Introduction to Genetics The Work of Gregor Mendel

Introduction to Genetics The Work of Gregor Mendel

Genetics • Scientific study of heredity • Gregor Mendel –Born in 1822 in Czech Republic –Worked in monastery garden while teaching H. S. (math & science) –Worked w/ true-breeding pea plants • If allowed to self-pollinate, produce offspring identical to themselves

Genes and Dominance • Mendel studied 7 traits –Specific characteristic that varies from one individual to another– color, height –Each trait had two contrasting characters – greed seeds vs. yellow –Crossed true-breeding plants of each type to opposing character

Genes and Dominance • True-breeding yellow seed X Truebreeding green seed • Original pair of plants = P (parental) generation • Offspring = F 1 (first filial) • Offspring of crosses between parents w/ different traits = hybrids

• What did the F 1 hybrids look like? Did they look like a blend of both parents? No! • All F 1 offspring only showed the character of one parent.

Mendel’s Two Conclusions • 1. Biological inheritance is determined by factors that are passed on from one generation to the next –Genes – chemical factors that determine traits

• Each trait that Mendel studied was controlled by one gene that occurred in two contrasting forms –Ex: Gene for Plant Height = One form for tall one for short • Alleles – different forms of a gene

• 2. Principle of Dominance – some alleles are dominant and others are recessive –If there is a dominant present, that form is shown –If there are two recessive present, the recessive is shown

Segregation • Did the recessive alleles disappear, or were they still present ? –To find the answer, he allowed F 1 generation plants to self-pollinate to create an F 2 generation • What happened? –Traits reappeared. ¼ of the F 2

Segregation, cont’d • Law of Segregation –Two alleles separate from each other so that each gamete carries only a single copy of each gene –Ex: Fig. 11 -5

Introduction to Genetics and Probability

Genetics and Probability • Probability –The likelihood that a particular event will occur • Ex: tossing a quarter –Heads = 1 in 2 –Tails = 1 in 2 – 3 tails in a row ½ x ½ = 1/8 –Principles can be used to predict outcome of genetic crosses

Genetic Vocabulary • Character – Detectable inheritable feature of an organism • Trait – Variant of inheritable character = allele / alleles • Dominant – Capital letter (SS) • Recessive – Lower case (ss) • Two alleles for each character – Mom and dad

Genetic Vocabulary • Genotype • Phenotype –The genetic –The makeup of physical an organism traits of an –Written in organism letter format –PP, pp, Pp

Genetic Vocabulary • Homozygous • Heterozygous –Having two identical alleles for a given trait –Having two different alleles for a given trait • PP • ss • Pp • Ss

Basic Crosses

Recessive/Dominant • action items required of you