Recommended%20Assignments

1
(No Transcript)
2
neo-Mendelian Genetics

• After re-discovery, Mendels postulates were
  applied to many genetic traits,
• However, some genetic data did not conform to the
  expected results,
• Continuous Variation
• vs.
• Discontinuous Variation

3
Alleles

• Alleles are alternate forms of the same gene,
• Wild-type allele the allele that occurs most
  frequently in the population,
• normal,
• usually dominant.

4
Wild-type vs. ?

• wild-type alleles are responsible for the most
  common phenotype,
• mutant alleles contain modified genetic
  information, compared to wild-type,

• mutant alleles are responsible for mutant
• phenotypes.

5
Dominance(not always complete)
phenotypes
A1 A2 hybrids
A2 A2
A1 A1
to each other
to each other
6
Incomplete Dominance

• expression of heterozygote phenotype resulting
  in offspring that do not resemble either parent,
• often, offspring phenotype is intermediate
  between those of the parents.

A1 and A2 are incompletely dominant in regards to
each other.
7
R1 red R2 white
Genotypes
Phenotypes
8
Phenotypic Ratio is Equal to Genotypic Ratio
Genotypes
Phenotypes
9
F2 Possible Ratios
R1 R1
R1 R2
R1 R2
R2 R2
10
Codominance

• expression of heterozygote phenotype resulting
  in offspring that resemble both parents,
• both parental traits show up equally and fully in
  the offspring.

A1 and A2 are codominant to each other.
11
CS spotted CD dotted
P
F2
12
F2 Possible Ratios
CS CS
CD CD
CS CD
CS CD
g 121 p 121
codominant
g 121 p 31
CS dom CD
g 121 p 121
incomplete dominance
13
Fig. 2-20
Think about this.
14
(No Transcript)
15
Lethal Alleles

• Essential alleles that if not expressed in a
  sufficient amount, result in lethality,
• recessive lethal allele homozygous recessive
  individuals die, heterozygous individuals live,
• dominant lethal allele homozygous recessive
  individuals die, heterozygous individuals die.

16
Recessive Lethal Alleles

• recessive lethal allele homozygous recessive
  individuals die, heterozygous individuals live,

Modifies Ratio
21 Genotypic Ratio all wild-type
17
Lethality Definitions

• Lethal phenotype doesnt reproduce,
• late onset lethal phenotypes,
• Lethal allele expression, or lack of expression
  causes death.

18
t no tail T wild-type
TT tailed cat
Tt no tail
tt lethal
19
t Manx T wild-type
Lack of T results in death, t is recessive t
does not result in death when T is present.
20
Dominant Lethal Alleles

• dominant lethal allele homozygous recessive
  individuals die, heterozygous individuals die,

The dominant allele is not lethal!
The recessive allele is the lethal, it acts as a
dominant lethal in the heterozygote.
21
Huntingtons Disease

• It is spoken of by those in whose veins the
  seeds of the disease are know to exist, with a
  kind of horror, and not at all alluded to except
  through dire necessity.

- George Huntington, 1872
22
Huntingtons

• Neurological and movement disorder with typical
  onset at about age 40,
• H wild-type h Huntington

HH wild-type
Hh late onset lethal
hh lethal

• On March 23, 1993, the Huntington's disease
  gene was discovered near the tip of chromosome 4.
  Discovery of the gene has led to direct, genetic
  testing for the disease.
• Gene therapy and other programs are underway
  and are highly encouraging.

23
Dominant Lethal Alleles

• dominant lethal allele dominant in regards to
  lethality,

H normal h Huntingtons
lethality is dominant.
24
Gamete Lethality11 ratio
Tt x Tt
1/4 Tt
1/4 Tt
1/4 tt
1/4 TT

• How could this happen, how would you test your
  hypothesis?

25
Reciprocal Crosses
YES
NO
26
Alexanders Stain
27
Pollen
28
More than Two Alleles?
29
Antigens and Antibodies
Antigen substance that stimulates an immune
response, especially the production of
antibodies. Antigens are usually proteins and/or
polysaccharides.
Antibody protein with the ability to bind to
specific molecules...
30
ABO and Allelic Interactions

• ABO blood groups,
• A and B antigens are on the surface of red blood
  cells,
• if you add an A-antibody to blood with type A
  antigens, the blood co-aggulates,
• if you add a B-antibody to blood with type B
  antigens, the blood co-aggulates,
• There are four recognizable phenotypes,
• A B AB O

31
Antigens, Antibodies and Coagulation
32
I Isoagglutinogen

• ...a gene with three alleles,
• ...codes for proteins that modify plasma membrane
  bound, glycosylated proteins in red blood cells.

33
A
B
O
IA
34
3 Alleles(4 phenotypes)
35
IA and IB are Codominant IA and IB are Dominant
to i
36
IA and IB are Codominant IA and IB are Dominant
to i
37

Know Genotype/Phenotype
38
Bombay Phenotype
How can this be?
39
H Substance
An entire H substance must be present to permit
the I gene to bind a sugar.
40
A
B
O
IA H_
ii H_
IA H_
41
No Antigenicity
Genotype hh
IA IA IAi
IB IB IBi
IA IB
ii
42
Bombay Phenotype
How can this be?
43
Epistasis

• a gene interaction in which the effects of one
  gene hides the effects of another gene,
• epistatic gene A genotype hides gene B
  phenotype,
• hypostatic gene B phenotype is hidden by gene A
  genoype.

44
ABO and H Alleles

• epistatic hh genotype hides AB phenotypes,
• h gene is epistatic to I gene,
• hypostatic AB phenotypes are hidden by hh
  genotypes,
• I gene is hypostatic to h gene.

45
Epistasis
Study this chart.

• Classes are masked, or underrepresented.

46
Genetics in the News
47
Penetrance

• the frequency at which individuals with a given
  genotype manifest a specific phenotype.

48
Penetrance

• 4 of 6 dogs, or 66 of the population shows the
  phenotype, at some level,
• penetrance is usually referred to as a
  percentage.

all the same genotype
49
Expressivity

• the degree, or range in which a phenotype of a
  specific genotype is expressed.

50
Expressivity

• range of phenotypes
• expressivity may be referred to as a percentage,
  or another quantifiable measure.

all the same genotype
51
Pentrance? Expressivity?
52
Pentrance? Expressivity?
53
Pentrance? Expressivity?
54
Pentrance? Expressivity?
55
Complementation

• process by which an allele of each of two mutant
  genes makes up for the defect in the other gene.

56
You Find Two Mutants With a Similar Phenotype
Are they the Same Genotype?
57
Possible Physiology
Enzyme A
Enzyme A
Enzyme A
Enzyme B
Enzyme B
Enzyme B
58
Complement
a B
a B
A b
A b
x
A b
a B
Two genes
59
Fail to Complement
A b
A b
A b
A b
x
A b
A b
1 gene
60
(No Transcript)
61
(No Transcript)
62
(No Transcript)
63
a
b
f
c
e
d
64
(No Transcript)
65
(No Transcript)
66
(No Transcript)
67
Assignments

• Read from Chapter 3, 3.6 (pp. 100-106),
• Master Problems3.12, 3.15, 3.20,
• Read Chapter 4, 4- 4.4,
• Chapter 4, Problems 1, 2,
• Questions 4.1 - 4.4, 4.6, 4.7, 4.9, 4.11 -4.14,
  4.19 - 4.20 a,b,c,d.