BIO 151 1st Edition Lecture 20 Outline of Last Lecture 1. Cell cycle checkpoints2. Cell cycle regulation3. Mitosis gets you genetically identical copies4. Lack of variability is evolutionary suicde5. Sexual reproduction meiosis6. What does a eukaryotic cell's chromosomes really look like?7. Important terminologyOutline of Current Lecture 1. Origins of genetic variation among offspring2. Independent assortment of chromosomes3. Crossing over4. Random fertilization5. Inheritance characteristics6. Cross plants with different traitsCurrent Lecture - in mitosis homologous chromosomes did not pair up- in meiosis homologous chromosomes do pair upOrigins of genetic variation among offspring:- the behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises in each generation- 3 mechanisms contribute to genetic variation- independent assortment of chromosomes- crossing over- random fertilizerIndependent assortment of chromosomes:- 2 equally probable arrangements of chromosomes at metaphase 1Crossing over:- mixes chromosomes even more- produces recombinant chromosomes, which combine DNA inherited from each parent- begins very early in prophase 1, as homologous chromosomes line up- chiasma formed - ends of chromosomes get cut off and swapped- homologous portions of 2 nonsister chromatids trade placesThese 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.- contributes to genetic variation by combining DNA from 2 parents into a single chromosomeRandom fertilization:- adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg)- the fusion of 2 gametes (each with 8.4 million possible chromosome combinations from independent assortment) produces a zygote with any of about 70 trillion diploid combinations- crossing over adds even more variation- each zygote has a unique genetic identity- so how does inheritance of characteristics work?- science of genetics - experiments by Gregor Mendel on peasInheritance of characteristics:- blending inheritance is wrong- purple and white pea plants- parental generation - pure breeding (P generation) = purple white- 1st filial generation (F2 generation)- 3 purple, 1 white- purple is dominant to white, white is recessive- P: a gene encoding an enzyme making a purple colored pigmentCross plants with different traits:- round peas dominant to wrinkled peas- at the chromosomal level- alleles for different traits- locus is region on chromosome that has that allele- why all this variation?- inherited variation keeps species adapting- explains why biology is variable even within a
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