Transcript Genetics
General Genetics (Practical Session) BIO221 Lecturer Alshehri, Dokhnah Saeed [email protected] nd 2 lab Identification of pure and hybrid Genotype (Testcross) Mendel's Hypothesis. The Testcross. Class Activities. Some practical Exercises. To explain his results, Mendel formulated a hypothesis that included the following: In the organism there is a pair of factors that controls the appearance of a given characteristic. (We call them genes.) The organism inherits these factors from its parents, one from each. • • Each is transmitted from generation to generation as a discrete, unchanging unit. When the gametes are formed, the factors separate and are distributed as units to each gamete. This statement is often called Mendel's rule of segregation. If an organism has two unlike factors (we call them alleles) for a characteristic, one may be expressed to the total exclusion of the other (dominant vs recessive). In order to test his hypothesis, Mendel predicted the outcome of a breeding experiment that he had not yet carried out. He crossed homozygous round peas (RR) with wrinkled (homozygous, rr) ones. In other case when he crossed hetrozygous round peas (Rr) with wrinkled (homozygous, rr) ones. In this case, onehalf of the seeds produced would be round (Rr) and one-half wrinkled (rr). The Question here is, If you have a member of your offspring that carries the dominant trait, and you want to know the genotype of that one. In other wards, is it pure or hybrid? How that can be worked out? in this case the tested individual is crossed with a recessive trait. If the offspring consist of tall plants only, the individual is pure. P TT × tt × T T t t F1 generation Tt Tt Tt Tt All of them are tall If the offspring consist of tall and short plants (1 :1) the examined plant is a hybrid. Tt X tt × T Tt t Tt t tt t tt half of them are tall : half of them are short A. B. C. If two black mice are crossed, and the offspring was a ten of black mice and a three of white ones. Which allele is dominant? Which allele is recessive? What are the genotypes of the parents? In drosophila, two red-eyed flies mate and yield 110 red-eyed and 35 brown-eyed offspring. Are the parents pure or hybrid for the trait? Diagram the cross and determine which allele is dominant. In Drosophila, a cross between a dark-body fly and a tan-body fly yield seventy six tan and eighty dark flies. Are the parents pure or hybrid for the trait? Which allele is dominant? Diagram the cross. A. B. In a case of mating between black pig (Bb) and white pig (bb). What are the phenotype and genotype ratio of the first generation? What are the genotype and phenotype ratio resulting from mating a black person from first generation back cross with: the Black father and the white one.