Heredity and Heredity and GeneticsGenetics

Just think…

“My parents have brown eyes, why are mine blue?”

“My brother is tall. Why am I short?”

“Why does my sister have blonde hair while mine is brown?”

Science can answer some of these questions…

Heredity- the passing of characters from parents to offspring

Genetics- the branch of biology that focuses on heredity

Gregor Mendel

Father of Genetics

During his early years at the monastery, Mendel began studying and breeding mice.During his early years at the monastery, Mendel began studying and breeding mice.

The bishop was not

pleased.

The bishop was not

pleased.

Brother Gregor settled on bees . . .

Brother Gregor settled on bees . . .

and peas. and peas.

Why Peas?

• The garden pea is a good subject for several reasons. Peas…– Have traits that are inherited by simple dominance,

one trait is dominant to another, ie. Tall is dominant to short in peas

– Have male and female reproductive parts enclosed on the same structure - mating can be controlled and done with the bristles of a brush

– Are small, grow easily, mature quickly, and produce many offspring (results can be quickly obtained and there are plenty of subjects to count)

Mendelian Theory of Heredity

(the foundation of genetics)1. For each inherited character, an

individual has two copies - one from mom and one from dad

2. There are different versions of genes = alleles

For example, the gene for pea seed color can be

green or yellow.

What are different alleles for eye color?

3. When two different alleles (versions) occur together, one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance.

Mendelian Theory of Heredity

(the foundation of genetics)

Dominant- the expressed form of the trait

Recessive- the trait that is not expressed if a dominant allele is present

Ex. E

Ex. e

4. When gametes are formed (in what process?) alleles for each gene separate - gametes only carry one allele for each characteristic

During fertilization, gametes unite - each gamete contributes one allele to the offspring.

Mendelian Theory of Heredity

(the foundation of genetics)

Modern Terms

Genotype- the genetic makeup of an organism (the set of alleles an individual has)

Phenotype- the physical appearance of an organism

Ex. EE, Ee, ee

Ex. Purple, tall, round

Modern Terms

• Homozygous- the two alleles present for a character are the same

ex. EE or ee

• Heterozygous- the two alleles present for a character are different

ex. Ee

Labeling the Generations

• P generation – parent generation

• F1 Generation – first filial, offspring of the P generation

• F2 generation – second filial, offspring of the F1 generation

Predicting Heredity…

ProbabilityThe likelihood that a specific event will occur

First Law: Each trial of a chance event is independent of all other trials of the same change

event.

Application: What is the chance that you will roll a 1 the first time you roll a dice?

What is the chance that you will roll a 1 the second time you roll a dice?

Second Law (also called Law of Muliplication): The chance of independent events occurring together is the product of the chances for each independent event occurring separately.

Application: Two people have a coin. They are tossing the coins at the same time. What is the chance that both will come up heads?

• What is the chance that both will come up tails?

ProbabilityWhat is the probability that a couple will

have four boys in a row?

½ x ½ x ½ x ½ = 1/16

1/2 1/2 1/2 1/2

Problem: If one out of two students is female and one out of eight students is left handed and one out of 12 is red haired, what is the probability that the next person you will see will be left-handed, red-haired girl?

Third Law (also called Law of Addition): The probability of an event that can occur in two or more different ways is the sum of the separate possibilities of those ways.

Application: Two people have a coin. They are tossing the coins at the same time.

What is chance that one will come up heads and the other come up tails?

Now, let’s see if this works in the real world…

• Each student will flip a penny 10 times and record the results. Based on probability, how many heads should there be? Tails?– Your results:

• Heads_______• Tails ________

– Class results:• Heads _______• Tails ________

– Which results are closest to your prediction based on probability? Yours or the classes?

Each student needs a penny and a partner!

• Each student with their partner each flip their penny. Record the results whether it be 2 heads, 2 tails or 1 heads and 1 tails. Do this 20 times.

• What is the predicted result based on probability?• Your results: HH_____ HT _____ TT_____• Class results: HH _____ HT _____ TT______

• Which are closer to the predicted results?

Yours or the classes? Why?

a. Miguel has just received an IPOD as a gift. He has downloaded 3 country music songs,1 rhythm and blues song, 5 rap songs, and 1 song that is the theme song to his favorite movie. If the IPOD is set on playing these songs at random, what is the probability that he will hear a country music song?

b. Sherri has a pocket full of colored candy jelly beans. She has 6 pink jelly beans, 3 yellow jelly beans, 10 green jelly beans, and 1 orange jelly bean. What is the probability that Sherri will select a green jelly bean and then, without replacing it, randomly select an orange jelly bean from her pocket?

Monohybrid Cross:a cross that shows the possible offspring

for one traitExample: Cross two heterozygote individuals:

Aa x Aa

A a

A

a

AA Aa

Aa aa

Genotypic Ratio: 1:2:1 Phenotype: 3 white:1 brown

A: White fur

a: Brown fur

Practice!Cross a HOMOZYGOUS dominant with a

HOMOZYGOUS recessive using the same trait.

A A

a

a

Aa Aa

Aa Aa

What is the genotypic ratio?

What is the phenotypic ratio?

4/4 which gives 1

4/4 which is 1 or 100% white fur

Practice!Cross a HOMOZYGOUS dominant with a

HETEROZYGOUS using the same trait.

A A

A

a

AA AA

Aa Aa

What is the genotypic ratio?

What is the phenotypic ratio?

2:2 which reduces to 1:1

4/4 white fur, which reduces to 1 or 100%

Test Cross

Animal breeders and horticulturists often need to know if an organism is homozygous dominant or heterozygous for a character. However, it is impossible to tell simply by looking at an organism.

They can use a test cross…

Test Cross

An individual whose phenotype is dominant, but whose genotype is not know, is crossed with a homozygous recessive individual.

(Based on the outcome of the cross, you can tell if the individual in question is homozygous dominant (TT) or heterozygous (Tt).)

Test CrossIs this purple flowering pea plant PP or Pp?Cross the unknown with a homozygous recessive individual.

Set up a Punnett squares:

Based on the actual outcome of the cross, determine the genotype of the unknown.

P? X pp

pp

P ppp

P PPp

Pp

pp

pp

Pp

PpPp

Pp

(If all offspring are purple, the unknown must have been PP)

Test Cross• Consider that tallness in pea plants is dominant

to dwarfism. A horticulturalist has a tall plant, however is unaware of its genotype. She has a contract to produce all tall plants. Show the test cross she will have to make in order to be sure that the tall plant she uses to make offspring is a purebreeding tall plant. What are the possibilities with a tall plant?

• The tall plant could be either TT or Tt. So you cross it will a tt.