1 / 75

Meiosis

Meiosis. Vocabulary. SOMATIC : Any cell except a sperm or egg AUTOSOME Any chromosome other than a sex chromosome (X or Y) GAMETE An egg or sperm. Mitosis allows asexual reproduction. Meiosis allows sexual reproduction. Parents are diploid.

ulf
Download Presentation

Meiosis

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

  2. Vocabulary • SOMATIC:Any cell except a sperm or egg • AUTOSOMEAny chromosome other than a sex chromosome (X or Y) • GAMETE An egg or sperm

  3. Mitosis allows asexual reproduction

  4. Meiosis allows sexual reproduction. Parents are diploid Homologous chromosomes are separated into single sets.

  5. Humans have 23 pairs of chromosomes.

  6. FEMALE • One pair (the sex chromosomes) are not identical in males. MALE Sex ratios: 106 boys: 100 girls (at birth)

  7. Karyotypesare pictures of chromosomes.

  8. Some (More) Vocabulary

  9. Alleles

  10. Eye Color

  11. Eye Color Brown, green

  12. Meiosis separates chromosome pairs to form haploid gametes. Meiosis I: Homologous pairs are separated (as sister chromatids) into 2 cells Meiosis II: Similar to mitosis: sister chromatids are separated = 4 haploid cells.

  13. MEIOSIS I Interphase I • Interphase is very similar to interphase in mitosis

  14. MEIOSIS I Prophase I • Double stranded chromosomes and spindle fibers appear; • Nuclear membrane and nucleolus fade (synapsis aligns homologous chromosomes)

  15. MEIOSIS I Metaphase I • Chromosome pairs (chromatids) line up • Spindle fibers attach to centromeres and centrioles

  16. MEIOSIS I Anaphase I • Chromatids separate from matching pair (independent assortment occurs here)

  17. MEIOSIS I Telophase I • Cytoplasm divides and 2 cells form • Each cell still has a diploid (2n) number

  18. MEIOSIS II Prophase II Metaphase II Anaphase II Telophase/cytokinesis II

  19. Meiosis II follows the same steps as mitosis • Key differences: • In interphase II, there is no replication of genetic material • When the sister chromatids separate during anaphase II, they are now haploid (1n) • After telophase II, you have 4 haploid (1n) cells with genetic variation (they are no longer identical) SUMMARY OF MEIOSIS II

  20. Genetic Variation Independent Assortment: Homologous pairs can separate in different parental combinations. 2n possible gametes created

  21. In humans: • 223 = 8 million possible gametes • This is without crossing over, which increases the number of distinct chromatids (exact number of chiasma determines how many different chromatids will exist) Possible Gametes

  22. Genetic Variation Crossing Over: During synapsis (Prophase I) portions of non-sister chromatids are exchanged.

  23. Genetic Variation Random Fertilization: Each sperm will fertilize and egg randomly 8 million possible gametes for each parent: 8,000,0002 = 64 trillion possible zygotes Without Crossing over. With it, there are even more!

  24. CROSSING OVER

  25. CROSSING OVER • These are a pair of homologous chromosomes with genes A - E.

  26. CROSSING OVER • These homologous chromosomes are made of 2 sister chromatids each. These are called TETRADS

  27. Synaptonemal Complex! CROSSING OVER • The tetrads line up side by side (synapsis) in Prophase I • Segments cross over(form chiasma) and the pieces are traded.

  28. CROSSING OVER • The sister chromatids end up with different copies of the genes.

  29. CROSSING OVER

  30. Noticethat genes that are located close together will not separate during crossing over as much as a pair of genes that are further apart.

  31. Frequency of Crossing Over • Measuring the frequency of crossing over tells you the distance between two genes (in map units)

  32. With all of the variation produced in meiosis, how can parents have IDENTICAL TWINS? • How does the production of sperm differ from production of egg? What do you think?

  33. Errors in meiosis are passed down to offspring (because they occur in sperm or eggs) • These errors can create sperm and eggs that have the wrong number or types of chromosomes Errors in Meiosis

  34. Deletion: part of a chromosome is deleted (removed) • Duplication: part of a chromosome is repeated • Translocation: part of a chromosome is moved to another chromosome • Inversion: part of a chromosome is removed, then flipped around and reattached Types of errors

  35. Inversion

  36. Non-disjunction • Failure of chromosomes to separate properly in meiosis • Meiosis I: homologues don’t separate • Meiosis II: Sister chromatids don’t separate

  37. Monosomy: one parent does not give a copy of one chromosome • There is only 1 total in the child • 45 instead of 46 total chromosomes • The only monosomy that we see in humans (that is nonfatal) is Turner syndrome Types of errors

  38. Females inherit only one X chromosome (XO), instead of XX • 1/2500 girls • 98% of fetuses with Turner Syndrome miscarry • Short stature, broad chest, webbed neck Turner syndrome

  39. Turner syndrome

  40. Trisomies • When one parent gives two copies of a chromosome • The child has 3 total of that chromosome (47 instead of 46 total chromosomes)

  41. Down’s syndrome • 3 copies of chromosome 21 • Impairment of cognitive ability (avg. IQ 50, vs. 100 in rest of population) • Almond-shaped eyes • Health problems: heart failure, GERD, ear infections, sleep apnea • 1/733 births • More common with older mothers, but 80% are born to women under 35 Trisomy 21

More Related