Chapter 14~ Mendel & The Gene Idea

Mendelian genetics 4 Trait –variant for a character ex: purple 4 True-breeding –all offspring same variety 4 Hybridization –Cross of two pure breeding 4 P generation = parents 4 F 1 generation = first filial generation

Leading to the Law of Segregation 4 Alleles = Different versions of genes –one from each parent 4 If the two alleles are different –the dominant allele is expressed – the recessive allele is “hidden” 4 Mendel’s Law of Segregation –The alleles for each character segregate during gamete production

Genetic vocabulary ……. 4 Punnett square: predicts the results of a genetic cross between individuals of known genotype 4 Homozygous: alleles are the same 4 Heterozygous: two alleles are different 4 Phenotype: an organism’s traits (what you SEE) 4 Genotype: an organism’s genetic makeup: TT, Tt, tt 4 Testcross: cross with a homozygous recessive x dominant phenotype (but unknown genotype)

The Law of Independent Assortment 4 Monohybrid cross vs. dihybrid cross 4 The two pairs of alleles segregate independently of each other. 4 Mendel’s Law of Independent Assortment

LE 14-8 P Generation F 1 Generation YYRR Gametes YR yr yyrr YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Sperm Eggs YR Yr yrYR yr Eggs YYRRYyRr yyrr yR yr Phenotypic ratio 3:1 F 2 Generation (predicted offspring) YYRR YYRrYyRRYyRr YYRrYYrrYyRrYyrr YyRRYyRryyRRyyRr YyRrYyrryyRryyrr Phenotypic ratio 9:3:3:1 YRYryRyr Sperm

Genes working together 4 Incomplete dominance: blending of the phenotypes of the 2 parents. –Ex: snapdragons 4 Codominance: two alleles affect the phenotype in separate ways –Ex: human blood types A & B 4 Multiple alleles: more than 2 possible alleles for a gene. –Ex: human blood types

LE Red C R Gametes P Generation CRCR CWCW White C W Pink C R C W CRCR Gametes CWCW F 1 Generation F 2 Generation Eggs CRCR CWCW CRCR CRCRCRCR CRCWCRCW CRCWCRCW CWCWCWCW CWCW Sperm

Gene Interaction 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

Pleiotropy

LE Sperm BC bCBc bc BbCcBBCcBbCCBBCC BbCC bbCCBbCc bbCc BbccBBcc BbCcBBCc BbCc bbCc Bbcc bbcc BC bC Bc bc BbCc Epistasis

Polygenic inheritance Quantitative variation usually is additive effect of two or more genes on a phenotype Skin color in humans is an example

Human disorders 4 The family pedigree: –Diagram showing family relationships: Circle - female Square - Male 4 Recessive disorders: –Cystic fibrosis –Tay-Sachs –Sickle-cell 4 Dominant disorders:Huntington’s

LE 14-14b First generation (grandparents) Ff FF or Ffff Ff ff Ff Second generation (parents plus aunts and uncles) Third generation (two sisters) Attached earlobe Free earlobe ffFF or Ff Recessive trait (attached earlobe)

LE 14-14a Wwww Ww wwWwww Ww WWww or Ww No widow’s peak Third generation (two sisters) Widow’s peak Second generation (parents plus aunts and uncles) First generation (grandparents) Dominant trait (widow’s peak)

TESTING Amniocentesis: (between week: 15-18) Prenatal diagnosis of chromosomal abnormalities 4CVS = Chorionic villi (villus) sampling (10-12 weeks)

Bozeman: Mr. Anderson 4 mPXkYhs mPXkYhs