Question 12

How can the number of genes coding for a characteristic influence variation?

Answer 12

• Discontinuous variation = characteristic determined by 1 gene
• Continuous variation = characteristic determined by more than 1 gene.

Question 13

What is stabilising selection?

Answer 13

occurs when environment stays the same - individual closest to the mean are favoured. Low diversity.

Question 14

What is directional selection?

Answer 14

Occurs when environmental conditions change. Individuals with phenotypes suited to new conditions + pass on genes. Over time the population will move towards these characteristics.

Question 15

What is Genetic Drift?

Answer 15

Change in a population’s mean characteristics due to chance rather than selective pressures.

Question 16

What is a genetic bottleneck?

Answer 16

Where a catastrophic event dramatically reduces the size of a population - thereby decreases allele variety in gene pool - causes large changes in allele frequencies.

Question 17

What is meant by the founder effect?

Answer 17

Small number of individuals of a population become isolated - limited gene pool - allele frequency differs from original population.

Question 18

What is the Hardy-Weinberg equation?

Answer 18

P+ Q = 1
Where P = Dominant alleles
and Q = recessive alleles

Question 19

What does the Hardy-Weinberg equation allow for?

Answer 19

Allows us to estimate allele frequency in a population + if allele freq. is changing over time.

Question 20

What is speciation?

Answer 20

When the genetic makeup of two isolated groups of a species becomes so different that they can no longer interbreed and create fertile offspring.

Question 21

What is allopatric speciation?

Answer 21

Speciation from a physical barrier, resulting in 2 different environments with different selection pressures, resulting in different favoured alleles.

Question 22

What is sympatric speciation?

Answer 22

Speciation from non-physical barrier - e.g. mutation that no longer allows two organisms to produce fertile offspring.

Question 23

What is artificial selection?

selective breeding

Answer 23

humans choosing particular organisms to breed in order to produce a desired characteristic in offspring

Question 24

What are the 5 factors affecting evolution?

Answer 24

Mutation
Natural Selection
Gene Flow
Sexual Selection
Genetic Drift

Question 25

What are the 5 assumptions for the Hardy Weinberg Principle

Answer 25

• No mutation
• no immigration / emmigration
• no selection pressures
• mating is random
• population is large
  (i. e. unrealistic expectations)

Question 26

What is Gene Pool ?

Answer 26

The total sum of all the alleles in a population at any one time.

Question 27

What is a gene?

Answer 27

a section of DNA that codes for a polypeptide or protein in an organism

Question 28

What is an allele?

Answer 28

one of multiple different forms of a gene