6.5 Traits and Probability EOC Practice 1. An experiment studies the effects of an experimental drug on the number of offspring a mother mouse has. 10 female mice are given the drug and then impregnated. The number of mice in their litters is compared to the litters of mice that did not take the drug. Find the: 1) Independent Variable 2) Dependent Variable 3) 1 constant 4) Control Graph the data Group A(Drug) Group B

6.5 Traits and Probability Targets 1. I can describe monohybrid and dihybrid crosses. 2. I can explain how heredity can be illustrated mathematically.

6.5 Traits and Probability KEY CONCEPT The inheritance of traits follows the rules of probability.

6.5 Traits and Probability Punnett squares illustrate genetic crosses. The Punnett square is a grid system for predicting all possible genotypes resulting from a cross. –The axes represent the possible gametes of each parent. –The boxes show the possible genotypes of the offspring. The Punnett square yields the ratio of possible genotypes and phenotypes.

6.5 Traits and Probability A monohybrid cross involves one trait. Monohybrid crosses examine the inheritance of only one specific trait. –homozygous dominant-homozygous recessive: all heterozygous, all dominant

6.5 Traits and Probability –heterozygous-heterozygous cross—1:2:1 homozygous dominant: heterozygous:homozygous recessive; 3:1 dominant:recessive

6.5 Traits and Probability heterozygous-homozygous recessive—1:1 heterozygous:homozygous recessive; 1:1 dominant:recessive A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype.

6.5 Traits and Probability Heredity patterns can be calculated with probability. Probability is the likelihood that something will happen. Probability predicts an average number of occurrences, not an exact number of occurrences. Probability = number of ways a specific event can occur number of total possible outcomes Probability applies to random events such as meiosis and fertilization.

6.5 Traits and Probability Probability- use of fraction or ratios to predict the likelihood of an event’s occurrence. In biology it is used to predict phenotype & genotype of offspring in breeding experiments; letter “P” designates it. Flipping 1 coin has 2 possible outcomes, you would expect each to come up about half the time so the probability, P = ½ Flipping 2 coins at same time has 4 possible outcomes. The probability of one of those outcomes is = to multiplying the individual’s separate probabilities. In other words 1 st coin probability of heads P 1 = ½. Second coin probability of heads P 2 = ½. Probability of both coins being heads, P 1 x P 2 = ½ x ½ = ¼.

6.5 Traits and Probability Instead of quarters now we are talking about genetic traits. Gametes from each parent, in this case the male alleles are both dominant while the female alleles are both recessive.

6.5 Traits and Probability A dihybrid cross involves two traits. Mendel’s dihybrid crosses with heterozygous plants yielded a 9:3:3:1 phenotypic ratio. Mendel’s dihybrid crosses led to his second law, the law of independent assortment. The law of independent assortment states that allele pairs separate independently of each other during meiosis.

6.5 Traits and Probability Self- fertilized cross w/ parents heterozygous for 2 genes. Genotype = GgWw for both parents

6.5 Traits and Probability In this diagram the parent is heterozygous for 2 genes; seed shape & seed color. So each parent produces gametes w/ 4 possible allele combinations. So each combination has P = ¼. Gametes combine during fertilization, so P x P = ¼ x ¼ = 1/16. This would be the genotype probability. The phenotype ratio would be 9:3:3:1. WHY?

6.5 Traits and Probability Using a Punnett Square Punnett Square- a grid for organizing genetic information. It shows probabilities not results. 1.Determine alleles in gametes of parents 2.Place alleles of one parent’s gametes along top of grid. Place those of other parent along the left side 3.Combine the alleles inside the boxes of the Punnett square. 4.Determine genotype & phenotype of offspring inside the boxes. Monohybrid Crosses- studying only one trait at a time. Punnett square has 4 boxes. Dihybrid Crosses- studying two traits at a time. Punnett square has 16 boxes. Test Cross- breeding an individual w/ unknown genotype w/ homozygous recessive individual. The resulting offspring will reveal what the genotype of the unknown was.