Genetic diversity can arise as a result of mutation or during meiosis Flashcards – AQA A-Level Biology - (7402)

What is a gene mutation?

A change in the DNA base sequence.

When can mutations arise spontaneously?

During DNA replication.

What effect do mutagenic agents have on the rate of mutation?

They increase the mutation rate.

What is a base substitution?

The replacement of one base with another.

Why does a base substitution not always change the amino acid sequence?

The genetic code is degenerate, so the substituted codon can encode the same amino acid.

What two other effects can a base substitution have on a codon?

It can change the amino acid encoded or produce a stop codon.

What is a base deletion?

The removal of a base.

How can a base deletion affect the amino acid sequence?

It can shift the reading frame, changing subsequent codons and potentially the amino acid sequence.

What is chromosome non-disjunction?

The failure of chromosomes to separate normally during cell division.

Which structures fail to separate in non-disjunction during the first versus the second meiotic division?

First division: homologous chromosomes. Second division: sister chromatids.

What chromosome-number changes can non-disjunction produce in haploid cells?

A haploid cell may have an extra chromosome or a missing chromosome.

What can result if a gamete affected by non-disjunction participates in fertilisation?

The resulting cell can have an altered chromosome number.

How many nuclear divisions occur in meiosis, and what cells are usually produced from one diploid parent cell?

Two divisions usually produce four haploid daughter cells.

When is DNA replicated relative to the two meiotic divisions?

Before the divisions; no further replication occurs between them.

After DNA replication, what does each chromosome consist of at the start of meiosis?

Two sister chromatids.

What separates in the first meiotic division, and what happens to the chromosome number?

Homologous chromosomes separate, reducing the chromosome number from diploid to haploid.

What separates in the second meiotic division?

Sister chromatids.

How many chromosomes from each homologous pair does a normal meiotic product contain?

One chromosome from each pair.

What are the number of divisions and the usual products of mitosis?

One nuclear division normally produces two genetically identical daughter cells with the same chromosome number as the parent cell.

How can meiosis be identified in a life cycle?

By a reduction from a diploid cell or stage to haploid cells or a haploid stage.

Are the haploid products of meiosis always gametes?

No. Haploid products need not be gametes in every life cycle.

How do homologous chromosome pairs orient relative to one another before they separate in meiosis I?

They orient independently of one another.

After homologues separate in meiosis I, how many chromosomes from each homologous pair does each daughter cell receive?

One chromosome from each pair.

What effect does independent segregation have on the chromosome combinations in the haploid products of meiosis?

It produces genetically different combinations of maternal and paternal homologues.

What is crossing over during meiosis?

Paired homologous chromosomes exchange corresponding sections of DNA between non-sister chromatids.

How does crossing over contribute to genetic variation among haploid products?

It creates chromatids with new combinations of alleles, which are distributed to daughter cells.

What happens to ploidy when two gametes fuse during fertilisation?

Two haploid gametes form a diploid cell.

How does random fertilisation increase genetic variation within a species?

Genetically different gametes can fuse in many combinations, producing cells with different allele combinations.