Meiosis. What is meiosis? How is it different from mitosis? Stages Genetic Variation

Transcription

1 Meiosis What is meiosis? How is it different from mitosis? Stages Genetic Variation

2 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)

3 Asexual reproduction Binary Fission separation of a parent into 2 or more individuals ex. bacteria

4 Asexual reproduction Fragmentation - body breaks into several pieces ex. worms

5 Asexual reproduction Budding - new individuals split off from existing ones. Bud may break off or remain attached to parent ex. jellyfish, corals, yeast

6 Asexual reproduction Regeneration renewal/re-growth of an organism from a segment of that organism ex. starfish, planaria

7 Asexual reproduction Sporulation production and release of spores ex. fungi, algae, protozoa

8 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

9 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

10 Sexual Reproduction 23 chromosomes + 23 chromosomes zygote 46 chromosomes (23 pair)

11 Sexual Reproduction Life Cycle for Animals Marriage Growth & Development

12 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

13 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?

14 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)

15 From Pearson Education Comparing Mitosis and Meiosis

16 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 Meiosis I Prophase II Metaphase II Anaphase II Telophase II Meiosis 2

17 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.

18 Oogeneis

19 Spermatogenesis

20 Genetic Variation Genetic variation is what makes organisms unique How does genetic variation occur? Genetic crossover Independent assortment Ransom fertilization

21 Genetic Variation Genetic Crossover the exchange of genetic material (genes) that can occur between homologous chromosomes during Prophase I Produces genetically unique chromosomes

22 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)

23 Independent Assortment

24 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

25 What is the evolutionary advantage of sexual reproduction? Sexual reproduction produces greater genetic variation than asexual reproduction. Provides greater opportunity for accelerated adaptation