Bio NOTES: Traits and Probability

1. Bio NOTES: Traits and Probability 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 gives the ratio of possible genotypes and phenotypes.

2. homozygous dominant x homozygous recessive = all heterozygous Monohybrid crosses examine the inheritance of only one specific trait

3. heterozygous x heterozygous = 1 homozygous dominant 2 heterozygous 1 homozygous recessive homozygous recessive x heterozygous = 2 heterozygous 2 homozygous recessive genotype ratio – 1:2:1 phenotype ratio – 3:1 genotype ratio – 1:1 phenotype ratio – 1:1

4. Example:Two pea plants cross, one homozygous dominant yellow seeds and the other homozygous recessive green seeds. What are the genotypes and phenotypes of the F1 generation? Key: Y=_______ and y= _______ P, Parents: ____ X ____ Yellow Green yy YY Y Y Results: F1 Genotypes: F1 Phenotypes: Yy Yy y 100% Yy Yy Yy y 100% Yellow Yy Yy Ex. Continued: What offspring would result from an F1 cross? F1, Parents: ____ X ____ Y y Results: F2 Genotypes: F2 Phenotypes: YY Yy Y 25% YY, 50% Yy, 25%yy y Yy yy 75% Yellow, 25% green An organisms phenotype is based on its genotype & its environment!! • A plant may have the GENES to grow tall, but not the sunlight.

5. Monohybrid Crosses can be used in REVERSE to find the genotypes of an “unknown” parent. Ex): A homozygous recessive bald cat had 4 kittens, two were bald like their mother and the other two were hairy. What was the genotype of the father cat? Hairy Bald Key: H=_______ and h= _______ Mom Cat Geno: ____ Dad Geno: HH or Hh? _________________ hh Father is Hh!! h h h h F1:  2 Bald 2 Hairy H H Hh Hh Hh Hh H h Hh Hh hh hh Test Cross: A process that uses an organisms phenotype to determine its genotype. The unknown is crossed with an organism that is homozygous recessive (because it cannot hide any traits). T T T t Ex): In pea plants, tall plants are dominant to short. Tall plants could be TT or Tt. Determine the genotype of an tall pea plant. t Tall Tall t Tall Short t Tall Tall t Tall Short TT Tt _____ X t t ____X t t ?? X t t

6. Dihybrid Cross 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 independentassortment. The law of independent assortment states that allele pairs separate independently of each other during meiosis.

7. Probability = number of ways a specific event can occur number of total possible outcomes 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 applies to random events such as meiosis and fertilization.

8. Questions and Practice Problems: Phenotype • An organisms physical characteristics are called its: _________ • An organisms genetic make up is called its: ____________ • Alternative forms of a gene are called: ___________ • Examples of allele alternatives are: Tall and _______ pea plants Straight Hair & __________ • Indicate: Homozygous Dominant (HD), Homozygous Recessive (HR) or Heterozygous (HE) AA=____ Rr=____ bb=____ E1E2=___ Xx=____ • If green hair is dominant to white hair indicate the phenotypes below. GG = _____________ Gg=____________ gg=____________ • Cross a homozygous dominant three-eyed alien with a homozygous recessive one-eyed alien. Determine the F1 genotypes & phenotypes. Genotype Alleles Short Curly Hair HE HR HE HE HD Green Hair Green Hair White Hair Key: __=__________ __= __________ P, Parents: ____ X ____ T T Results: F1 Genotypes: F1 Phenotypes: T Three eyes t Tt Tt 100% Tt t One eye t Tt Tt 100% Three eyes TT tt