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Mitosis & Meiosis

Mitosis and meiosis are crucial processes in cell division with distinct roles in growth, repair, and reproduction. Understand the differences between mitosis and meiosis, the concepts of diploid and haploid cells, sex chromosomes, and the importance of chromosome replication. Explore how these processes lead to the formation of gametes and the inheritance of genetic traits. Discover the significance of chromosomes, alleles, genotypes, and phenotypes in genetics.

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Mitosis & Meiosis

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  1. Mitosis & Meiosis What’s the difference?

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

  3. Mitosis • 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?

  4. 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.

  5. 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!

  6. 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

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

  8. 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)

  9. CHROMOSOME NUMBER • Number of chromosomes in body cells of a species is diploid = 2n (n is the number of different chromosomes; 2n = 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?

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

  11. 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.

  12. 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)?

  13. MEIOSIS IT’S ALL ABOUT SEXUAL REPRODUCTION…

  14. 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 46chromosomes; human sperm and egg cells each have 23 chromosomes

  15. 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) !!!

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

  17. 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.

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

  19. 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

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