1 4 Chapter 14~ Mendel & The Gene Idea

2 Mendel’s Discoveries 4 Blending- Hereditary Material –Both parents contribute genetic material 4 Inheritable factors –Genes - passed from generation to generation 2

3 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, first offspring)

4 Leading to the Law of Segregation 4 Alternative versions of genes (alleles) account for variations in inherited characteristics 4 For each character, an organism inherits 2 alleles, one from each parent 4 If the two alleles differ, then one, the dominant allele, is fully expressed in the organism’s appearance; the other, the recessive allele, has no noticeable effect on the organism’s appearance 4 The alleles for each character segregate (separate) during gamete production (meiosis). 4 Mendel’s Law of Segregation

5 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 an unknown dominate phenotype with a homozygous recessive phenotype

6 Monohybrid Cross 4 Cross between 2 parents that are both heterozygous for 1 trait 6

7 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

8 Non-single gene genetics, I 4 Incomplete dominance: appearance between the phenotypes of the 2 parents. Ex: snapdragons 4 Codominance: two alleles affect the phenotype in separate, distinguishable ways. Ex: Tay-Sachs disease Ex: Roan cattle

9 Non-single gene genetics, II 4 Multiple alleles: more than 2 possible alleles for a gene. –Ex: human blood types –(A and B alleles are both dominant = codominant / O allele is recessive) 9

10 Non-single gene genetics, III 4 Pleiotropy: genes with multiple phenotypic effect. –Ex: sickle-cell anemia causes problems with blood which causes other problems

11 Non-single gene genetics, IV 4 Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus. – Ex: mice coat C leads to deposition of color while B or b leads to the color. BBcc would be white even though the genes code for black 11

12 Non-single gene genetics, V 4 Polygenic Inheritance: –an additive effect of two or more genes on a single phenotypic character –Ex: human skin pigmentation and height –- i.e. the more dominant the alleles the more color 12

13 Human disorders 4 The family pedigree Male = Square Female = Circle If phenotypic trait is present it is shown by shading the symbol Dominant = widow’s peakDominant = Free earlobe

14 Human disorders 4 Recessive disorders: –Cystic fibrosis –Tay-Sachs –Sickle-cell - blood disorder –Hemophelia- blood disorder 4 Dominant disorders: –Huntington’s –Acondroplasia (dwarfism) 14 4 How do they stay in population? 4 Carriers- individuals not exhibiting phenotype, but can pass the gene to offspring)

15 Recessive Disorders 4 Cystic fibrosis 15

16 Recessive Disorders 16

17 Test is available - will determine if individual has Huntington’s No cure - Do you find out? How does it stay? Affects show up after reproductive years.

18 TESTING FOR DISORDERS 4 Testing in womb: –amniocentesis –chorionic villus sampling (CVS) 18