Segregation diagrams are useful because they allow geneticist to make predictions.

Example: What is the chance that this brown-eyed couple will have a blue-eyed baby? Bb BB B b B B BB BB Bb Bb 0% chance

The ability to make predictions becomes important when dealing with genetic disorders/diseases.

The man and the woman below have achondroplasia (dwarfism) The man and the woman below have achondroplasia (dwarfism). If this couple has children, will the children also have achondroplasia?

To answer this question, we have to figure out if the disorder is dominant or recessive.

The FGFR3 gene codes for cartilage protein mutation ONE COPY ACHONDROPLASIA IS DOMINANT From Dad From Mom

Achondroplasia = A; regular height = a fatal Aa: dwarf aa: regular FGFR3 FGFR3 mutation mutation From Dad From Mom A a a A

If these two people have a baby, how will the baby turn out? Aa Aa AA: 25% Aa: 50% A a A a aa: 25% AA Aa Aa aa

This explains the family below: AA: 25% Aa: 50% aa: 25%

However, we cannot say with absolute certainty what the outcome of this cross will be. We can only determine the probability.

Probability 50% chance of heads 50% chance of tails The chance that an event will occur; expressed as a percentage. C P

Probability Practice Female: 6/8 = 3/4 = 75% Solid: 4/8 = 1/2 = 50% Black/solid: 2/8 = 1/4 = 25% Black nose: 8/8 = 100% male male female female female female female female

Segregation diagrams are not the only way to determine probability Segregation diagrams are not the only way to determine probability. You can also use a Punnett square.

Punnett Square Diagram that shows the probable outcome of a genetic cross; used by geneticists to make predictions. P P

gametes Offspring

Offspring (two alleles) Curly = H; straight = h HH Gametes (one allele) hh H H Probabilities: HH: 0% h Hh Hh Hh: 100% hh: 0% Curly: 100% h Hh Hh Straight: 0% Offspring (two alleles)

Make a blank Punnett square in your notes Make a blank Punnett square in your notes. Include the probabilities section: Probabilities: HH: Hh: hh: Curly: Straight:

Use the Punnett square to solve the genetics problem below. Hh Probabilities: hh H h HH: 0% h Hh hh Hh: 50% hh: 50% Curly: 50% h Hh hh Straight: 50%

#48 in SG: Mendel’s P generation cross. Probabilities: t t TT: 0% T Tt Tt Tt: 100% tt: 0% Tall: 100% T Tt Tt Short: 0% FI generation

In genetics, an organism can be described by its genotype or its phenotype. Tall Tall Short TT Tt tt

Genotype Tall Tall Short TT Tt tt An organism’s allele combination. Geno = gene. A G

Phenotype Tall Tall Short TT Tt tt The way the organism looks. Pheno = physical. L P

What is the genotype of person A? B C Brown Brown Blue BB Bb

What is the phenotype of person B? C Brown Brown Blue BB Bb

What is the phenotype of person C? B C Brown Brown Blue BB Bb

A B C What is the only possible genotype for a blue-eye phenotype? Brown Brown Blue BB Bb bb

A B C Which two people have the same phenotype? Brown Brown Blue BB Bb

A B C Do they also have the same genotype? No! Brown Brown Blue BB Bb

Two organisms can have the same phenotype, but different genotypes. Tall Tall Short TT Tt tt

Brown (B) is dominant; black (b) is recessive What is the phenotype of dog #2? Black 1 4 2 3 5 6 Brown (B) is dominant; black (b) is recessive

Brown (B) is dominant; black (b) is recessive What is the genotype of dog #2? bb 1 4 2 3 5 6 Brown (B) is dominant; black (b) is recessive

Brown (B) is dominant; black (b) is recessive What is the phenotype of dog #6? Brown 1 4 2 3 5 6 Brown (B) is dominant; black (b) is recessive

Brown (B) is dominant; black (b) is recessive What are two possible genotypes for dog #6? BB or Bb 1 4 2 3 5 6 Brown (B) is dominant; black (b) is recessive

A genotype may either be homozygous or heterozygous TT Tt tt

Homozygous TT Tt tt Genotype with the same alleles. Homo = same. S A S

Heterozygous TT Tt tt Genotype with different alleles. Hetero = different. D A D

A B C Which people have a homozygous genotype? Brown Brown Blue BB Bb

A B C What word describes person B’s genotype? Heterozygous Brown Blue BB Bb bb

Which person is homozygous dominant? B C Brown Brown Blue BB Bb bb

Which person is homozygous recessive? A B C Brown Brown Blue BB Bb bb

To have a recessive phenotype, the genotype must be homozygous. Blue Short tt bb

Genetics Problem #3: Black Parents, White Baby Dark skin (D) is dominant; light skin (d) is recessive

Create a Punnett square showing how this type of inheritance is possible. Probabilities: D d DD: 25% Dd: 50% D DD Dd dd: 25% Dark: 75% d Dd dd Light: 25%

45. If this couple decides to have another baby, what is the probability that the baby will have light skin? 46. If this couple decides to have another baby, what is the probability that the baby will have dark skin? 47. If this couple decides to have another baby, what is the probability that the baby will be a carrier? 25% 75% 50%