Unit 2 – Inheritance and Genetic Diversity

Question-and-answer flashcards reviewing key concepts of chromosomes, meiosis, genetic diversity mechanisms, and related terminology.

What are homologous chromosomes?

A matching pair of chromosomes—one maternal, one paternal—that carry the same gene loci but possibly different alleles.

How do autosomes differ from sex chromosomes?

Autosomes are non-sex chromosomes; sex chromosomes (X and Y in humans) determine biological sex.

Which cellular process produces haploid gametes from diploid cells?

Meiosis.

During which phase of meiosis does crossing over occur?

Prophase I.

What is crossing over?

The exchange of genetic material between non-sister chromatids of homologous chromosomes, producing recombinant chromatids.

Why does crossing over increase genetic diversity?

It creates new allele combinations on each chromatid, leading to genetically unique gametes.

What is independent assortment?

Random orientation of homologous chromosome pairs along the metaphase I plate, causing random segregation of maternal and paternal chromosomes.

During which phase of meiosis does independent assortment occur?

Metaphase I.

Why is independent assortment important?

It ensures that each gamete receives a random mix of maternal and paternal chromosomes, increasing genetic variation.

List the stages of meiosis I in order.

Prophase I, Metaphase I, Anaphase I, Telophase I, Cytokinesis I.

List the stages of meiosis II in order.

Prophase II, Metaphase II, Anaphase II, Telophase II, Cytokinesis II.

What happens during anaphase I?

Homologous chromosomes move to opposite poles while sister chromatids stay attached.

What happens during anaphase II?

Sister chromatids split at the centromere and move to opposite poles.

After meiosis I, how many chromosomes does each daughter cell contain?

23 chromosomes (still duplicated as chromatids).

How many total daughter cells result from meiosis II?

Four haploid (n) daughter cells.

Differences between mitosis and meiosis.

Mitosis produces two identical diploid cells with no crossing over; meiosis produces four non-identical haploid cells with crossing over and independent assortment.

Which structure holds sister chromatids together until anaphase?

The centromere.

What is a tetrad?

The structure formed by a pair of homologous chromosomes (two pairs of sister chromatids) during prophase I.

Define nondisjunction.

Failure of chromosomes or chromatids to separate properly during meiosis, leading to gametes with abnormal chromosome numbers.

What are spindle fibres and what is their role in meiosis?

Microtubule structures that attach to centromeres and pull chromosomes/chromatids to opposite poles.

What are the specific stages of interphase

Gap 1, Synthesis and Gap 2

What happens in Gap 1?

The cell grows

What happens in the synthesis phase?

The cell replicates its DNA turning one chromosome into 2 genetically identical chromatids

What happens in Gap 2?

The cell continues to grow and checks off all previous steps

What happens in Prophase I?

• Chromosomes condense in the nucleus

• The nuclear membrane breaks down and disappears

• Centrioles moves towards opposite ends of the cell

• Spindle fibres begin to form

• Crossing over can occur

What happens in Metaphase I?

• Spindle fibres fully form and attach to the centromere

• Fibres pull the chromosomes to the middle of the cell

• Homologous chromosomes line up randomly in homologous pairs

What happens in Telophase I?

• New nuclear membrane forms at either end

• Spindle fibres disintegrate

• Cleavage furrow forms

• Homologous chromosomes arrive at opposite poles

What happens in Cytokinesis I?

• Cytoplasm divides

• Organelles distribute themselves

• Separates into 2 daughter cells

What is the between Telophase I and Telophase II?

Instead of the homologous chromosomes arriving at opposite ends the chromatids become chromosomes and the chromosomes gets densely packed together at either end of the cell.