Transcript Mendel and the Gene Idea - Ludlow Independent Schools

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
F1
F2
Tall X short (TT x tt)
all Tall (Tt)
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
Phenotype
TT X tt
Tt X Tt
TT X TT
tt X tt
TT X Tt
Tt X tt
all Tt
1TT:2Tt:1tt
all TT
all tt
1TT:1Tt
1Tt:1tt
all Dom
3 Dom: 1 Res
all Dom
all Res
all Dom
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
A
B
AB
O
Genotypes
IA IA or IAi
IB IB or IBi
IAIB
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 Formal
R=FXMXD
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
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.