9.1 - 9.4 Genetic diversity

Question 1

Define mutation

Answer 1

A change in the structure or quantity of an organisms DNA

Question 2

Define gene mutation

Answer 2

A change to one or more nucleotide bases

Question 3

Define chromosome mutation

Answer 3

A change in the structure or number of chromosomes

Question 4

Define polyploidy

Answer 4

Changes in whole sets of chromosomes

Question 5

When are gene mutations most likely to arise?

Answer 5

During DNA replication

Question 6

What are the six type of gene mutations?

Answer 6

1. Substitution - replace a base
2. Addition - add a base
3. Deletion - remove a base
4. Inversion - flip a sequence of bases so they are read backwards
5. Translocation - move a sequence of bases from one place to another
6. Duplication - repetition of a sequence of bases

Question 7

Explain how a substitution of one base could result in a non-functional protein

Answer 7

• Base triplet on DNA is different
• Different codon on mRNA following transcription
• Different tRNA binds to mRNA during transcription
• Different amino acid is incorporated into polypeptide chain
• Hydrogen/ionic/disulphide bonds form in different places
• The tertiary structure of the protein is changed so it is non-functional

Question 8

Define mutagenic agent

Answer 8

Something that can increase the rate of gene mutation

Question 9

Give examples of a mutagenic agent

Answer 9

High energy radiation:

• Can ionise chemicals in DNA and change the overall structure
• e.g X-rays, gamma rays and UV radiation

High energy particles:

• Can ionise chemicals in DNA and change the overall structure
• e.g alpha or beta particles

Chemicals:

• Can alter bases
• e.g benzene, mustard gas, tobacco tar, pesticides

Question 10

Define non-disjunction

Answer 10

When a chromosome fails to separate into to two chromatids during anaphase. This leaves one daughter cell with an extra chromosome.

Question 11

What is meiosis?

Answer 11

Nuclear division that produces 4 genetically different daughter cells. The cells produced are gametes (sex cells).

Question 12

What is the importance of meiosis?

Answer 12

1. Chromosome number is halved (produces haploid daughter cells) - So when gametes fuse they maintain the correct number of chromosomes
2. Genetic variation is introduced (all gametes genetically unique) - Enables natural selection

Question 13

What are the two ways meiosis introduces genetic variation?

Answer 13

1. Crossing over during meiosis 1
2. Independent segregation in meiosis 1 and 2

Question 14

Define independent segregation

Answer 14

When homologous chromosomes line up randomly during meiosis 1 meaning the daughter cells receive a random combination of maternal and paternal chromosomes

Question 15

What is the formula for the number of possible combinations during independent segregation?

Answer 15

2ⁿ

n = The number of homologous pairs

Question 16

What is crossing over?

Answer 16

• Homologous chromosomes pair up (to form a bivalent)
• Equal lengths of chromatids are exchanged between non-sister chromatids at points called chiasmata
• This creates new combination of alleles called recombinations

Question 17

Define genetic diversity

Answer 17

The number of different alleles of genes in a population

Question 18

Describe how genetic diversity enables natural selection

Answer 18

• Greater genetic diversity
• Greater variety of alleles in gene pool
• Greater variety of phenotypes in a population
• More likely that some members of the population would survive an environmental change
• Enables natural selection

Question 19

Describe the process of natural selection

Answer 19

• There is genetic variation in a population and random genetic mutations may create new alleles
• Some alleles have advantageous effects due to selection pressure
• Individuals with these characteristics have increased reproductive success, therefore allele more likely to be passed on to next generation
• Frequency of advantageous allele increases

Question 20

Define selection pressure

Answer 20

A factor that limits the survival of a population and results in evolutionary changes

Question 21

Give 4 examples of selection pressures

Answer 21

• Food availability
• Harsh abiotic conditions
• Predators
• Disease

Question 22

Describe a selective advantage for the selection pressure of predators

Answer 22

Adaptation to not be seen or to be able to escape being eaten

Question 23

Describe a selective advantage for the selection pressure of food availability

Answer 23

Adaptation to eat the available food, produce the correct enzymes

Question 24

Describe a selective advantage for the selection pressure of disease

Answer 24

Resistance to the disease or ability to survive the disease

Question 25

Describe a selective advantage for the selection pressure of harsh abiotic conditions

Answer 25

Adaptation to survive condition

Question 26

Describe anatomical adaptations

Answer 26

Improvements in physical characteristics that allow an organism to be more competitive

Question 27

Describe physiological adaptations

Answer 27

Improvements in biological processes that allow an organism to be more competitive

Question 28

Describe behavioural adaptations

Answer 28

Improvements in behaviour that allow an organism to be more competitive

Question 29

Describe stabilising selection

Answer 29

This is a type of natural selection in which genetic diversity decreases as the population stabilises on a particular trait value. Extreme phenotypes are selected against; it favours the norm (the mean). This is the most common mechanism of action for natural selection. Organisms with mean phenotype more likely to survive and reproduce

Question 30

Describe disruptive selection

Answer 30

When natural selection selects for two or more extreme phenotypes that each have specific advantages. Organisms at both extremes more likely to survive and reproduce

Question 31

Describe directional selection

Answer 31

This occurs when natural selection favours a single phenotype and therefore allele frequency continuously shifts in one direction. Organisms at one extreme more likely to survive and reproduce

Question 32

To do:

Answer 32

- More about meiosis - Required practical 6 and aseptic technique

Question 33

Describe what happens to chromosomes in meiosis

Answer 33

1.  Chromosomes condense 2.  Chromosomes associate in homologous pairs / form bivalents 3.  Crossing-over 4.  Join to spindle fibres 5.  At middle of cell 6.  Join via centromere 7.  Homologous chromosomes move to opposite poles 8.  (Pairs of) chromatids separated in 2 nd division

Question 34

Meiosis results in genetic variation in the gametes which leads to variation in the offspring formed by sexual reproduction. Describe how meiosis causes this variation and explain the advantage of variation to the species

Answer 34

1.  Crossing-over 2.  Independent segregation of (homologous) chromosomes in meiosis I 3.  Independent segregation of chromatids in meiosis II 4.  Different adaptations 5.  Some survive 6.  To reproduce 7.  Pass on allele 8.  Allows for changing environment