3.4.3 Genetic Diversity Can Arise as a Result of Mutation/During Meiosis

Question 1

(Genetic Diversity due to Mutation/Meiosis) Define the term ‘gene mutation’.

Answer 1

Any change to the quantity of bases or base sequence in the DNA.

Question 2

(Genetic Diversity due to Mutation/Meiosis) What will gene mutation result in? (3)

Answer 2

• This will result in a change in the amino acid sequence of the polypeptide, altering the R-group interactions.
• This changes the tertiary structure and function…
• Can arise spontaneously during DNA replication.

Question 3

(Genetic Diversity due to Mutation/Meiosis) Due to the degenerate nature of the genetic code, what does not all base substitutions cause?

Answer 3

A change in the sequence of encoded amino acids.

Question 4

(Genetic Diversity due to Mutation/Meiosis) Explain the nature of a ‘base deletion’ gene mutation.

Answer 4

One nucleotide is replaced by a different one, changing the codon.
- May result in the same amino acid as genetic code is degenerate (silent).
- Alters a single amino acid, changing the tertiary structure / R group interactions of the protein.
- Result in a stop codon.

Question 5

(Genetic Diversity due to Mutation/Meiosis) Explain the nature of a ‘base substitution’ gene mutation.

Answer 5

One nucleotide is removed.
- Alters the reading frame.
- All codons / amino acids altered from this point.

Question 6

(Genetic Diversity due to Mutation/Meiosis) How does transcription differ between eukaryotes and prokaryotes? (3)

Answer 6

Eukaryotic genes often have ‘non-coding sequences’ of DNA called introns.

Introns are transcribed but then spliced or “cut out” from pre-mRNA in the nucleoplasm.

Mature mRNA (exons only) then leaves to be translated.

Question 7

(Genetic Diversity due to Mutation/Meiosis) How can a base substitution mutation affect the function of a protein?

Answer 7

Altering a single DNA base will alter the mRNA ‘codon’ on transcription of the gene.

May encode for a different amino acids / R group.

Affects the polypeptide folding and tertiary structure / R group interactions.

Polypeptide may be dysfunctional e.g. ‘active site of an enzyme’ no longer complementary to substrate.

Silent mutations change the codon to another that still encodes for the same amino acid - polypeptide unaffected.

Question 8

(Genetic Diversity due to Mutation/Meiosis) What can mutagenic agents do? (2)

Answer 8

Mutagenic agents can alter the nucleotide base sequence of DNA.
Can increase the rate of gene mutation.

Question 9

(Genetic Diversity due to Mutation/Meiosis) List 3 mutagenic agents.

Answer 9

Ionising radiation e.g. UV light, X rays
Asbestos
Carcinogens - chemicals e.g. tobacco

Question 10

(Genetic Diversity due to Mutation/Meiosis) Define the term ‘diploid’.

Answer 10

Diploid cells contain 2 x n chromosomes. There are ‘pairs’ of each type (homologues).

Diploid cells are the product of fertilisation (n + n + 2n).

Question 11

(Genetic Diversity due to Mutation/Meiosis) Define the term ‘haploid’.

Answer 11

Haploid cells contain n chromosomes. One of each type.

Haploid cells are gametes or ‘sex cells’.

Question 12

(Genetic Diversity due to Mutation/Meiosis) What does ‘n’ stand for in regards to chromosomes?

Answer 12

The number of ‘types’ of chromosome an organism has. Each type has its own particular set of genes.

Question 13

(Genetic Diversity due to Mutation/Meiosis) Outline the human life cycle. (3)

Answer 13

Both diploid (2n) parents produce haploid (n) gametes through meiosis.

Two haploid gametes (sex cells) fuse together to form a diploid (2n) zygote.

Zygote grows by mitosis (2n).

Question 14

(Genetic Diversity due to Mutation/Meiosis) Detail ‘homologous’ chromosomes.

Answer 14

2 chromosomes that possess the same genes at the same gene loci.

May not possess the same alleles.

Located in diploid (2n) cells.

One is paternally derived male gamete and the other maternally derived female gamete.

Question 15

(Genetic Diversity due to Mutation/Meiosis) Define the term ‘allele’.

Answer 15

An alternative version of the same gene.

Question 16

(Genetic Diversity due to Mutation/Meiosis) What do alleles possess?

Answer 16

A different nucleotide base sequence, which may alter the polypeptide the gene encodes for.

Question 17

(Genetic Diversity due to Mutation/Meiosis) Outline the stages of Meiosis 1 (3).

Answer 17

1. Homologous chromosomes pair up in synapsis.
2. ‘Crossing over’ rearranges alleles on homologous pairs of chromosomes.
3. ‘Independent segregation’ / separation of homologues to produce 2 now haploid cells.

Question 18

(Genetic Diversity due to Mutation/Meiosis) Outline the stages of Meiosis 2 (3).

Answer 18

1. Cells align individual chromosomes in metaphase 2.
2. Chromatids are separated.
3. Product = 4 haploid cells that are genetically non-identical.

Question 19

(Genetic Diversity due to Mutation/Meiosis) How does meiosis produce genetically non-identical daughter cells?

Answer 19

Independent segregation.

Question 20

(Genetic Diversity due to Mutation/Meiosis) Detail what occurs during independent segregation. (3)

Answer 20

1. During Metaphase 1, pairs of homologous chromosomes align on the metaphase plate.
2. The orientation of one pair is random with respect to another.
3. Due to different paternal/maternal alleles, this can produce genetical non-identical gametes when meiosis is repeated.

Question 21

(Genetic Diversity due to Mutation/Meiosis) Detail what occurs during crossing over. (4)

Answer 21

1. Synapsis occurs where homologous chromosomes “pair up” in Meiosis 1.
2. Non-sister chromatids overlap forming chiasmata.
3. The same section of homologous DNA is exchanged by recombination.
4. Due to different alleles, new allele sequences are created.

Question 21

(Genetic Diversity due to Mutation/Meiosis) How does meiosis produce genetically non-identical daughter cells?

Answer 21

Crossing over.

Question 22

(Genetic Diversity due to Mutation/Meiosis) Differences between Mitosis & Meiosis: How many divisions does each process have?

Answer 22

Mitosis: 1
Meiosis: 2

Question 23

(Genetic Diversity due to Mutation/Meiosis) Differences between Mitosis & Meiosis: What does each process produce?

Answer 23

Mitosis: 2 daughter cells (2n - diploid)
Meiosis: 4 daughter cells (n - haploid)

Question 24

(Genetic Diversity due to Mutation/Meiosis) Differences between Mitosis & Meiosis: What is the purpose of both processes?

Answer 24

Mitosis: Growth and repair
Meiosis: Sexual reproduction

Question 25

(Genetic Diversity due to Mutation/Meiosis) Differences between Mitosis & Meiosis: Are they genetically identical or genetically non-identical?

Answer 25

Mitosis: Genetically identical
Meiosis: Genetically non-identical (different alleles, not different genes).

Question 26

(Genetic Diversity due to Mutation/Meiosis) Differences between Mitosis & Meiosis: How are chromosomes dealt with in each process?

Answer 26

Mitosis: Chromosomes are dealt with independently.
Meiosis: 1st division separates homologous pairs - independent segregation.

Question 27

(Genetic Diversity due to Mutation/Meiosis) Differences between Mitosis & Meiosis: Chromatid separation?

Answer 27

Mitosis: Only chromatids are separated.
Meiosis: 2nd division separtes chromatids.

Question 28

(Genetic Diversity due to Mutation/Meiosis) How can nondisjunction during meiosis result in chromosomal mutation?

Answer 28

Failure to separate a pair of homologous chromosomes in meiosis 1.