3.4.3 Genetic diversity: Mutations and meiosis

What is a gene mutation?

• A change in the number of chromosomes

• A change in the base sequence of chromosomes

• The process of cell division

• The pairing of homologous chromosomes

Answer explanation

A gene mutation refers to a change in the base sequence of chromosomes, which can affect how genes function. This distinguishes it from changes in chromosome number or processes like cell division.

When do gene mutations most commonly arise?

• During protein synthesis

• During DNA replication

• During translation

• During fertilisation

Answer explanation

Gene mutations most commonly arise during DNA replication when the DNA is copied. Errors can occur in this process, leading to mutations. This is more frequent than during protein synthesis, translation, or fertilization.

Which of the following is NOT a type of gene mutation mentioned in the text?

• Base deletion

• Base substitution

• Chromosome inversion

• None of the above

Answer explanation

Chromosome inversion is not a type of gene mutation; it refers to a rearrangement of chromosome structure. Base deletion and base substitution are both recognized types of gene mutations.

Why do not all base substitutions result in a change in the amino acid sequence?

• Because of the degenerate nature of the genetic code

• Because all codons code for the same amino acid

• Because DNA cannot be mutated

• Because of chromosome non-disjunction

Answer explanation

Not all base substitutions change the amino acid sequence due to the degenerate nature of the genetic code, where multiple codons can code for the same amino acid, allowing some mutations to be silent.

What effect do mutagenic agents have on gene mutation?

• They decrease the rate of gene mutation

• They have no effect on gene mutation

• They increase the rate of gene mutation

• They repair gene mutations

Answer explanation

Mutagenic agents are substances that increase the frequency of mutations in DNA. Therefore, they increase the rate of gene mutation, making the correct answer 'They increase the rate of gene mutation'.

What is chromosome non-disjunction?

• The deletion of a base in DNA

• The failure of chromosomes to separate properly during meiosis

• The substitution of one base for another

• The replication of DNA

Answer explanation

Chromosome non-disjunction refers to the failure of chromosomes to separate properly during meiosis, leading to gametes with an abnormal number of chromosomes. This can result in genetic disorders.

What can chromosome non-disjunction lead to?

• Mutations in the base sequence

• Mutations in the number of chromosomes

• Crossing over

• Independent segregation

Answer explanation

Chromosome non-disjunction results in an abnormal number of chromosomes, leading to conditions like Down syndrome. This is a mutation in chromosome number, making 'Mutations in the number of chromosomes' the correct choice.

How many nuclear divisions occur during meiosis?

• One

• Two

• Three

• Four

Answer explanation

Meiosis consists of two nuclear divisions: meiosis I and meiosis II. These divisions reduce the chromosome number by half, resulting in four haploid cells from one diploid cell. Therefore, the correct answer is two.

How many daughter cells are usually produced from a single diploid parent cell during meiosis?

• Two

• Three

• Four

• Eight

Answer explanation

During meiosis, a single diploid parent cell undergoes two rounds of division, resulting in four haploid daughter cells. Therefore, the correct answer is four.

What is the ploidy of the daughter cells produced by meiosis?

• Diploid

• Triploid

• Haploid

• Tetraploid

Answer explanation

The daughter cells produced by meiosis are haploid, meaning they contain half the number of chromosomes compared to the original diploid parent cell. This reduction is essential for sexual reproduction.