Inheritance Why we look the way we do
Transcript Inheritance Why we look the way we do
Why we look the way
We look the way we do because we inherit certain
traits from our parents, from the texture of our
hair to the color of our eyes.
All these traits that make up how we look are carried
in our DNA (deoxyribonucleic acid).
DNA is found in the nucleus
of the cell.
The Role of Genes in
• Chromatin is in the
nucleus of a cell
• Chromatin forms into
• Chromosomes are partly
composed of DNA
Source of photos: Mitosis Stages
• DNA is genetic material
• DNA carries information about
an organism that is passed
from parents to offspring
• Some of the DNA in
chromosomes consists of genes
A gene is found on a
chromosome. A chromosome
contains many genes.
What is a Gene?
• A gene is a section of DNA that
controls a trait that an
• Genes are like recipes. Just as a
recipe contains instructions for
preparing food, genes contain
instructions for building and
• Two parents supply genetic material that
determines the characteristics of their
offspring. (In other words, each parent
supplies genes that determine the traits of
• In sexual reproduction, the offspring will not
be identical to the parents.
• (In asexual reproduction, which involves only
one parent, you’ll remember, the offspring will
be identical to the parent.)
• Where do we see asexual reproduction?
How are Traits Expressed in
• An offspring receives
traits from both
• Dominant traits hide recessive traits. In other
words, even if an offspring receives one dominant
and one recessive trait, the offspring will express
only the dominant trait.
• Recessive traits are only expressed when
provided by both parents. In other words, the
offspring must receive recessive traits from both
the male and female parent. If either parent
passes on a dominant trait, the recessive trait will
Pinkies lean away from each other: dominant
Pinkies lean toward each other: recessive
Thumbs: Straight thumb (dominant trait) vs.
Curved thumb (recessive trait) When viewed
from the side as in the illustration below,
curved thumbs can be seen as part of a circle.
Free ear lobes
Attached ear lobes
No mid-digit hair
Left thumb over
Second toe longest
No cleft chin
Right thumb over
Big toe longest
• Tongue Roller
• Not a Tongue Roller
• Widow’s peak
• Straight hairline
• Cleft Chin
• No Cleft Chin
• Second toe longest
• Big toe longest
Are you an alien?
Are any of these traits learned?
Traits are inherited, not learned. Behavior is
Inherited or Acquired?
• Behavior is the way animals act and react
• Instinct is a form of behavior animals are born
• Other animal behaviors are learned or acquired
through experience or study.
• Birds know how to build a nest. That is an instinct.
• Birds learn how to fly. Their parents teach them.
That is a learned or acquired behavior.
Instinct or Acquired?
Birds fly south for the winter.
Salmon swim miles upstream against
strong currents to lay their eggs.
A bee stings its enemies.
An animal avoids an electrified fence.
A caterpiller spins a cocoon.
A raccoon stands perfectly still if it senses
Instinct or Acquired?
An armadillo jumps straight up when
A child says “please” and “thank you” at
A dog sits before getting a treat.
A black bear hibernates in the winter.
A robin gathers food to feed her young.
A sea lion balances a ball on the tip of its
A cat drinks water when it is thirsty.
DOMINANT OR RECESSIVE?
Brown eyes are dominant.
Colored eyes are recessive.
Earlobes: Free ear lobes (dominant trait) vs.
Attached ear lobes (recessive trait)
Free earlobes are those that hang below the
point of attachment to the head. Attached ear
lobes are attached directly to the side of the
Left thumb on top: dominant
Right thumb on top: recessive
Dimples: Dimples (dominant trait) vs. No
dimples (recessive trait)
Dimples are natural dents in the face to the
right or left of the mouth. If a person has only
one dimple, they should be counted as having