Download Sexual Cell Reproduction

Unit 3 – Cell Division, Genetics and
Molecular Biology
TODAY: CELL DIVISION - MITOSIS
 Outcomes
 Be
able to define:
 Chromosome,
chromatid, chromatin, centromere
 Somatic vs germ cells
 Autosome vs sex xsomes
 Chromosome number (haploid, diploid, polyploid)
 Be
able to explain the cell cycle
 Be able to explain stages of Mitosis

MEIOSIS – TOMORROW
***Bring 4 coloured pens tomorrow***
DNA and
Chromosomes



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Chromosomes are composed
of DNA and proteins
Chromatin – uncondensed
strands of DNA
Duplicated xsomes are called
sister chromatids
Sister chromatids are joined
at the centromere (condensed
strands of DNA)
Chromosome Number


The number of individual xsomes varies from one species
to another
Human somatic (body) cells have 46 xsomes
 22
pairs of homologous xsomes (autosomes)
 1 pair of sex xsomes (X, Y)


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Cells that contain pairs of homologous xsomes are called DIPLOID (2n)
Cells that contain unpaired xsomes are called HAPLOID (n)
Some organisms are POLYPLOID
Chromosome Number

Haploid number is designated as n

For Humans
n
= 23 (gametes)
Therefore our diploid number (somatic cells) is:
 2n = 46

For fruit flies (Drosophila)
n
=4
 What is the diploid number?
Heredity and Genes



The passing of genes from one
generation to another is called heredity
Your biological traits are controlled by
genes, located on every chromosome, in
every cell in your body
Your characteristics are a result of
interactions of genes from both parents
Principles of Cell Division


Somatic cells (body cells) undergo mitosis
Germ cells (sex cells) undergo MEIOSIS
Principles of Mitosis

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All cells are formed from pre-existing cells
Initial cell is referred to as the mother/parent cell,
subsequent cells are called daughter cells
Mitosis: Division of a mother/parent cell to produce
two identical daughter cells
2 phases of Mitosis:
 Division
of the nucleus
 Division of the cytoplasm and organelles
The Cell Cycle - continuous


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Division Phase: MITOSIS
Interphase:
Uncondensed xsomes



G1 (gap 1)
 Rapid growth
S (Synthesis)
 Duplication of xsomes
G2 (gap 2)
 More cell growth, prepares
for cell division
Stages of Cell Division
Cell division occurs in phases
 It is continuous processes (cells do not pause
between phases)
(1) Interphase – no cell division occurs
(2) Mitosis – cell division

 Prophase
 Metaphase
 Anaphase
 Telophase
Interphase (G1, S, G2)




When the cell is not dividing
Cells spend the majority of their time in interphase
During interphase cells undergo normal cell activity:
 Grow
 Absorb and transport nutrients, as well as eliminate
waste
 Metabolize substances
During interphase, cells get ready to divide again by
duplicating their chromosomes
Mitosis (PMAT)

Prophase



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Metaphase

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Xsomes line up at equatorial plate (individually)
Anaphase

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Chromatin condenses (chromosomes are visible)
Nuclear membrane dissolves
Centrioles to poles (spindle forms)
Centromeres split – sister chromatids are pulled apart
Telophase



Nuclear membrane re-forms
Xsomes uncondense
CYTOKINESIS occurs
Cell Clock – Regulation of the cell cycle
•Not completely understood
•What we do know
•Specialized cells have a lifespan controlled by some biological
clock
•Age (telomere size)
•Specialized cells undergo mitosis less frequently (if at all)
compared to unspecialized cells
•Ex. Nerve cell vs skin cell
•Regulatory signals within the body serve as START and STOP
signals for cell division
•Interruption of the regulatory signals can cause uncontrolled
growth (cancer)
Karyotyping


The particular set of xsomes that an individual
posesses
Image of the condensed xsomes
STOP SLOTH!!!