1. Aim: DNA and Gene Expression
Notepack # 33
Aim: DNA and Gene Expression

2. What is a Gene?
A gene is a section of DNA that codes for a particular protein.
DNA uses the language of nucleic bases (A, T, C & G) to produce a specific code that translates into a protein made up of different combinations of amino acids.
The combination of the amino acids produces a protein with a specific shape, therefore, producing a protein that preforms a specific function.

3. How many genes do we have?
A human’s DNA contains hundreds of thousands of genes, which are all duplicated.
It is important to remember that each individual inherits a set of genes from their mother and another set from their father. This creates two sets of genes.

4. Gene Expression
Gene expression refers to how a characteristic or trait may appear as the results of a gene being turned on or turned off.
Gene expression can occur as the results of two possibilities:
Dominant and Recessive Genes
Environmental Factors

5. Dominant and Recessive Genes
Dominant and recessive genes refer to the fact that some genes have more influence (Dominant) over a characteristic than other genes (Recessive).
Example: The gene for eye color is located at the same location on chromosome 14. Due to a mutation that occurred thousands of years ago, the gene for brown eyes mutated to blue eyes.
The gene for brown eyes is “stronger” than the gene for blue eyes.
To have brown eyes, the individual can have any of these combinations of genes. Brown eyes from one parent and brown eyes from another; or Blue eyes from one parent and brown eyes from the other.
To get blue eyes, the only combination that would give blues eyes is if both parents gave the blue eyed gene.

7. Punnet Squares
Punnet squares is a simple tool used to predict the possibility of characteristic to occur.
Punnet squares uses a set of paired genes from the mother and father to come up with a possible combination of genes from the respected egg and sperm.
Dominate genes are represented by capital letters and recessive genes are represented by lower case letters.

8. B = Brown Eyes
b = Blue Eyes
B B
B B B
BB BB
100% Brown
0% Blue b
Bb Bb
100% Brown
0% Blue
Bb Bb
BB BB
B b
b b B b
BB Bb b
bb bb
75% Brown
25% Blue
0% Brown
100% Blue
Bb bb
bb bb

9. Environmental Factors
The environment can also affect how genes are expressed.
Some genes are sensitive to a particular factor that exist in the environment, such as: temperature, light, and nutrition. These factors can affect how characteristic are expressed.
Tanning is an example of gene expression based on the environment. In the summer your skin gets darker because of the intensity of the sun’s rays; but in the winter your skin gets lighter.

10. Examples of environmental factors causing gene expression.
Lives in Massachusetts Lives in Florida

12. SUMMER
WINTER

13. Non covered grass Grass covered for a
few days with a board

14. Taxi Driver for 42 years

15. What happens if an individual inherits more than a pair of genes?
In rare occasions, during fertilization, an individual can inherit more than a pair of genes (sometimes only one gene).
This occurs when an egg or sperm contains more than 23 chromosomes (or less than 23).
If the individual inherits an extra chromosome number 21, the characteristics that are regulated by that chromosome will amplify resulting in exaggerate characteristics.
If the individual is missing a single chromosome like chromosome number 15, the characteristics that are regulated by that chromosome will express underdeveloped characteristics

16. Individuals with 3 chromosome 21

17. Individuals with only 1 chromosome 15

18. Karyotyping
Karyotyping is a technique used to determine if an unborn child has a chromosomal disorder. (extra set of chromosomes)
Karyotyping involves taking a sample of the fetus’s cell (through a sample of amniotic fluid or a snip of the placenta) and examining the cell’s chromosomes.
Technicians look for cells that are ready to divide and count the chromosomes.
If any abnormalities exist, the parents will have the option to keep or abort the fetus.