Chapter 14 Mendel and the Gene Idea

Inheritance

Genetics

Genetic Theories 1

Genetic Theories (cont.)

Gregor Mendel

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

Reasons for Mendel's Success

u Mendel was a pea picker. u 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

4

Law of Segregation

Mendel’s Experiments

Vocabulary

Helpful Vocabulary

6 Mendelian Crosses are Possible Cross Genotype Phenotype TT 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

Number of Kinds of Gametes

Equation The formula 2 n can be used, where “n” = the number of heterozygous traits. Ex: TtRr, n=2 2 2 or 4 different kinds of gametes are possible. TR, tR, Tr, tr

Dihybrid Cross

Results u 9 Tall, Red flowered u 3 Tall, white flowered u 3 short, Red flowered u 1 short, white flowered Or: 9:3:3:1

Law of Independent Assortment

Comment

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 I A I A or I A i B I B I B or I B i AB I A I B 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

Epistasis in Mice

Problem u Wife is type A u Husband is type AB u 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 Formal R = F X M X D R = risk F = probability that the female carries the gene. M = probability that the male carries the gene. D = Disease risk under best conditions.

Example

Risk Calculation u Wife = probability is 1.0 that she has the allele. u Husband = with no family record, probability is near 0. u Disease = this is a recessive trait, so risk is Aa X Aa =.25 u R = 1 X 0 X.25 u R = 0

Risk Calculation u 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

Multifactorial Diseases

Ex. Heart Disease

Summary u Know the Mendelian crosses and their patterns. u Be able to work simple genetic problems (practice). u Watch genetic vocabulary. u Be able to read pedigree charts.

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