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The Genetic Engine
How Genetics Works
created by Candace Seeve
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 is DNA?
• DNA—The chemical
inside the nucleus of
a cell that carries the
genetic instructions
for making living
organisms.
What does DNA look like?
A DNA molecule has two strands of bases twisted
around each other and linked together between the
bases (It looks like a twisted ladder).
bases
DNA strand
How is DNA stored in the cell?
DNA is coiled tightly into an x-like called a
chromosome stored in the nucleus of
every cell.
Chromosomes viewed under a microscope.
What is a Gene?
•A specific sequence of bases in DNA that
contains the “code” for making an organism.
• Genes are called the “basic unit of heredity”
because they are passed on 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 from one generation to the
next generation by reproduction.
Gregor Mendel
(1822-1884)
Mendel’s hypothesis
1. Each adult has two of every
gene.
2. In reproduction, each parent
contributes one of every gene to
its offspring so that the offspring
has two full sets of genes too.
3. The combination of genes
determines the traits that the
offspring has.
HE WAS RIGHT!!!
“The Father of Modern Genetics”
Genes, Alleles, and Chromosomes
There is more than one
version of a gene & the
different versions are called
alleles.
Heterozygous—Individual has 2
different alleles for a gene.
Homozygous—Individual has the 2
same alleles for a gene.
Humans have 23 pairs of chromosomes.
Genotype & Phenotype
• Genotype—The specific combination of
alleles of an individual.
• Phenotype—The observable traits of an
organism that are a result of its genotype
and its environment.
genotype
phenotype
+
environment
Sexual Reproduction
• Requires two individuals. Each individual
contributes genetic information, so that the
offspring will inherit ½ 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 that is
identical to itself. The offspring will have
the same genes as its parent.
– Examples: bacteria & plants
Natural Selection &
Adaptation
Mutation
A change in a DNA
sequence.
-Can be good!!! Mutations can change a trait that improves
the survival of an organism.
-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.
Adaptation by Natural Selection:
1. A heritable mutation in a gene
changes a trait and increases an
individual’s fitness.
2. The offspring 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 shaped beaks that could
use the different food sources.
Adaptation:
beak sizes and shapes are
specialized to the different food
sources on the island.
Natural Selection at Work!
Organism:
A species of scale-eating fish called cichlids
living in Africa's Lake Tanganyika.
Adaptation:
There are two types of scale-eating
cichlids—cichlids with their mouth’s
turned to the left or to the right—that
prey on the scales of other fish in the
lake.
Selection:
If there are more “left-handed” cichlids the
other fish learn to watch their right side and
the “right-handed” cichlids easily eat scales
and their population increases until the prey
fish learn to watch their left side and the
advantage changes.
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
• The lab technique of removing, modifying
or adding genes to an organism in order to
introduce a useful trait.
– Yellow/golden rice with vitamin A for eye
health in poor countries.
My Research:
Identify genes responsible for drought
resistance
and disease resistance in loblolly pine
trees.
Why
study
loblolly
pine?
Why
study
disease
& drought
resistance?
How are we using Genetics?
1. We examined the sequence of bases in thousands of genes in more
than 300 loblolly pine trees to identify the common alleles of those
genes.
2. We examined the phenotypes of those individuals. We did
experiments to test if some of the trees could resistant disease or grow
better in droughts.
3. We used computer programs to find relationships between the drought
& disease resistant phenotypes and the alleles that they had. We can
use this information in the future for selective breeding programs.
Genetics Vocabulary Words
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Genetics
DNA
Gene
Chromosome
Sexual Reproduction
Asexual Reproduction
Vocabulary
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Heredity
•Heterozygous
•Homozygous
Genotype
Phenotype
Asexual reproduction
Sexual reproduction
Allele
Vocabulary
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Mutation
Fitness
Adaptation
Natural selection
Selective breeding
Genetic engineering