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Mendel’s GeneticsJohann Gregor Mendel

•Born – 1822

•Occupations:

-beekeeper

-gardener

-monk

-teacher

-scientist

1843

Mendel entered

Augustinian

Abbey of St

Thomas in Brno,

Austria

Education:

1851 – sent to

University of

Vienna

(Austria) to

become a

math and

science

teacher

The Monastery's Garden

1856 to 1863

Cultivated and

tested pea plants to

study how

inherited traits are

passed from

generation to

generation1865 – presented his research findings to scientists

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Mendel’s research and

findings in genetics were

rejectedMendel became

the abbot (chief

administrator)

of the monastery

Mendel died in 1884 at

age of 61

The next abbot burned all of

Mendel’s papers

In 1900, his work was rediscovered

by Hugo de Vries and Carl Correns

They repeated his experiments and came

to the same conclusions (verification)

Mendel’s Experiments

• Mendel noticed that traits exist in one of two forms. Ex. tall or short, round or wrinkled

• Pea plants had 7 “either-or traits”

• Used true breeding plants (pure breeding)

• Controlled the breeding • First experiments were

monohybrid crosses (cross one trait at a time)

• Mendel used pollen to fertilize selected

pea plants.

Mendel controlled thefertilization of his pea plantsby removing the male parts,or stamens.

He then fertilized the femalepart, or pistil, with pollen froma different pea plant.

– P generation crossed to produce F1 generation

– interrupted the self-pollination process by removing male flower parts

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• Mendel allowed the resulting plants to

self-pollinate.

– Among the F1 generation, all plants had purple flowers

– F1 plants are all heterozygous

– Among the F2 generation, some plants had purple

flowers and some had white

Mendel’s Experiments

Here are the steps:Pure breeding Pure breeding

tall X short

pea plants pea plants

All tall pea plants

Out of every 4 plants –

3 were tall and 1 was short

I am

planting

some true

breeding

short pea

plants

Now I am planting some

true breeding tall pea plants

Now I am going to cross

pollinate these parents

Pollen

And collect their seeds

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Now I am going to take

these F1 seeds and plant

them

What will these plants

look like????

The F1 generation is all tall??

What happened to the short

trait?

I bet the short trait is hiding

somewhere! I am going to

self pollinate the F1 plants

And collect their seeds Now I am going to take

these F2 seeds and plant

them

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I wonder what the F2

generation will look like!

Wow! There is the short

trait! But only 1 in 4.

Mendel’s Experiments:

P Generation

Tall Short

True-breeding

Mendel’s Experiments:

F1 Generation

TallTall

100% tall

Mendel’s Experiments:F2 Generation

Tall Tall Tall Short

Ratio = 3 talls to 1 Short

Mendel’s Experiments:

P Generation

Tall Short

True-breeding

plants

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Mendel’s Experiments:

P GenerationF1 Generation

Tall Short TallTall

Mendel’s Experiments:

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Mendel’s Experiments

Tall X ShortPlants Plants

All tall plants

3 tall plants to 1 short plant

Mendel’s Crosses with yellow/green

Characters

investigated by

Mendel

Mendel observed

the

same results

every time

he crossed two

different

forms of a trait.

• Mendel observed patterns in the first and

second generations of his crosses.

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Mendel’s conclusions

1. Biological inheritance is determined

by factors (or GENES) that are passed

from one generation to the next.

2. One trait = one gene = two contrasting

forms (ALLELES)

3. “Principle of Dominance” – some

alleles are dominant and some are

recessive. One form of a trait, the

dominant trait, prevents the expression

of the recessive trait.

4. Law of Segregation- when gametes

are formed the pair of genes (alleles)

responsible for each trait separate.

Sex cells – eggs and sperm- must contain

only a single copy of each allele the

parent has for a gene.

Terms to Know!!

• Dominant

• Recessive

• Homozygous

• Heterozygous

• Genotype

• Phenotype

Mendel’s Experiments

Tall X ShortPlants Plants

All tall plants

3 tall plants to 1 short plant

TT tt

Tt

3Tall: 1 short1 TT: 2Tt: 1 tt

The same gene can have many versions.

• A gene is a piece of DNA that directs a cell to make a certain protein.

• Each gene has a locus, aspecific position on a pair of

homologous chromosomes.

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• An allele is any alternative form of a gene

occurring at a specific locus on a

chromosome.

– Each parent donates one allele for every

gene.

– Homozygous

describes two alleles that are the same at a

specific locus.

– Heterozygousdescribes two alleles

that are different at a specific locus.

• Alleles can be represented using letters.

– A dominant allele is expressed as a phenotype

when at least one allele is dominant.

– A recessive allele is expressed as a phenotype

only when two copies are present.

– Dominant alleles are

represented by uppercase letters; recessive alleles

by lowercase letters.

Punnett squares are used to predict

genetic crosses.• The Punnett square is a grid system for predicting

all possible genotypes resulting from a cross.

– The axes representthe possible gametes

of each parent.

– The boxes show the

possible genotypesof the offspring.

• The Punnett square yields the ratio of

possible genotypes and phenotypes.

Monohybrid

• A monohybrid cross involves one trait.

• Ex. Height

• Probability

• In a homozygous dominant x homozygous

recessive cross:

• Genotypic results: all heterozygous

• Phenotypic results: all dominant

– In a heterozygous x heterozygous cross

• Genotypic Results are: 1:2:1 (homozygous dominant:

heterozygous:homozygous recessive)

• Phenotypic Results are: 3:1 (dominant:recessive)

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• In a heterozygous x homozygous recessive

– Genotypic results: 1:1 heterozygous:homozygous recessive

– Phenotypic results: 1:1 dominant:recessive

TESTCROSS

• A cross between an organism with an

unknown genotype and an organism with the

recessive phenotype.

A monohybrid cross involves one trait.

• Monohybrid crosses examine the inheritance of only one specific trait.

– homozygous dominant x homozygous recessive: all heterozygous, all dominant

– Heterozygous x heterozygous—1:2:1

(homozygous dominant:

heterozygous:homozygous recessive); 3:1

dominant:recessive

• heterozygous-homozygous recessive—1:1

heterozygous:homozygous recessive; 1:1

dominant:recessive

• A testcross is a cross between an organism

with an unknown genotype and an organism

with the recessive phenotype.