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

True-breeding yellow seed X True- breeding green seed Original pair of plants = P (parental) generation Offspring = F1 (first filial) Offspring of crosses between parents w/ different traits = hybrids Genes and Dominance

What did the F1 hybrids look like? Did they look like a blend of both parents? No! All F1 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 F1 generation plants to self-pollinate to create an F2 generation What happened? –Traits reappeared. ¼ of the F2 plants showed the recessive allele

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

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

Pea Traits

Basic Crosses

Recessive/Dominant action items required of you