The Father of Genetics Gregor Mendel Gregor Mendel

The Father of Genetics Gregor Mendel

Gregor Mendel • When did he live? • Where did he work? • Mid-1800’s • Central Europe

Gregor Mendel • What was his job? • A monk, who taught and took care of the monastery garden.

One type of plant in the garden was the common pea plant

Gregor Mendel • How did he become the “Father of Genetics”? • He was always interested in how traits are passed from one generation of plants to the next. • Had two great teachers who taught him: – LEARN by EXPERIMENTING – USE MATH TO HELP YOU INTERPRET DATA

What did Mendel want to know? • Like many others, he wondered if – traits from parents were blended in the offspring… • White parent + Purple parent → Lavender offspring – OR, if – traits from the parents retained their separate identities in the offspring • White parent + Purple parent → White or Purple offspring

Pea Plants • Mendel knew that some pea plants have purple flowers and some have white flowers. Read

Pea Plants Normally Self. Fertilize Produce pollen (sperm)

True-Breeding • Mendel noted that whenever a plant with purple flowers self-pollinated, all of the offspring had purple flowers. Purple + Purple produced Purple offspring • He also noticed that self-pollinating white-flowered plants always produced offspring with white flowers. White + White produced White offspring

Mendel wondered… • What would happen if pollen from a white-flowered plant fertilized an egg from a purple-flowered plant? • White + Purple ? ? ?

Cross-Pollination • Mendel developed a way to use pollen (sperm) from one stock of plants to fertilize an egg from another stock of plants. • What was his IV? • What was his DV?

LE 14 -2 Removed stamens from purple flower Transferred spermbearing pollen from stamens of white flower to eggbearing carpel of purple flower Parental generation (P) Carpel Stamens Pollinated carpel matured into pod Planted seeds from pod First generation offspring (F 1) Examined offspring: all purple flowers

Sperm from purple plant + egg from white plant purple baby plant How can this be explained? ? ?

Mendel Proposed • Biological inheritance is determined by factors (genes) that are passed from one generation to the next. • There are contrasting forms (alleles) of each factor. • Organisms have two alleles for each gene, but pass only one of those to their offspring.

Dad was Mom was Babies were and purple in color

If babies were and purple in color, what does that tell us about the purple gene compared to the white gene? Mendel proposed that purple was dominant over white.

What would happen if he allowed two plants to mate?

LE 14 -3 P Generation (true-breeding parents) Purple flowers White flowers F 1 Generation (hybrids) F 2 Generation All plants had purple flowers

He noticed the same pattern for six other traits

LE 14 -5_2 P Generation Appearance: Genetic makeup: Purple flowers PP White flowers pp P p Gametes F 1 Generation Appearance: Genetic makeup: Purple flowers Pp 1 Gametes: 2 1 P p 2 F 1 sperm P p PP Pp Pp pp F 2 Generation P F 1 eggs p 3 : 1 For each characteristic, there alternate versions (alleles) of the gene (ex – purple or white). An organism inherits two alleles for each characteristic, one from each parent. If the organism inherits two different alleles, then the dominant allele determines the appearance, and the recessive one has no noticeable effect. When gametes (eggs and sperm) are formed, the two alleles separate, and each gamete gets one or the other, not both.

Note that Mendel figured this all out before anyone even knew about DNA or chromosomes • About 40 years after his death, his work was rediscovered, and chromosomes were observed using microscopes

Example Trait – Gene for Plant Height • Alleles: – T: dominant, tall – t: recessive, short Genotype TT (homozygous) Tt (heterozygous) tt (homozygous) Phenotype tall short

Punnett Squares – a way to show the alleles of the parents and offspring T t Tt Tt • Parents: TT x tt • The possible alleles in the gametes produced by the parents are shown on the top and left • The possible genotypes of the offspring are shown within the

Mate a plant homozygous for tallness with a plant homozygous for shortness (TT x tt) Offspring: T T 100% tall t Tt Tt Heterozygous tall

What if you mate two heterozygotes (Tt x Tt)? Offspring: t T T t TT Tt Homozygous tall Heterozygous tall 75% tall 25% short Tt tt Heterozygous tall Homozygous short