1. The Basics of Genetics
6 Laws about Heredity

2. 1. Traits are passed or inherited
from one generation to the next.
• Your genetic instructions are located in the nucleus of
every cell, stored within chromosomes.

3. How will your traits be passed on to
your future children?
• Fathers pass genetic
instructions to
offspring through
sperm cells.
• Mothers pass genetic
instructions to
offspring through egg
cells.

4. 2. Genes control the traits of an
organism.
•No, not
THAT
Gene!

5. 2. Genes control the traits of an
organism.
• A gene is a section of
a chromosome, that
codes for a specific
trait.
• Chromosomes are
made of tightly wound
strands of DNA

7. 3. Organisms inherit genes in pairs,
one from each parent.
• Human sex cells (sperm
or egg) contain 23
chromosomes each.
• When the egg is
fertilized, the embryo
will have 46
chromosomes in each of
its cells, which is the
correct number of
chromosomes for a
human.

8. Sexual Reproduction
(2 parents) creates unique offspring.
• In plants, male
chromosomes are
passed through pollen
grains to female egg
cells. Once
fertilized, these eggs
will develop into
seeds.
• The new plants will
receive a combination
of traits from both
parents.

9. 4. Some genes are dominant,
while others are recessive.
• “Stronger” traits are
called dominant.
• “Weaker” traits are
called recessive.
• Geneticists use
symbols (letters) to
represent the different
forms of a gene.

10. Dominant traits are
represented by a capital letter.
• Yellow seeds
are
dominant……..
Y

11. Recessive genes (for the same trait)
are represented by THE
SAME letter, but it is lower case .
Green seeds are
recessive……….
y
Dominant (yellow) = Y
Recessive (green) = y

12. Pea Plant Genotype
• In pea plants, tall
is dominant over
short. The letter
used to represent
the tall gene is T
(BIG T).
• The short gene is
Tall =T represented by t
Short = t (little t).

13. In humans, brown eyes are dominant
over blue.
Brown = B
Blue = b

14. 5. Dominant genes hide recessive genes
when an organism inherits both.
• Y + y = yellow seeds
(yellow is dominant)
• T + t = tall plant (tall
is dominant)
• B+ b = brown eyes
(brown is dominant)

15. A PUREBRED organism has two of
the same genes for a trait.
• TT = purebred TALL
• tt = purebred SHORT
• This genotype is also
called
HOMOZYGOUS

16. A HYBRID organism has two
different genes for a trait.
• Tt = hybrid TALL
(tall is dominant)
• This genotype is also
called
HETEROZYGOUS

17. Will a hybrid human with the genes
Bb have brown or blue eyes?
• Bb = Brown eyes
• The dominant gene (brown), will be expressed in a
hybrid.

18. Why must all blue eyed people be
PUREBRED for that trait?
• If the dominant gene is present, it will always be
expressed.
• The only possible gene combination for blue eyes is
bb

19. 6. Some genes are neither dominant
nor recessive. These genes show
incomplete dominance.
• If an organism shows
INCOMPLETE
DOMINANCE for a
trait, the hybrid will
show a blend of the
two traits.

20. Human Hair Texture
• Because neither curly
nor straight hair is
recessive, no lower
case letters are used.
• CC = curly hair
• CS = wavy hair
• SS = straight hair

21. These basic laws of inheritance control
the traits of all living organisms on
Earth.