Download Multiple Alleles, Polygenic and Sex

Name: ____________________________ Date:_________________________
Topic:
Multiple Alleles, Polygenic
and Sex-linked Notes
Objective: SWBAT understand the outcome of the cross for multiple alleles,
Questions/Main Ideas:
polygenic inheritance and sex-linked traits.
What is multiple alleles?
Why is blood type
important?
What is Epistasis?
Multiple alleles – more than 2 alleles produces 3 or more genotypes.
Blood Types:
Genotypes
Phenotypes
IaIa or Iai; AA or AO
A
IbIb or Ibi; BB or BO
B
Ii; OO
O
IaIb; AB
AB
-
Because transfusion of the wrong blood type can cause death
Type O is the universal donor, type AB is the universal
acceptor
- Can be used in parental disputes:
Example: if the mother is type A and the child is AB, can the
dad be type O? NO why not?
Epistasis= One allele hides the effects of another allele
Example: Labradors. The dominant allele (E) determines whether the skin will have
pigment. The dominant allele (B) determines how dark it is (color).
What is polygenic
inheritance?
What are sex-linked
traits?
Possible Genotypes
Phenotype
Explanation
BBee
Bbee
bbee
Yellow
No Pigment
bbEE
bbEe
Chocolate
Recessive Color + Pigment
BBEE
BbEE
BBEe
BbEe
Black
Dominant Color + Pigment
Polygenic Inheritance- more than one pair of genes influencing a trait.
Examples: hair color, skin color, eye color
Sex-linked Traits
- 46 chromosomes- 23 pairs ( 22 pairs of autosomes and 1 pair of sex
chromosomes)
- Male  XY
- Female  XXXX
-
What is colorblindness?
What is Hemophilia?
What is Duchenne
Muscualr Dystrophy?
What is testcross?
Summary:
Genes located on the X or Y chromosomes
Most sex-linked genes are found on the X
chromosome
- The human Y chromosome is much smaller and appears
to contain only few genes.
- Father determines the sex of the offspring
- The chance is always 50-50 for either sex
- A recessive gene has no matching gene on the Y
- More Sex linked disorders are found in males
Sex linked disorders:
1. Colorblindness- the inability to distinguish certain colors
- Three human genes associated with colorvision
are located on the X chromosomes
- Red-green colorblindness is the most common form
- In the US, 1 in 10 males and 1 in 100 females have
color- blindness.
- Why the difference? Males have just one X
chromosome.
- Therefore, their genotypes will be XCY or XcY.
- Females have two X chromosomes. Therefore, their genotypes would be
XCXC (normal), XCXc (carrier), and XcXc is colorblind.
2. Hemophilia
- A sex-linked disorder in which a protein for normal blood clotting is missing.
- About 1 in 10,000 males has a form of hemophilia.
- Hemophiliacs can bleed to death from minor cuts; may suffer internal bleeding
from bumps or bruises.
3. Duchenne Muscular Dystrophy
- A sex-linked disorder that results in the progressive weakening and loss of
skeletal muscle.
- 1 in 3000 males (US) has the condition.
Testcross – A Way to Determine Certain Genotypes
- A testcross is a genetic cross of an organism showing the recessive phenotype
with an organism showing the dominant phenotype.
- This is done to determine if the organism with the dominant phenotype is
homozygous dominant or heterozygous dominant.