Molecular Biology and Genetics - Lecture Fourteen : Eukaryotic Cell Division - Meiosis
7 important questions on Molecular Biology and Genetics - Lecture Fourteen : Eukaryotic Cell Division - Meiosis
What is the Sexual Life Cycle like ?
- Haploid : Cell with a single set of chromosomes (n)
- Diploid : Cells with a double set of chromosomes (2n)
- Meiosis halves the chromosome number (2n --> n) so that when two gametes fuse they don't form a zygote with 4n chromosomes
What is the structure of Meiosis ?
- Meiosis I (2n → 2x n) :
- Meiosis II (2 x n → 4 x n)
- 4 x haploid cells with unreplicated (single-stranded) chromosomes produced
- Cytokinesis (cell separation) isn’t a specific meiosis I or II phase, however, it is a part of the overall meiotic phase
Explain the 4 stages in Meiosis I ?
- Homologous chromosomes align and synapse
- Crossing over between non-sister chromatids occurs at chiasmata
- Crossing over results in chromatids now being a mix of pieces from each homologous chromosome
METAPHASE I :
- Paired homologous chromosomes move to metaphase plate
- Chiasmata (not kinetochores, as in mitosis) line up on metaphase plate
ANAPHASE I :
- Recombined homologous chromosomes separate
- Sister chromatids remain attached
- Haploid cells with duplicated chromosomes (the pairs of sister chromatids) form
- Haploid because only half the genetic information is in each new cell
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What are the 3 important events related to Meiosis and Genetic diversity and Also explain its importance ?
- Independent Assortment and Law of Segregation
- Crossing over
- Random Fertilisation
IMPORTANCE ??
- Genetic diversity introduces a range of different alleles into the ecosystem
- Some of these alleles may be valuable in survival (e.g. resisting disease, predators, other environmental stresses, decreased offspring/sib-sib competition)
- These more advantageous alleles will be ‘selected for’ (increase in frequency) by nature (natural selection)
- This enhances the evolutionary potential of a species
What is Independent Assortment/Law of Segregation ?
- A particular allele a gamete receives for a specific trait, will not influence the type of allele received for another specific trait.
- Each gamete receives only a single allele for a specific trait (law of segregation)
What is Crossing over in meiosis ?
What is Random Fertilisation in Meiosis ?
- A gamete’s genome doesn’t affect its chance of being fertilised
- Every gamete has the same chance of fertilising
- Total zygote combinations = 2n (gamete 1) x 2n (gamete 2) Where n = number of chromosomes
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