Lecture # 6Date _________ 4 Chapter 14~ Mendel & The Gene Idea

Mendelian genetics 4 Character (heritable feature, i.e., fur color) 4 Trait (variant for a character, i.e., brown) 4 True-bred (all offspring of same variety) 4 Hybridization (crossing of 2 different true- breds) 4 P generation (parents) 4 F 1 generation (first filial generation)

Mendel’s Four Laws 4 First- alternative versions of genes account for variations in inherited characters (alleles) 4 Second-for each character, an organisms inherits two alleles one form each parent 4 Third- dominant (shows) and recessive alleles (not shown) 4 Fourth- law of segregation (alleles separate)

Genetic vocabulary……. 4 Punnett square: predicts the results of a genetic cross between individuals of known genotype 4 Homozygous: pair of identical alleles for a character 4 Heterozygous: two different alleles for a gene 4 Phenotype: an organism’s traits 4 Genotype: an organism’s genetic makeup 4 Testcross: breeding of a recessive homozygote X dominate phenotype (but unknown genotype)

The Law of Independent Assortment 4 Law of Segregation involves 1 character. What about 2 (or more) characters? 4 Monohybrid cross vs. dihybrid cross 4 The two pairs of alleles segregate independently of each other. 4 Mendel’s Law of Independent Assortment

Non-single gene genetics, I 4 Incomplete dominance: appearance between the phenotypes of the 2 parents.(intermediate) Ex: snapdragons 4 Codominance: two alleles affect the phenotype in separate, distinguishable ways. (both expressed) Ex: Tay-Sachs disease 4 Multiple alleles: more than 2 possible alleles for a gene. Ex: human blood types

Non-single gene genetics, II 4 Pleiotropy: genes with multiple phenotypic effect. Ex: sickle-cell anemia 4 Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus. Ex: mice coat color 4 Polygenic Inheritance: an additive effect of two or more genes on a single phenotypic character Ex: human skin pigmentation and height

Human disorders 4 The family pedigree 4 Recessive disorders: Cystic fibrosis Tay-Sachs Sickle-cell 4 Dominant disorders: Huntington’s 4 Testing: amniocentesis chorionic villus sampling (CVS)