Bio 201 1st Edition Lecture 29Outline of Last Lecture I. Spindle Assembly CheckpointA. Role of TensionII. CytokinesisA. In AnimalsB. In Plants Outline of Current LectureI. Sexual Reproduction AdvantagesII. MeiosisIII. Chiasma/Crossing Over/ RecombinationCurrent LectureI. Sexual Reproduction Advantages-Fission + Mitosis=2nd generation cells are genetically identical to parents-Sexual Reproduction=Combining genetic information from 2 parent cellsnext generation is genetically different from parents-We need diversity in life, and sexual reproduction gives us that.-Problem? How do you prevent the genome from doubling every time you combine genetic information from 2 parent cells?-Solution: Halve genomes before combining (Meiosis)II. Meiosis These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-Meiosis I- Separation of homologous chromosomes, chiasma occurs. 1. Homologous chromosomes align on metaphase plate and exchange genetic information (chiasma) 2.Segregation of homologs (sister chromatids remain together) 3. Cytokinesis-Meiosis II- Separation of sister chromatids. 4. Chromosomes align on metaphase plate. 5. Separation and Segregation of sister chromatids, 6. Cytokinesis-4 gametes-Diploid parent cell (1mother, 1 father gene) 2N,1X2N,2X1N,2X1N,1XN=# chromosome copies X=# homologous chromosomesIII. Chiasma/ Crossing Over/ Recombination-One sister of each of the 2 homologs exchange DNA @metaphase 1. Results in 2 completely new chromosomes that are genetically distinct from each other and the parent. The possibilities are endless. -To calculate, we out the #homologs^#dif chromosomes-Humans are diploid and have 23 chromosomes in meiosis so 2^23=8,388,608 possibilities.-Nondisjunction during either phase of meiosis leads to aneuploidy-Nondisjunction is almost always lethal before or after fertilization-Normal=normal diploid. N+1=trisomy (rarely compatible with life). N-1=aneuploidy (incompatible with life except when aneuploidy occurs on the sex chromosome) -EXAMPLE) down syndrome is trisomy on chromosome 21. Turner’s syndrome is aneuploidy of sex
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