MEIOSISSexual Reproduction

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?

Chromosome – DNA - Gene

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

Single Vs. Double Chromosome

Synthesis Phase

Watch it!? What’s different in meiosis vs. Mitosis?!

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

Prophase I - SynapsisHomologous chromosomes

sister chromatids sister chromatidsTetrad

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)

Crossing Over - variation nonsister chromatids

chiasmata: site of crossing over

Tetrad

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

Chromosomes line up on the equator (with 2 chromatids)

metaphase platemetaphase plate

Metaphase II

Chromatids move to opposite poles

Anaphase II

Nuclear membrane forms 4 haploid daughter cells are produced

Telophase II

n=23

n=23

n=23

n=23

sperm

haploid (n)

meiosis II

n=23

n=23

meiosis I

2n=46

sex cell

diploid (2n)

In the female – division of cytoplasm is unequal

In groups of three – four: Your genes are:

◦ Eye color (you pick the colors)◦ ?

Go through the process of meiosis Describe the 4 traits of your gametes

Have two of your gametes “get together”

Go through the process of mitosis with your zygote

Identify the traits of your two cells!