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1st….HOMEWORK!
Why do you think that more money is spent on treatment than on prevention?
Who benefits from this?
What lifestyle changes could we encourage in attempt to reduce the incidence of cancer?
It has been suggested that people who put themselves at risk of cancer (by certain lifestyle choices) should have to pay more for health insurance and life insurance.
Strongly Agree Strongly Disagree
Agree Disagree
By the end of this lesson you will… Know the difference
b/w haploid & diploid cells
Understand the process of meiosis
Understand how genetic variation occurs
Learn some new terminology:◦ Gamete◦ Tetrad◦ Homologous
chromosomes◦ Single vs double
chromosomes◦ Chiasmata
Why is Meiosis important?
Genetic Variation!
Tongue Roller? Dimples? Straight / Bent Thumb? Hair on midsection of finger?
Our ________ cells have 46 chromosomes (diploid)
Biological mother & Father
Human _______ cells have 23 chromosomes (haploid)
HUMAN CELLS
Somatic
Sex
Sex cells divide to produce gametes (sperm or egg).
Gametes have half the # of chromosomes.
Occurs only in gonads (testes or ovaries).
Male: spermatogenesisFemale: oogenesis
The fusion of a sperm and egg to form a zygote.
A zygote is a fertilized egg
n=23egg
sperm n=23
2n=46zygote
23 Pairs of Homologous Chromosomes
eye color locus
eye color locus
hair color locus
hair color locus
Cell division that reduces the chromosome number by one-half.
four phases:a. prophase Ib. metaphase Ic. anaphase Id. telophase I
Meiosis I
Longest and most complex phase (90%). Chromosomes condense. Synapsis occurs: homologous
chromosomes come together to form a tetrad.
Tetrad is two chromosomes or four chromatids
Prophase I
Crossing over: segments of nonsister chromatids break and reattach to the other chromatid.
Genetic material is exchanged
Chiasmata are the sites of crossing over.
Crossing Over (Prohpase I)
Homologous chromosomes attach to the spindle fibres and line up on the equator
Metaphase I
metaphase plate
Anaphase I Homologous
chromosomes separate and move towards the poles.
Sister chromatids remain attached at their centromeres.
Cytoplasm divides forming 2 cells
Nuclear membrane forms
Each cell has half the number of chromosomes (reduced from 2n to n)
Telophase I
Remember: Meiosis II is similar to mitosis
There is NO DNA replication Prophase II – nuclear membrane dissolves and spindle fibres form
Meiosis II
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