genetics ch 3 notes Griffith 9th ed

genetics ch 3 notes Griffith 9th ed - CHAPTER 3 NOTES...

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CHAPTER 3 NOTES - Mendel was analyzing descendants of pure lines that differed in tow characters. - Dyhybrid- a double heterozygote such as A/a * B/b - Dihybrid crosses - A cross between two individuals identically heterozygous at two loci— for example, A B / a b × A B / a b. - Mendel’s Second Law - different gene pairs assort independently in gamete formation o For two heterozygous gene pairs A/a and B/b, the “b” allele is just as likely to end up with an “A” allele. Law applies to genes in diff. chromosomes. o 2 alleles for a gene are packed into separate gametes o Alleles get back together after fertilization. - Law of independent assortment - genes on different chromosomes are transmitted independently of one another. - Mendellian Ratios describe that equal segregation and independent assortment are fundamental hereditary processes found throughout nature. o Ratios: 3:1:1:1, 9:3:3:1 and 1:1:1:1 - Independent assortment on haploids o Fusion of parental cells result in transient diploid - meiocyte that is a dihybrid A/a; B/b and the randomly sampled products of meiosis. 3.2.1 Geneticist can work in either of two directions: (1) predicting the genotypes of parents by using ratios of progeny or (2) predicting progeny ratios from parents of known genotype. Methods of independent assortment: (A) Punnett squares can be used to show hereditary patterns based on one gene pair, two gene pairs, or more. - as long as 2 non-allelic genes are on diff. chromosomes: o They will assort independently o Can FOIL to find gametes (combine first, outers, inners, lasts). (B) The branch diagram is easier to create and is adaptable for phenotypic, genotypic, or gametic proportions. - Used for independent assorting, non-allelic genes only (genes on diff. chromosomes).
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- Useful for dihybrids and up o Ex AaBbCC X AabbCC what is the probability will have baby AabbCC. ASK TEACHER !! - Use dash notation if looking for phenotypic rations only; A- means AA or Aa. (C) To simplify, we can use a statistical approach, which constitutes a third method for calculating the probabilities (expected frequencies) of specific phenotypes or genotypes coming from a cross: (1) Product Rule - The probability of two independent events occurring simultaneously is the product of the individual probabilities. - The focus is on outcomes A and B (2) Sum Rule - The probability that one or the other of two mutually exclusive events will occur is the sum of their individual probabilities. - The focus is on the outcome A or A . *** IF question asks how many progeny do we need to grow? First calculate the proportion of progeny expected to be of that genotype. Book example=256. approach by probability of complete failure where 1-1/256)=255/256 extending idea to sample size “n” = (255/256)n. The probability of obtaining once success is 1 minus the probability of total failure 1-(255/256)n = .95 or 95%. **** If asking how many distinct genotypes will a cross produce?
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genetics ch 3 notes Griffith 9th ed - CHAPTER 3 NOTES...

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