4 - The Cell Cycle, Mitosis, Meiosis Flashcards by mikayla kozarchuk

What are the two cell types based on chromosome content? Where are they found? What is the difference?

Gametes and Somatic Cells.
Gametes only in the genitals.
Somatic cells are diploid, gametes are haploid.

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Define haploid and diploid.

Haploid (n): No homologous pairs

Diploid (2n): Homologous Pairs (2 codes for every gene)

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How many chromosomes are in a diploid cell? A haploid cell?

Diploid - 46 (2 pairs of 23)

Haploid - 23, unless in meiosis, then 46 (2 identical sets)

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Define homologous chromosomes

Chromosomes with same centromere position, length and genes, but different alleles.

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Define gene

A section of DNA coded for a particular trait (unit of heredity)

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Define alleles

Particular versions of genes for particular versions of a trait (blue vs brown eyes have different alleles in the eye colour gene)

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Define locus

The location of specific genes on a chromosome

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What are autosomes

Autosomal chromosomes (1-22) which code for somatic characteristics
Autosomal pairs are homologous but not identical

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Define sex chromosomes

23: code for sex determination

Sex chromosomes pairs are homologous in girls but not guys. (X&Y are different)

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What are the two stages of the cell cycle?

Interphase and mitosis or meiosis

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What are the characteristics of interphase?

 chromosomes present as chromatin

 normal cellular metabolic activities occurring e.g. protein synthesis

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What are the stages of interphase?

G1, S, G2

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Describe G1

 growth, metabolism

 at end of G1, centrosomes replicate

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What happens to cells that will not divide?

They enter G0 (permanent G1)

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Describe S phase

 chromosomes replicate, but are still present as chromatin (not individually visible)

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What are sister chromatids?

Replicates of original chromosomes made in S phase.
 attached to each other at an area of DNA called the centromere
 kinetochore proteins (produced during S phase) attach to each centromere to form the kinetochore

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What is the kinetochore

protein + DNA complex, 1 per chromatid

site of attachment of spindle microtubules

Describe G2

 growth, metabolism

 production of enzymes & other proteins needed for cell division

What are the two parts of the mitotic phase of the cell cycle?

Mitosis

Cytokinesis

What are the stages of mitosis?

P-MAT
Prophase
Metaphase
Anaphase
Telophase

What is cytokinesis? When does it begin?

division of cytoplasm

begins during anaphase

When is mitosis complete?

When cytokinesis is complete

 daughter cells go into interphase (G1)

Describe Mitotic prophase

 chromosomes condense (thicken, coil) from chromatin form - become individually visible
 nucleoli disappear and nuclear envelope breaks up
 centrosomes move to either pole
 microtubules form spindle apparatus (starting at centrosomes) + attach to kinetochore proteins (called kinetochore microtubules)
 Spindle moves chromosomes toward cell equator

Describe mitotic metaphase

 46 chromosomes line up on cell equator

Describe mitotic anaphase

 as the spindle microtubules shorten, the kinetochores are pulled away from each other – causing separation of centromeres, which results in separation of the chromatids  46 chromatids migrate to each pole  cytokinesis (division of cytoplasm) begins

Describe mitotic telophase

 chromosomes uncoil to chromatin  nucleoli, nuclear envelope reappear  spindle disassembles  cytokinesis completes (or may end after telophase ends) [reverse prophase]

How many gametes are produces in mieotic division?

What stage is in between meiosis I and II?

interkinesis

What is the purpose of meiosis I?

Division of Homologous pairs.

Describe meiosis I prophase

i. homologous chromosomes attach together = tetrads (4 chromatids in a row) ii. crossing over occurs • piece of 1 chromatid exchanges with matching piece from a chromatid of the homologous chromosome i.e. non-sister chromatid • acts to increase genetic diversity

Describe meiosis I metaphase

 23 tetrads line up along cell equator

Describe meiosis I anaphase

 tetrads (homologous chromosome pairs) separate and migrate to opposite poles i.e. 1 homologous chromosome (with 2 sister chromatids) goes to each pole  chromatids DON’T separate

Describe meiosis I telophase

same as mitotic telophase

Describe meiosis II

– same as mitosis except with 23 chromosomes instead of 46 a) prophase II b) metaphase II - 23 chromosomes line up at equator c) anaphase II - 23 chromatids migrate to each pole d) telophase II

What are germ cells? How are they formed?

Germ cells are the diploid cells that divide into gametes. They are formed by mitosis.

What is the primary (1st degree) oocyte/spermocyte?

The 2n germ cell that will divide into 4 gametes.

What is the secondary (2nd degree) oocyte/spermocyte?

The n intermediate cells formed by meiosis I that will each divide into 2 gametes.

What is the ovum/spermatozoon?

The n gametes formed by meiosis II

When does meiosis II occur in 2nd oocytes?

After fertilization

Describe fertilization

 spermatozoon (n) contacts and penetrates 2nd oocyte (n) = fertilization  triggers completion of meiosis II in 2nd oocyte – forms ovum (egg)  then ♂ + ♀ pronuclei unite  pronucleus = nucleus of sperm/egg post-fertilization but prior to fusion  new cell = zygote (2n)