Who was this Mendel and what the heck is he doing in a monastery? • born in 1822 • trained himself to be a naturalist early in life • worked as a substitute science teacher • failed the qualifying exams to be a regular high school teacher! • joined a monastery in Brunn, Austria • sent to Vienna U. to study science and math

MendelWeb Mendel’s

first

published

work:

"Versuche über Pflanzen-Hybriden“ or Experiments in Plant Hybridization was a landmark in clarity and insight!

Trained as a mathematician and a biologist, he figured out the laws of inheritance… mathematically!!

The work of Gregor Mendel • worked with pea plants… …he called them his children!

Why pea plants??? There was a long-standing tradition of breeding pea plants at the monastery where Mendel lived and worked

Science Humor

So…they were readily available and they come in lots of varieties!

…there were plants with different flower colors, seed color, flower position etc..

Mendel’ Pea Plants

Mendel based his laws on his studies of garden pea plants. Mendel was able to observe differences in multiple traits over many generations because pea plants reproduce rapidly, and have many visible traits such as: Seed Color Plant Height Green Yellow Tall

Short

Pod color

Green

Yellow

Seed Shape

Pod Shape Wrinkled Round Smooth Pinched

‘Brother Greg... We grow tired of peas again!!!’

And best of all… Pea plants flowers can reproduce by themselves

This allowed Mendel to see if strains were true breeding and to produce hybrids

How Mendel made hybrids… He’d then tie little bags around the flowers to prevent contact with stray pollen.

Mendel’s Experiments Mendel noticed that some plants always produced offspring that had a form of a trait exactly like the parent plant. He called these plants “purebred” plants. For instance, purebred short plants always produced short offspring and purebred tall plants always produced tall offspring.

X Purebred Short Parents

Short Offspring

X Purebred Tall Parents

Tall Offspring

Mendel’s First Experiment Mendel crossed purebred plants with opposite forms of a trait. He called these plants the parental generation , or P generation. For instance, purebred tall plants were crossed with purebred short plants.

X

Parent Tall P generation

Parent Short P generation

Offspring Tall F1 generation

Mendel observed that all of the offspring grew to be tall plants. None resembled the short short parent. He called this generation of offspring the first filial , or F1 generation, (The word filial means “son” in Latin.)

Mendel’s Second Experiment Mendel then crossed two of the offspring tall plants produced from his first experiment. Parent Plants

Offspring

X

Tall F1 generation

3⁄4 Tall & 1⁄4 Short F2 generation

Mendel called this second generation of plants the second filial, F2, generation. To his surprise, Mendel observed that this generation had a mix of tall and short plants. This occurred even though none of the F1 parents were short.

The results of Mendel’s monohybrid crosses led him to propose… 1. All organisms contain two “units of heredity” for each trait (alleles). Genes- a segment of DNA that carries hereditary instructions and is passed from parent to offspring Alleles- multiple forms of the same gene Heredity- the passing of traits from parent to offspring.

2. Dominant and recessive alleles… …and organisms can have any combination of the two alleles (2 dominants, 2 recessives or a mixture 1 dominant and 1 recessive). Dominant trait- the trait observed when at least one dominant allele for a characteristic is inherited Recessive trait- a trait that is apparent only when two recessive alleles for the same characteristic are inherited

Purebred - all of the offspring will have the same trait as the parent when self-pollinated Hybrid- an organism has two different alleles for a trait

3. The Law of Segregation – during gamete formation, alleles separate randomly into separate gametes.

A bit of genetic jargon… phenotype vs. genotype What the organism looks like – its What alleles Physical the organism makeup has - its genetic makeup

More jargon… homozygous vs. heterozygous P

2 of the same alleles: RR or rr

2 different alleles: Rr

p

A Punnett square

A Punnett square… Gametes from one parent r R Gametes from other parent

R

RR round

r

Rr round

Rr round rr wrinkled

Ratio: 3:1 or ¾ round, ¼ wrinkled

These slides are a combination of two power point presentations on Gregor Mendel Original presentations can be found at: wsscience.wikispaces.com/file/view/Genet ics+Gregor+Mendel.ppt p5cdn4static.sharpschool.com/UserFiles/ Servers/Server.../Mendel.pptx