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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!)
Box 40
Box 51
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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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Box 36
Tumors = masses of uncontrollably dividing cells
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Box 44
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?
Skip Box 59
Box 71
For Sexual Reproduction, where egg For Sexual Reproduction, where egg and sperm unite to make an embryoand sperm unite to make an embryo
Box 72
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