Mitosis Meiosis Whats the difference Write down these

Mitosis & Meiosis What’s the difference?

Write down these terms: Mitosis Karyotype Meiosis Allele Diploid Genotype Haploid Phenotype Sex chromosomes in a Male? Dominant Sex chromosomes in a Female? Recessive Number of chromosomes in a Homozygous person? Heterozygous Pedigree

Mitosis is the process where one cell divides into 2 identical cells This is how we go from 1 cell (the fertilized egg) to millions of cells! It is also HOW we grow & repair our bodies. What has to happen BEFORE mitosis can occur?

The DNA has to replicate ( be copied!) All 46 chromosomes (yes, MOST human cells have 46 chromosomes) have to be copied so both DAUGHTER cells get the same 46 chromosomes that were in the parent cell.

What is a Chromosome? The structure that the DNA forms in our cells The DNA is associated with proteins that compact it so it fits and is organized inside the nucleus!

Parent cell Chromosomes are copied and double in number (sister chromatids are attached at by the centromere Chromosomes now split 2 daughter cells identical to original

Animation of mitosis: http: //www. cellsalive. com/mitosis. htm

So, we’ve got 46 chromosomes. How many different PAIRS of chromosomes do we have? Are ALL the pairs the same? 23 pairs of chromosomes Yes & No- 2 copies of chrom 1, 2 copies chrom 2……, except for the sex chromosomes (X & Y) in MEN ( XY) & Women (XX)

CHROMOSOME NUMBER Number of chromosomes in body cells of a species is diploid = 2 n (n is the number of different chromosomes; 2 n = 2 copies of each different chromosome) The number of chromosomes in egg and sperm cells (gametes) is haploid which is “n”, or 1 copy of each different chromosome What are diploid and haploid for us?

Diploid= 46 chromosomes =2 copies of 23 different chromosomes (1 -22 + XX or XY) Haploid = 1 copy of 23 different chromosomes (1 -22 + X or Y)

Where does each chromosome of the pair come from? (Ex. You’ve got 2 copies of chr 1 - where did each copy come from? ) One chromosome comes from MOM, and one chromosome comes from Dad So, who determines the sex of the baby? ? DAD- He is the ONLY parent that can contribute the Y chromosome that makes the fetus male.

How do the gametes (sex cells) end up with only 23 chromosomes? THINK MEIOSIS!! WHY do they need to be haploid (only 1 copy of each chromosome or 23 total chromosomes)?

MEIOSIS IT’S ALL ABOUT SEXUAL REPRODUCTION…

MEIOSIS A type of cell division where the number of chromosomes is reduced by half ONLY occurs in gonads (ovaries or testes) during formation of gametes (egg or sperm) Human body cells have 46 chromosomes; human sperm and egg cells each have 23 chromosomes

Gametes are haploid for SEXUAL REPRODUCTION! When egg and sperm combine during fertilization, each brings half the total number of chromosomes for that species Half + half = whole In humans, 23 chromosomes (from Dad) + 23 chromosomes (from Mom) = 46 chromosomes (child) !!!

FERTILIZATION egg + sperm = zygote 23 + n Haploid 23 = n + haploid 46 2 n = diploid

Summary of Meiosis Type of cell division used to form the gametes (egg & sperm) where chromosome number is reduced to haploid (n). Meiosis is necessary for sexual reproduction. It involves 2 cell divisions, NOT 1 like in mitosis.

Animation of Meiosis http: //www. cellsalive. com/meiosis. htm

MORE ABOUT CHROMOSOMES In humans, there are 22 different “regular” chromosomes (numbered 1 to 22 by size & shape) and 2 different sex chromosomes The sex chromosomes are X and Y Which sex chromosomes are in a girl? XX Which are in a boy? XY