Human traits can be inherited in different ways. Dominant traits will show up if there is one dominant gene, while recessive traits require two recessive genes. Examples of incomplete dominance are pink snapdragons and people with both round and sickle-shaped blood cells. Sickle-cell anemia results when someone inherits two genes for sickle-shaped blood cells. Blood types are determined by the A, B, and O genes. Colorblindness is inherited through the X chromosome.

1. 27:2 Human Traits
• Objectives:
• Compare recessive and dominant traits with
incomplete dominance
• Describe different ways human traits can be
inherited

2. Review
• One dominant gene is needed for a trait to
show up
• Two recessive genes are needed for a
recessive trait to show up
• Examples of recessive traits are: straight
hair, short eyelashes
• Examples of dominant traits are: curly hair,
the ability to roll your tongue, dimples

3. • Free earlobes
• dominant dimples
• curly hair
• Human
• Traits
• attached earlobes
• recessive no dimples
• straight hair

4. Incomplete Dominance
• Incomplete dominance is when a new trait
is formed. Neither gene is dominant over
the other.
• The gene is heterozygous, but the dominant
trait is not seen. A new trait is formed that
is a blend of the dominant and recessive
trait

5. • When a pure dominant red snapdragon
flower is mated with a pure recessive white
snapdragon the results is that the offspring
is a heterozygous pink flower

6. • The genes them selves do not change, just
the resulting traits change.
• If the genes are separated then we see the
red and white genes again.
• If two pink flowers
are mated then
they produce red,
white and pink
offspring

7. Sickle-Cell Anemia
• Most people have blood cells that are round
• Some people have cells that are shaped like
a sickle that is used to cut grass. These cells
are called sickle cells.
• Some people have both shape blood cells

8. • Sickle-Cell Anemia is a genetic blood
disorder that is more common among
African-American people.
• It is a genetic blood disorder where the
blood cells are shaped like a sickle.

9. • This shape cell does not move through the
capillaries very well because their shape causes
the capillaries to become clogged
• They also cannot carry enough oxygen to the body
tissue
As a result a
person with
sickle-cell
anemia can
suffer serious
health problems.

10. If both parents carry the sickle-cell then one out of four
offspring would have round cells, two out of four would have
both round and sickle cells and one out of four would have all
sickle-cells. This child would have Sickle-Cell Anemia.

11. Blood Types in Humans
• There are four blood types in humans
• A, B, AB, O
• Three genes control blood type but people
only have two of them
• A and B are dominant to O

12. The A or B gene is dominant to the O
gene type

13. Genes on the X Chromosome
• Sex chromosomes carry genes
• Because females have two X chromosomes,
they have two genes for some traits
• Males only have one gene for these traits
because they have only have one X
chromosome. These genes are not on the Y
chromosome

14. • When the XY chromosomes are together
the genes on the X chromosome control the
trait
• Colorblindness is a trait controlled by the X
chromosome, so it is not found on the Y
chromosome

15. • Being color blind means not being able to
see red and green as two separate colors
• Not being able to red and green is a
recessive trait.
C - dominant
Able to see red
and green
c- recessive