Genetic variation within populations is caused by mutations, immigration, and natural selection acting on individuals with different traits. Environments change over time, applying selective pressure that can cause populations to evolve through mechanisms like isolation and variation between individuals. DNA contains the genetic code through combinations of bases (A, T, G, C) that provide instructions for building proteins. Genes are sequences of DNA that determine traits; each gene has two alleles that may be dominant or recessive. Punnett squares predict offspring traits by combining parental alleles. Gregor Mendel first showed dominant and recessive inheritance through pea plant experiments. Genotype is an organism's genetic makeup, while phenotype describes how traits appear. Inheritance passes genes from generation to

1. Genetic Variation
www.alsa.org
Dr. G.D. HANDE

2. Goal
To learn the basic genetic
mechanisms that determines the traits
expressed by individuals in a
population

3. Natural Selection Theory
Variation in a population of organisms
Results of Mutations
Results of Immigration
Result of survival features of individual
organisms

4. Natural Selection Theory
Environments are dynamic
Changing resources
Climate (long term weather)
Natural disasters

5. Natural Selection Theory
Selective Pressure
Environmental changes can cause
pressure
Organisms unable to adapt quickly
enough will die
Organisms that adapt are able to pass
on their successful traits to future
generations

6. Natural Selection Theory
Isolation
If one portion of a population is
separated from another portion then a
new species may evolve

7. Natural Selection Theory
Mechanisms for population change
Key to change is variation among the
individuals in the population
Individuals are unique due to their genes

8. Genetics

9. Genetics
Nucleic Acids
Huge molecules that
hold information
DNA
(deoxyribonucleic
acid) is the nucleic
acid that holds all
the genetic
information for
organisms
ghr.nlm.nih.gov

10. DNA
Genetic code of all living things
Complete set of blueprints and operating
instructions for assembling and managing
one particular kind of organism
Has four basic building blocks
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)

11. DNA
A and T can only bond with each
other
G and C can only bond with each
other
When four bases bond together in a
long chain they form a double helix
(ladder)
Typical DNA molecule may be about
5 cm long

12. DNA
DNA found in the nucleus of the cell
DNA is coiled into a compact structure
called a chromosome
Every cell in every plant and animal has a
completed set of chromosomes that define
the organism
Every time the cell divides to produce two
daughter cells the complete set of
chromosomes is produced

13. Chromosome, Gene, DNA
www.phoenix5.org

14. Genes determine traits
Genes: are the units of heredity that is a
sequence of bases (A,T,G,C) that give
instructions on how to assemble a certain
protein
Genes are the sugars, phosphates, and
bases along the DNA strand in the
chromosome
The proteins go to the cells to make things
such as fats, bone, muscle, nerves, and
everything else in a living organism

15. Alleles
www.monteweston.com

16. Alleles
Each gene has two copies which are called
the alleles.
(2 alleles= 1 gene)
Dominant allele the allele that controls
what will happen or which trait will be
exhibited (Capital Letter)
Recessive allele the allele that is
“overruled” and this trait or function will not
be seen because of the dominant allele
(Lower case letter).

17. Punnett Squares
A technique for predicting the
characteristics of offspring
Example of Punnett Square

18. Punnett Square
Always put the dominant allele (G)
before the recessive allele (g) so
you would write Gg
Results:
One homozygous dominant (GG)
Two heterozygous (Gg)
One homozygous recessive (gg)

19. Discovery of Heredity
Gregor Mendel
Scientist pioneer to work with
pea plants to show how a
species can exhibit certain
characteristics from one
generation to the next.
He was the scientist to support
the idea of dominant (capital
letter) and recessive (lower case
letter) traits.
history.nih.gov
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kentsimmons.uwinnipeg.ca

20. Genotype
Genotype
Genotype is the genetic makeup
of the organism (genes/letters)
Example:
(letters represent trait…color in this
case)
Pea flower color B=dominant
allele (purple), b=recessive allele
(white)
A purple offspring would have
either a BB or Bb genotype
A white offspring would only have
a bb genotype
www.eastbaymom.com

21. Phenotype
Phenotype: how the
organisms looks
(trait/picture)
Example: purple flower,
white flower, tall plant,
short plant

22. Inheritance
Inheritance is passing genetic
information from one generation to
the next
You inherited alleles from your
parents