Chapter 9 Genetics

Chapter 9 Genetics I) What is genetics A) Definition: study of heredity B) Inherited: traits passed o from parents to their young. C) Trait: a feature that a livig thing can pass on to its young. D) Heredity: the passing of traits from parents to their young. II)Mendel’s early experiments A) Gregor Mendel – 1822-1884 – monk – laid down the foundation for the modern study of genetics B) Used pea plants; they have a number of contrasting traits that can be easily distinguished. C) Developed a number of types of lines of plants that were pure for each of the 7 pairs of traits. 1) Pure line: a group of living things that produce young having only one form of a … D) Parental generation (P1): E) Smooth + wrinkled = smooth. F) First filial generation (F1): offspring form a paarental cross. G) Hybrid: offspring of two parents that differ in one or more inherited traits. H) Monohybrid cross: cross that involves one pair of contrasting traits (cross of F1 hybrids) III)Second Filial Generation A) Mendel used letters to represent the paired genes controlling inherited traits. B) 2 genes in a pair may be alike = Homozygous. 1) YY or yy

C) 2 genes in a pair which are different = heterozygous. 1) Bb or Yy D) Hybrids of F1 generation, one gene determined the expression of a trait while the contrasting trait did not show up. 1) Dominance: in a hybrid organism (result of F1 cross) a gene that prevents the expression of another gene. 2) Resessive: the gene that is NOT expressed. E) Principle of Dominance: in a hybrid organism, one gene determines the expression of a particular trait and prevents the expression of the contrasting form of that trait. 1) Y = yellow 2) y = green F) Principle of Segregation: reason why traits disappeared in F1 generation but reappeared in F2 generatioin. 1) In any cross, each parent gave only one gene to each gamete. 2) Genes were segregated G) Genotype: the genetic makeup of an organism. 1) RR = round – homozygous 2) Rr = round – heterozygous 3) rr = wrinkled - homozygous H) Phenotype: outward appearance of an organism 1) Phenotype for genotype RR or Rr is round (dominant). I) Allele: name for a chromosome in a pair that determines a trait’s location. J) Test Cross: a cross showing a dominant trait but of uncertain genotype and a homozygous for a trait.

IV)Dihybrid Cross A) cross with TWO factors or sets of traits. V) Principle of Independent Assortment A) During gamete formation, the genes for one trait are separated and distributed to the gametes independently of the genes for other traits. VI)Incomplete Dominance A) A condition in which a hybrid has a phenotype (outward appearance) between contrasting traits of its parents. VII)Multiple Genes: more than one gene determines a trait A) EX: Blood types