3U N7 Multiple Alleles
February 21, 2013
Thursday, February 21st
1) Take­up yesterday's questions
2) Multiple Alleles
­ note
­ text practice questions
* Test on Monday
* Research Assignment ­ due Monday
Multiple Alleles
The existence of multiple alleles means that there may be many possible genotypes for a particular gene, and many possible phenotypes
Examples:
• Eye colour in fruit flies
• Blood types
Blood Types
Multiple Alleles in Fruit Flies p. 143 • Blood types in humans involves three alleles
• A person can have one of four blood types: (use Symbol I for the gene )
6 possible genotypes
A, B, AB, or O
The alleles for blood types
A and B are codominant
but are dominant over the
allele for type O
p.147
Blood Types continued
Why are blood types important?
The letters of the blood type refer to two types of carbohydrates, A and B, that are found on the surface of red blood cells (RBC's).
A person's RBC's may be coated with either carbohydrate A (blood type A) or carbohydrate B (blood type B), both carbohydrates (AB), or neither (blood type O)
When someone requires a blood transfusion, it is critical
to match the recipient's blood type with a compatible donor blood type.
If incompatible, the recipient will have a potentially fatal immune response.
The immune system detects cells that appear foreign. So, someone with blood type A has an immune system that recognizes red blood cells with carbohydrate B as foreign and will try to destroy them. Immune system proteins called antibodies will bind to the foreign carbohydrates, causing the donor RBC's to clump together.
3U N7 Multiple Alleles
February 21, 2013
Sample Problem
Summary of Blood Types
Blood Type
A
Able to receive blood from Able to donate blood to
A, O
A, AB
B, AB
B
B, O
AB
A, B, AB, O
AB
O
O
A, B, AB, O
A man has blood type A and his wife has blood type B. A child has blood type O.
Explain how they are the parents of this child.
woman
Which blood type is known as the universal donor? Type O
Which blood type is known as the universal recipient? AB
In addition to the A and B antigens, there is a third antigen called the Rh factor, which can be either present (+) or absent ( – ). In general, Rh negative blood is given to Rh­negative patients, and Rh positive blood or Rh negative blood may be given to Rh positive patients.
IB IO
IA IAIB IAIO
man
IO IBIO IOIO
Traits Influenced by Multiple Genes
• Traits such as pea plant height, snapdragon flower colour and ABO blood type are under the control of a single gene.
Dogs, cats, horses, and chimpanzees are among the species with known blood type variations
The Environmental Influence on Traits
In genetics "environment" refers to the conditions in which a cell or organism lives.
For example, temperature can have a very interesting effect on phenotypes.
The Siamese cat is covered in creamy white fur, except on its ears, face, feet and tail. The pattern is due to a mutation in a gene for pigment production. As a result, the enzyme responsible for black fur is sensitive to heat. The enzyme is active only in the cooler temperatures found at the cat's extremities. Polygenic Inheritance
• Some traits are influenced by more than one gene
• In humans, eye colour and height exhibit polygenic inheritance
• It is the interaction of several different genes that can influence phenotype. • The amount of protein made by genes working together results in variation among a population