1 / 26

Unveiling Meiosis: A Dive into Sexual Reproduction

Discover the intricate process of meiosis creating gametes, leading to genetic diversity. Learn about key stages, errors, and consequences such as aneuploidy and polyploidy. Explore syndromes like Down syndrome and Turner syndrome.

atalo
Download Presentation

Unveiling Meiosis: A Dive into Sexual Reproduction

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. Creation of Gametes • Asexual reproduction yields two identical organisms (with exception of mutations) • Sexual reproduction merges the genes of the two parents • Result: two versions of each chromosome • Called homologous chromosomes • Organism is diploid (2n=46) • All somatic cells are diploid

  3. All can be lined up based on size, creates a karyotype

  4. First 22 are autosomes • Chromosome 23 is the sex chromosome • Haploid (n=23) sex cells merge to create a zygote in sexual reproduction • Meiosis creates these sex cells (gametes) • The overall process is the sexual life cycle

  5. Interphase I of Meiosis Homologous chromosomes Chromosomes replicate Homologous chromosomes separate Meiosis I Meiosis II Sister chromatids separate

  6. Interphase I • Similar to mitosis, chromatin replicates • Centrioles replicate, proteins form around to make the centrosomes • Also called the microtubule organizing centre • Collectively, with microtubules, is called mitotic spindle

  7. Prophase I • Longest part of meiosis • Chromatin condenses, chromosomes become visible • Homologous chromosomes come pair up, forming a tetrad – called synapsis • The chromatids can overlap, called a chiasmata • All other features are similar to mitosis

  8. Metaphase I • Almost identical to metaphase in mitosis, with the tetrad exception

  9. Anaphase I • Sister chromatids remain attached, tetrads separate (cells are now haploid) • This is the independent assortment mentioned previously

  10. Telophase I • Homologous chromosomes are at opposite poles of cell • Each end is now haploid • Cytokinesis takes place simultaneously • Some cells proceed to interphase II, others directly to prophase II • No cells replicate chromatin again

  11. Prophase II • Spindle forms again, chromosomes move towards equator

  12. Metaphase II • Closely resembling mitosis, metaphase plate is formed

  13. Anaphase II • Sister chromatids finally separate

  14. Telophase II • Mitotic spindle breaks down, nucleus reforms around two daughter nuclei

  15. Errors • Some of the processes can go awry • If anaphase I or II does not proceed correctly, the chromosomes may not be shared evenly • This is called nondisjunction • More of a problem if it occurs during meiosis I • Can take place in mitosis, but not as much of a concern

  16. An abnormal chromosome number is called aneuploidy • If faulty gamete succeeds in fertilization, the offspring with have health consequences • If a gamate with an extra chromosome fertilizes, the zygote is trisomic (2n+1) • If the gamete has a chromosome missing, the zygote is monosomic (2n-1) • Ex. Extra chromosome 21 – Down syndrome

  17. If the extra chromosome is an X in a male (XXY), called Klinefelter syndrome • The individual will have male sex organs, but the testes will be abnormally small, and he will be sterile • As well, femine characteristics such as breast enlargement is common

  18. Final example is Turner syndrome • Example of monosomyX • Individuals are classified X0, and are female • However, sex organs do not mature at adolescence and secondary sex characteristics fail to develop

  19. Polyploidy • Also possible for anaphase I or II to completely fail and all chromosomes move to one cell • Referred to as polyploidy • Could have three chromosome sets (triploidy, 3n) or four (tetraploidy, 4n)

More Related