1 / 8

What is Crossing Over?

What is Crossing Over?. A Chromosome from your MOM. A Chromosome from your DAD. The Chromosomes that end up EGG or SPERM cells. Homologous Chromosomes Crossing Over. Ref: http://gnn.tigr.org/whats_a_genome/Chp3_2.shtml. It is the exchange or transfer of genes between HOMOLOGOUS CHROMOSOMES.

ronald
Télécharger la présentation

What is Crossing Over?

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. What is Crossing Over?

  2. A Chromosome from your MOM A Chromosome from your DAD The Chromosomes that end up EGG or SPERM cells. Homologous Chromosomes Crossing Over Ref: http://gnn.tigr.org/whats_a_genome/Chp3_2.shtml It is the exchange or transfer of genes between HOMOLOGOUS CHROMOSOMES

  3. When Does it Happen? Meiosis creates reproductive cells needed for sexual reproduction which can increase genetic diversity in a species. Mitosis creates genetically identical cells by asexual binary fission. During Prophase I of Meiosis Remember the differences between Mitosis and Meiosis?

  4. An actual microscope image of homologous chromosomes crossing over From: http://www.ultranet.com/~jkimball/BiologyPages/M/Meiosis.html#crossing_over

  5. BOTTOM LINE It’s Why You and Your Brother or Sister Don’t Look Identical!(or like anyone else either)

  6. Human Meiosis and Crossing OverThe Basics

  7. 1 46 chromosomes: DIPLOID (23 pairs) Chromosomes get copied during Interphase 2 3 46 chromosomes AND their copies: still DIPLOID After MEIOSIS I there are 23 chromosomes PLUS THEIR MODIFIED COPIES in each: now HAPLOID 5 6 After MEIOSIS II there are 23 SINGLE chromosomes in each of these 4 cells: still HAPLOID Human Meiosis and Crossing Over • Before meiosis begins, there are homologous pairs (MOM & DAD) ; only one pair shown, but really 23. • The MOM and DAD chromosomes are NOT IDENTICAL, but they do code for the same traits. For example, assume that the “A” and “a” are genes that code for hair color. A=brown and a=blonde. Since “A” is dominant, the person that this cell belongs to must have brown hair. • Now, during Interphase, DNA is COPIED!! • During Prophase of Meiosis I, Crossing OverMIXESmoms and dads genes. Because of the mixing, the copies are not exact copies anymore; you might call them “modified” copies. • During Anaphase of Meiosis I, the HOMOLOGOUS PAIRS get separated, but still have their modified COPIES WITH THEM. • During Anaphase of Meiosis II, the modified COPIES get SEPARATED. • QUESTION: The 4 cells at the bottom are SPERM cells. If each of them fertilize an egg, which of them MUST create a person with brown hair? 4 CROSSINGOVER

  8. END

More Related