Post on 14-Dec-2015
Multiple Alleles• Traits are the result of
more than 2 types of alleles
• Example: blood typing• There are 3 different
alleles for blood type (A, B, & O)
• A is dominant to O• B is also dominant to O• A and B are both
codominant
Blood Transfusions• Blood can only be transferred to a body of a person who's immune
system will "recognize" it. • Type A = A antigens• Type B = B antigens • Type O = No antigens• O is the universal donor
– a person can receive a transfusion from O blood without having an immune response
• AB is the universal recipient – because a person with AB blood has both the A and B antigens
already in the body
Sex-linked Traits A gene that is found only on
the X chromosome and not the Y chromosome
Examples: Colorblindness Hemophilia Duchenne Muscular
Dystrophy Male Pattern Baldness
Female Male
Sex-linked Traits More common in men
because they only have one X chromosome
Females need to have the gene on both X’s to have the trait
Females that are heterozygous for the trait are carriers
Carriers appear normal but can pass the trait to their offspring
Colorblindness Recessive trait on X
chromosome Condition in which certain
colors cannot be distinguished
Red/Green color blindness is most common (about 99%)
Causes problems in distinguishing reds and greens
No treatment Life is normal
Hemophilia Recessive trait on the X
chromosome Bleeding disorder in which
the blood does not clot normally
Persons with hemophilia may bleed for a longer time than others after an injury or accident
They also may bleed internally, especially in the joints
Live life cautiously, receive treatments to help blood clot normally
Duchenne Muscular Dystrophy
Caused by a recessive gene on the X chromosome
Rapidly-worsening muscle weakness that starts in the legs and pelvis, and later affects the whole body
No cure Treatment is aimed at control of
symptoms to maximize the quality of life
Death usually occurs by age 25
Sample Problem: Male Pattern Baldness
1. Unlike all the other crosses there is information that we know before we ever read the problem. We know that a XX female is going to mate with a XY male. So, you can set up your square ahead of time.
XX XY
XX XY
X Y X
X
2. Next, you have to read the problem and figure out what the sex-linked condition is and write down the allele you want to use for the problem and set up a key!
Baldness is a sex-linked trait. The allele for baldness is recessive and is carried on the X chromosome. The Griffin family lives in a town called Quahog. The father, Peter, has a gene for normal hair. The wife, Lois, is a carrier for baldness. Peter and Lois have 3 kids: Chris, Meg, and Stewie. The kids want to know what is the probability they will develop baldness?
Setting up your key What letters will Peter have since he is a male? XY What letters will Lois have since she is a female? XX Decide what letter you will use for the trait B = normal, b= bald
3. Reread the problem and find the parents genotypes using the key you just made
So, Peter is XY and Lois is XX Now you have to add the allele for
baldness to all of the X chromosomes as described in the problem
Peter XBY Lois XBXb
XBXB XBY
XBXb XbY
XB Y
XB
XbPheno: ¼ female, normal
¼ female, carrier
¼ male, normal
¼ male, bald
Geno: ¼ XBXB
¼ XBXb
¼ XBY
¼ XbY