BIOL 240 1st Edition Lecture 4 Outline of Last Lecture I. Mendel’s experiment1. Why peas?2. Experimented characteristics3. Monohybrid crosses4. ConclusionsII. Genetic Terminology1. Phenotype2. Genotype3. Gene4. AlleleOutline of Current Lecture I. Dihybrid CrossesII. Mendel’s Law of Independent AssortmentIII. Chromosome Theory of HeredityCurrent LectureI. Dihybrid Crosses—a cross with two pairs of contrasting traits (i.e. a child with blue orbrown eyes and with blonde or brown hair)1. Mendel uses peas in his experiment; peas that are either yellow or green, round or wrinkled. First, he crossed all possible combinations of parents (yellow and round with green and wrinkled, AND yellow and wrinkled with green and round). In both cases, the offspring were all yellow and round. Since they were all yellow and round, two were crossed together. The offspring resulted in a 9:3:3:1 ratio. Where did this come from?2. Product Rule of Probability: for crosses with two pairs of contrasting traits, to get the probability of the offspring being A “and” B, multiply the probability of it being A by the probability of it being B. This will only work if the probabilities are independent of each other. II. Mendel’s Law of Independent Assortment1. For each experiment Mendel conducted involving more than two pairs of contrasting traits, all of his crosses resulted in a 9:3:3:1 ratio. He concludes that different genes separate independently of each other.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.2. Independent Assortment: during gamete formation, genes segregate independently. For example, two parents with AaBb could produce AB, Ab, aB, orab offspring with the same frequency.3. The Punnett Square—a helpful table that can help display all possibilities during adyhibrid or even trihybrid cross. Let’s look at an example using Mendel’s peas. For this example, let yellow and round both be dominant (yellow=GG and round=WW) and let green and wrinkled both be recessive (green=gg and wrinkled=ww). There are two possibilities for the first initial parent cross: yellow and round (GGWW) with green and wrinkled (ggww) OR yellow and wrinkled (GGww) with green and round (ggWW). In both cases, the offspring will result in yellow and round (GgWw). Since there are two pairs of contrasting traits, we must consider all possibilities of gene segregation. This means that GgWw can segregate into GW, Gw, gW, or gw.GW Gw gW gwGWGGWWyellow, roundGGWwyellow, roundGgWWyellow, roundGgWwyellow, roundGwGGWWyellow, roundGGwwyellow, wrinkledGgWWyellow, roundGgwwyellow, wrinkledgWGgWWyellow, roundGgWwyellow, roundggWWgreen, roundggWwgreen, roundgwGgWwyellow, roundGgwwyellow, wrinkledggWwgreen, roundggwwgreen, wrinkledJust as Mendel discovered, we can see the 9:3:3:1 ratio:Yellow and round (9/16)Green and round (3/16)Yellow and wrinkled (3/16)Green and wrinkled (1/16)*These can be obtained by the Sum Law: the probability of A or B = p(A) + p(B) aslong as A and B are mutually exclusive outcomes, meaning there aren’t any otherexplicit probabilities of obtaining A or B individually. Dr. McKee used a great example during lecture about how to think through such problems…I suggest taking a double look over that if you are confused.III. Chromosome Theory of Heredity1. Genes are located on specific areas on chromosomes, known as loci, or locus. Homologous chromosomes have the same genes at the same loci. Mendel showed that an organism inherits one allele from each gene from each parent.2. Because of this, meiosis generates genetic variation. This is why you look similar, yet different from your
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