Fundamentals of Genetics

(chapter 9)

Who was Gregor Mendel?

~An Austrian monk that is

considered to be the

“father of genetics”

~Used pea plants for research

What did he find?

Purple x purple = purple offspring

White x white = white offspring

He crossed one white and one purple from these offspring.

What do you think he found?

Purple crossed with white = all purple?????

How is this possible???

He then let the purple offspring self-pollinate.

• 3 purple flowers : 1 white flower

He tried it with other traits…

What ratio did he repeatedly see???

How did Mendel explain his results?

• Every trait is controlled by 2 inherited GENES.

ALLELE: form of a specific gene, represented by a letter

If 2 alleles differ, one is dominant over the other

(this trait will be expressed)

The other one is recessive

(it will be masked by the dominant allele)

What would have to happen in order to see a recessive trait expressed???

Genetic Crosses• Capital letters = dominant alleles

• Lowercase letters = recessive alleles

• Use the SAME letter to represent both alleles!

• Example:

Flower color: purple = P freckles: F

white = p no freckles= f

Seed color: green = G

yellow = g

• Genotype: actual alleles from parents (letters)

Phenotype: physical appearance of organism (no letters: what does it look like?

what traits does it have?)

Both alleles are same = homozygous

Both alleles are different = heterozygous

Try this: Let’s use freckles.

Having freckles is dominant= F No freckles = fHow would you show an individuals genotype if they were:

Homozygous dominant for freckles?

Homozygous recessive for freckles?

Heterozygous for freckles?

• Brown eyes = B• Blue eyes = b

Write the genotype for an individual that is:

Blue eyed:________________________

Homozygous dominant for eye color:____________

Heterozygous for eye color:___________________

Homozygous recessive for eye color:________

What genotypes can a person have if they have brown eyes?_____________

♦ Both parents have 2 ALLELES for each GENE.

♦ Alleles are represented on the AXES.

♦ Meiosis:chromosomes & alleles are SEPARATED.

♦ Each GAMETE gets one of the ALLELES.

♦ Each parent contributes only 1 allele to offspring.

♦ Only 1 allele from each parent is in each box.

♦ Each box ends up with 2 total alleles, one from the MOTHER and one from the FATHER.

♦ There is a 50% chance of receiving either allele from either parent.

Monohybrid Cross• Cross involving one contrasting trait

Use a Punnett square to predict probabilities…

Cross a heterozygous purple flower with a

homozygous recessive white flower.

__________X_________

Genotypic ratio:

____________:_____________:____________

Phenotypic ratio:

______________________:_______________________

Genotypic ratio:

____________:_____________:____________

Phenotypic ratio:

______________________:_______________________

Genotypic ratio:

____________:_____________:____________

Phenotypic ratio:

______________________:_______________________

Genotypic ratio:

____________:_____________:____________

Phenotypic ratio:

______________________:_______________________

Incomplete Dominance

• Display a trait that is in between the 2 parents traits

• Snapdragon flowers:

• Red = RR

• White =rr

• Pink = Rr

Try it:• Red flowers (R ) are incompletely dominant

over white flowers (r). Cross a:

Pink flowered plant with a white flowered plant

Codominance

• 2 dominant alleles are expressed at same time

• Horse color:

• Red = RR

• White = WW

• Red and white = RW (roan)

Try It:

• Cross a red horse with a white horse: