Meiosis & Reproduction Chapter 7

objectives Recognize that during meiosis, the formation of sex cells, chromosomes are reduced to half the number present in the parent cell Explain how fertilization restores the diploid number of chromosomes Recognize cells both increase in number and differentiate, becoming specialized in structure and function, during and after embryonic development Identify factors (e.g. Biochemical, temperature) that may affect the differentiation of cells and the development of an organism Distinguish between asexual (i.e. binary fission, budding, cloning) and sexual reproduction Describe the advantages and disadvantages of asexual and sexual reproduction with regard to variation within a population

VI. Meiosis A.Two divisions of the nucleus B.Results in the formation of 4 gametes (egg, sperm) C.Reduces the number of chromosomes by half (in humans from 46 to 23)

Stages of Meiosis I 1.*Prophase I- crossing over occurs, portions of one chromosome are broken and exchanged with portions of the other homologue **results in genetic variability

2. Metaphase I- homologous chromosomes pair up together at the equator

3. Anaphase I- spindle fibers shorten and homologous chromosomes separate and move toward opposite poles

4. Telophase I and Cytokinesis

Meiosis II- same as mitosis 1. Prophase II 2. Metaphase II 3. Anaphase II 4. Telophase II & Cytokinesis

Females- meiosis is called oogenesis, forms 1 ovum and 3 polar bodies, occurs in ovaries

Males- meiosis is called spermatogenesis, forms 4 sperm cells, occurs in testes

Meiosis video

Sexual Reproduction- requires egg and sperm 1. Zygote- fertilized egg, first cell of new offspring

2. Zygote divides by mitosis many times to produce a blastula (hollow ball of cells) Zygote 1 division Blastula 24 hours after conception 5 days after conception

3.Gastrula- one side of the blastula collapses and cells begin to change into 3 layers Blastula Gastrula

4. The 3 gastrula cell layers begin to differentiate (change) into specific kinds of cells

Asexual Reproduction- does not require egg and sperm 3 Types: 1. Budding

2. Regeneration

3. Binary Fission

Advantages/Disadvantages Sexual reproduction- *provides genetic variability to the population Asexual reproduction- *produce many offspring in a short time *offspring have the exact same DNA as parent *all mutations in DNA get passed to offspring