Ch. 3 Section 1

Ch. 3 Section 1

The Work of Gregor MendelThe Work of Gregor Mendel

What comes to mind when you hear the

word inheritance?

Every living thing has a set of characteristics inherited from its

parents

Genetics - The study of heredity

What comes to mind when you hear the

word inheritance?

Every living thing has a set of characteristics inherited from its

parents

Genetics - The study of heredity

Gregor MendelGregor Mendel

Austrian monk

Studied biological inheritance

Studied math & science

Loved gardening

Mendel began conducting studies on the pea plants in the garden

Austrian monk

Studied biological inheritance

Studied math & science

Loved gardening

Mendel began conducting studies on the pea plants in the garden

FertilizationFertilization

The female portion of the flower produces egg cells

The male portion of the flower produces

sperm cells (in pollen)

When the egg and sperm join through sexual reproduction, fertilization

occurs!

The female portion of the flower produces egg cells

The male portion of the flower produces

sperm cells (in pollen)

When the egg and sperm join through sexual reproduction, fertilization

occurs!

Fertilization produces a new cell

Pea plants are usually self-pollinating

This means that sperm cells in pollen fertilize the egg cells of the same flower.

The seeds produces from by self-pollination only have ONE parent and therefore end up being identical to that parent!

Mendel referred to these types of pea plants as TRUE-BREEDING

Fertilization produces a new cell

Pea plants are usually self-pollinating

This means that sperm cells in pollen fertilize the egg cells of the same flower.

The seeds produces from by self-pollination only have ONE parent and therefore end up being identical to that parent!

Mendel referred to these types of pea plants as TRUE-BREEDING

True-Breeding

The new pea plants look exactly like the parent pea plants!

True-Breeding

The new pea plants look exactly like the parent pea plants!

While Mendel did in fact study true- breeding plants, he wanted to produce seeds by joining male and female reproductive cells from 2 DIFFERENT plants

Meaning the egg from one plant and the pollen from a different plant.

But how did he do this???

While Mendel did in fact study true- breeding plants, he wanted to produce seeds by joining male and female reproductive cells from 2 DIFFERENT plants

Meaning the egg from one plant and the pollen from a different plant.

But how did he do this???

To prevent self-pollination, Mendel cut away

the male pollen bearing parts of the plant.

He then dusted the pollen from another plant

onto the flower

This process is called CROSS- POLLINATION

To prevent self-pollination, Mendel cut away

the male pollen bearing parts of the plant.

He then dusted the pollen from another plant

onto the flower

This process is called CROSS- POLLINATION

Cross-PollinationCross-Pollination

Cross-PollinationCross-Pollination

Produces plants that have 2 parents

This allowed Mendel to cross-breed plants with different characteristics

He then studied the results…

Produces plants that have 2 parents

This allowed Mendel to cross-breed plants with different characteristics

He then studied the results…

Genes & DominanceGenes & Dominance

Mendel studied 7 different pea plant traits

A trait is a specific characteristic such as flower

color or plant height

Each of the traits that Mendel studied had 2 contrasting forms

Example: tall vs. short green seed vs. yellow seed round seed vs. wrinkled seed

Mendel studied 7 different pea plant traits

A trait is a specific characteristic such as flower

color or plant height

Each of the traits that Mendel studied had 2 contrasting forms

Example: tall vs. short green seed vs. yellow seed round seed vs. wrinkled seed

Mendel’s StudiesMendel’s Studies

Mendel crossed plants with each of the 7 contrasting forms.

He then studied their offspring...what did they end up looking like?

Mendel referred to the parent plants (the original ones used) as the P-Generation

The “P” stands for parental

Mendel crossed plants with each of the 7 contrasting forms.

He then studied their offspring...what did they end up looking like?

Mendel referred to the parent plants (the original ones used) as the P-Generation

The “P” stands for parental

The offspring from the P-Generation are called the F1 Generation

Or “First Filial” generation

In Latin, Filius or Filia means son or daughter

The offspring of crosses between parents with different traits are called HYBRIDS

The offspring from the P-Generation are called the F1 Generation

Or “First Filial” generation

In Latin, Filius or Filia means son or daughter

The offspring of crosses between parents with different traits are called HYBRIDS

So What Do the F1 Hybrids Look Like???

So What Do the F1 Hybrids Look Like???

Do the characteristics of the parents just blend in the offspring?

NO!

To Mendel’s surprise, all of the offspring had

the character of only one of the parents!

The character of the other parent seemed to have disappeared….

Do the characteristics of the parents just blend in the offspring?

NO!

To Mendel’s surprise, all of the offspring had

the character of only one of the parents!

The character of the other parent seemed to have disappeared….

Mendel Drew 2 ConclusionsMendel Drew 2 Conclusions

1. Biological inheritance is determined by factors that are passed from one generation to the next.

• The chemical factors that determine these traits are called GENES

• Each of the traits Mendel studied was controlled by a gene that occurred in 2 contrasting forms

• These different contrasting forms are called ALLELES.

- The gene for plant height occurs in 2 forms…..tall alleles, short alleles

1. Biological inheritance is determined by factors that are passed from one generation to the next.

• The chemical factors that determine these traits are called GENES

• Each of the traits Mendel studied was controlled by a gene that occurred in 2 contrasting forms

• These different contrasting forms are called ALLELES.

- The gene for plant height occurs in 2 forms…..tall alleles, short alleles

2nd Conclusion2nd Conclusion

The Principle of Dominance

• This states that some alleles are dominant and others are recessive.

• An organism with a dominant allele for a particular trait will always exhibit that form of the trait.

The Principle of Dominance

• This states that some alleles are dominant and others are recessive.

• An organism with a dominant allele for a particular trait will always exhibit that form of the trait.

An organism with a recessive allele for a particular form of a trait will exhibit that form ONLY when the dominant allele is not

present.

In Mendel’s experiments,• The allele for tall plants was dominant and

the allele for short plants was recessive

• The allele for yellow seeds was dominant and the allele for green seeds was recessive.

An organism with a recessive allele for a particular form of a trait will exhibit that form ONLY when the dominant allele is not

present.

In Mendel’s experiments,• The allele for tall plants was dominant and

the allele for short plants was recessive

• The allele for yellow seeds was dominant and the allele for green seeds was recessive.

SegregationSegregation

So what happened to the recessive alleles…did they disappear in the F1 generation?

To answer this question, Mendel allowed all 7 kinds of F1 hybrid plants to produce and F2 generation

The F2 generation was produced through self-pollination

***remember this means that the egg and sperm are from the same plant!

So what happened to the recessive alleles…did they disappear in the F1 generation?

To answer this question, Mendel allowed all 7 kinds of F1 hybrid plants to produce and F2 generation

The F2 generation was produced through self-pollination

***remember this means that the egg and sperm are from the same plant!

The F1 CrossThe F1 Cross

When Mendel compared the F2 plants, he discovered that the traits controlled by the recessive alleles had reappeared!!!

Roughly 1/4 of the F2 plants showed the recessive allele and the trait that went with it.

When Mendel compared the F2 plants, he discovered that the traits controlled by the recessive alleles had reappeared!!!

Roughly 1/4 of the F2 plants showed the recessive allele and the trait that went with it.

Why Did This Happen?Why Did This Happen?

Mendel assumed that the dominant allele had masked the recessive allele in the F1 generation.

But there’s more to it…

The individual alleles actually separate for each parent so that more combinations are possible.

You don’t just get your mothers alleles or just your fathers alleles…you get a combination of the two.

Mendel assumed that the dominant allele had masked the recessive allele in the F1 generation.

But there’s more to it…

The individual alleles actually separate for each parent so that more combinations are possible.

You don’t just get your mothers alleles or just your fathers alleles…you get a combination of the two.