Chapter 14: Mendel and the Gene Idea

Genetic Terminology

• Character– Trait

• True-breeding• Hybridization– P generation– F1 generation

– F2 generation

Mendel’s Ideas• For each trait an organism inherits two alleles• If the alleles are different…– Dominant– Recessive

Mendel’s Laws

• Law of Segregation– Alleles for each character separate during gamete formation

Mendel’s Laws• Law of independent assortment– Pairs of alleles separate individually

Rules of Probability

• Rule of multiplication– Examples• 2 coins land heads up• Parent is YyRr, gamete will carry Y, R• Parents are YyRr, offspring will be YYRR

• Rule of Addition– Event can occur two or more ways– Example• Two ways to produce heterozygote if parents are Pp

Rules of Probability

• PpYyRr x Ppyyrr• What is the probability of offspring having

recessive phenotype for at least two of the three traits– ppyyRr– ppYyrr– Ppyyrr– PPyyrr– ppyyrr

Types of inhertiance

• Incomplete dominance– Snapdragons

• Co-dominance– M,N,MN blood groups

• Multiple alleles– ABO blood groups• Surface carbohydrate• Alleles

ABO Blood Groups

Types of Inheritance

• Pleiotropy– Sickle Cell Anemia

• Epistasis– Coat color in mice

• Polygenic traits– Eye color– Skin color

Pedigrees

Genetic Disorders• Recessive– Tay Sachs– Cystic Fibrosis– Sickle Cell Anemia– Phenylketonuria (PKU)

• Dominant– Achondroplasia– Huntington’s

• Multifactorial– Heart disease, diabetes, cancer, alcoholism,

schizophrenia, manic-depressive disorder

Chapter 15: The Chromosomal Basis of Inheritance

Thomas Morgan’s Experiment• White type restricted to males– Sex-linked• Recessive-

– Father to son

– Linked genes• Passed as unit• Same chromosome

Sex-Linked Disorders

• Duchenne’s– Loss of muscle strength and coordination

• Hemophilia– Failure of blood to clot

• Red-green colorblindness– Primarily males

Chromosomal Complications

• Non-disjunction– Aneuploidy• Trisomy

– Down’s Syndrome– Patau Syndrome– Edward’s Syndrome– Klinefelter’s Syndrome

• Turner’s Syndrome

Chromosomal Complications• Deletion– Cri-du-chat

• Translocation– Chronic myelogenous

leukemia

• Inversions• Duplications

Chi Square Analysis

• Used to determine if there are deviations for the phenotypic ratio of the F2 generation within the limits expected by chance

– Null hypothesis

– Formula X2 = ∑ (o – e)2

e

Chi Square Analysis

• Degrees of freedom• Chi square– Critical value• Reject hypothesis

Probability 1 2 3 4

0.05 3.84 5.99 7.82 9.49

0.01 6.64 9.21 11.30 13.20

0.001 10.8 13.8 16.3 18.5