01:16:19 - Dr. Kate Tsai PDF

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Dr. Kate Tsai...

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01/16/19 Chapter 2 o Humans have 8 million different combinations to make distinct gametes o Differences between Mitosis and Meiosis o Mitosis  Singular nuclear division  Results in the same # of chromosomes  Yields genetically identical cells o Meiosis  Two cell divisions yield 4 cells (usually)  Newly formed cell has ½ # of starting chromosomes (Anaphase)  Genetically variable cells (cross over/random distribution of chromosomes) o Unequal cytokinesis o Division of the cytoplasm o Almost all of the cytoplasm is pushed to one side o One cell is much larger, the other one is called a polar body and will not become a gamete Chapter 3 o Mendel’s Pea Plants o Effectiveness was because of:  Good choice of subject – easy to grow, grows rapidly, produces many offspring  Had genetically pure stocks of different types of peas to start studies  Avoided characters that exhibited variation (yellow or green, round or wrinkled)  Used experimental approach o Vocab  Gene: a genetic factor that helps determine a characteristic  Allele: one of two or more alternate forms of a gene (round vs. wrinkled)  Locus: specific place on a chromosome occupied by an allele  Genotype: set of alleles that an individual possesses  Heterozygote: an individual possessing two different alleles at a locus  Homozygote: an individual possessing two of the same alleles at a locus  Phenotype: the appearance or manifestation of a character  Character: an attribute or feature o Only Genotype is inherited o Different alleles occupy the same locus (place on chromosome) on homologous chromosomes

o Monohybrid Cross  First experiment: homozygous round seeds crossed with homozygous wrinkled seeds  Seconds experiment: intercrossed plants (only round seeds) from the results of the first experiment  Results: ¾ round seeds, ¼ wrinkled seeds o All 7 characteristics Mendel studied yielded this 3:1 ratio in the F2 generation  Each trait has 2 different “unit factors” that result in different traits, gives 3 possible combinations  Dominance/Recessiveness traits were discovered  Principle of Segregation – each individual diploid organism possesses two alleles for any particular characteristic. Two alleles segregate into gametes, and this occurs randomly and in equal proportions o Dihybrid Cross  Two traits crossed  Round, yellow seeds (RRYY) cross with wrinkled, green seeds (rryy)  Got a 9:3:3:1 ratio  Principle of Independent Assortment – alleles at different loci separate independently of one another...