Let’s look at this again Genetics (Recap) Let’s look at this again

Gene The part of a chromosome that codes for a specific trait Has two Alleles One from mom and other from dad Can either be dominant or recessive If Dominant (T)  then the trait will be expressed If Recessive (t)  then the trait can only be expressed when there’s another recessive allele What is a Gene?

How Are They Written? A gene is homozygous (pure) when both alleles are the same Ex. TT (homozygous dominant) or tt (homozygous recessive) A gene is heterozygous (hybrid) when both alleles are different Ex. Tt Genotype Name of the gene: TT, Tt or tt Phenotype What the gene looks like or does… Ex. albinism genotype is aa but the phenotype is lack of skin or hair color How Are They Written?

What is a Monohybrid Cross? A cross that involves only one gene: Example: A homozygous dominant tall plant is crossed with a heterozygous tall plant. Give the genotypic and phenotypic ratios for the offspring: T T TT x Tt Genotype Ratio: T T T T T 2TT and 2Tt Phenotype Ratio: t T t T t 4 Tall Plants What is a Monohybrid Cross?

What Are Some Examples? In silkworms a single gene determines the color of the cocoon. The yellow cocoon allele is dominant. It is indicated by “C”. The white allele is recessive, and indicated by “c”. Complete the following Punnett Square assuming a homozygous dominant male fertilizes a homozygous recessive female. C C CC x cc Genotype Ratio: 4Cc c C c C c Phenotype Ratio: 4 yellow cocoons C c C c c What Are Some Examples?

The length of fur in guinea pigs is controlled by a single gene. The dominant allele “F” produces short fur. The recessive allele “f” produces long fur. Complete the following Punnett Square assuming a heterozygous male fertilizes a homozygous recessive female F f Ff x ff Genotype Ratio: 2 Ff and 2 ff f f f F f Phenotype Ratio: 2 short haired 2 long haired F f f f f What Are Some Examples?

What is a Dihybrid Cross? A Cross that involve TWO traits In race horses, black hair (F) and a trotting gait (G) are dominant traits. Recessive traits are chestnut hair (f) and a pacing gait (g). The genes for hair color and gait are on two different chromosomes. Determine the possible offspring from a cross between two heterozygous black Trotters. FfGg x FfGg Gamete Combinations: FG Fg fG fg What is a Dihybrid Cross? FG fG fg Fg

FG Fg fG fg FFGG FFGg FfGG FfGg FFgg Ffgg ffGG ffGg ffgg FG Fg fG fg Genotype Ratio: FFGG l, FFGg ll, FfGG ,ll FfGg llll, FFgg l , Ffgg ll, ffGG l, ffGg ll, ffgg l,

Remember: FF or Ff: Black Hair ff: Chestnut Hair GG or Gg: Trotting Gait gg: Pacing Gait So: Black Hair Trotters: 9 Chestnut Trotters: 3 Black Hair Pacers: 3 Chestnut Pacers: 1

What is Incomplete Dominance? When traits mix like paint Example: When Red snapdragons are crossed with white snapdragons the resulting offspring are pink. RR x WW R R Genotype Ratio: 4 RW W R W R W Phenotype Ratio: 4 Pink R W R W W What is Incomplete Dominance?

What is Incomplete Dominance? When traits mix like paint Example: Cross a pink snapdragon with another pink snapdragon. RW x RW R W Genotype Ratio: 1 RR, 2 RW, 1 WW R R W R R Phenotype Ratio: 1 Red, 2 Pink, 1 White R W W W W What is Incomplete Dominance?

What is Codominance? IAIA X ii IA IA i i IAi When both forms of a trait are displayed at the same time Example ABO blood Types Type A: IAIA, or IAi Type B: IBIB, or IBi Type AB: IAIB Type O: ii Cross a homozygous type A with a type O Genotype Ratio: 4 IAi Phenotype Ratio: 4 Type A IAIA X ii IA IA IAi i i What is Codominance?

IAIB X ii IA IB i i IBi IAi Cross a type AB with a type O Homozygous type A: IAIB Type O: ii Genotype Ratio: 2 IAi; 2 IBi Phenotype Ratio: 2 Type A 2 Type B Probabilities: Type A: 2 out of 4 Type B: 2 out of 4 IAIB X ii IA IB IBi IAi i i

Show the genotype and phenotype ratios for a cross between a homozygous tall (T), Red snapdragon (R) and a homozygous short (t), white snapdragon (W). Show the genotype and phenotype ratios for a cross between an albino (aa) type O man and a homozygous normal (AA) type AB woman. Quiz (55 pts each)