27:2 Human Traits

• Objectives:

• Compare recessive and dominant traits with incomplete dominance

• Describe different ways human traits can be inherited

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

• Free earlobes

• dominant dimples

• curly hair

• Human

• Traits

• attached earlobes

• recessive no dimples

• straight hair

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

• 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

• 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

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

• 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.

• 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.

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.

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

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

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

• 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

• 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