GeneticsGenetics

MendelMendel

HeredityHeredity

HeredityHeredity is the passing of traits from is the passing of traits from parents to offspring.parents to offspring.

GeneticsGenetics

GeneticsGenetics—the study of how traits are —the study of how traits are passed from parents to offspring.passed from parents to offspring.

Gregor Mendel – “The father of genetics”Gregor Mendel – “The father of genetics”

Gregor MendelGregor Mendel

Austrian monk studied genetics in the 1850’s.Austrian monk studied genetics in the 1850’s. Did controlled breeding experiments with pea Did controlled breeding experiments with pea

plants because:plants because: Reproduced quickly – lots of dataReproduced quickly – lots of data Easily observed traits (flower color, pea shape)Easily observed traits (flower color, pea shape) Could control which pairs of plants reproducedCould control which pairs of plants reproduced

Pollination in pea plantsPollination in pea plants

Sexual reproductionSexual reproduction Pollen (sperm) from stamen lands on pistil Pollen (sperm) from stamen lands on pistil

(eggs)(eggs) 2 ways of pollination:2 ways of pollination:

Self-pollinationSelf-pollination Cross-pollinationCross-pollination

Self-pollinationSelf-pollination

Cross-pollinationCross-pollination

Mendel’s experimentsMendel’s experiments

Started with “True-Breeding Plants” (plants Started with “True-Breeding Plants” (plants that produce offspring with traits that that produce offspring with traits that match the parent when self-pollinated)match the parent when self-pollinated)

Cross-pollinated hundreds of plants for Cross-pollinated hundreds of plants for different traitsdifferent traits

Mendel’s resultsMendel’s results

First-Generation Crosses

HybridHybrid

Science Use the offspring of two animals or plants with different forms of the same trait

Common Use having two types of components that perform the same function, such as a vehicle powered by both a gas engine and an electric motor

Mendel’s resultsMendel’s resultsSecond-Generation (Hybrid) Crosses

Mendel’s resultsMendel’s results

All first generation hybrid plants always All first generation hybrid plants always only exhibit one of the traits.only exhibit one of the traits.

Second generation hybrid plants express Second generation hybrid plants express the dissapeared trait (25% of the offspring)the dissapeared trait (25% of the offspring)

Mendel’s conclusionsMendel’s conclusions

Two factors, one from each sperm and Two factors, one from each sperm and one from each egg, control each inherited one from each egg, control each inherited trait.trait.

Mendel’s conclusionsMendel’s conclusions

First generation hybrids had one factor for First generation hybrids had one factor for each trait:each trait: Purple x White = (one purple factor, one white Purple x White = (one purple factor, one white

factor)factor) Why only purple flowers?Why only purple flowers?

Mendel hypothesized: Purple factor is Mendel hypothesized: Purple factor is dominant – blocks white factordominant – blocks white factor

Mendel’s conclusionsMendel’s conclusions

Dominant trait: genetic factor that blocks Dominant trait: genetic factor that blocks another genetic factoranother genetic factor

Recessive trait: genetic factor that is Recessive trait: genetic factor that is blocked by the presence of a dominant blocked by the presence of a dominant factorfactor

Mendel’s conclusionsMendel’s conclusions

First generation hybrid x first generation First generation hybrid x first generation hybrid (Each plant has one dominant hybrid (Each plant has one dominant factor and one recessive factor)factor and one recessive factor)

75% of plants purple (at least one 75% of plants purple (at least one dominant factor)dominant factor)

25% of plants white (two recessive factors)25% of plants white (two recessive factors)