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The Genetic Engine
How Does it Work?
PEER.tamu.edu 2010
What is “Genetics”??
• The study of how traits are inherited
(passed on to the next generation) and
how differences among individuals arise
• The study of the cellular compounds that
carry genetic information
What are DNA?
• The molecules that
carry the genetic
instructions for
making living
organisms
What does DNA look like?
A DNA molecule looks like a twisted ladder! It has
two strands of bases twisted around each other
and linked together between the bases.
bases
DNA strand
How is DNA stored in the cell?
DNA is coiled tightly into an x-like structure
called a chromosome. Chromosomes
are in the nucleus of every cell.
Chromosomes viewed under a microscope.
What is a Gene?
•A specific sequence of bases pairs that
contains the “code” for making a protein
• Genes are called the “basic unit of heredity”
because they are passed from parents to
offspring.
Reproduction
Reproduction
• Reproduction: the process by which
organisms generate new individuals of the
same kind
• Heredity: the passage of genetic
instructions, through reproduction, from
one generation to the next
Gregor Mendel
(1822-1884)
Mendel made several
hypotheses:
1. Each adult has two of every gene.
2. In reproduction, each parent
contributes one of each gene to its
offspring, so that the offspring has
two full sets of genes too.
“The Father of Modern Genetics”
3. The combination of genes
determines the traits of the offspring.
He was right!
Genes, Alleles, and Chromosomes
Each gene can have two or
more versions; the different
versions are called alleles.
Heterozygous: Individual has 2
different alleles for a gene
Homozygous: Individual has the 2
of the same alleles for a gene
Humans have 23 pairs of
chromosomes for a total of 46.
Genotype & Phenotype
• Genotype: The specific combination of
alleles of an organism
• Phenotype: The observable traits of an
organism; are the result of the interaction
between genotype and environment
genotype
phenotype
+
environment
Sexual Reproduction
• Requires two individuals
• Each individual contributes genetic information,
so the offspring will inherit half of their DNA from
each parent. The offspring will all be different
from either parent.
• Examples: plants & animals
Sexual Reproduction
Like its parents, the offspring will have 2 of every gene. One is from
its father (blue) and one is from its mother (pink). The different
combinations of genes will produce unique offspring.
Asexual Reproduction
• One organism produces offspring
• All offspring are identical (have the same
genes) as each other and as the parent.
– Examples: bacteria & plants
Natural Selection &
Adaptation
Mutation:
A change in a DNA
sequence
-They can be good!!! Mutations can change a trait in such a
way that the survival of the organism is improved.
-Some mutations are
inherited; some are
not. Inherited
mutations can affect
the long-term survival
of a whole population
of organisms.
Fitness & Adaptation
• Fitness: How well an organism is able to
survive in its environment and transmit its
genes to the next generation
• Adaptation: A characteristic or trait that
improves an organism’s fitness
4 Types of Adaptations:
• Reasons for adaptation
– To suit their environment
– To protect them from predators
– To help them find food
– To help them reproduce
How do adaptations happen??
Adaptation by Natural Selection: the
process where heritable traits that make
an organism more “fit” for its environment
become more common over many
generations
The Process of Adaptation by
Natural Selection:
1. A heritable mutation in a gene
changes a trait and increases an
individual’s fitness.
2. The offspring of that individual are
more fit and reproduce more
themselves.
3. After many generations, most (or all)
of the individuals have the new trait.
Finches and Natural Selection:
Organism:
Galapagos finches
Selection:
Competition for food selected for
different beak shapes
Adaptation:
beak sizes and shapes are
specialized to the different food
sources on the islands
More Natural Selection at Work!
Organism:
A species of scale-eating fish called cichlids
that live in Africa's Lake Tanganyika
Adaptation:
There are two types of scale-eating
cichlids—those with mouths turned to
the left and those to the right—that prey
on the scales of other fish in the lake
Selection:
If there are more “left-handed” cichlids, fish
in the lake learn to watch their right side and
the “right-handed” cichlids get more food and
their population increases. Eventually, the
prey fish learn to watch their left side and the
advantage switches.
LH
RH
Artificial selection
Selective breeding: the
selection of certain seeds or
animals for reproduction in
order to influence the traits
inherited by the next
generation
How Artificial Selection Affects
our Dinner Table
Giving Thanks - Science
Supersized Your Turkey
Dinner!!
Genetic Engineering…
is the lab technique of removing, modifying,
or adding genes to an organism
– Often the goal is to introduce a useful trait
• Example: yellow/golden rice with vitamin A for eye
health
Vocabulary Words
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Genetics
Heredity
DNA
Gene
Chromosome
Allele
Genotype
Phenotype
Heterozygous
Homozygous
Mutation
Fitness
Adaptation
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Asexual reproduction
Sexual reproduction
Natural selection
Selective breeding
Genetic engineering