Chapter 16 pt.3 – Meiosis and Comparison to Mitosis

Question-and-answer flashcards covering chromosome number changes, stages and events of meiosis, comparison to mitosis, and mechanisms promoting genetic variation.

What is the chromosome number change from a diploid human cell to a haploid gamete after meiosis?

46 chromosomes (diploid) are reduced to 23 chromosomes (haploid).

How many total cell divisions occur in meiosis?

Two consecutive divisions: meiosis I and meiosis II.

How many cells and of what ploidy are produced at the end of meiosis?

Four haploid cells.

During which meiotic division do homologous chromosome pairs separate?

Meiosis I (specifically Anaphase I).

During which meiotic division do sister chromatids separate?

Meiosis II (specifically Anaphase II).

What structure forms when homologous chromosomes pair up side-by-side during prophase I?

A bivalent (also called a tetrad).

What is synapsis?

The process of homologous chromosomes pairing to form a bivalent during prophase I.

Which protein structure physically connects homologous chromosomes during synapsis?

The synaptonemal complex.

What is crossing over?

The physical exchange of DNA segments between nonsister chromatids of homologous chromosomes in a bivalent.

How does crossing over contribute to a species?

It increases genetic variation among offspring.

What is a chiasma?

The visible site where crossing over has occurred and homologous chromosome arms remain connected.

At what stage does the chiasma first appear microscopically?

Late prophase I.

What key events characterize prophase I?

Chromosomes condense, bivalents form, crossing over occurs, and the nuclear envelope begins to break down.

What is the alignment pattern of chromosomes during metaphase I?

Homologous pairs (bivalents) align as a double row on the metaphase plate.

How are sister chromatids attached to spindle poles during meiosis I?

Each pair of sister chromatids in a bivalent is attached to microtubules from only one pole.

When does the cell become haploid in meiosis?

Immediately after meiosis I is complete.

Is there an S phase between meiosis I and meiosis II?

No, DNA is not replicated again between the two divisions.

Which meiotic phase closely resembles mitosis in its mechanics?

Meiosis II (because sister chromatids separate similar to mitosis).

What happens to chromosomes during telophase I?

Sister chromatids reach opposite poles, decondense, and nuclear membranes reform, yielding two haploid nuclei.

What is the final result of meiosis II?

Four genetically unique haploid cells, each with single-chromatid chromosomes.

How many homologous pairs does a human diploid cell contain before meiosis begins?

23 homologous pairs (46 total chromosomes).

Which three key differences distinguish meiosis from mitosis?

Synapsis and bivalent formation, crossing over, and separation of homologous chromosomes (instead of sister chromatids) during the first division.

What type of daughter cells does mitosis produce regarding ploidy and genetic identity?

Two diploid daughter cells that are genetically identical to the parent cell.

What type of daughter cells does meiosis produce regarding ploidy and genetic identity?

Four haploid daughter cells that are genetically diverse.

In mitosis, how are sister chromatids attached to poles during prometaphase?

Each chromatid is attached to microtubules from both poles.

In meiosis I, which chromosomes align along the metaphase plate?

Homologous pairs (bivalents), not individual sister chromatids.

What is the ploidy and chromatid status of chromosomes immediately after meiosis I?

Cells are haploid, and each chromosome still has two sister chromatids.

During which stage of meiosis II do sister chromatids align on the metaphase plate?

Metaphase II.

Why is meiosis essential for sexual reproduction?

It halves the chromosome number, allowing fertilization to restore diploidy and generating genetic variation among offspring.

What happens to kinetochore microtubules during anaphase II?

They shorten to pull sister chromatids (now individual chromosomes) toward opposite poles.