Introduction Introduction to Geneticsto Genetics

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Your Favorite Science Teacher (that would be me)

Learning Goal:Students will be able to explain the basic principles of heredity by demonstrating the following…

- distinguish between dominant and recessive traits- use human examples- use punnett squares

4= I know it & can teach it!

3= I know it

2= I know some of it

1= I know a little of it

0= What?

Heredity The passing on of characteristics from

parents to offspring

GeneticsThe branch of biology that studies heredity

Gregor Mendel He was an Austrian monk 1st person to study heredity He was able to predict how traits are

transferred from one generation to the next

Studied garden peas– He would transfer pollen from one plant

to another plant with different traits

Controlled Experiment: only studied one trait at a time! (what a fantastic scientist!!)

The Pea Plants

Mendel studied several traits

Mendel’s Pea Experiments Mendel chose pea plants

because their traits were easy to see and distinguish.

He crossed plants with two different traits, for example purple flowers with white flowers.

He started his experiments with purebred plants.

Purebred plants ALWAYS produce offspring with the same trait as the parents. For example, if the parents are tall, all offspring will be tall. If the parents are short, all offspring will be short.

Let’s take a look at how that is…but first… some definitions!

Dominant: visible, observable trait of an organism that masks a recessive form of the trait. This trait is expressed ANYTIME the dominant allele is present. Expressed with a capital letter.

Recessive: a hidden trait of an organism that is masked by a dominant trait. This trait is only expressed if both alleles are recessive. Expressed with a lowercase letter

Dominant and Recessive Traits

It seemed to Mendel, that for each characteristic in peas, one trait was stronger than the other.

He called the “stronger” one, the dominant trait.

He called the “hidden” one, the recessive trait.

Learning Goal:Students will be able to explain the basic principles of heredity…

- distinguish between dominant and recessive traits- use human examples- use punnett squares 4= I know it & can

teach it!

3= I know it

2= I know some of it

1= I know a little of it

0= What?

And a couple more… Allele: gene form for each variation of a

trait (ex. Gene for short plants (t); gene for tall plants (T) )

Genotype: the gene combination of an organism, made up of 2 alleles (ex: Tt) – the capital/lowercase letter is extremely important!

Phenotype: the way an organism looks and behaves (ex: tall plants, white flowers, etc.)

And two more… Heterozygous (hybrid):

different alleles: Tt

Homozygous (purebred): same alleles: TT or tt– Homozygous Dominant: TT– Homozygous Recessive: tt

No more definitions… I promise… well… at least for a couple more

slides!

Understanding Mendel’s Experiments

Part I (flower color)2 alleles

for purple

PP

Pp

2 alleles for white

pp

1 allele for purple. 1 allele for white

heterozygous

homozygous homozygous

The result…One purple plant (PP) was bred with one

white plant (pp). The result was 4 purple plants. Let’s look at a Punnett Square:

Plant One

Plant Twop

p

P P

Pp Pp

Pp Pp

heterozygous heterozygous

heterozygous heterozygous

Plant One

Plant Twop

p

Pp Pp

Pp Pp

P P

The genotypes in the boxes are the possible offspring of the two plants. Since each has the dominant allele (P) all the plants will be PURPLE. The PHENOTYPE would be PURPLE

Confused Yet??Let’s take it one step further!

Let’s cross two of the offspring from the first cross (remember, they were all Pp)

Understanding Mendel’s Experiment

Part II1 allele for purple 1 allele for white

2 alleles for purple

PP

1 allele for purple 1 allele for white

Pp

2 alleles for white

pp

PpPp

The Result…

Plant One

Plant TwoP

p

P p

PP Pp

Pp pp

One purple plant (Pp) was bred with one purple plant (Pp). The result was 3 purple plants and one white plant.

What is the phenotype of each plant???

Plant One

Plant TwoP

p

P p

PP Pp

Pp pp

Purple!

Purple!

Purple!

WHITE!

Let’s take a more in depth look at genotype & phenotype

Genotype: Pp, PP, pp

Phenotype: Purple, Purple, white

What if…. G= green, g= blue

Genotype:GG

Gg

gg

Phenotype:Green

Green

Blue

Learning Goal:Students will be able to explain the basic principles of heredity…

- distinguish between dominant and recessive traits- use human examples- use punnett squares 4= I know it & can

teach it!

3= I know it

2= I know some of it

1= I know a little of it

0= What?

Creating your own punnett square

What are the possible offspring if you cross a short tailed cat (heterozygous- Ss) with a long tailed cat (homozygous – ss)? Short tails are dominant.

Cat One

Cat Twos

s

S s

Ss ss

Ss ss

Cat One

Cat Twos

s

S s

Ss ss

Ss ss

Possible offspring: Ss (short tail) or ss (long tail)

What percent chance is there, if the cats produce ONE kitten, that it will have a short tail?

50% - a 2 out of 4 chance!

Try another…What are the possible offspring if you cross two 2-eyed monsters (heterozygous – Ee)? E= 2 eyes, e = 3 eyes

Monster One

Monster Two E

e

EE Ee

Ee ee

E e

Monster One

Monster Two E

e

EE Ee

Ee ee

E e

EE = two eyes

Ee, Ee = two eyes

ee = three eyes

A Question to Ponder…

Can two species have different GENOTYPES but the same PHENOTYPE???

ABSOLUTELY!

2 species can have different genotypes, but have the same phenotype.

Example:

TT= tall

Tt= tall

Both species have different GENOTYPES, but they are both TALL (phenotype!)

What questions do you have?

Learning Goal:Students will be able to explain the basic principles of heredity…

- distinguish between dominant and recessive traits- use human examples- use punnett squares 4= I know it & can

teach it!

3= I know it

2= I know some of it

1= I know a little of it

0= What?

F1 Generation Mendel called the parent plants the P generation. He called the offspring from the parents the F1

generation. F is from the Latin word, filial, which means son. When Mendel crossed pure pea plants with purple

flowers with pure pea plants with white flowers, all the F1 generation had purple flowers.

P Generation

F1 Generation

F2 Generation When he crossed the F1 generation peas with one another,

only some of the offspring had purple flowers. These formed the F2 generation.

Mendel found that in the F2 generation, ¾ of the plants had purple flowers and ¼ of them had white flowers.

F1 Generation

F2 Generation

x

Mendel’s Amazing DiscoveryMendel did the same experiment with all 7 traits that he studied and discovered the same pattern each time: In the F1 generation, one trait was always hidden. That trait appeared in the F2 generation in about ¼ of the plants.

Purebred P Generation

Cross Pollination

Hybrid F1 Generation

Hybrid F1 Generation

Self-Pollination

Hybrid F2 Generation

There is always an exception to the rule…

Codominance

In codominance, the alleles are neither dominant, nor recessive. Neither allele is masked by the other.

Roan CowIs both white and red