CAN YOU SEE ALL THE PRETTY COLORS?? Are females genetically superior to males? Let’s find out!!
All of the traits we have discussed this far such as… Eye color Hair color Dimples Fire breathing involve genes located on the autosomes. What are the autosomes? Let’s find out!
AUTOSOMES= The first 22 pairs of homologous chromosomes. All of the chromosomes surrounded by the blue box are autosomes
If a trait is autosomal, the pattern of inheritance is the same in males and females! In other words, both males and females have an equal chance of inheriting the condition. This isn’t true for all traits. Some traits that we inherited from our parents are located on the 23 rd pair of chromosomes. Do you know what name is given to the 23rd pair of chromosomes???
I hope you said they are called the sex chromosomes. The Sex Chromosomes
Females inherit two “X” chromosomes for their 23 rd pair. Look! Two “X” chromosomes that are the same size
Males, however, have one “X” chromosome and one “Y” chromosome. Look! A male with an “X” and a “Y” chromosome
Today we will explore why males are more likely to inherit sex linked conditions. These sex linked conditions include… Muscular Dystrophy Hemophilia Colorblindness
Let’s take a simple colorblind test! As you observe the following slides, you are to determine the letter or number that you see. Please do not yell out your ideas. Remember to give everyone a chance. If you are unable to see the letter or number, it’s not a big deal. You may simply have the genetic inability to distinguish that particular color.
DID YOU SEE A 25?
DID YOU SEE A 45?
DID YOU SEE A 29?
DID YOU SEE A 6?
DID YOU SEE A 56?
DID YOU SEE A 8?
The individual with normal color vision will see a 5 revealed in the dot pattern. An individual with Red/Green (the most common) color blindness will see a 2 revealed in the dots. An individual who can’t see the big circle at all needs glasses.
So, why are males affected by sex linked conditions like hemophilia and color blindness more often than females???
Females have two “X” chromosomes Look! Two nice HOMOLOGOUS chromosomes!!!
In Order for a female to show a sex linked recessive condition, she needs two recessive alleles. One on each chromosome. B= Normal Visionb=Color blind BBB B Will she be color blind? Why? I hope you said NO! She has two dominant alleles. As a result, she has normal vision.
BBb b Will this female be color blind? This female is known as a CARRIER. She is normal BUT she carries the recessive allele for the condition. NOPE!!!
bbb b Will this female be color blind??? How many of the recessive alleles did she need to inherit in order to be considered color blind? Yes!!! TWO
So, why are guys more likely to inherit sex linked recessive conditions? Look at that “Y” chromosome
As we just saw, females inherit two genes for color vision on the sex chromosomes. One from mom and one from dad. How many genes for color vision do males inherit? WHY?? JUST ONE!!!
The male “X” chromosome is a normal sized chromosome just like the two female “X” chromosomes. BB See. It’s the same size.
The “Y” chromosome is not the same size as the “X” chromosome. As a result, there is/are no genes for color blindness or hemophilia, etc… on the “Y” chromosome. BB THE “Y” CHROMOSOME LOOK! NO GENES
WHY IS THIS BAD FOR MALES????
WILL THIS MALE BE COLOR BLIND? BB NOPE! WHY? He has the dominant allele on his “X” chromosome. As a result he has normal vision.
WILL THIS MALE BE COLOR BLIND? bb YEP! WHY? He has the recessive allele. As a result, he is colorblind.
LET’S TRY SOME PROBLEMS!!!
Sex Linked Inheritance Practice A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color-blind marries a color- blind male. What is the probability that a son of this couple will be color-blind?
When reporting the answer to a sex linked problem you must separate out the males from females. Ex:
Sex Linked Inheritance