Post on 14-Jan-2016
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
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
Blastula24 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 sperm3 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