Bellringer Mon, 12/71. Mitosis=cell reproduction in which two cell aremade from one cell (Asexual reproduction)

2. Meiosis=cell reproduction that forms eggs and sperm (sexual reproduction)

REMINDERS: Progress ReportsGrades this Wed,LAB FEE anytime!!!

Reminders, Review and Something NewReminders, Review and Something New

• ChromosomesChromosomes = condensed = condensed chromatin (DNA), chromatin (DNA), 46 in 46 in Humans, 23 pairsHumans, 23 pairs

• Genes-Genes- sections of a chromosome sections of a chromosome responsible for one trait (eye responsible for one trait (eye color, height, etc)color, height, etc)

Remembering Meiosis

• Mitosis is a process that occurs in almost every cell of your body (body cells), except the sex cells, or gametes.

• Mitosis = My toe sis, it happens in your toes!

• Meiosis is a process of cell division that doesn’t happen in your toes, it only happens in your sex cells, gametes

• Meiosis = My OH! Sis (as in uh-oh!)

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Cancer• Cancer cells do not respond to the signals that regulate growth

of most cells.• They divide uncontrollably and form masses of cells called

Tumors that can damage the surrounding tissues.

Untreated Breast CancerUntreated Breast Cancer Tumor on the eyeTumor on the eye

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Tumors = masses of uncontrollably dividing cells

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How many chromosomes do we have?

•23-Mother + 23-Father = Total 46

•Chromosomes 1 to 22- autosomes•Chromosome #23- sex chromosome

What is MEIOSIS?A type of cell division that results in 4 daughter cells with half as many chromosomes as the parent cells!

Gamete Formation

• Why do we even have Meiosis?

• To make gametes (eggs and sperm).

• Male gametes = sperm

• Female gametes = eggsWhy do we need eggs and sperm?Why do we need eggs and sperm?

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For Sexual Reproduction, where egg For Sexual Reproduction, where egg and sperm unite to make an embryoand sperm unite to make an embryo

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MeiosisMeiosis

Parent cell – chromosome pair

Chromosomes copied

1st division - pairs split

2nd division – produces 4 gamete cells with ½ the original no. of chromosomes

• only gametes or sex cells • gametes: males-sperm and females-eggs

What cells go through meiosis?

Why 1/2 the chromosomes in gametes? Why 1/2 the chromosomes in gametes?

• the male and female gametes need to provide ½ the male and female gametes need to provide ½ the chromosomes each – so the offspring has 1/2 the chromosomes each – so the offspring has 1/2 the genes from the mother and 1/2 the father!the genes from the mother and 1/2 the father!

Rules of Meiosis

1. Chromosomes are found in homologous pairs.

2. Chromosomes carry genes.

3. Genes are parts of a chromosome responsible for a trait: eye color, height, hair type, etc.

What are Homologous chromosomes?

Paired chromosomes with genes for the same traits arranged in the same order

Again, how many chromosomes do we have?

23 (Maternal) + 23 (Paternal)= Total 46

• Gametes (sex cells)-

haploid

n = number of chromosomes from each parent

n•Body cells

diploid 2n

Diploid vs. HaploidOrganism Gamete (n) Body Cell (2n)

Humans 23 46

Mosquito 3 6

Toad 11 22

Potato 24 48

Dog 39 78

Stages of MeiosisMeiosis I and Meiosis II

Meiosis IProphase I: homologous pairs, pair up. Crossing over occurs!

Metaphase I: chromosomes meet at the middle of the cell

Anaphase I: homologous chromosomes (each with 2 chromatids) move to opposite ends

Telophase I: 2 nuclei form, original cell divides

Meiosis IINo INTERPHASE or DNA copied between I and IIProphase II: chromosomes come together again and start to move toward the equator

Metaphase II chromosomes line up in the middle

Anaphase II: chromatids separate to opposite poles

Telophase II: two nuclei form - and cells divide

Meiosis – PMAT I and II Meiosis – PMAT I and II Parent cell

4 gametes

1st division

2nd division

Results after meiosis…4 Sex cells (gametes) that are haploid (n) - half as many chromosomes as parent cell (2n)

In females = one large egg cell and 3 polar bodies

In males meiosis results in 4 sex cells

* FYI: meiosis produces roughly 250,000,000 sperm per day all their adult life

Fertilization

Egg (n) + Sperm (n) = Zygote (2n)

A fertilized egg with diploid set of chromosomes.

After fertilization, thezygote divides bymitosis and becomes anembryo.

Later, the embryo becomes a fetus

Zygote>Embryo>Fetus

2 Key Differences Between Mitosis and Meiosis

1. Look at the Way Chromosomes Pair and Align

Mitosis

The first (and distinguishing) division of meiosis

2. Crossing-Over

Chromosomes exchange genetic material between homologous pairs!

Meiosis error - fertilizationMeiosis error - fertilization

Should the gamete with the Should the gamete with the chromosome pair be fertilized chromosome pair be fertilized then the offspring will not be then the offspring will not be ‘normal’.‘normal’.

In humans this often occurs In humans this often occurs with the 21with the 21stst pair – producing pair – producing a child with Downs Syndromea child with Downs Syndrome

Meiosis – division errorMeiosis – division error

Chromosome pair

21 trisomy – Downs Syndrome21 trisomy – Downs Syndrome

Can you see the extra 21st chromosome?

Is this person male or female?

Boy or Girl? The Y Chromosome “Decides”

X chromosomeY chromosome

Boy or Girl? The Y Chromosome “Decides”

Watch and Listen for the difference between Meiosis and Mitosis!!

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio17.swf::Comparison+of+Meiosis+and+Mitosis