Genetics: Punnet Squares

4/7/2015
A specific region of DNA that codes for a particular protein Punnett Squares

Dominant Alleles - use a capital letter to represent them
Recessive Alleles - use a lower case letter to represent them Example: Brown is dominant = B Blue is recessive = b ***Dominant trait is expressed unless both alleles are recessive***
Homozygous: purebred - Two of the same alleles for one trait - Will have two of same letters: BB or bb
Heterozygous: hybrid Alleles are different versions of the same gene - Ex. Purple flowers and white flowers
Genotype - genetic makeup for a specific set of genes - represented by 2 letters: BB, Bb, bb
Phenotype - physical characteristics or traits - what it looks like: Brown or blue eyes Example: Bb (genotype) carries one allele for brown and one for blue eyes, however they will have brown eyes (phenotype)
BB
Brown eyes
Bb
Brown eyes
bb
Blue eyes - Two different alleles for one trait - Will have two different letters: Bb 1 4/7/2015 A) BB A) Bb B) Brown hair B) Bb C) bb
A) BB A) BB
B) Bb B) Bb
C) bb C) bb
What is the probability of rolling a 6 on a die?
The likelihood that an event will occur
Probability = # of one kind of possible outcome = % total # of all possible outcomes When the word or is used you add the odds 1/6 + 1/6 = 2/6 When the word and is used you multiply the odds 1/6 x 1/6 = 1/36 - 1/6
What is the probability of rolling a 6 or a 5 on a dice cube? - 1/6 + 1/6 = 2/6
What is the probability of rolling a 6 and a 5? - 1/6 x 1/6 = 1/36 2 4/7/2015
Predicts all possible genotypes resulting from a cross
Mendel’s Generations: P = parents F1 = offspring (1st generation) F2 = offspring of F1 (2nd generation) 1. Identify the dominant and recessive traits 2. Identify the phenotype of each parent 3. Identify the genotype of each parent 4. Fill in the Punnett Square 5. Write the phenotype ratio 6. Write the genotype ratio Step 1: identify the dominant and recessive traits Purple is dominant (P) White is recessive (p) Step 2: identify the phenotype of each parent Purple flower X white flower Step 3: identify the genotype of each parent Pp X pp p Pp Pp p pp pp Step 5: Write the genotype ratio 50% Pp Step 6: Write the phenotype ratio 50% purple Step 4: fill in Punnett Square p p P Pp Pp p pp pp - Organisms inherit 2 copies of each gene, one from each parent - During gamete formation genes separate and only one version makes it into the gamete (egg or sperm) p P Step 3: identify the genotype of each parent Pp X pp 50% pp 50% white 3 4/7/2015 Law of Independent Assortment Law of Dominance - allele pairs separate independently of each other during meiosis (gamete formation) - More likely to be separated: * if on different chromosomes * the further apart on a chromosome - Traits have two alleles (one from the female and one from the male) - Some alleles are dominant (A) and some are recessive (a) Mendel’s Experiments
Dihybrid Crosses Mendel’s Results
Conducted experiments that examined the inheritance of 2 different traits: Ex: flower color and pea shape Wondered if traits would be passed on together or separately Using purebred plants, he conducted many experiments using a variety of trait combinations Ex: flower color and pea shape pea shape and pod color Cross 2 purebred plants
The F1 generation of crossing 2 purebred plants would result in heterozygous plants: The plants all expressed the dominant gene but carried the gene for the recessive trait (how did he know that?) When Mendel crossed the F1 generation which was heterozygous for both traits, he discovered that the F2 generation expressed all combinations of the 2 traits 4 4/7/2015 Mendel’s Conclusion
Law of Independent Assortment Dihybrid Crosses are used to show how alleles independently sort
Process (steps) are just like monohybrid crosses (single trait) with one extra step - Allele pairs, one from mom and one from dad, separate independently of each other during meiosis. Process for doing dihybrid problems Step 1: Identify dominant and recessive traits Step 2: Identify the phenotypes of each parent Step 3: Identify the genotypes of each parent Step 4: Determine possible allele combinations using FOIL method Step 5: Complete Punnett Square Step 6: Write out phenotypes and ratios Step 7: Write out genotypes and ratios Step 4: Use F.O.I.L. to identify all possible allele combinations: RY, Ry, rY, ry RrYy Use combinations to fill in Punnett Square: RY, Ry, rY, ry
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