History of GeneticsHistory of Genetics

During the 1860’s, During the 1860’s, an Austrian monk an Austrian monk and and teacherteacher named named Gregor Gregor MendelMendel experimented with experimented with peapea plants to see if plants to see if he could find a he could find a pattern in the way pattern in the way certain certain traitstraits are are handed down from handed down from one generation to one generation to the next generation.the next generation.

The passing of genetic traits from The passing of genetic traits from parents to offspring is called parents to offspring is called heredityheredity..

From working with plants, Mendel From working with plants, Mendel knew that sometimes a trait in one knew that sometimes a trait in one generation (parents) would not generation (parents) would not appear in the next generation appear in the next generation ((offspringoffspring). Then the trait would ). Then the trait would show up in the next generation.show up in the next generation.

Pea plants Pea plants were a good were a good choice to study choice to study for these for these reasons:reasons:

(1) (1) grow quicklygrow quickly (2) (2) many many

different kinds different kinds availableavailable

(3) (3) able to self-able to self-pollinatepollinate

A self-pollinating plant has both A self-pollinating plant has both malemale and and femalefemale reproductive reproductive structuresstructures

In cross-pollination, pollen from In cross-pollination, pollen from one plant one plant fertilizesfertilizes the ovule of the ovule of a a flowerflower on a different plant. on a different plant.

Mendel only studied one Mendel only studied one characteristic at a time, such as characteristic at a time, such as flower color .flower color .

Mendel’s First Mendel’s First ExperimentsExperiments

Mendel crossed Mendel crossed purple flowers with purple flowers with whitewhite flowers. The flowers. The offspring from this offspring from this cross is called cross is called firstfirst--generation plants generation plants (F1). All were (F1). All were purple—Where did purple—Where did the white flower the white flower trait go???trait go???

Dominant traitDominant trait= = the the traittrait observed observed in the first in the first generation when generation when parentsparents that have that have different traits are different traits are bredbred

Recessive traitRecessive trait= a = a trait that trait that reappears in a reappears in a second generation second generation after disappearing after disappearing in the first in the first generationgeneration when when parents with parents with different traits are different traits are bredbred

Mendel’s Mendel’s Second Second ExperimentsExperiments

Mendel allowed Mendel allowed first-generation first-generation plants to plants to self-self-pollinatepollinate. The . The recessive trait for recessive trait for white flowers white flowers reappeared in the reappeared in the secondsecond generationgeneration..

Gone, but Not Gone, but Not ForgottenForgotten Mendel realized that his results Mendel realized that his results

proved that each plant has proved that each plant has twotwo sets of instructions for each sets of instructions for each traittrait. . Each parent would then donate Each parent would then donate oneone set of instructions. set of instructions.

Mendel’s work wasn’t widely Mendel’s work wasn’t widely recognized until after his death, recognized until after his death, more than 30 years later.more than 30 years later.

A Great IdeaA Great Idea MendelMendel knew from his experiments that knew from his experiments that

there must be there must be twotwo sets of instructions for sets of instructions for each characteristiceach characteristic scientists now call these scientists now call these instructions for an inherited traits “instructions for an inherited traits “genes”genes”

Each parent gives one set of genes to the Each parent gives one set of genes to the offspringoffspring—the different forms of a gene are —the different forms of a gene are known as known as allelesalleles, like hair color, like hair color

Dominant alleles are shown with a capital Dominant alleles are shown with a capital letterletter

Recessive alleles are shown with a Recessive alleles are shown with a lowercaselowercase letter letter

Phenotype & GenotypePhenotype & Genotype

Organism’s Organism’s appearance is appearance is known as its known as its phenotypephenotype– Examples: hair Examples: hair

color, eye color, eye color, widow’s color, widow’s peak, etc.peak, etc.

Both inherited alleles Both inherited alleles together form an together form an organism’s organism’s genotypegenotype– homozygoushomozygousorganisorganis

m with two m with two dominantdominant or or two two recessiverecessive alleles, like RR or rr alleles, like RR or rr for flower colorfor flower color

– HeterozygousHeterozygous organism that has one organism that has one

dominant and one dominant and one recessiverecessive allele, like allele, like Rr for flower colorRr for flower color

Label each genotype as “HOM” for Label each genotype as “HOM” for homozygous or “HET” for homozygous or “HET” for

heterozygousheterozygous

Hh: ____Hh: ____ AA: ____AA: ____

ww: ____ww: ____ Gg: ____Gg: ____

Ff: _____Ff: _____ SS: ____SS: ____