Genes and
Variation
What determines the phenotypes
for a given trait?
What is the
difference between
GENOTYPE and
PHENOTYPE?
Recall:
GENOTYPE: Specific combination
of alleles
PHENOTYPE: Physical,
physiological, and
behavioral
characteristics
Genetics
and
the
Evolutionar
y Theory
Natural
selection acts
on an organism’s
characteristics,
not on its
alleles.
Observe and record various
traits among your classmates (or
within your families)
1.
2.
3.
4.
5.
Ear lobe attachment (free or
attached)
Tongue rolling ability
Hairline (widow's peak or
straight)
Eye color
Height (approximate)
These traits are determined
by a single gene.
SingleGene
Traits
They typically exhibit clear,
distinct phenotypes
(observable characteristics).
Inheritance patterns often
follow Mendelian genetics
(dominant and recessive
alleles).
Ear lobe attachment:
Example
s of
singlegene
traits:
•Free earlobes are often dominant, while attached
earlobes are recessive.
Tongue rolling:
•The ability to roll the tongue is often a dominant
trait.
Widow's peak:
•A widow's peak (a V-shaped hairline) is often a
dominant trait.
Eye color (in some simplified cases):
•While eye color is complex, some simplified examples,
like brown versus blue eyes, are often used to
demonstrate single gene traits.
Certain genetic disorders:
•Cystic fibrosis and sickle cell anemia are examples
of disorders caused by mutations in a single gene.
These traits are
influenced by multiple
genes.
Polygenic
Traits
They exhibit a wide range
of phenotypes, often with
continuous variation.
Environmental factors can
also play a significant
role.
Height:
Example
s of
polygen
ic
traits:
• Many genes contribute to a person's height, leading
to a wide spectrum of heights within a population.
Skin color:
• Multiple genes determine the amount and type of
melanin in the skin, resulting in a continuous range
of skin tones.
Eye color (complex versions):
• While simple brown vs blue can be used to describe
single gene traits, the vast amount of variation in
eye color is due to multiple genes.
Weight:
• Numerous genes, along with environmental factors
like diet and exercise, influence a person's
weight.
Intelligence:
• Cognitive abilities are influenced by a complex
interplay of many genes and environmental factors.
Number of genes: Single-gene traits
involve one gene; polygenic traits
involve multiple genes.
KEY
DIFFERENCES
:
Phenotypic variation: Single-gene
traits have distinct phenotypes;
polygenic traits have continuous
variation.
Inheritance patterns: Single-gene
traits often follow simple Mendelian
patterns; polygenic traits have more
complex inheritance patterns.