1	Peas and Probability The union of gametes can be described by probability rules
2	Reading Assignment The reading for today’s lecture is chapter 13. This material must be read carefully. Most of you will need to read this chapter a few times. Try to do the problems at the end of the chapter after the first reading. Reread the appropriate sections until you are familiar with the conventions and logic of genetics problems.
3	Transmission of Traits from one generation to the next Peas normally self-fertilize. The male and female gametes produced within a single flower fertilize each other to produce peas. Varieties of peas that maintain the same traits from generation to generation are called “true-breeding” (which contrasts with individuals whose offspring are variable).
4	Pea Varieties Variety A Axial flowers Yellow seeds Round seeds Inflated pods …. Variety B Axial flowers Green seeds Wrinkled seeds Inflated pods ….
5	Cross-fertilization contrasted to the normal self-fertilization Cross-fertilization was done by transferring the pollen from Variety A to the stigma of an emasculated flower of Variety B. The word “cross” is has come to mean “to mate and produce offspring”, but originally referred to cross-fertilization between varieties instead of allowing an individual to self. A cross between 2 varieties can be done two ways, either A or B can be the female parent with B and A, respectively the male. The pair of crosses is called ‘reciprocal crosses’.
6	Offspring Phenotypes of cross between varieties A & B 454 offspring (individual peas and plant that grew from the pea.) All axial flowers All round seeds All yellow seeds All inflated pods The progeny from a cross between 2 true-breeding lines is known as the F1.
7	All F1 individuals look like variety A.
8	F1 allowed to self – Offspring of selfed F1 is called F2 F2 Seed Color: Mendel observed 416 YELLOW and 140 GREEN seeds. F2 Seed shape: Mendel observed 423 ROUND and 133 WRINKLED seeds.
9	Green & Wrinkled were ‘masked’ in F1
10	Mendel allowed the F2 to self to form an F3 generation. The F2 YELLOW seeds were of two types. Some YELLOW seeds produced all YELLOW progeny in the F3, others produced mostly YELLOW seeds with some GREEN mixed in. In the F3 all the GREEN F2 seeds produce ONLY GREEN seeds in the F3 (so GREEN is always true-breeding).
11	Mendel’s Hypothesis Mendel explained the F2 and F3 results by hypothesizing there were two factors, yellow and green, and that each plant had two factors. The original varieties (parents) had either 2 green or 2 yellow but the F1 plant had one yellow and one green factor.
12	Mendel’s Idea in Color 1
13	Mendel’s Idea in Color 2
14	From colors to letters Rules for naming genes Seed shape is controlled at a LOCUS, a place on a chromosome. A locus is symbolized with letters. Different characters (color, shape, etc) are controlled by separate loci each of which needs a distinct symbol. ALLELES are the specific genetic material at a locus. The dominant allele is shown as a capital letter, the recessive allele as lower case. Alleles should be italicized. G = yellow allele, g = green allele R = round allele, r = wrinkled allele
15	Conventional Symbols
16	Expectations Each individual offspring results from the union of male gamete and a female gamete. If there are multiple types of gametes, the probability that a particular gamete is involved in a particular fertilization is proportional to the frequency of that type in the gamete pool, separately for each sex, of course.
17	Expectations for each offspring
18	Expectations for Multiple Offspring
19	Probabilities
20	Outcome Proportions The observed total number(s) in each category can be compared to the numbers expected in each category with the χ2 (Chi-squared) test. Next lecture the use of the χ2 (Chi-squared) test will be explored.
21	Problems
22	Vocabulary Locus Allele Phenotype Genotype Proportion Expected number True breeding Expected proportion Dominance Recessive Heterozygous Homozygous Reciprocal cross F1 F2 gametic genotype