Meiosis and Sexual Reproduction

Topics

Reminders

• Lecture 5 Aug 30 1995
• Campbell chp 12, pp 244-256
• Emphasis: class outline
• Study questions pp 256
• Examine study outline on pp 256-257

1. Introduction

• Meiosis
  • Genetics and variation
• Sexual reproduction
  • Two parents are required
  • Greater variations exist
  • Gametes are produced during meiosis
  • Asexual reproduction

2. Genes, DNA and Chromosomes

• Traits are inherited
• Genes consist of DNA
• Genes are on chromosomes and their specific location is called a locus
• Genes are encoded and most synthesize a specific enzyme

3. Sexual Life Cycles

• Emphasis on humans, although the process is very similar in most animals and plants
• Fig 12.4

Other Important Terms

• Homologous chromosomes
• Sex chromosomes
• Autosomes
• Haploid
• Diploid
• Fertilization
• Zygote

4.Meiosis, Mechanism (Fig. 12.7)

• Meiosis I
  • Interphase I, duplication of chromosomes

4. a Meiosis I

• Prophase I, synapsis and tetrads (4 chromatids)

4. b Meiosis I

• Metaphase I, paired chromosomes align

4. c Meiosis I

• Anaphase I, homologous chromosomes (each consisting of two chromatids) move to opposite poles

4. d Meiosis I

• Telophase I and Cytokinesis, two cells form, each consist of one set of homologous chromosomes

4. e Meiosis II

• Prophase II cells prepare for second division

4. f Meiosis II

• Metaphase II, each chromosome (2 chromatids) aligns on metaphase plate

4. g Meiosis II

• Anaphase II, chromatids separate and become chromosomes

4. h Meiosis II

• Telophase II and cytokinesis, four daughter cells are now formed and are haploid

5. Meiosis, comparision to Mitosis

• synapsis and tetrad formation
  • variation
• reduction of chromosomes (diploid to haploid)

6. Genetic Variation

• Independent assortment
• Crossing over
• Random fertilization

7. Role of Variation in Evolution

• Important for raw material for natural selection and evolution