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Why do I Look This Way?
Elementary Genetics
Chromosomes
Chromosomes carry
the genetic information
of the individual.
Each chromosome is
made of a single
strand of DNA
Humans have 23
pairs of
chromosomes
Gender
 You have two chromosomes that determine
your gender
Females have XX
Males have XY
Here are the gender
possiblilities
 From mother XX
from father XY
gender
X
X
Female
X
Y
Male
X
X
Female
X
Y
Male
Where are the
chromosomes located?
The chromosomes are
in the nucleus of each
cell. Every cell has the
exact same ones.
When the cells duplicate
(mitosis), they make exact
copies of the chromosomes.
 Sex cells have half as many
chromosomes.
Sex Cells
 Duplicate through MEIOSIS
 Have half as many chromosomes as
other cells
 Are called “eggs” in females
 Are called “sperm” in males
 Must join to begin life
Why is sexual
reproduction
important?
 Keeps species from dramatically
overpopulating
 Insures that parents are old enough to
care for young
 Makes individuals that are not identical
 Allows elimination of weak traits
traits
 Some traits are dominant while others
are recessive
 You inherit one chromosome from each
parent (each with a trait marker)
 You will exhibit the trait which is dominant
Eyes, for example:
 Brown eyes are dominant over blue
 Your mother could have blue eye if she has
bl bl
 Your father might have brown eyes if he has
BR bl You could get:
 bl BR You would have BR eyes
 bl bl
You would have bl eyes
 bl BR You would have BR eyes
 bl bl
You would have bl eyes
OR:
 Your mother might have brown eyes if
she has BR bl
 Your father might have brown eyes if he
has BR bl You could get:




BR BR
BR bl
bl BR
bl bl
You would have BR eyes
You would have BR eyes
You would have BR eyes
You would have bl eyes
Just a note:
 While it its generally true that brown eye
genes are dominant over green eye
genes which are both dominant over blue
eye genes, variations can occur.
Because many genes are required to
make eye color pigments, there is a way
called genetic compensation to get brown
or green eyes from blue-eyed parents.
The double helix structure was
discovered due to the work of
three scientists:
 Rosalind
Franklin
 James
Watson
 Francis
Crick