Genetics (Recap) Let’s look at this again

What is a Gene? 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

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

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: TT x Tt TT T t TTTT TtTt Genotype Ratio: 2TT and 2Tt Phenotype Ratio: 4 Tall Plants

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. CC x cc CC c c Cc Cc CcCc Genotype Ratio: 4Cc Phenotype Ratio: 4 yellow cocoons

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 Ff x ff Ff f f Ff ff Ffff Genotype Ratio: 2 Ff and 2 ff Phenotype Ratio: 2 short haired 2 long haired

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: FGFgfGfg FG Fg fGfg

FFGGFFGgFfGGFfGg FFGgFFggFfGgFfgg FfGGFfGgffGGffGg FfGgFfggffGgffgg FGFgfGfg FG Fg fG fg Genotype Ratio: FFGG l, FFGg ll,FfGG,llFfGg 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 RR W W RW RW RWRW Genotype Ratio: 4 RW Phenotype Ratio: 4 Pink

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

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

Cross a type AB with a type O Homozygous type A: I A I B Type O:ii Genotype Ratio: 2 I A i; 2 I B i Phenotype Ratio: 2 Type A 2 Type B Probabilities: Type A:2 out of 4 Type B:2 out of 4 IBiIBiIAiIAi IBiIBiIAiIAi I A I B X ii IAIA IBIB i i