Unit 7 bio test 2
What is meiosis
- Division of genetic material to produce daughter cells with half the hereditary material found in the parent cell
- involved only in the production of gametes (eggs and sperm)
- basis of sexual reproduction and genetic inheritance
Mitosis Vs meiosis
- mitosis: homologs line up independently, each cell will get the same genes
- Meisos: homologs line up in pairs, positioning (and allocation) is random
- meiosis seperates homologs, mitosis seperates chromatids
Steps for meiosis (prophase) - synapsis and crossing over (1,2,3)
1. Interphase: chromosomes replicated but not condenses
2. Early prophase I: chromosomes condense, nuclear envelop breaks up, spindle forms, synapsis of homologs
3. Late prophase I: crossing over on non-sister chromatics, recombination of genes
Meta/Ana/Telophase - seperating homologs (4,5,6
4. metaphase I: tetras (mixed up non sister chromatids) migrate to metaphase plate
5. Anaphase I: homologs begin to seperate
6. Telophase I and Cytokinesis: chromosomes move to opposite sides of cell, cell divides
Meisosis II - seperating chromatids (7,8,9)
7. Prophase II: spindle apparatus forms inside each cell
8. Metaphase II: chromosomes line up of spindle
3. Anaphase II: sister chromatids begin to seperate
4. Telophase II and cytokinesis: chromosomes seperate; cell divides again
What are some mistakes in Meiosis (2)
1. improper distribution of chromosomes to each daughter cell "non disjunction" -> results in gametes with abnormal number of particular chromosome
2. Extra copy: trisomy (downsyndrome), one copy: monosomy, no copy nullisomy (barely ever survive, most miscarriges)
- can occur during meiosis I (seperation of homologs) or meiosis II (seperation of chromatids)
What causes Non-Disjunction of chromosome 21 in meiosis I
- both copies of homologs go into one gamete instead of splitting up durng telophase/cytokineses
- results in a gamete with no chromosome from gamete 21
what is aneuploidy
- aneuploidy occurs when gametes have an abnormal number of chromosomes, results in miscarrigies and is almost always lethal
Meiosis and sexual production (4)
- each cell produced by meiosis receives a different combonation of chromosomes
- different complementary genes
offspring distinct from each other and from their parents
- haploid gamete (n) fuse at fertilation, restoring normal complement of chromosomes (2n)
- If the haploid number is 3, 2^3 = 8 possible combinations due to meiosis 1 assortment alone
how does meiosis creat offspring with genetic variability
- recombintion during prophase I
- Independant assortment of homologs during meta/ana/ telophase of meiosis II an meiosis I
Alternatives to Meiosis: asexual reproduction
- an organism well adapted to its environment can clone itself at an incredibly rapid rate
- many protists, plants, some fungi, some animals (insects, fish, reptiles)
what are 5 advantages of sexual reproduction
1. allows natural selection againt delirious alleles of genes
2. in asexual production, all offspring would inherit a damaged genes
3. sexually reproducing individuals will produce some offspring that lack the damaged alleles of parent
4. should have adaptive advantage
5. genetic variation better equips a species to survive environmental change