Changes in Genetic Makeup of a Population

Question 1

Evolution

Answer 1

The gradual change in heritable traits in a population over time

Question 2

Gene pool

Answer 2

all the available alleles for a gene within a breeding population of organisms

Question 3

Allele frequency

Answer 3

the relative frequency a version of a gene (allele) has within a population

Question 4

Mutation

Answer 4

any change in genetic code.
Two types of mutations:
- point mutations
-block mutations

Question 5

Point Mutations

Answer 5

changes to a single base pair.

Types of point mutations: - silent mutations

• missense mutations
• nonsense mutations
• frameshift mutations

Question 6

Silent mutations

Answer 6

base substitution mutations that lead to no change in the amino acid sequence of the corresponding protein

Question 7

Missense mutations

Answer 7

a mutation that causes a different amino acid to be added to the polypeptide chain

Question 8

Nonsense mutation

Answer 8

mutation that results in a premature STOP codon

Question 9

Frameshift mutations

Answer 9

a change in the reading frame (e.g. due to the insertion or deletion, but not a substitution)

Question 10

Block Mutation

Answer 10

changes to entire segments of DNA

types of block mutations:

• deletion
• duplication
• translocation
• inversion
• insertion

Question 11

Deletion

Answer 11

a portion of the chromosome is removed

Question 12

Duplication

Answer 12

part of chromosome is copied, resulting in chromosome having two or more copies of that section

Question 13

Translocation

Answer 13

part of two chromosomes are swapped.

Reciprocal translocation - two chromosomes exchange material

Question 14

Inversion

Answer 14

a segment of chromosome is removed, then replaced in reverse order

Question 15

Insertion

Answer 15

part of one chromosome is added to a different chromosome

Question 16

Natural Selection

Answer 16

process by which heritable traits increase an organism’s chance of survival and reproduction - these traits are favoured over less beneficial traits

> physical agents (e.g. climate change and foot shortages)
biological agents (e.g. infectious diseases, predation, competition)
chemical agents (e.g. pollutants in soil and water)

Question 17

Principle of Natural Selection

Answer 17

These conditions must be met for natural selection to occur:

• Organism must be able to reproduce
• Members of the population must have variations (phenotypes)
• Traits must be heritable and provide an advantage against certain selective pressures

Question 18

Levels of selection

Answer 18

Complete selection against a phenotype occurs when any organism with a given phenotype cannot reproduce because of death before reproductive age is reached or because of sterility

Partial selection against a phenotype occurs when mating involving that phenotype produce on average fewer viable and fertile offspring relative to other mating.

Question 19

Genetic drift

Answer 19

no apparent reason causes a change in allele frequency

Question 20

Bottleneck Effect

Answer 20

random, drastic reduction in a population (e.g. due to a natural disaster), which changes the gene pool – the gene pool is then limited to the alleles the survivor has - this does not include population reductions because of environmental changes

Question 21

Founder effect

Answer 21

where members of a larger population establish a new population in a new (biologically) isolated area. The gene pool of the new population is limited to those the founder carried

Question 22

Allopatric Speciation

Answer 22

• Occurs when a population of a species becomes permanently geographically isolated, resulting in no gene flow between them and other populations.

Question 23

Factors that can split a population into geographically isolated groups

Answer 23

> quick acting (e.g. habitat fragmentation owing to clearing or construction)
slow acting (e.g. change of a river course)
even slower geological processes (e.g. uplift of mountains or rising sea levels)

Question 24

Steps of speciation

Answer 24

1. GEOGRAPHICAL ISOLATION: a permanent geographical barrier forms (e.g. a mountain or river), separating one part of the population from the rest – prevents gene flow between the 2 populations
2. SELECTION PRESSURES: the 2 populations experience different selection pressures and mutations, resulting in changes to their gene pool and allele frequencies
3. DIFFERENCES ACCUMULATE: over many generations the differences accumulate, to the point where if they came into contact again, they would no longer be able to produce viable, fertile offspring – they’re now separate species

Question 25

Differences in phenotypic characteristics that would prevent the ability to mate and produce viable and fertile offspring include

Answer 25

• Mating call: one population’s mating call may not be recognised by another population
• Structural isolation: population’s not mating with each other because they are physically unable to (e.g. size of dogs)
• Temporal isolation: populations are separated from each other by time (e.g. plants flowering at different times of the year)
• Geographical isolation: populations are separated by a geographical barrier (e.g. mountain, river) and cannot come into contact in the wild

Question 26

Sympatric speciation

Answer 26

Evolution of a new species from a surviving ancestral species while both continue to inhabit the same geographic region.

Question 27

Subspeciation

Answer 27

Geographical barrier, genetic variation exists and populations have different pressures. Gene flow is limited, not stopped.

Question 28

Artificial selection

Answer 28

Humans pick organisms with desirable traits.