Introduction to genetics

• Biology chapter 11

• Mr. Hines

• 11.1 The work of Gregor Mendel

What makes you unique?

A. Nearly all living things are unique in some way.

B. Humans for example all have different facial

features that can be easily recognized by friends

and family.

C. Traits – specific characteristics that vary from one

organism to another – example – eye color, hair

color, height, intelligence, shape of ears, etc..

D.

Traits

Take a minute to write down 5 of

your best traits.

Inheritance – the genes that you get from your parents that determines your traits – example eye color from mom, hair color from dad.

What is genetics? The scientific study of heredity

What is heredity? The scientific study of inheritance – huh? Inheritance and heredity are the same thing

In other words, genetics is the study of how 2 parents can create offspring that will be similar to both parents, but not quite like either parent.

You are a mix between mom and dad, but you are different from them both – genetics

Checkpoint:

• What is a trait?

__________________________________

• What is genetics?

__________________________________

Gregor Mendel’s Peas

Inheritance is not limited to humans and is found in all forms of life.

Gregor Mendel was and Austrian monk who led the way to understanding genetics with his work with pea plants.

He was in charge of the garden in his Monastery – there he studied plants and his discoveries changed biology forever.

He discovered that sexual fertilization in

plants was done with 2 separate parts of a

plant – the flower.

Here are the basic parts of a flower.

1. Stamen (male part) carries pollen (sperm)

2. Pistil (female part) carries ovule (egg)

Basic flower parts review

When pollen (sperm) makes contact with the

ovule (egg), fertilization occurs.

Fertilization – process in sexual reproduction

in which male and female reproductive

cells join to form a new cell.

Many plants such as peas have flowers that

can fertilize themselves – self pollination.

This means that one plant acts as both

parents.

In the case of self pollination, the offspring

will look just like the parent

The traits will be the same.

Self pollination is similar to you mating with

you – the offspring would be --- you.

If you fertilized yourself and had children,

your children would be identical copies of

you.

Mendall based his experiments from plants

that were self pollinated.

Offspring – new life that forms after fertilization – You are the offspring of your parents

Mendel knew that if he were to study genetics, self pollination could not be permitted.

Self pollination and true breeding are the same thing.

In order to all study genetics, he had see

fertilization of 2 different plants(2

different parents)

He did this by cutting off the pollen bearing

male parts (stamens) of the pea flowers

and pollinated them from other pea plants.

Checkpoint

What part of the flower hold the sperm?

_________________

What part of the flower holds the egg?

__________________

How did Mendell avoid self pollination in pea

plants? _________________

Genes and Dominance Mendel studied 7 different pea plant traits.

Each trait had 2 contrasting characters – such

as seed color – seed color could be green

or yellow.

In order to study genetics, he crossed (mated)

plants with contrasting traits. For

example, he crossed plants that had green

seeds with plants that had yellow seeds.

P Generation F1 Generation F2 Generation

Tall Short Tall Tall Tall Tall Tall Short

Section 11-1

Principles of Dominance

P Generation F1 Generation F2 Generation

Tall Short Tall Tall Tall Tall Tall Short

Section 11-1

Principles of Dominance

P Generation F1 Generation F2 Generation

Tall Short Tall Tall Tall Tall Tall Short

Section 11-1

Principles of Dominance

D. When you cross (mate) parents with

different traits, the offspring are called

hybrids.

E. Hybrid – offspring of crosses between

parents with different traits. For example

– if you mate a black cat with a white cat,

the offspring (kitten) is called a hybrid.

Even if the kitten from this cross comes out

black, it is still a hybrid (because of its

black and white parents)

F. Important notation to learn – page

264

1. P stands for parents

2. F1 stands for first generation of offspring

3. F2 stands for second generation of

offspring

G. So what happens when you cross a plant

with yellow seeds with a plant of green

seeds? (P generation) What will the

offspring have? (F1 generation)

H. Mendel noticed that the offspring had only

one trait from one parent – the other trait

from the other parent seemed to disappear.

For example – when yellow seeds were

crossed with green seeds, the offspring all

had yellow seeds.

Yellow seed x Green seed

Mendel concluded that inherited traits are

passed from one generation to the next.

Today, we say that these inherited traits come

from genes.

Gene – Sequence of DNA that codes for a

protein and thus determines a trait

In other words, a gene is a segment of DNA,

which is found on a Chromosome.

Chromosomes are made of many genes.

So right now we are speaking of 1 gene that

controls seed color.

There are 2 variations of that gene – one

variation of this gene is for yellow seed

and the other variation is for green seed.

We call the different variations of a single

gene an allele.

Allele – one of a different number of forms of

a gene.

For example – eye color is a gene. There are

3 basic alleles for the eye color gene –

green eyes, blue eyes, and brown eyes.

CHECK POINT

What does it mean to cross 2 parent pea

plants? ____________________

What is a hybrid?

_______________________________

What is a gene?

_________________________________

What is an allele? ___________________

IV. Gene dominance

A. Another conclusion from Mendel is that

some alleles are dominant and some are

recessive.

B. Dominant – Overpowering, expressive

C. Recessive – Overpowered, unexpressive

D. Example – when a pea plant with green

seeds was crossed with another pea plant

with yellow seeds, the offspring all had

yellow seeds. This shows that the gene

for the yellow seed is dominant and the

gene for the green seed is recessive.

E. The only time that a trait of a recessive

allele will show up in the offspring is

when there is no dominant gene to

overpower it.

Check point

What is a dominant allele? ______________

What is a recessive allele? _____________

What happens when a dominant and a

recessive allele are both present during a

crossing? _____________________

V. Segregation

A. So what happened to the recessive allele? Did it just disappear, or is it still hanging around somewhere?

B. In order to find out, Mendel crossed the F1 generation of pea plants.

C. When the F1 generation has been successfully mated, the new offspring are called the F2 generation. The F2 generation are the grandchildren of the P generation

D. Mendel noticed that when the F2

generation grew up, the recessive alleles

reappeared. In other words, the green

seeds were back. How can this be?

E. Mendel concluded that during the mating

process, the allele for each trait must be

somehow separated from each other.

F. This could be explained in gametes.

G. Gamete – specialized cell involved in

sexual reproduction. (sperm cells (male)

and egg cells (female) are gametes.)

• H. Key point – When each F1 plant

flowers and produces gametes, the two

alleles segregate from each other so that

each gamete carries only a single copy of

each gene. Therefore, each F1 plant

produces two types of gametes – those

with the allele for yellow seed and the

allele for green seed.

Self pollination