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a short introduction before taking genetics
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GeneticsGeneticsGenetics
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 JournalsGenetic Journals• American Journal of Medical
Genetics Clinical Genetics
• Developmental Genetics Human Molecular Genetics
• Genetics European J. of Human Genetics
• Genetics Selection Evolution Nature Genetics
• Genetika Fungal Genetics and Biology
• Genome Cancer Genetics and Cytogenetics
• Genomics American J. Human Genetics
• Hereditas Opthalmic Genetics
• Japanese Journal of Human Genetics Human Genetics
• Journal of Heredity Current Genetics
• Molecular Biology and Evolution Animal Genetics
• Molecular Ecology Brazilian J. Genetics
• Molecular and General Genetics Biochemical Genetics
• Theoretical and Applied Genetics J. of Medical 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.
• Genes - cannot be observed directly
• Phenotypes - observed directly
** inheritance of phenotypes used to infer the inheritance of genes
Mendelian Genetics
Mendel’s ExperimentsSeven 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.
FertilizationMommy DaddyDaddy
BABYBABY
Self-Fertilization
• When an organism has both male and
female gametes, they are able to self-
fertilize.
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
T t
T
T
TT
TT
Tt
Tt
MOM
DAD
Punnett SquarePunnett Square
(Monohybrid Cross)(Monohybrid Cross)
T t
T
t
TT
Tt
Tt
tt
MOM
DAD
Punnett SquarePunnett Square
T t
t
t
Tt
Tt
tt
tt
MOM
DAD
Punnett SquarePunnett Square
t t
t
t
tt
tt
tt
tt
MOM
DAD
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
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.
Principle of Segregation
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
T t
t
t
Tt
Tt
tt
tt
Heterozygous
Known homozygous
recessive
1/2Tall
1/2Short
Test Cross
T T
t
t
Tt
Tt
Tt
Tt
Homozygous
Known homozygous
recessive
AllTall
N0Short
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