Genetics (Recap)

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

2. 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?

3. 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?

4. 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?

5. 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 What Are Some Examples? c

6. 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 What Are Some Examples? f

7. 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

8. FG Fg fG fg FG Fg fG fg Genotype Ratio: FFGgll, FfGG ,ll FfGgllll, FFGG l, FFggl , Ffggll, ffGG l, ffGgll, ffgg l,

9. 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

10. 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 What is Incomplete Dominance? W

11. 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 What is Incomplete Dominance? W

12. IAi IAi IAi 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 IAIAX ii IA IA i i What is Codominance?

13. IAi IBi IAi IBi 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 IAIBX ii IA IB i i