Mendelelian Genetics (pgs.262-273) Mendelian Genetics 5/23/2019 Mendelelian Genetics (pgs.262-273)

Responsible for the Laws governing Inheritance of Traits Gregor Mendel (1822-1884) Responsible for the Laws governing Inheritance of Traits

Gregor Johann Mendel Austrian monk Studied the inheritance of traits in pea plants Developed the laws of inheritance Mendel's work was not recognized until the turn of the 20th century

Mendelian Genetics 5/23/2019 Gregor Johann Mendel Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants He found that the plants' offspring retained traits of the parents Called the “Father of Genetics"

Eight Pea Plant Traits Seed shape --- Round (R) or Wrinkled (r) Seed Color ---- Yellow (Y) or  Green (y) Pod Shape --- Smooth (S) or wrinkled (s) Pod Color ---  Green (G) or Yellow (g) Seed Coat Color ---Gray (G) or White (g) Flower position---Axial (A) or Terminal (a) Plant Height --- Tall (T) or Short (t) Flower color --- Purple (P) or white (p)

Mendel’s Pea Plant Experiments

Mendel’s Experiments 1. He crossed true breeding parents (P Generation): Tall x short AA x aa 2. He counted the offspring produced in the first generation (first Filial or F1). Findings: the offspring were always the same (They all expressed the same trait- TALL). They were all Aa.

3. The F1 offspring were then crossed with each other. Aa (tall) x Aa (tall) The second generation of offspring are called the F2 Findings: 3:1 ratio, 3 offspring would express the same trait (TALL) as their parents and 1 offspring would look like one of the grandparents(SHORT) (3 Tall : 1 short)

GENES DIDN’T DISAPPEAR 2 things learned SOME GENES ARE DOMINANT OVER OTHER ONES. GENES DIDN’T DISAPPEAR

Genetic Terminology Alleles - two forms of a gene (dominant & recessive) Represented by two letters, AA, Aa, aa

Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R) Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r)

Homozygous – two identical alleles (e. g Homozygous – two identical alleles (e.g. AA, aa) also called purebred Heterozygous – two different alleles (e.g. Aa) also called hybrid Genotype- genetic makeup of an of an organism (letters) Phenotype- physical make up of an organism

Parental P1 Generation = the parental generation in a breeding experiment. F1 generation = the first-generation offspring in a breeding experiment. (1st filial generation) From breeding individuals from the P1 generation F2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation) From breeding individuals from the F1 generation

Punnett Square Used to help solve genetics problems

DIHYBRID CROSSES A cross (or mating) between two organisms where two genes are studied is called a DIHYBRID cross.

BEYOND DOMINANT & RECESSIVE Some alleles are neither dominant nor recessive and many traits are controlled by multiple alleles or multiple genes.

Incomplete Dominance One allele is not completely dominant over another. R = Red W = White

Both alleles contribute to the phenotype. Codominance Both alleles contribute to the phenotype.

Multiple Alleles Many genes have more than two alleles for a given trait. See page 273 in text.

AB - universal acceptor O – universal donor Multiple Alleles AB - universal acceptor O – universal donor

How is sex determined? Male – XY Female -XX

Sex Linked Genes that are carried by either sex chromosome are said to be sex linked

Independent Assortment Genes for different traits can segregate independently during the formation of gametes.

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