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Cell Reproduction
Mitosis – asexual reproduction– 1 cell produces 2 identical cells
Meiosis – sexual reproduction– 1 parent cell produces 4 cells with ½ the
number of chromosomes as the parent
Why Cells Divide
Growth
Repair
Reproduction
When Cells Divide
Surface Area/Volume Ratio determines the maximum size of any cell.
Cells can’t get bigger, so they divide.
Terminology
Parent cells for new daughter cells
Chromosomes contain DNA & genes
Homologous Chromosomes (a pair)
Phases of Mitosis
Interphase
Chromosomes are uncoiled DNA replicates Centrioles replicate
INTERPHASE
DIVISION
Prophase
Chromosomes coil - appear double stranded
Nucleolus & nuclear membrane disappear
Centromere and chromatids are visible Centrioles form aster rays & spindle
fibers as they move to the poles
Metaphase
Double stranded chromosomes individually line up on the equator
Centromeres attach to a spindle fiber CENTROMERE
CHROMATIDCENTRIOLE
Anaphase
Chromosomes split & separate and are pulled to opposite poles of the cell by the spindle fibers
Telophase
Cytoplasm divides (cytokinesis) New nuclear membranes form
Cell Division and Reproduction
Sexual Reproduction– 2 parents needed.– Offspring are similar to, but not
identical to the parents.– Genetic variations contribute to
evolution of species.
Chromosome Number
Each species has a specific chromosome number.
Homologous chromosomes - 2 of a same pair. Have the same number and types of genes. One from egg, other from sperm.
Gametes - reproductive cells. Have half the chromosome number. They have only one chromosome of each pair.
Chromosome Number
Haploid - half chromosome number Sex cells (n)
Diploid - pairs of chromosomes Body cells (2n)
Meiosis - reduction division reduces chromosome number to haploid.
Phases of Meiosis
One DNA replication followed
by two cell divisions.
Interphase I
DNA replicated
Centrioles replicated
Prophase I
Chromosomes coil Centrioles move to poles Spindle fibers and asters form Nuclear membrane disappears Homologous chromosomes
synapse & crossing over occurs
Metaphase I
Homologous chromosomes line up at the equator in pairs
Crossing over occurs between homologs
Anaphase I
Homologous chromosomes separate and move to poles
Telophase I
Cytokinesis occurs forming 2 haploid cells
Cells contain double stranded chromosomes at this point
Interphase II
No DNA replication
Chromosomes uncoil
Centrioles replicate
Rest same as Mitosis
Prophase II - Chromosomes coil.
Metaphase II - Line up on equator.
Anaphase II - Split at centromere and move to opposite poles.
Telophase II - Cytokinesis results in 4 haploid cells.
Spermatogenesis
Sperm cell formation 4 equal sized gametes form
46D46
23D
23D
23
23
23
23
Oogenesis
Egg cell formation 1 large egg + 3 polar bodies (die)
46 46D
23D
23D
23
23
23
23
Mitosis vs. Meiosis
23
46
46
23D 23D
23 23 23 23
Meiosis
Mitosis
Diploid Cells
FertilizationHaploid
Cells
Gametes
Zygote
Genetic Variations
Sexual reproduction (fertilization)
Meiosis - independent assortment
Meiosis - crossing over
Random Mutations
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