Review of Terminology

Genotype HereditaryInformationHereditary Information internally coded, inheritable informationinternally coded, inheritable information Genotype can be determined by direct observation of DNAGenotype can be determined by direct observation of DNA

Phenotype A phenotype describes any observed quality of an organism, such as its shape, development, or behaviorA phenotype describes any observed quality of an organism, such as its shape, development, or behavior organismdevelopment behavior organismdevelopment behavior outward, physical appearanceoutward, physical appearance Traits are small parts of the phenotype of an organism, such as the red color seen in the flower petalsTraits are small parts of the phenotype of an organism, such as the red color seen in the flower petals genotype +environment → phenotype genotype + environment → phenotype

Heterozygous Having two different alleles for a single trait.Having two different alleles for a single trait. RrRr

Homozygous Having identical alleles for a single trait.Having identical alleles for a single trait. RR or rrRR or rr

Constructing a Punnett Square

What is a PUNNETT SQUARE? A tool to predict the probability of certain traits in offspring that shows the different ways alleles can combine A way to show phenotype & genotype A chart that shows all the possible combinations of alleles that can result when genes are crossed

What is a PUNNETT SQUARE? Letters stand for dominant and recessive alleles An UPPERCASE letter stands for a DOMINANT allele lowercase letters stand for recessive alleles

Using a PUNNETT SQUARE To set up a Punnett square, draw a large square, and then divide it into 4 equal sections (also squares). It should look something like this:

Using a PUNNETT SQUARE Now you need two parents to mate, ones with a known genotype For example, a red flower (genotype Rr) and a white flower (genotype rr). Rr x rr

Using a PUNNETT SQUARE Place one of the parents on top, and one on the left. You should get a something similar to this:

Using a PUNNETT SQUARE Finally, take each letter in each column and combine it with each letter from each row in the corresponding square. You should now have a picture close to this:

Using a PUNNETT SQUARE The two-letter combinations are the possible genotypes of offspring They are: Rr, Rr, rr, and rr genotypes

Probability Total possible combinations (number of squares in the table) becomes the denominator

Probability Count the number squares for each combination Rr = 2 (numerator) rr = 2 (numerator)

Probability Put the pieces together Probability (chance) that a flower will have: –red phenotype, Rr = 2/4 or 50% –white phenotype, rr = 2/4 or 50%

Probability Flip a coin ONCE Number of total possible outcomes (this becomes the denominator) Count the number of times you get a head or tail (numerator) Probability = numerator/denominator

Probability Flip a coin ONCE Number of total possible outcomes (this becomes the denominator) = 2 (head or tail) Count the number of times you get a head or tail (numerator) –Head = 1 –Tail = 0 Probability of getting Head = numerator/denominator = ½ = 0.5

Probability Flip a coin TWICE Number of total possible outcomes (this becomes the denominator) = 4 (HH, HT, TH, TT) Count the number of times you get each combination (numerator) : –HH = 1 –TT = 1 –HT or TH = 2 Probability of both HEADS = numerator/denominator = 1/4 = 0.25 Probability of both TAILS = numerator/denominator = 1/4 = 0.25 Probability of HEAD AND TAIL = numerator/denominator = 2/4 = 0.5 H H T T HH TH HT TT