Download Notes-Sex Linked Traits and Polygenic Traits

How is sex determined? Pg. 12-13


Sex determination
Thomas
While studying fruit flies (≈1910) ____________
Hunt Morgan discovered that some traits
_________________
were inherited differently in males and females.
How is sex determined?


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 .
___________________
How is sex determined?

In humans, the specific chromosomes that control the
inheritance of sex characteristics are named the
X and ___
Y chromosomes.
____


Both genders have two sex chromosomes: Female
XX and males have ____.
XY
have ____
* *Think of
the “y” in
boy
Are you colorblind?

What number do you see?
Are you colorblind?

What number do you see?
Are you colorblind?

What number do you see?
Why are more males colorblind than
females?

Genes which are located on the sex
chromosomes are said to be sex-_______.
linked
 Not
all genes on the sex chromosomes control gender
(i.e. color-blindness and hemophilia)
• Colorblindness is a sex-linked
trait. The gene that controls it is
located on the X chromosomes
Why are some traits more common in
men than women?


Sex-linked traits occur more frequently in
_________because they have only ______
1
X chromosome.
men
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.
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 = Normal Female
XNXn = Carrier Female
XnXn = Color-blind Female
XNY = Normal Male
XnY = Color-blind Male
How is color-blindness inherited?


Cross a carrier female for colorblindness with a male
that is normal for colorblindness.
NXn
NY
X
X
What are the genotypes of the parents? _______X______
XN
XN
Y
Xn
XNXN XNXn
XNY
XnY
What is the probability that one of
their children will be colorblind?
25% (1/4)
__________
What is the probability of a son
being colorblind?
50% (1/2)
_____________
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
Xn XNXn XNXn
NY XNY
X
Y
100% (2/2)
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.
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
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.
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.
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).
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
Lightest skin tone
aabbCC
AaBbCc
AABbCc
AABBCC
Darkest skin tone