Genetics Thomas Hunt Morgan – Lexington, KY native and graduate of U.K in Revolutionized the study of genetics

Inheritance Every living thing has a set of characteristics inherited from its parents – heredity. Genetics – the scientific study of heredity.

Gregor Mendel Austrian monk named Gregor Mendel is considered the grandfather of genetics. Worked in monastery and taught high school Also tended monastery garden and his worked changed biology forever.

Fertilization Gregor Mendel worked with garden peas Each flower produces pollen which contains male’s reproductive cells – sperm The female portion of the flower produces egg cells Male and female sex cells = gametes. During sexual reproduction, male and female reproductive cells join, a process called fertilization.

Fertilization Fertilization produces a new cell = embryo Pea flowers self-pollinate, meaning that the sperm cells fertilize egg cells in the same flower. These seeds inherit all of the characteristics of their parents. In effect they have a single parent

True-Breeding True-breeding organisms are those that produce offspring identical to themselves. A stock of tall plants would produce tall plants A stock of short plants would produce short plants Some plants bred only green seeds, others only yellow seeds

Cross-Pollination Mendel wanted to produce seeds by joining male and female cells from different plants He had to prevent self- pollination so he cut off the male parts (ouch) and then dusted pollen from another plant onto the flower

Traits Mendel studied 7 different pea plant traits A trait is a specific characteristic, such as seed color, that varies between individuals. Mendel crossed plants with each of the seven varying characteristics with contrasting plants.

Father, Son, Hybrid The original pair of plants is called the P (parental) generation Their offspring are called the F1 (first filial) generation. – Filius and filia are Latin for “son” and “daughter” The offspring of crosses between parents of different traits are called hybrids. P

Genes and Alleles Did the traits blend in the offspring? No, not at all. All of the offspring had the trait of only one of the parents. The other trait seemed to have disappeared completely. Mendel made two conclusions: – 1. Inheritance passed from one generation to the next. Now we call these factors passed genes. – 2. Each trait had two forms. These forms of each gene are called alleles. For example: the gene for plant height has two forms: one that produces tall plants and another that produces short forms. Short and tall are alleles of the plant height gene.

Genes and Dominance The principle of dominance states that some alleles are dominant and others are recessive. An organism with a dominant allele for a trait will always exhibit that form; it is dominant. An organism with a recessive allele for a trait will only exhibit that form when the dominant form is absent. In Mendel’s pea, the allele for tall plants was dominant over the allele for short plants.

Dominance - Clarification Just because an allele of a gene is dominant, doesn’t mean it is necessarily superior or even more common, it is simply just dominant. Achondroplasia (dwarfism) is a dominant form Huntington’s disease, a neurological disorder, is dominant

F 1 Cross Mendel asked another question: had the recessive alleles disappeared or were they still present in the F1 plants? So he allowed all seven kinds of F1 hybrids to produce an F2 generation by self-pollination. He found that in the F2 generation, the recessive traits reappeared, in about ¼ of plants

F 2 Generation

Principle of Segregation After viewing his results, Mendel suggested that the alleles for height, color, etc. segregated from each other during the formation of gametes. When each F1 plant flowers and produces gametes, the two alleles segregate from each so that each gamete carries only a single copy of each gene. Therefore, each F1 plant produces two types of gametes – those with the allele for tallness and those with the allele for shortness.

Segregation of Alleles Capital T’s represent the allele for Tallness – dominant allele = capital letter Lowercase t’s represent the allele for shortness – recessive allele = lowercase letter.

Gregor Mendel Song About Gregor Mendel