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Quiz 4 answers http://webct.mun.ca:8900/
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Mendelian Genetics
Topics:

-Transmission of DNA during cell division
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


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Mitosis and Meiosis
- Segregation
- Sex linkage ( problem: how to get a white-eyed female )
- Inheritance and probability
- Independent Assortment
- Mendelian genetics in humans
- Linkage
- Gene mapping


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-Gene mapping in other organisms
(fungi, bacteria)
- Extensions to Mendelian Genetics
- Gene mutation
- Chromosome mutation
(- Quantitative and population genetics)
B2900

Mutation
Source of genetic variation:
Gene Mutation
 - somatic, germinal
Chromosome mutations (Ch. 11)
 - structure
(deletion, duplication, inversion, translocation)
- number

Chromosome Mutation
(2. changes in number)
Euploidy: variation in complete sets of chromosomes
Aneuploidy: variation in parts of chromosome sets

Euploidy
1x monoploid (1 set) = n
2x diploid (2 sets) = 2n
3x triploid
4x tetraploid
5x pentaploid polyploid (> 2 sets)
6x hexaploid n = # chromosomes in the gametes
2n 4n

Polyploids
Autopolyploids: within one species
Allopolyploids: from different, closely related species

Polyploids
Larger than Diploids

Polyploids
Triploids: = 3n
- problems with pairing during meiosis
- unbalanced gametes
- usually sterile
Applications: seedless fruits, sterile fish aquaculture

Formation of Triploids n
= 3n n n n
Polar bodies n
2n n
= 3n

Triploids (3x)
Why can’t a triploid produce viable gametes ?

Fig. 11-5

x = 1
Triploids (3x)
Gametes

Triploids x = 2
Gametes viable or
Nonviable

Viable Gametes from Triploids
Probability
(2x or x gamete) = x - 1
0.2
0.1
0.5
0.4
0.3
2
# of chrs
3
4 if x = 10 Prob. = 0.002 of viable gametes
0
0 5 10 15 20
Number of Chromosomes
25 30 35

Triploid Fish
Frankenfish-Biotech
3n carp

Autotetraploid

Autotetraploid
Doubling of chromosomes: 2x----> 4x
Even number of chromosomes: normal meiosis
2<---->2 segregation------> functional gametes

Polyploids
Autopolyploids: within one species
Allopolyploids: from different, closely related species
Hybridization

Origin of
Wheat
Fig. 11-10
Allopolyploid
2n = 14, n = x = 7
Chromosome sets:
A, B, D
7 7 7
Triploid
7 14
2n = 28 n = 14 hybrid
2n = 42 x = 7 n = 21

Polyploidy
Plants: speciation (wheat)
Animals: - rare (sex determination)
- fish (salmon: tetraploid)
- parthenogenetic animals
123 11 22 12 12

Plant Polyploids
90
80
70
60
50
40
30
30 40 50 60 70 80 90
Latitute North

Chromosome Mutation
(changes in number)

Euploidy: variation in complete sets of chromosomes
Aneuploidy: variation in parts of chromosome sets

Aneuploidy
Nullisomics (2n - 2)
Monosomics (2n - 1)
Trisomics (2n + 1) normal

Aneuploidy
Nullisomics (2n - 2)
- lethal in diploids
- tolerated in polyploids
Monosomics (2n - 1)
- disturbs chromosome balance
- recessive lethals hemizygous
Trisomics (2n + 1)
- sex chromosomes vs autosomes
- size of chromosome

Aneuploidy
Non-disjunction: Gametes
Meiosis I n + 1 n - 1
Meiosis II n + 1 n - 1 n n x n - 1 ---------> 2n - 1 monosomic n x n + 1 ---------> 2n + 1 trisomic

Human Aneuploids
13
21
18
X
Y

Aneuploidy
Humans: (live births)
Monosomics - XO Turner syndrome
- no known autosomes
Trisomics XXY Klinefelter sterile male
XYY fertile male ( X or Y gametes)
XXX sometimes normal
21 Down
18 Edwards syndromes
13 Patau

Downs Births per 1000
25
20
15
10
5
2 %
0
20 25 30 35 40 45 50
Maternal Age (years)

0.62 %
50 %

Mutations Causing Death and
Disease in Humans
Gene mutations:
% of live births
1.2
Chromosome mutations: 0.61

Chromosome Mutations
(Humans)
% of spontaneous abortions
Trisomics 26 %
XO 9 %
Triploids 9 %
Tetraploids 3 %
Others 3 %
Chromosome 50 % abnormalities

Chromosome Mutations
Comparison of euploidy with aneuploidy
Aneuploids more abnormal than euploids: likely due to gene imbalance
Plants more tolerant than animals to aneuploidy and polyploidy
(animal sex determination)

Summary
Mutation - gene
- chromosome
(structure, number)
Detecting - cytology
- phenotype genetic analysis
Rate of mutation - low
Mutation - source of genetic variation
- evolutionary change

Chapter References
Mitosis and Meiosis
Ch. 4 p. 100 – 112 Prob: 10, 11, 12, 18, 19
Mendelian Inheritance
Ch. 5 p. 118 – 129 Prob: 1 – 3, 5, 6, 7, 8, 9
Recombination, linkage maps
Ch. 6 p. 148 – 165 Prob: 1-5, 7, 8, 10, 11, 14
Extensions to Mendelian Genetics
Ch. 14 p. 459 – 473 Prob: 2, 3, 4, 5, 6, 7
Chromosome Mutations
Ch. 11 p. 350 – 377 Prob: 1, 2

Mendelian Genetics
Topics:

-Transmission of DNA during cell division







Mitosis and Meiosis
- Segregation
- Sex linkage
- Inheritance and probability
- Independent Assortment
- Mendelian genetics in humans
- Linkage
- Gene mapping




-Gene mapping in other organisms
(fungi, bacteria)
- Extensions to Mendelian Genetics
- Gene mutation
- Chromosome mutation

Genetics
Part I Part II
Molecular Mendelian

Chromosome Theory of
Inheritance
- genes organized into chromosomes
- correlation: Genetics & Cytology
- theory can explain segregation and independent assortment

Two types of nuclear division
1. Mitosis (somatic tissue)
2. Meiosis (germ tissue)

Mendelian Genetics
• Meiosis and mitosis
• Segregation and independent assortment
• Sex linkage, sex determination
• Pedigrees
• Linkage, recombination and linkage maps

Mendelian Genetics
• Gene linkage: 3 point test cross, tetrad analysis
• Extensions
(dominance, multiple alleles, pleiotropy, epistasis, penetrance and expressivity)
• Mutation: gene mutation chromosome mutation (number structure)

Mendelian Genetics
Applications
Genetic markers as tools:
- human diseases
- population genetics
- genetic structure (gene flow)
- systematics and phylogeny
- forensics

Mendelian Genetics in Humans
Determining mode of inheritance
Problems:
1. long generation time
2. can not control matings
Alternative:
* information from matings that have already occurred “
Pedigree
”

Human Pedigrees
Pedigree analysis:
• trace inheritance of disease or condition
• provide clues for mode of inheritance
• however, some pedigrees ambiguous

Human Pedigrees
Pedigree analysis: dominant vs recessive autosomal vs sex linked

Linkage:
Human Genetic Diseases
Linkage:
• organization of genes and genome
• marker genes linked to:
Disease genes

Mutation
Gene Mutation
- somatic, germinal
- detecting mutations
Chromosome mutations
- structure
- number

Chromosome Mutation
(changes in number)
Euploidy: variation in complete sets of chromosomes
Aneuploidy: variation in parts of chromosome sets

Careers in Genetics cytogenetics molecular genetics human genetics population genetics quantitative genetics developmental genetics immunogenetics etc. etc.

Genetics Courses
B2900 Principles of Evolution and Systematics
B2060 Principles of Cell Biology
B3530 Developmental Biology
B4241 Advanced Genetics
B4250 Evolutionary Genetics
B4900 Biotechnology
Honours Thesis Research in Genetics

Announcement
NSERC
Undergraduate Student
Research Awards (USRA) in
Universities
16 weeks $5,625 www.nserc.ca
MUN deadline Early Jan, 2006