Chapter 14~ Mendel & The Gene Idea

Mendelian genetics Trait True-breeding Hybridization variant for a character ex: purple True-breeding all offspring same variety Hybridization Cross of two pure breeding P generation = parents F1 generation = first filial generation

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

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

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

LE 14-8 P Generation YYRR yyrr Gametes YR yr YyRr F1 Generation Hypothesis of dependent assortment Hypothesis of independent assortment Sperm 1 YR 1 Yr yR yr Sperm 4 4 1 4 1 4 Eggs 1 YR yr 2 1 2 1 YR Eggs 4 YYRR YYRr YyRR YyRr 1 YR F2 Generation (predicted offspring) 2 YYRR YyRr 1 Yr 4 YYRr YYrr YyRr Yyrr 1 yr 2 YyRr yyrr 1 yR 4 YyRR YyRr yyRR yyRr 3 4 1 4 1 yr 4 Phenotypic ratio 3:1 YyRr Yyrr yyRr yyrr 9 16 3 16 3 16 3 16 Phenotypic ratio 9:3:3:1

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

LE 14-10 P Generation Red CRCR White CWCW Gametes CR CW Pink CRCW F1 Generation Gametes 1 1 2 CR 2 CW Sperm 1 2 CR 1 2 CW Eggs F2 Generation 1 CR 2 CRCR CRCW 1 2 CW CRCW CWCW

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

Pleiotropy

Epistasis LE 14-11 BbCc BbCc Sperm BC bC Bc bc BC BBCC BbCC BBCc BbCc 9 3 4 16 16 16

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

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

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

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

Bozeman: Mr. Anderson https://www.youtube.com/watch?v=rIe7mPXkYhs