Chapter 14 Mendel and the

Gene Idea

Inheritance

Genetics

Genetic Theories

1

Genetic Theories (cont.)

Gregor Mendel

Mendel’s paper published in 1866, but was not recognized by Science until the early 1900’s.

Reasons for Mendel's Success

Mendel was a pea picker.

He used peas as his study organism.

Why Use Peas?

Cross-pollination

Self-pollination

Mendel's Work

Monohybrid or Mendelian Crosses

P Generation

Offspring

Another Sample Cross

P1 Tall X short (TT x tt)

F1 all Tall (Tt)

F2 3 tall to 1 short

(1 TT: 2 Tt: 1 tt)

Results - Summary

Mendel's Hypothesis

Mendel's Hypothesis

Mendel's Hypothesis

4

Law of Segregation

Mendel’s Experiments

Vocabulary

Helpful Vocabulary

6 Mendelian Crosses are Possible

Cross Genotype PhenotypeTT X tt all Tt all Dom

Tt X Tt 1TT:2Tt:1tt 3 Dom: 1 Res

TT X TT all TT all Dom

tt X tt all tt all Res

TT X Tt 1TT:1Tt all Dom

Tt X tt 1Tt:1tt 1 Dom: 1 Res

Test Cross

Dihybrid Cross

Dihybrid Cross

Results

9 Tall, Red flowered 3 Tall, white flowered 3 short, Red flowered 1 short, white flowered

Or: 9:3:3:1

Law of Independent Assortment

Probability

Genetic Ratios

Rule of Multiplication

Example: TtRr X TtRr

Comment

Variations on Mendel

Incomplete Dominance

Result

Another example

Codominance

Result

Multiple Alleles

Result

Alleles and Blood Types

Type Genotypes

A IA IA or IAi B IB IB or IBi AB IAIB

O ii

Comment

Epistasis

Gerbils

In Gerbils

CcBb X CcBb

Brown X Brown

F1 = 9 brown (C_B_)

3 black (C_bb)

4 albino (cc__)

Result

Problem

Wife is type A Husband is type AB Child is type O

Question - Is this possible?

Comment - Wife’s boss is type O

Bombay Effect

Genotypes

Bombay - Detection

Polygenic Inheritance

Genetic Basis

Result

Genetic Studies in Humans

Pedigree Chart Symbols

Male

Female

Person with trait

Sample Pedigree

Dominant Trait Recessive Trait

Human Recessive Disorders

Sickle-cell Disease

Tay-Sachs

Cystic Fibrosis

Recessive Pattern

Human Dominant Disorders

Inheritance Pattern

Genetic Screening

General FormalR = F X M X D

R = riskF = probability that the female

carries the gene.M = probability that the male

carries the gene.D = Disease risk under best

conditions.

Example

Risk Calculation Wife = probability is 1.0 that

she has the allele. Husband = with no family

record, probability is near 0. Disease = this is a recessive

trait, so risk is Aa X Aa = .25 R = 1 X 0 X .25 R = 0

Risk Calculation

Assume husband is a carrier, then the risk is:

R = 1 X 1 X .25

R = .25

There is a .25 chance that any child will be albino.

Common Mistake

Carrier Recognition

Fetal Testing

Amniocentesis

Chorionic Villi Sampling

Newborn Screening

Newborn Screening

Multifactorial Diseases

Ex. Heart Disease

Summary

Know the Mendelian crosses and their patterns.

Be able to work simple genetic problems (practice).

Watch genetic vocabulary. Be able to read pedigree charts.

Summary

Be able to recognize and work with some of the “common” human trait examples.