Genetics
Genetics Genetics: Scientific study of heredity Heredity: Passing of traits from parents to offspring Trait: Each different form of a characteristic Genetics was founded with the work of Gregor Mendel
Mendel’s Garden Mendel was master of the monastery garden Mendel planted two stock of peas in two different areas-----one area always producing tall pea plants and another area only short plants Mendel wanted to explain why this is-----ANY IDEAS?
Mendel’s peas cont. Collected seeds from his pea plants and recorded each plant’s traits and seeds Through this, Mendel saw variation in the characteristics of pea plants
Mendel’s Garden Peas Mendel observed seven characteristics of pea plants A characteristic is a heritable feature A trait is a specific characteristic, such as seed color or plant height, that varies from one individual to another The characteristics that Mendel observed were: Plant Height (long and short) Flower Position along stem (axial and terminal) Pod Color (green and yellow) Pod Appearance (Inflated and constricted) Seed texture (round and wrinkled) Seed Color (yellow and green) Flower Color (purple and white)
Mendel’s Experiments Problem: Mendel wondered if he could produce short plants from tall plants. Procedure 1: Mendel crossed 2 tall purebred pea plants 30 times Purebred: offspring of many generations that have the same trait Result: ALL TALL PLANTS
Mendel’s Experiment Procedure 2: Mendel decided lets cross one purebred tall plant from one pea stock with a purebred short plant from another pea stock and did this 30 times Result: All Tall Plants!!!!!!!! Mendel liked where he was going with this and called this the F1 Generation=First Offspring Generation He also called the two original plants in this cross (1 tall and 1 short) the P generation (Parental Generation)
Mendel’s Experiment Procedure 3: Lets cross two of the F1 generation (tall) pea plants and see if we can get a short plant and did this 28 times Result: For every four plants, 3 were tall and 1 was short!!!!!!!! Why did this occur??????
Support for Mendel’s Conclusions Factors that Mendel studied are called alleles, or alternate forms of a gene. One allele from each trait is passed from each parent to their offspring. Genes determine traits
Mendel’s Results and Characteristics Mendel concluded that inherited characteristics are controlled by factors that occur in plants In his experiments on pea plants, one factor in a pair masked the other. Trait that masked the other was called the dominant trait Trait that was masked was called the recessive trait
Alleles Every individual has 2 alleles for every trait One from each parent Dominant alleles for a trait will always show that trait Recessive alleles will exhibit that trait only when the dominant allele is not present Symbols: Dominant=Capital Letter (T, R, B) Recessive=Lower Case Letter (t, r, b) NOTE: Does not matter what letter you chose to represent a trait as long as you use the same letter for dominant and recessive
Mendel’s Methods Pollination-occurs when pollen grains produced in the male anthers are transferred to the female stigma. Mendel used cross-pollination techniques in which pollen is transferred between flowers of two different plants. Self-pollination was prevented by removing all of the anthers from the flowers of a plant.
Mendel’s Experiments
Law of Segregation That a pair of factors is segregated, or separated, during the formation of gametes
Law of Independent Assortment Factors of individual characteristics are distributed to gametes independent of one another. The law of independent assortment is observed only for genes that are located on separate chromosomes or are far apart on the same chromosome.
Independent Assortment
Punnett Squares Possible Allele Combinations using symbols: Heterozygous: Organisms that have a dominant and a recessive allele for a trait (Tt) Homozygous: organism that have two identical alleles for a particular trait (TT or tt) Two dominant alleles (TT) is HOMOZYGOUS DOMINANT Two recessive alleles (tt) is HOMOZYGOUS RECESSIVE