Genetics

Mendel studied pea plants - 7 pairs of traits: 1. Height –Tall, short 2. Seed shape – Round, wrinkled 3. Seed color – Yellow, green 4. Flower position – Axial, terminal 5. Pod color - Green, yellow 6. Flower color – Purple, white 7. Pod shape – Inflated, constricted

Mendel’s Laws of Genetics Traits are controlled by factors (genes) that occur in pairs

2. Principle of dominance and recessiveness – the dominant gene will be expressed , it will cover the recessive gene T = tall (dominant) t = short (recessive) TT = tall (pure dominant) tt = short (pure recessive) Tt = tall (hybrid)

3. Law of segregation – genes are separated during the formation of gametes (homologous chromosomes are separated during meiosis, gametes are haploid) 4. Law of independent assortment – many traits are inherited independent of other traits (they are on different chromosomes)

Vocabulary: P1 = parent generation f1 = first generation of offspring f2 = second generation of offspring Genotype= actual genes TT = homozygous dominant tt = homozygous recessive Tt = hybrid, heterozygous

Phenotype = appearance (tall, short, etc Phenotype = appearance (tall, short, etc.) Allele = genes for the same trait, T and t are alleles for the trait of height Punnett Square – chart used to predict the traits of offspring

Punnett square problems have 4 parts: P1 statement Punnett square Genotype Phenotype

Ex: P1 = Aa x Aa f1 genotype f1 phenotype 1 dominant 3 axial 2 hybrid 1 terminal 1 recessive Dad is written first, his alleles go on the side of the Punnett square Mom is written next, her alleles go on the top of the Punnett square

Two factor crosses - follow the same rules but you compare 2 traits at the same time Ex: P1 = RrTt x RrTt Dad is written first and on the side. Mom is written next and on the top. Use foil to determine the alleles: (first, outer, inner, last) RT, Rt, rT, rt

Ex: P1 = RrTt x RrTt Follow dad’s pattern. Whichever letter is first for dad is first for the entire problem. The first genotype word describes the first pair of alleles, the next word describes the second pair.

Ex: P1 = RrTt x RrTt F1 genotype 1 dominant, dominant 2 dominant, hybrid 2 hybrid, dominant 4 hybrid, hybrid 1 dominant, recessive 2 hybrid, recessive 1 recessive, dominant 2 recessive, hybrid 1 recessive, recessive F1 phenotype 9 Round, Tall 3 Round, short 3 wrinkled, Tall 1 wrinkled, short

P1 = Aa x Aa P1 = RrTt x RrTt Monohybrid cross: Both parents are hybrid for one trait Genotype ratio = 1:2:1 Phenotype ratio = 3:1 Dihybrid cross: Both parents are hybrid for both traits Phenotype ratio = 9:3:3:1