genetics i. i. mendelian 1. history a. introduction

GeneticsI.

Mendelian

1. History

A. Introduction

a. C. Darwin & A. Wallace == blending

b. In 1860, G. Mendel & F. Unger == mixing

1. Monohybrid Cross

B. Experimental Design

a. Definition

b. Terms

i. Self vs. Cross Fertilization

ii. Traits vs. Characteristics

c. Process

Figure 10.1

Figure 10.2

i. Outcomes for a one trait cross or Monohybrid crossesii. Principle All traits are paired and sorted into gametes

Figure 10.3

d. Terms

Gene versus Allele

Homozygous versus Heterozygous

Dominance versus Recessive

Genotype versus Phenotype

e. Testcross

Figure 10.4

2. Dihybrid Cross

a. Definition

b. Process

Always start these crossing questions by figuring out how many and what type of gametes are produced by the parents.

i. Outcomes for a Dihybrid crosses

Figure 10.6

Dihybrid Heterozygous cross =

Phenotypic ratio= 9:3:3:1, Genotypic ratio= 1:1:2:2:4:2:2:1:1

Dihybrid Heterozygous cross Homozygous Dominant =

Phenotypic ratio = all dominant, Genotypic ratio = 1:1:1:1

ii. Principle Each pair of alleles and chromosomes sort independently into gametes.

AaBb X AABBGametes AaBb = AB, Ab, aB, & ab; AABB=

AB only

i. Outcomes

AaBb X AaBbGametes AaBb = AB, Ab, aB, & ab

for both

II. Variation on Mendel

A. Incomplete Dominance

Incomplete dominance appears to be a blending of the two alleles vs. complete dominant. Figure

10.9

B. Co-Dominance

Co-dominance expression of alleles yields both traits in heterozygote.

AA aa

Aa

C. Multiple Alleles

Multiple alleles are needed to give the expression of the trait.

Figure 10.10

D. Penetrance

Timing of expression of traits in the phenotype.

1. Pleitrophy

E. Gene Interactions

Pleitrophy one gene = many different effects

Figure 10.13

2. Polygenic

Polygenic = Continuous Variation of Expression of traits

Figure 10.11

3. Epistasis

Epistasis = Interference of expression between different genes

III. Classical Genetics

A. History

1. W. Bateson & R. Punnett (1908) Punnett Square

2. T. Morgan (early 1900’s) used fruit flies

WHY?

Recombination experiments

Developed karyotyping techniques,

Figure 9.1

Figure 10.17

linkage group studies,

Figure 10.16

& sex linkage studies

Figure 10.15

3. A. Sturtevant

a. mapping

V. Detection of Problems

A. Karyotyping

B. Amniocentesis == Cellular and Chemical Analysis

C. Ultrasound gives a visual image of the fetus

D. Chorionic Villi Sampling== placenta samples

E. Fetal Tissue

F. Pedigrees == familial history

Figure 13.7

Figure 13.8

Figure 13.9

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