1. How is sex determined? Pg. 12-13
Sex determination
While studying fruit flies (≈1910) ____________ _________________ discovered that some traits were inherited differently in males and females.  
Thomas
Hunt Morgan

2. How is sex determined? sex chromosomes
Trying to try to figure out why, Morgan looked at the chromosomes and realized that one pair of chromosomes didn’t look the same in males (however in females they were the same).
The above two chromosomes which appeared to determine the gender of an individual are called ___________________ .
sex chromosomes

3. * *Think of the “y” in boy
How is sex determined?
In humans, the specific chromosomes that control the inheritance of sex characteristics are named the ____ and ___ chromosomes.
Both genders have two sex chromosomes: Female have ____ and males have ____. X Y XX XY
* *Think of the “y” in boy

4. Are you colorblind?
What number do you see?

5. Are you colorblind?
What number do you see?

6. Are you colorblind?
What number do you see?

7. Why are more males colorblind than females?
Genes which are located on the sex chromosomes are said to be sex-_______.
Not all genes on the sex chromosomes control gender (i.e. color-blindness and hemophilia)
linked
Colorblindness is a sex-linked trait. The gene that controls it is located on the X chromosomes

8. Why are some traits more common in men than women?
Sex-linked traits occur more frequently in _________because they have only ______ X chromosome.
If disorders are recessive, a female needs 2 copies of it to get the disorder while men only need 1. They don’t have a second allele to “mask” the recessive one.
men 1

9. How are sex-linked traits inherited?
Color-blindness
____________________ (Xn) is a very common sex-linked trait and is recessive to normal vision (XN). More males have this disorder than females.
XNXN =
XNXn =
XnXn =
XNY =
XnY =
Normal Female
Carrier Female
Color-blind Female
Normal Male
Color-blind Male

10. How is color-blindness inherited?
Cross a carrier female for colorblindness with a male that is normal for colorblindness.
What are the genotypes of the parents? _______X______
XNXn
XNY
XN Xn
What is the probability that one of their children will be colorblind? __________ XN Y
XNXN
XNXn
25% (1/4)
What is the probability of a son being colorblind? _____________
XNY
XnY
50% (1/2)

11. How is color-blindness inherited?
Cross a normal female and a colorblind male. What is the probability that their daughter will be a carrier?
XN XN
100% (2/2) Xn Y
XNXn
XNXn
XNY
XNY

12. Are all differences between males and females sex-linked trait?
Sex-influenced traits:
Traits that have an equal chance of being passed down to males or females, but do not show up equally. Due to the hormonal differences between a male and female, these genes are not expressed equally. 
Example: Some genes for baldness are sex-influenced. The dominant gene that causes baldness in a male does not cause baldness in a female.

13. Are all traits controlled by only 1 gene?
What are some examples of traits you can think of that have a range of phenotypes?
Eye color:
Blue, Green, Brown, Hazel

14. Are all traits caused by only 1 gene?
What are some examples of traits you can think of that have a range of phenotypes?
Hair color:
black to blonde and everything in between.

15. Are all traits caused by only 1 gene?
Polygenic Traits are controlled by the interaction of more than one gene. In humans, there are several obvious examples of polygenic traits such as hair color, eye color, height and skin tone. Traits that are polygenic tend to show great degrees of variation.

16. Are all traits caused by only 1 gene?
Skin color is caused by at least 3 different genes that code for the production of pigment. The more dominant genes that you have, the more pigment is produced (and therefore the darker your skin).

17. Are all traits caused by only 1 gene?
If two parents have a moderate skin tone (AaBbCc), the graph below shows the probability of having a child with each skin tone.
aabbcc aabbCC AaBbCc AABbCc AABBCC
Lightest skin tone Darkest skin tone