meiosis and mitosis

Purpose of Meiosis

Produce Gamaetes (sex calls)

Homologous Chromosomes

same size, genes, centromere location

Prophase 1 (Meiosis)

- Number membrane dissolves
- Chromatin condenses into chromosomes
- Centrioles to poles
- Spindle fibres form
- Synapis Occurs
- Crossing Over occurs (swap DNA stuck together as pairs)
- Tetards form

Gamete

sex cell

Zygote

a cell produced by the fusion of two gametes

Haploid

number of chromosomes in gamete (1/2 of diploid number)
1n# = 23 for humans

Diploid

# of chromosomes in somatic cells
2n# = 46 for humans

Somatic Cells

Human body cells

Crossing Over

Join together (synapsis)
DNA randomly swaps

Metaphase I (Meiosis)

- Spindle fibres join poles to equator
- Tetards to equator

Anaphase I (Meiosis)

Spindle fibres pull tetard apart, chromosomes to poles
*Disjunction = Separation of tetard

Telophase I (Meiosis)

Nucluear membrane reforms
Chromosomes stretch into chromatin
Spindle fibres dissolve

Prophase II

Nuclear membrane dissolves
Chromatin condenses into chromosomes
Centrioles to poles
Spindle fibres form

Metaphase II

Spindle fibres join poles to equator
Chromosomes move to equator

Anaphase II

Spindle fibres pull chromosomes to poles

Telophase and Cytokinesis (Meiosis)

Nuclear membrane reforms
Chromosomes stretch into chromatin
Spindle fibres dissolve
Cytokinesis: Cell splits
# of chromosomes per cell: 2
Haploid

Mitosis

The purpose of mitosis is to reproduce, grow and repair
it occurs in somatic cells

Interphase

G1 (20%): Cell growth (not dividing)
S (50%): DNA and centrioles doubles
G2 (20%): Cell growth
Labels; Centrioles, Nuclear membrane, chromatin

Prophase

Nuclear Membrane dissolves
Chromatin condenses in chromosomes
*animal cell only* Centrioles start to move to poles (equator)
Spindle fibres start to form
Labels; Chromosomes, Centrioles

Metaphase

Spindle fibres join centrioles at poles to centromeres
Chromosomes move to equator
Labels; Chromosome spindle fibre

Anaphase

Spindle fibres pull chromosomes apart and to the poles
Labels; Chromosomes

Telophase

Nuclear membrane reforms
Spindle fibres dissolve chromosomes stretch into chromatin

Cytokenisis

After telophase, the resulting in the two cells separate.
Animal cell; cleavage furrow
Plant cell; a cell plate
# of chromosomes -> 4 (Diploid)

DNA

contains genetic information that makes the organism unique, super stringy and messy

chromatin

threads of genetic material, later condenses into chromosomes

chromosome

made up of two sister chromatids, held together by a centromere

centromere

holds the two sister chromatids together

sister chromatid

identical half of the chromosome, held together by the centromere

How many chromosomes do we have

46

disjunction

separation of tetrad

fertilization

- the formation of a zygote by the fusion of two gametes
- gametes join to make a diploid zygote

Synapsis

Physical pairing of homologous chromosomes during Prophase 1

Tetrad

Pair of homologous chromosomes -> each with two sister chromatids

Embryo

cells differentiate, grow