Genetic diversity and Adaptation

Question 1

Stabilising selection

Answer 1

Natural selection which favours individuals closer to the mean. This removes the extremes of a population

Question 2

Natural selection

Answer 2

The process by which the frequency of advantageous alleles gradually increases in a population’s gene pool over time

Question 3

Directional selection

Answer 3

Natural selection which favours individuals either left/right of the mean. This changes the traits of a population over time

Question 4

Mutagenic agent

Answer 4

Something which increases the rate of gene mutations above the normal rate

Question 5

Gene mutation

Answer 5

A change to at least one nucleotide base in DNA or the arrangement of bases

Question 6

Examples of a mutagenic agent

Answer 6

Ionising radiation (UV rays)
Chemicals (formaldehyde)
Viruses (HPV)

Question 7

Chromosome mutation

Answer 7

A change to the number or structure of chromosomes that can occur spontaneously

Question 8

How does a gene mutation lead to a difference in an organism’s phenotype?

Answer 8

The change in the triplet code of DNA changes the polypeptide chain and therefore the tertiary protein. This deformed protein will change a characteristic

Question 9

What feature of the genetic code negates base substitution gene mutations?

Answer 9

The degenerate nature

Question 10

What is a base substitution mutation?

Answer 10

A nucleotide with a different nitrogenous base is switched with the original nucleotide

Question 11

What is a base deletion mutation?

Answer 11

A nucleotide is lost from the DNA code

Question 12

Why are base deletion mutations more impactful that base substitution mutations?

Answer 12

Base deletion mutations cause a ‘frame shift’ in the triplet code affecting the whole polypeptide.
Base substitution mutations affect one amino acid each

Question 13

Why can an incorrect amino acid have no effect on a protein?

Answer 13

That amino acid may form no ionic, hydrogen or disulfide bonds in the tertiary structure

Question 14

What does meiosis produce?

Answer 14

4 genetically different, haploid daughter cells

Question 15

What does mitosis produce?

Answer 15

2 genetically identical, diploid daughter cells

Question 16

What does meiosis use at the start?

Answer 16

A body cell

Question 17

What does mitosis use at the start?

Answer 17

A body cell

Question 18

What 2 ways does meiosis introduce variation?

Answer 18

Independent segregation
Crossing over

Question 19

Crossing over

Answer 19

The process in meiosis I in which chromatids wrap around one another and their alleles are exchanged at equivalent portions

Question 20

Independent segregation

Answer 20

The random position of homologous chromosomes in meiosis I that produces genetic variation

Question 21

How do the chromosomes line up in Meiosis I?

Answer 21

Double file

Question 22

How do the chromosomes line up in Meiosis II?

Answer 22

Single file

Question 23

What 2 cells can Meiosis produce?

Answer 23

Sperm
Ovum

Question 24

Why are chromosomes often coloured differently in diagrams?

Answer 24

To illustrate the paternal and maternal sets

Question 25

What is the stage of crossing over called once alleles are exchanged?

Answer 25

Synapsis

Question 26

What is it called where the alleles separate from their chromosome?

Answer 26

Point of breakage

Question 27

When does crossing over occur?

Answer 27

In meiosis I when the homologous chromosomes line up together

Question 28

What is the haploid number?

Answer 28

n (the number of chromosomes in either the maternal or paternal set)

Question 29

What is the diploid number?

Answer 29

2n (the full number of chromosomes in a body cell)

Question 30

What is the haploid number in humans?

Answer 30

n = 23

Question 31

What is the diploid number in humans?

Answer 31

n = 46

Question 32

What is the possibility of chromosome combinations in human gametes?

Answer 32

2 to the power of 23 (8,388,608)

Question 33

How is the possibility of chromosome combinations in gametes calculated?

Answer 33

2 to the power of n (the haploid number)

Question 34

Why is the number of actual possibilities of chromosome higher than in gametes?

Answer 34

Variation increases as a sperm and egg fuse as that is random

Question 35

What is the actual number of possibilities of chromosome combinations?

Answer 35

(2 to the power of n) squared

Question 36

What is the actual number of possibilities of chromosome combinations in humans?

Answer 36

7.0368744x10 to the power of 13

Question 37

What does natural selection need?

Answer 37

Genetic diversity

Question 38

Genetic diversity

Answer 38

The number of different alleles in a population

Question 39

How does genetic diversity influence natural selection?

Answer 39

A range of different alleles provides a wider range of characteristics, so there is a greater chance that there is a characteristic better suited to the (changing) environment

Question 40

Why are all alleles not all passed on?

Answer 40

Only certain individuals are reproductively successful

Question 41

What does stabilising selection do to the normal distribution curve?

Answer 41

Make it skinnier and taller

Question 42

What does directional selection do to the normal distribution curve?

Answer 42

Push it either left or right

Question 43

Hybridisation

Answer 43

The combining of genes of different varieties or species of organisms to produce a hybrid

Question 44

Polyploidy

Answer 44

Organisms that have additional complete sets of chromosomes

Question 45

How can Polyploidy arise?

Answer 45

The chromosomes do not separate into 2 distinct sets during meiosis so diploid gametes are possible Or Hybrids that have a chromosome number which is a multiple of a the original number can undergo meiosis

Question 46

When a diploid gamete fuses with a haploid gamete it is called?

Answer 46

Triploid

Question 47

When a diploid gamete fuses with another diploid gamete it is called?

Answer 47

Tetraploid

Question 48

Nondisjunction

Answer 48

A gamete has an extra/one less individual chromosome

Question 49

Why does nondisjunction occur?

Answer 49

A homologous pair of chromosomes fails to separate in Meiosis

Question 50

Human example of nondisjunction

Answer 50

Down's syndrome (extra chromosome 21)

Question 51

What do random mutations often result in?

Answer 51

A new allele which is often harmful to the organism's survival

Question 52

What happens to the advantageous alleles over time?

Answer 52

It replaces another non-advantageous allele in the population