Genetic Crosses & Punnett Squares

Important Terms Dominant Trait : the trait that shows when two different alleles for the trait are inherited ex- tongue rolling Dominant Trait : the trait that shows when two different alleles for the trait are inherited ex- tongue rolling Recessive Trait : the trait that seems to disappear when two different alleles for the trait are inherited ex- non-rolling Recessive Trait : the trait that seems to disappear when two different alleles for the trait are inherited ex- non-rolling

Important Terms Phenotype : an organism’s physical appearance ex- tall, short, white flowers, green seeds Phenotype : an organism’s physical appearance ex- tall, short, white flowers, green seeds Genotype : an organism’s gene code ex- Tt, TT, tt, WW, Ww, yy Genotype : an organism’s gene code ex- Tt, TT, tt, WW, Ww, yy

Important Terms Heterozygous : having dissimilar pairs of alleles for any hereditary characteristic ex- Tt, Ss, Ll, Mm (hybrid) Heterozygous : having dissimilar pairs of alleles for any hereditary characteristic ex- Tt, Ss, Ll, Mm (hybrid) Homozygous : having identical pairs of alleles for any given pair of heredity characteristic ex- tt, SS, LL, mm (purebred) Homozygous : having identical pairs of alleles for any given pair of heredity characteristic ex- tt, SS, LL, mm (purebred)

Punnett Squares Used to illustrates how the parents’ alleles might combine in offspring. Used to illustrates how the parents’ alleles might combine in offspring. Used to predict the probability or % chance of an offspring's genotype and phenotype Used to predict the probability or % chance of an offspring's genotype and phenotype Reginald Punnet developed the Punnett Square in 1910

Punnett Squares The top of the Punnett Square shows one of the parent’s alleles, the side of the Punnett square shows the other parent’s alleles for the trait The top of the Punnett Square shows one of the parent’s alleles, the side of the Punnett square shows the other parent’s alleles for the trait t t T TT T

Mendel’s Laws of Inheritance Law of Dominance: In heterozygous genotypes, dominant alleles hide recessive alleles when both are inherited by an organism.

Mendel’s Laws of Inheritance The Law of Segregation: Each organism has 2 alleles for a gene and only one allele from each gene pair will be passed on to the offspring.

Homozygous/Heterozygous Cross a homozygous dominant tall plant with a homozygous recessive short plant. Cross a homozygous dominant tall plant with a homozygous recessive short plant. What letters would you use to represent this cross? Dominant trait = tall Dominant trait = tall Recessive trait = short Recessive trait = short T = tall T = tall t = short t = short Hmzg / Htzg

What is the genotype of a homozygous dominant tall plant? What is the genotype of a homozygous dominant tall plant? Genotype Genotype % TT % Tt % tt  TT TT x tt TT x tt What is the genotype of a homozygous recessive short plant? What is the genotype of a homozygous recessive short plant?  tt t t T TT T Phenotype Phenotype % tall % short Tt

2. Cross a heterozygous brown haired rabbit with a homozygous recessive white haired rabbit. o What letters would you use to represent this cross? Dominant trait = brown hair Dominant trait = brown hair Recessive trait = white hair Recessive trait = white hair B = brown B = brown b = white b = white

What is the genotype of a heterozygous brown haired rabbit? What is the genotype of a heterozygous brown haired rabbit? Genotype Genotype % BB % Bb % bb  Bb Bb x bb Bb x bb What is the genotype of a homozygous recessive white haired rabbit? What is the genotype of a homozygous recessive white haired rabbit?  bb b b BbBb Phenotype Phenotype % brown % white bb Bb 0 50

3.. Cross a homozygous dominant long haired guinea pig with a heterozygous long haired guinea pig. o What letters would you use to represent this cross? Dominant trait = long hair Dominant trait = long hair Recessive trait = short hair Recessive trait = short hair L = long L = long l = short l = short

What is the genotype of a homozygous dominant long haired guinea pig? What is the genotype of a homozygous dominant long haired guinea pig? Genotype Genotype % LL % Ll % ll  LL LL x Ll LL x Ll What is the genotype of a heterozygous long haired guinea pig? What is the genotype of a heterozygous long haired guinea pig?  Ll L l LL LL Phenotype Phenotype % long % short LLLl LLLl

4. Cross a heterozygous wrinkly elephant with another heterozygous wrinkly elephant.  What letters would you use to represent this cross? Dominant trait = wrinkly skin Dominant trait = wrinkly skin Recessive trait = smooth skin Recessive trait = smooth skin W = wrinkly W = wrinkly w = smooth w = smooth

What is the genotype of a heterozygous wrinkly-skinned elephant? What is the genotype of a heterozygous wrinkly-skinned elephant? Genotype Genotype % WW % Ww % ww  Ww Ww x Ww Ww x Ww What is the genotype of a heterozygous wrinkly-skinned elephant? What is the genotype of a heterozygous wrinkly-skinned elephant?  Ww W w WwWw Phenotype Phenotype % wrinkly % smooth Wwww WWWw

Phenotype Phenotype % round % wrinkled 5.A plant that is homozygous dominant for round seeds is crossed with a heterozygous plant. What is the probability that the offspring will have wrinkled seeds? RR x Rr RR x Rr R r RRRR RRRr RRRr R = round Genotype Genotype % RR % Rr % rr r = wrinkled