Cell Division Meiosis Cell Division Meiosis Abnormal Meiosis.
Meiosis - Biologythestudyoflivingthings.weebly.com/.../1/3/4/4/13444842/meiosis_ppt.pdf · What is...
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Reproduction
Asexual – reproduction resulting from mitosis (or a similar process) that involves only one parent; the offspring are genetically identical to the parent (a clone)
Sexual – reproduction resulting from an exchange of genetic material; in most organisms this involves the fusion of gametes (formed during meiosis)
Asexual reproduction
Binary Fission – separation of a parent into 2 or more individuals
ex. bacteria
Budding - new individuals split off from existing ones. Bud may break off or remain attached to parent
ex. jellyfish, corals, yeast
Asexual reproduction
Regeneration – renewal/re-growth of an organism from a segment of that organism
ex. starfish, planaria
Asexual reproduction
Disadvantages: DNA varies little between organisms, which may result in organisms not being able to adapt to a changing environment Advantages: • Produce many offspring in short period of time without using energy to produce gametes or to find a mate • Offspring are perfectly adapted to current environment, therefore often used in stable environments
Asexual reproduction
Sexual Reproduction
Disadvantages: Sexual reproduction uses a lot of metabolic energy in the development and maintenance of gametes, as well as a lot of biochemical resources Advantages: • Frequent production of new combinations of genes • Flexibility in the gene pool of a population helps insure the survival of a species, especially if there is rapid or sudden change in the environment
Mitosis vs. Meiosis
MITOSIS MEIOSIS
type of reproduction asexual sexual genetically ___ to parent identical unique
# divisions 1 2
# cells produced 2 4
cell type somatic gamete
# chromosomes diploid haploid
What is Meiosis?
• Meiosis- cell division that produces gametes (sperm and egg)
– This produces reproductive cells, which are genetically unique, through a series of cell divisions.
– Ensures that humans have the same number of chromosomes in each generation.
THINK: what would happen if sperm and egg cells were diploid?
How is Meiosis Different from
Mitosis?
• There are 2 divisions in meiosis – Meiosis I and meiosis II
• The result is 4 cells instead of 2
• In meiosis II, the DNA is not replicated again. (No interphase)
• The final number of chromosomes is 23 in humans (egg has 23 and sperm has 23)
• This is haploid (n)
Stages of Meiosis There are 2 divisions of the nucleus in meiosis
– Interphase (DNA replication)
– Prophase I – Metaphase I – Anaphase I – Telophase I
NO DNA replication
– Prophase II – Metaphase II – Anaphase II – Telophase II
Meiosis I
Meiosis 2
One parent cell produces four daughter cells. Daughter cells have half the number of chromosomes found in the original parent cell and are genetically unique.
Genetic Variation
Genetic variation is what makes organisms unique
How does genetic variation occur? Genetic crossover
Independent assortment
Ransom fertilization
Genetic Variation
Genetic Crossover
the exchange of genetic material (genes) that can occur between homologous chromosomes during Prophase I Produces genetically unique chromosomes
Genetic Variation
Independent assortment: homologous chromosomes are randomly sorted/distributed during meiosis
–Leads to several possible combinations of genes (why siblings aren’t always identical)
Genetic Variation
Random fertilization
• During meiosis, 4 gametes are produced… which one will fertilize to produce a zygote?
• The chance that a particular egg or sperm will fertilize is random