Transcript Chapter 10
Bellringer In humans, pointed eyebrows (B) are dominant over smooth eyebrows (b). Mary’s father has pointed eyebrows, but she and her mother have smooth. • What is the genotype of her father? • What are the chances that her future sibling will have smooth eyebrows as well? Which of these would be a normal gamete? • • • • • GgRr GRr Gr GgR None of these are normal gametes. Chapter 10 Meiosis and Sexual Reproduction Why Mitosis? Mitosis maintains the same chromosome number in the daughter cells as were found in the original cell. Why Meiosis? Meiosis (or reduction division) reduces the chromosome number from 2N to N during the production of gametes. Asexual Reproduction • Only one parent • Advantages: – Fast – Many offspring – All identical—good when well adapted to the environment – No need to find a mate Disadvantage: no variations Figure 13.1 The asexual reproduction of a hydra Sexual Reproduction • Usually involves two parents • Involves two events: meiosis and fertilization • Advantage: recombination of the inherited traits of two parents; therefore, offspring may be able to survive environmental changes or other stress Figure 13.2 Two families Vocabulary • • • • • Diploid (2N) Haploid (1N) Autosomes Sex chromosomes Homologous chromosomes Figure 13.4 The human life cycle Figure 13.5 Three sexual life cycles differing in the timing of meiosis and fertilization (syngamy) Figure 13.6 Overview of meiosis: how meiosis reduces chromosome number Figure 13.7 The stages of meiotic cell division: Meiosis I Figure 13.10 The results of crossing over during meiosis Figure 13.9 The results of alternative arrangements of two homologous chromosome pairs on the metaphase plate in meiosis I Figure 13.7 The stages of meiotic cell division: Meiosis II Meiosis Square Dance • https://www.youtube.com/watch?v=iCL6d0 OwKt8 Three Sources of Variation in Sexual Reproduction 1. Crossing-over 2. Independent assortment (223 possible combinations 8 million possibilties!) 3. Random fertilization Compare Mitosis and Meiosis • DNA replication • Number of divisions • Type of cell you start with • Where it occurs • When it occurs • Role • Product • Events Figure 13.8 A comparison of mitosis and meiosis Spermatogenesis Oogenesis Genetic Abnormalities related to meiosis: sex chromosomes • Turner Syndrome (XO) • Poly-X syndrome (XXX) • Klinefelter Syndrome (XXY) • Jacob Syndrome (XYY) Why no YO? Genetic Abnormalities related to meiosis: autosomal • Down Syndrome (trisomy 21) • Trisomy 18 • Trisomy 13 • Few other autosomal abnormalities are known or occur in high frequencies – WHY? Do not survive past the first year of life Remember… • These are not gene mutations – they are IMBALANCES IN NORMAL CHROMOSOME NUMBER • How are these diagnosed? Figure 13.3 Preparation of a human karyotype (Layer 1) Figure 13.3 Preparation of a human karyotype (Layer 2) Figure 13.3 Preparation of a human karyotype (Layer 3) Fetal material can be obtained three ways: 1. Amniocentesis 2. Chorionic villi sampling 3. IVF Controversial…why? Figure 13.3 Preparation of a human karyotype (Layer 4) Figure 13.x2 Human female chromosomes shown by bright field G-banding Figure 13.x3 Human female karyotype shown by bright field G-banding of chromosomes Figure 13.x5 Human male karyotype shown by bright field G-banding of chromosomes What causes chromosomal issues like these: NONDISJUNCTION?