Mitosis & meiosis Flashcards by Ellen Thomas

What are the 3 main stages of the cell cycle?

Growth/interphase, mitosis and cytokinesis (cytoplasmic division)

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What phases are there within the interphase?

G1 (growth 1)
S (synthesis)
G2 (growth 2)

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What happens in G1 phase?

Cellular contents (excluding chromosomes) are duplicated

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What happens in S phase?

Each of the 46 chromosomes are duplicated by the cell

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What happens in G2 phase?

The cell double checks the duplicated chromosomes for errors, and repairs any errors.

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What are the stages in mitosis?

PPMAT

Prophase
Prometaphase
Metaphase
Anaphase
Telophase

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What happens in prophase of mitosis?

Chromatin condenses into chromosomes
There are now chromosomes each made up of 2 sister chromatids

Centrosomes nucleate microtubules and move to opposite poles of the nucleus

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What happens in prometaphase?

Nuclear envelope breaks down

Microtubules invade nuclear space

Chromatids attach to microtubules

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What happens in metaphase?

Chromosomes line up at the equator of the cell

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What happens in anaphase?

Sister chromatids are separated and pushed to opposite poles of the cell

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What happens in Telophase?

Nuclear membranes reform

Chromosomes unfold into chromatin

Cytokinesis begins

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How would you recognise cells in prophase?

Cells have dark condensed chromosomes

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How would you recognise cells in metaphase?

Dark chromosomes line up along middle

Thick stripe in middle of cell

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How would you recognise cells in anaphase?

Chromosomes lined up in 2 lines at opposite poles of the cell

Two dark stripes either side of cell

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How would you recognise cells in Telophase?

Look to be about to divide

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What is mitosis?

Cell division that results in 2 daughter diploid cells each having the same number of chromosome (46) and genetically identical

What is meiosis?

Cell division that results in 4 haploid cells being produced from 1 diploid one.

Happens in two sections:
Meiosis 1 & Meiosis 2

Name the stages of meiosis in order?

MEIOSIS 1
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1

MEIOSIS 2
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2

Which cells does meiosis occur in?

Gametes

What happens in prophase 1 of meiosis?

Chromosomes pair and ‘crossing over’ occurs - recombinant chromosomes are formed

What happens in prometaphase 1 of meiosis?

Spindle apparatus is formed and attaches to spindle fibres by kinetochores

What happens in metaphase 1 of meiosis?

Homologous pairs of chromosomes are arranged as a double row along the equator

Arrangement along equator is random

What happens in anaphase 1 of meiosis?

Homologous chromosomes are separated and move to opposite poles

So there are entire chromosomes at each pole

What happens at Telophase 1?

Nuclear membrane reforms and cytokinesis begins to occur

Meiosis ? separates pairs of homologous chromosomes?

Meiosis ? separates each chromosome into two chromatids?

What happens in prophase II of meiosis?

Chromosomes condense and nuclear membrane dissolves | Spindle fibres form

What happens in metaphase II of meiosis?

Chromosomes line up along centre and spindle fibres attach to centromere

What happens in anaphase II of meiosis?

Centromeres divide and sister chromatids move to opposite poles

What happens in Telophase II of meiosis?

Chromosomes get to opposite ends of pole and nuclear membrane reforms

Is meiosis I or meiosis II the same as mitosis?

Meiosis II

Briefly describe sperm production (spermatogenesis).

Primordial germ cells > lots of mitoses > Spermatogonia Meiotic divisions begin at puberty Cytoplasm divides evenly After meiosis II there are 4 equal gametes Takes 60-65 days Millions of mature sperms continuously produced

How many sperms per ejaculate?

100-200 million

Briefly describe egg production (oogenesis).

Primordial germ cell > 30 mitoses > oogonia Oogonia enter prophase of meiosis I by 8th month of development (pre-birth) Process suspended until puberty Cells enter ovulation Cytoplasm divides unequally Meiosis II is only completed if fertilisation occurs

What does Mendel's 2nd law state?

In the inheritance of more than one pair of traits in a cross simultaneously, the factor responsible for each pair of traits are distributed to the gametes.

What is non-disjunction?

Failure of chromosomes to separate in meiosis I OR failure of sister chromatids to separate in meiosis II

When does crossing over occur in meiosis?

Prophase I

What's the difference between numerical and structural chromosomal abnormalities?

Numerical: Down's syndrome for example - failure at anaphase chromosomes are not split, 3 copies of chromosome 21 end up in one gamete Structural: Deletion, duplication or translocation of bases/genes