1 / 14

Meiosis and Sexual Lifecycles

Meiosis and Sexual Lifecycles. Chapter 13. Objectives. Understand the meaning of “SEX” Understand the process of meiosis Understand the need to undergo meiosis as sexual organisms. Need For Sex. Sex: results in the recombination of genetic information

trang
Download Presentation

Meiosis and Sexual Lifecycles

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Meiosis and Sexual Lifecycles Chapter 13

  2. Objectives • Understand the meaning of “SEX” • Understand the process of meiosis • Understand the need to undergo meiosis as sexual organisms

  3. Need For Sex • Sex: results in the recombination of genetic information • Organisms with sexual lifecycles have a greater range of genetic variation that may result in a greater ability to adapt to an environment • Meiosis is key to enhancing this variation

  4. Sex Terms • Diploid: having 2 of each chromosome type • Haploid: having a single representative of each chromosome type • Homologous chromosomes (homologues): chromosomes from different parents that are of the same type (contain similar information) • Sister Chromatids: 2 “identical” strands of DNA connected by a centromere that contains a kinetochore. Makes up each member of a homologous pair

  5. Mitosis produces 2 daughter cells daughters are clones of the parent daughter cells are diploid growth, replacement, repair Meiosis produces up to 4 daughter cells daughters are distinct from parents daughter cells are haploid generation of gametes (sex cells): egg & sperm Comparison

  6. Meiosis (the process) • Meiosis: nuclear division with a reduction in chromosome number by half • Two parts to the process • Meiosis I: separation of homologous pairs • Meiosis II: separation of sister chromatids (just as in mitosis)

  7. Meiosis I • Prophase I: same as mitosis • Metaphase I: both members of a homologous pair arrange themselves as a tetrad (synapsis) along the metaphase plate; crossover (chiasma) may occur • Anaphase I: Kinetochore remains intact and homologous pairs are separated as spindle fibers shorten

  8. Meiosis II • Telophase I: same as mitosis (includes cytokinesis) • Meiosis II is the same process as mitosis except starting from Telophase I instead of Interphase • no doubling of DNA has occurred • Result is up to four daughter cells

  9. Genetic Variation • Variation in the DNA of a zygote can be induced by three different methods occurring the during sexual cycle • Random fertilization: 8+ million possible combinations of sperm and egg = 70,368,744,000,000 possible combinations • Independent Assortment • Crossing over

  10. Independent Assortment • There are about 8 million possible combinations of chromosomes based on random assortment of the different types in the human genome (8,388,744). • This occurs during Anaphase I of meiosis as homologous pairs are separated • Genes that do not reside on the same chromosome may sort independent of one another

  11. Crossing Over • During tetrad formation (Prophase I) chromosomes may cross (chiasma). • Sometimes genetic information may be exchanged between homologues further shuffling the genetic information of the eventual gamete (4,951,760,200,000,000,000,000,000,000 different zygotes with a single crossover)

More Related