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Do Now:. What is Mitosis? What are the phases of mitosis? How many chromosomes are in a human body (somatic) cell?. Sexual reproduction. How is sexual reproduction different from asexual reproduction?. Sexual Reproduction. Transfer of genetic material from one organism to another

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do now

Do Now:

What is Mitosis?

What are the phases of mitosis?

How many chromosomes are in a human body (somatic) cell?

sexual reproduction
Sexual reproduction
  • How is sexual reproduction different from asexual reproduction?
sexual reproduction3
Sexual Reproduction
  • Transfer of genetic material from one organism to another
  • Gametes: special sex cells
    • One male, one female
  • Fertilization: fusion of the nuclei of male and female gametes
  • Zygote: single cell formed from fusion
  • Somatic cells: body cells (in humans they have 46 chromosomes)
  • Homologous chromosomes: chromosomes that are grouped together to make up a pair (23 pairs in human somatic cells)
  • Special kind of cell division that forms gametes
    • Gametes have half the number of chromosomes as the parent cell.
vocab continued
Vocab continued…
  • Diploid: 2n
    • Characteristic of cells that have ALL homologous chromosomes
    • Ex. Somatic cells
  • Haploid: n
    • cells that have only one chromosome from each pair (monoploid)
    • Ex. Gametes, spores (plants)
meiosis reduction division
Meiosis: reduction division
  • Each cell divides TWICE.
  • Chromosomes replicate only ONCE.
  • Takes place in special cells
  • Cells start out with diploid number of chromosomes.
  • Each original cell produces four daughter cells, each with the haploid number of chromosomes.
stages similar to mitosis
Stages similar to mitosis
  • Each of the two divisions show a prophase, metaphase, anaphase, and telophase stage similar to mitosis.
order of stages
Order of stages
  • Prophase I
  • Metaphase I
  • Anaphase I
  • Telophase I
  • Prophase II
  • Metaphase II
  • Anaphase II
  • Telophase II
prophase i
Prophase I
  • Each pair of chromatids line up with homologous pair and become fastened at centromeres.
    • Synapsis: pairing of homologous pairs
    • Tetrad: each group of 4 chromatids
    • Crossing-over: exchange of segments between chromatids during synapsis
  • Nuclear membrane disappears
  • Spindle fibers form
metaphase i
Metaphase I
  • Centromeres of tetrads line up on the equator
  • Tetrads fastened to spindle microtubules at centromeres
anaphase i
Anaphase I
  • Disjunction: separation of homologous chromosomes of each tetrad
  • Cluster of chromosomes around each pole is haploid (BUT each chromosome is double stranded)
telophase i
Telophase I
  • End of 1st meiotic division
  • Cytoplasm divides
  • 2 daughter cells with half the number of parent cell’s chromosomes, but with each chromosome in replicated form
  • Cell is ready for next division
    • Exactly like mitosis
prophase ii
Prophase II
  • Each of the daughter cells forms spindle and double-stranded chromosomes move toward middle of spindle
metaphase ii
Metaphase II
  • Chromosomes fastened to spindle microtubules at centromeres
  • Centromeres line up on the equator
  • Chromosomes still have 2 strands or chromatids
anaphase ii
Anaphase II
  • Centromeres divide
  • 2 chromatids separate, each becoming a single-stranded chromosome
  • 2 chromosomes move toward opposite ends of spindle
telophase ii
Telophase II
  • Both daughter cells divide forming 4 haploid cells.
  • In each cell, chromosomes return to interphase state, and nuclear membrane forms again.