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Genetics
Genetics
What is Genetics ?
Genetics is the study of heredity and variation
Examples of genetic variation
1. Domesticated species
2. Human genetics
3. Natural Populations
History of Genetics
•Domestication of animals
•Cultivation of plants
Cultivated varieties
Animal Breeds
Human Genetic
Variation
Variance
Which suspect matches the
blood stain ?
Bloodstain
Ethical Issues
Boot GM out of animal feed
Cloning
Genetic Journals
• American Journal of Medical
Genetics Clinical Genetics
• Developmental Genetics Human
Molecular Genetics
• Hereditas Opthalmic Genetics
• Japanese Journal of Human
Genetics Human Genetics
• Journal of Heredity Current
Genetics
• Genetics European J. of Human
Genetics
• Molecular Biology and
Evolution Animal Genetics
• Genetics Selection Evolution
Nature Genetics
• Molecular Ecology Brazilian J.
Genetics
• Genetika Fungal Genetics and
Biology
• Molecular and General Genetics
Biochemical Genetics
• Genome Cancer Genetics and
Cytogenetics
• Theoretical and Applied
Genetics J. of Medical Genetics
• Genomics American J. Human
Genetics
• Trends in Genetics
Basic Concepts of Genetics
Nucleus - contains genetic material
DNA - genetic material
4 bases (nucleotides G, C, A, T)
Gene - functional unit of heredity
sequence of 4 nucleotides
Chromosome -linear DNA molecule
Basic Concepts of Genetics
Cell/nuclear division
• Mitosis (somatic tissue):
identical cells
• Meiosis (germ tissue):
gametes
Basic Concepts of Genetics
• Mendelian Genetics
(transmission genetics)
• Molecular Genetics
(hereditary material)
Historical Notes
1865 Gregor Mendel
- controlled genetic
experiments (garden peas)
- statistical regularity
- theory of inheritance
Understanding Genetics
• Relationship between:
GENOTYPE
ENVIRONMENT
PHENOTYPE
set of genes
morphology
inherited
physiology
behaviour
Mendelian Genetics
Requirements:
1. Attributes of the phenotype that
vary among individuals
2. Phenotypic variation caused by
genetic differences
Genotype and Phenotype
• The genotype is our actual genes. We
cannot see our genes.
• The phenotype is the physical expression of
those genes.
Mendelian Genetics
• Genes - cannot be observed directly
• Phenotypes - observed directly
** inheritance of phenotypes used to
infer the inheritance of genes
Mendel’s Experiments
Seven Pea varieties “True Breeding Lines”
Character “traits”
Phenotypes
1. seed shape
round, wrinkled
2. seed colour
yellow, green
3. flowers (pods)
axial, terminal
4. pods
full, constricted
5. pods
yellow, green
6. flowers
violet, white
7. stem
tall, dwarf
Fertilization
Gametes carry the genetic information about
an organism.
The male gamete produce Sperm.
The female gametes produce Eggs.
The process in which one gamete is united
with another is called Fertilization.
Fertilization
Mommy
Daddy
BABY
Self-Fertilization
• When an organism has both male and
female gametes, they are able to selffertilize.
Advantages
• easy to grow
• matures in a season
• self-fertilizing
• easy to cross-fertilize
Dominance
• Some characteristics overshadow others
when crossed.
• This is referred to as a Dominant trait.
• The unseen trait is said to be Recessive.
• Dominant traits are represented on
charts by a capital letter.
• Recessive traits are represented by a
lower case letter
Pure Lines
(Homozygous)
• When an organism is said to be of pure
lines, it means their genotype is two
identical alleles.
• TT is the pure line for a tall plant.
• tt is the pure line for a short plant.
Hybrids
(Heterozygous)
• When parents of two different pure lines
are crossed, the offspring are called
hybrids.
• A hybrid’s genotype consists of two
different alleles.
• The genotype Tt would be a tall plant
hybrid.
Homozygous and Heterozygous
• When an organism has identical alleles,
it is said to be homozygous.
• TT, and tt would both be homozygous
• When an organism has two different
alleles, it is heterozygous.
• Tt is heterozygous.
Punnett Square
T
T
T
T
TT
TT
TT
TT
Cross Pollination
Punnett Square of Cross
Pollination
MOM
DAD
T
T
T
t
TT
Tt
TT
Tt
Punnett Square
(Monohybrid Cross)
MOM
DAD
T
t
T
t
TT
Tt
Tt
tt
Punnett Square
MOM
DAD
t
t
T
t
Tt
tt
Tt
tt
Punnett Square
MOM
DAD
t
t
t
t
tt
tt
tt
tt
Mendel’s Experimental Approach
Suitable experimental organism
• examine few traits in each experiment
• accurate quantitative records
• analyzed data
formulated hypotheses
Genetic Analysis (pea shape)
Hypothesis to explain results
1. Hereditary determinants (genes)
2. Each adult plant has a gene pair
F1 plants: one gene dominant phenotype
one gene recessive phenotype
Hypothesis (continued)
3. Members of a gene pair segregate equally
into the gametes
4. Each gamete has only one member of a gene pair
5. Gametes combine at random to form zygote
Hypothesis
Self Fertilization
Test of Equal
Segregation Hypothesis
Principle of Segregation
Three parts:
1. Hereditary characteristics are determined
by distinct units or factors.
2. For each characteristic, an individual
carries two factors, one inherited from each
parent.
3. The two factors of each pair segregate from
each other and end up in separate gametes.
If a plant is short, what is its
genotype?
• It must be homozygous recessive, tt.
If a plant is tall, what is its
genotype?
• It could be homozygous dominant, or
heterozygous. TT, or Tt.
• To determine which genotype it is we use a
test cross.
Test Cross
Heterozygous
Known
homozygous
recessive
t
t
T
t
Tt
tt
Tt
tt
1/2
Tall
1/2
Short
Test Cross
Homozygous
Known
homozygous
recessive
t
t
T
T
Tt
Tt
Tt
Tt
All
Tall
N0
Short
Genetic Terminology
Genes: hereditary elements
• Alleles: forms of a gene: A a
• Heterozygote: Aa
• Homozygotes: AA aa
• Genotype: Genetic makeup
• Phenotype: What we actually see
• Dominance AA, Aa same phenotype
Summary
Experimental:
1. Two pure breeding lines
2. Cross --------> F1 hybrid
3. Self F1 ------> F2
Summary
Results:
1. F1 one phenotype
2. F2 3:1 ratio of 2 phenotypes
Summary
Inference:
1. Single major gene
2. dominant phenotype
3. equal segregation
4. existence of genes inferred