B9 - Genetic Diversity & Adaptation

Question 1

What is gene mutation?

Answer 1

Gene mutation = change in the sequence of base pairs in DNA

Question 2

How can mutations in the DNA base sequence happen?

Answer 2

• Deletion of nucleotides
• Insertion of extra nucleotides
• Substitution of nucleotides

Question 3

What is the substitution of nucleotides?

Answer 3

DNA base is randomly swapped for a different base
This type of mutation only changes the triplet

Question 4

What are the 3 types of substitution mutations?

Answer 4

• Silent mutations: mutation does not alter the amino acid sequence due to the degenerate nature of DNA
• Missense mutations: mutation alters a single amino acid in the peptide chain
• Nonsense mutations: the mutation creates a premature stop codon meaning the polypeptide chain produced is incomplete which affects final protein structure & function

Question 5

What are mutagenic agents?

Answer 5

Environmental factors that increase the mutation rate of cells

Question 6

What is a non-disjunction mutation?

Answer 6

When chromosomes fail to separate during meiosis which occurs spontaneously. Resulting in gametes which may contain one extra copy OR no copies of a particular chromosome

Question 7

What is independent assortment?

Answer 7

Homologous chromosomes line up in a random order → each one gets sorted into gametes randomly → each daughter cell has a random combination of chromosomes

Question 8

What is crossing over in meiosis?

Answer 8

The exchange of alleles, as bits of a chromatid break during meiosis, and re-join to its sister chromatid

Question 9

What are homologous chromosomes?

Answer 9

A set of one maternal and one paternal chromosome that pair up with each other

Question 10

How are chromosomes counted?

Answer 10

The number of centromeres present

Question 11

What are the steps of meiosis 1?

Answer 11

Prophase I: replicated chromosomes line up side by side in homologous pairs & crossing over occurs
Metaphase I: homologous chromosomes line up along the equator of the cell and independent assortment occurs
Anaphase I: homologous chromosomes separate, centromeres do not separate
Telophase I: nuclear envelope forms around the separated groups of chromosomes
Cytokinesis occurs & the end product of meiosis I is two haploid cells

Question 12

What are the steps of meiosis 2?

Answer 12

• No interphase between meiosis I and meiosis II so the DNA is not replicated
• Prophase II: chromosomes condense & spindles form
• Metaphase II: chromosomes line up in a single file along the equator of the cell
• Anaphase II: centromeres divide & individual chromatids are pulled to opposite poles
• Telophase II: nuclear envelope forms around the four groups
• Cytokinesis occurs again & the end product of meiosis II is: four haploid cells that contain the same the number of centromeres in meiosis I, but now only have half the number of chromosomes

Question 13

How do you calculate the number of possible chromosomal combinations resulting from meiosis?

Answer 13

2^n where n is the haploid number (23 in humans)

Question 14

How do you calculate the number of combinations of chromosomes after the random fertilisation of two gametes?

Answer 14

(2^n)^2 where n is the haploid number

Question 15

What is genetic diversity?

Answer 15

The number of different alleles of genes in a population

Question 16

How is genetic diversity achieved?

Answer 16

Diversity is achieved by mutation which increases the size of the gene pool, increasing genetic diversity

Question 17

What is selection pressure in natural selection?

Answer 17

Environmental factors act as selection pressures which increase the chance of individuals with specific, advantageous phenotypes surviving and reproducing over less suited individuals. These individuals have a higher fitness (their ability to survive & pass on their alleles) and possess better adaptations for their environment

Question 18

What does it mean if a population has a small gene pool?

Answer 18

If a population has a small gene pool or very low genetic diversity, they are less able to adapt to changes in their environment and become vulnerable to extinction

Question 19

How does natural selection occur?

Answer 19

Random mutation can produce new alleles of a gene. Mutations can be harmful or neutral, but under certain conditions, can be beneficial to individuals. Increased chance of survival and increased chance of reproductive success. Advantageous allele is passed onto the next generation. Over several generations, the new allele will increase in frequency in the population

Question 20

What is the founder effect?

Answer 20

Occurs when a small number of individuals from a large parent population start a new population. Only some of the total alleles from the parent population will be present. These remaining alleles may lead to phenotypes that are not largely present in the parent population. A stepping stone to speciation

Question 21

What is the bottleneck effect?

Answer 21

Occurs when a previously large population suffers a dramatic fall in numbers. Environmental event occurs →reduces number of individuals → reduces the genetic diversity of the population (as alleles are lost). Surviving individuals may breed and reproducing with close relatives

Question 22

What is directional selection?

Answer 22

Environmental factors that affect the chance of survival of an organism are selection pressures. Directional selection is natural selection that produces a gradual change in allele frequencies over several generations

Question 23

What is stabilising selection?

Answer 23

Stabilising selection is natural selection that keeps allele frequencies relatively constant over several generations, unless there is a change in the environment

Question 24

What are the 3 types of adaptations?

Answer 24

Anatomical adaptations - structural/physical features

Physiological adaptations - biological processes within the organism

Behavioural adaptations - the way an organism behaves