3.4.3 Genetic diversity can arise as a result of mutation or during meiosis

Question 1

Q: What are the two main types of gene mutations?

Answer 1

A: The two main types of gene mutations are base deletion and base substitution.

Question 1

Q: What is a gene mutation?

Answer 1

A: A gene mutation is a change in the base sequence of chromosomes. These mutations can occur spontaneously during DNA replication.

Question 2

Q: What happens during a base deletion mutation?.

Answer 2

A: During base deletion, a nucleotide is lost from the DNA sequence, potentially causing a frameshift that alters the entire amino acid sequence downstream

Question 3

Q: What is base substitution in gene mutations?

Answer 3

A: Base substitution is when one nucleotide in the DNA sequence is replaced with another. This may or may not affect the amino acid sequence due to the degenerate nature of the genetic code.

Question 4

Q: What does the “degenerate nature of the genetic code” mean?

Answer 4

A: It means that multiple codons can code for the same amino acid. Therefore, some base substitutions do not change the amino acid sequence, leading to a “silent” mutation.

Question 5

Q: How do mutagenic agents affect gene mutation?

Answer 5

A: Mutagenic agents increase the rate of gene mutation by causing changes in the DNA sequence.

Question 6

Q: What is chromosome non-disjunction?

Answer 6

A: Chromosome non-disjunction occurs when chromosomes fail to separate properly during meiosis, leading to mutations in the number of chromosomes.

Question 7

Q: What is meiosis?

Answer 7

A: Meiosis is a type of cell division that produces four genetically different haploid daughter cells from a single diploid parent cell through two nuclear divisions.

Question 8

Q: How does independent segregation contribute to genetic diversity?

Answer 8

A: During meiosis, homologous chromosomes are randomly distributed to daughter cells. This independent segregation creates genetic variation as different combinations of maternal and paternal chromosomes are passed to the offspring.

Question 9

Q: What is crossing over, and how does it increase genetic diversity?

Answer 9

A: Crossing over is the exchange of genetic material between homologous chromosomes during meiosis. This process creates new combinations of alleles, further increasing genetic variation among daughter cells.

Question 10

Q: What is the difference in outcomes between mitosis and meiosis?

Answer 10

A: Mitosis results in two genetically identical diploid daughter cells, while meiosis produces four genetically different haploid daughter cells.

Question 11

Q: How does random fertilization increase genetic variation?

Answer 11

A: Random fertilization involves the combination of two haploid gametes, each with a unique set of chromosomes. This further increases genetic diversity within a species.

Question 12

Q: Describe how a gene mutation can lead to the production of a non-functional enzyme.
(5 marks)

Answer 12

Marking Points:

Change in DNA/Base Sequence: Mutation changes the base sequence of DNA.
mRNA Sequence Change: This leads to a change in the sequence of mRNA transcribed from the gene.
Altered Amino Acid Sequence: The mRNA sequence change may lead to a change in the sequence of amino acids in the protein.
Change in Tertiary Structure: The altered amino acid sequence can cause changes in the folding of the polypeptide chain, altering the enzyme’s tertiary structure.
Loss of Active Site Functionality: If the active site shape changes, the enzyme may no longer bind to its substrate, resulting in a non-functional enzyme.

Question 13

Q: Explain how independent segregation of homologous chromosomes during meiosis contributes to genetic variation.
(3 marks)

Answer 13

Marking Points:

Random Assortment: Homologous chromosomes are randomly assorted to daughter cells during meiosis I.
Different Combinations: This creates different combinations of maternal and paternal chromosomes in the gametes.
Genetic Variation: This results in offspring with varied genetic combinations, contributing to genetic diversity in the population.

Question 14

Q: Describe the process of crossing over and explain how it increases genetic diversity.
(4 marks)

Answer 14

Marking Points:

Synapsis of Homologous Chromosomes: Homologous chromosomes pair up during prophase I of meiosis.
Chiasma Formation: Chromatids of homologous chromosomes exchange segments at points called chiasmata.
Recombination of Alleles: This exchange results in new combinations of alleles on each chromosome.
Increased Genetic Diversity: As a result, the gametes formed have varied combinations of alleles, increasing genetic diversity in the offspring.

Question 15

Q: What is chromosome non-disjunction, and how can it lead to genetic disorders?
(3 marks)

Answer 15

Marking Points:

Definition: Non-disjunction occurs when chromosomes fail to separate properly during meiosis.
Abnormal Chromosome Number: This results in gametes with an abnormal number of chromosomes.
Genetic Disorders: If such a gamete is involved in fertilization, it can lead to disorders like Down syndrome, where the offspring has an extra chromosome (trisomy).

Question 16

Q: Explain how meiosis and fertilization contribute to genetic variation in offspring.
(5 marks)

Answer 16

Marking Points:

Independent Assortment: Meiosis I involves the independent assortment of homologous chromosomes, creating varied combinations of chromosomes in gametes.
Crossing Over: Crossing over during prophase I of meiosis introduces new combinations of alleles on chromosomes.
Random Fertilization: During fertilization, any sperm can fuse with any egg, creating numerous possible genetic combinations.
Genetic Variation: These processes ensure that each offspring has a unique genetic makeup.
Evolutionary Significance: This genetic variation is crucial for natural selection and adaptation in populations.

Question 17

Q: Describe how mutagenic agents can increase the rate of gene mutation.
(3 marks)

Answer 17

Marking Points:

Increase in DNA Damage: Mutagenic agents, such as UV radiation or certain chemicals, increase the rate of DNA damage.
Interference with DNA Replication: These agents can interfere with DNA replication, leading to errors in the sequence of bases.
Increased Mutation Rate: As a result, the likelihood of mutations occurring during replication is increased, potentially leading to genetic disorders or cancer.