Genetics

Introduction to Genetics Gregor Mendel- 19th Century (1800’s) Austrian monk 1st important studies of heredity Heredity– Passing on of characteristics from parents to offspring

Chose to study the pea plant (Piscium sativum) Reproduce sexually Both male and female gametes are on the same flower

Mendel studied only one trait at a time Traits are passed from parent to offspring

Pea plant’s structure Allowed Mendel to fertilize plants Reproduce and develop quickly They appeared to have traits that were either one or the other (green OR yellow, smooth OR wrinkled)

Gamete = male or female sex cells

Transfer of male gamete (pollen) to female sex structure (pistil) = pollination Fertilization = Joining of male and female sex cells Forms a zygote- fertilized egg

Rule of Unit Factors Found on chromosomes in egg and sperm Mendel concluded that 2 alleles control each trait One from ma, one from pa Those 2 alleles code for genes Alternate forms of a gene are called alleles Found on chromosomes in egg and sperm

Rule of Dominance There are generally 2 alleles for a given trait Dominant = Expressed when at least one dominant allele present Recessive = Must have two recessive alleles to be expressed

Here is an example. . . . The tall allele (T) is dominant over the short, recessive allele (t) in pea plants Therefore; TT = tall; Tt = tall; tt = short Letters for the alleles are decided by the dominant trait.

Genotype The genetic makeup of an individual The letters Includes both genes in a homologous pair of chromosomes Pure bred YY, TT, PP, GG, yy, tt, pp, gg Hybrid Yy, Tt, Pp, Gg

Phenotype The outward expression of a trait Ex: Brown fur, attached ears, cleft chin, widows peak

Homozygous The two alleles in a gene pair are identical TT, tt, PP, pp, GG, gg Also called Purebred A purebred Friesian

Heterozygous The two alleles for a particular trait are different. Tt, Pp, Gg, Hh, Nn, Mm Also called hybrid “Hercules” the Liger

Law of segregation Alleles separate when gametes are made during Meiosis (a process we will go into later) Half the gametes will contain one gene/allele the other half will contain the other gene/allele

Genetics and Punnett Squares Punnett square show possible offspring of parents with a specific trait Possible gametes of parents are letters on outside H h HH Hh H Hh h hh

Recessive Traits Cystic fibrosis- Type of lung disease Tay Sachs- mental/physical break down Albinism

Dominant Traits Huntington disease- nerve cells break down over time Polydactyly