Inhertiance and Selection

Question 1

Genotype

Answer 1

The genetic constitution of an organism.

Question 2

Phenotype

Answer 2

Observable characteristics of an organism.

Question 3

Gene

Answer 3

Section of DNA that usually determines a single characteristic of an organism.

Question 4

Locus

Answer 4

The position of a gene on a chromosome.

Question 5

Allele

Answer 5

Alternate form of a gene.

Question 6

Homologous chromosomes

Answer 6

Two loci that can each carry one allele of a gene.

Question 7

Co-dominance

Answer 7

Two alleles both contribute to the phenotype.

Question 8

Monohybrid Inheritance

Answer 8

The inheritance of a single gene.

Question 9

Pure breeding

Answer 9

Results in two alleles that are the same for a particular gene.

Question 10

Gene pool

Answer 10

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

Question 11

Allelic frequency

Answer 11

The number of times an allele occurs within the gene pool.

Question 12

What are the 5 conditions of the Hardy-Weinberg principle?

Answer 12

1. No mutations arise
2. There is no selection, all alleles are equally likely to be passed onto the next generation
3. Population size is large
4. The population is isolated, there is no flow of alleles out or into the population
5. Mating within the population is random

Question 13

Hardy-Weinberg Equation:

Answer 13

p² + 2pq + q² = 1

Question 14

What is a fault in the Hardy-Weinberg principle?

Answer 14

In practice not all alleles are equally likely to be passed onto the next generation. Only certain individuals will reproduce successfully to pass on their alleles.

Question 15

Outline how the reproductive success of individuals affects allele frequency in a population

Answer 15

1. All organisms produce more offspring than can be supported by the supply of food, light, etc.
2. Despite this overproduction, the population size remains constant
3. There is intra-specific competition
4. Within any population there will be a gene pool containing a wide variety of alleles
5. Some individuals will possess combinations of alleles that will make them better suited to the environment
6. These individuals with advantageous alleles will reproduce and pass on their alleles to the next generation
7. The new generation of individuals with advantageous alleles are more likely to survive
8. Over many generations, the number of individuals with advantageous alleles will grow at the expense of individuals with less advantageous alleles
9. The frequency of the advantageous alleles in the gene pool will increase whilst the less advantageous alleles will decrease

Question 16

Selection

Answer 16

The process by which organisms which are better suited to their environment survive and breed, while those that are less well adapted fail to do so

Question 17

Directional selection

Answer 17

When individuals who vary in phenotype in one direction from the mean of the population are favoured. This changes the characteristics of the population.

Question 18

Stablising selection

Answer 18

Where individuals with average phenotypes are selected. This preserves the characteristics of a population.

Question 19

Speciation

Answer 19

The evolution of a new species from existing species

Question 20

Species

Answer 20

A group of individuals with similar genes and who are capable of breeding with one another to produce fertile offspring (belong to the same gene pool)

Question 21

Geographical Isolation

Answer 21

When a physical barrier prevents two population from breeding with one another.

Question 22

Outline Speciation

Answer 22

1. Groups within a population become isolated in some way
2. The flow of alleles between them cease
3. The environmental factors each group encounters are different
4. Selection will affect the two populations in different ways and so the type and frequency of alleles in each will change
5. Each population will evolve along separate lines
6. In time, the gene pool of the two population will become so different that even if they are reunited they would be unable to breed to produce fertile offspring, they would be separate species

Question 23

Recessive allele

Answer 23

The condition in which the effect of an allele is apparent in the phenotype of a diploid organism only in the presence of another identical allele.

Question 24

Dominant allele

Answer 24

A term applied to an allele that is always expressed in the phenotype of an organism.