Download Alternate Patterns of Inheritance

Alternate Patterns of
Inheritance
The simple rules of
Mendelian inheritance
(complete dominanance)
do not always apply….
there are exceptions
1. Co-Dominance
 BOTH alleles are dominant
 In a heterozygous individual, BOTH are
expressed in original form
 Results in having characteristics of BOTH
parents
Co dominance
 Example
 Red flowers + white flowers  red/white
flowers
Co dominance
 Examples in humans:
 Blood types
 Sickle Cell Anemia
2. Incomplete Dominance
 NEITHER allele is dominant (equal)
 In a heterozygous individual NEITHER
original trait can be seen
 Results in a combined phenotype, or
blend
Incomplete dominance
 Example
 Red flowers + white flowers  pink flowers
 Example in humans: Skin color
3. Sex-linked traits
 Sex-linked gene is located on the X
chromosome
 The X chromosome is longer and has
more genes than y
 Therefore, sex-linked traits are always xlinked
X-linked traits
 Result
 Females will have 2 copies of the sex-linked
trait
 Males only have one copy of this gene
 Even if the gene is recessive, males only
need one gene to get the trait
 Therefore males exhibit some traits more
frequently than females
Example of
x-linked traits
 HEMOPHILIA
 Recessive disorder
 Missing a trait that codes for a protein
essential to blood clotting
 Bleeders disease – bleed very easily
 Females can get the disease, but usually act
as a carrier (have the gene/not the disorder)
HEMOPHILIA
 PHENOTYPE
 GENOTYPE
Normal female
X
X
Female carrier
Xh
X
Hemophiliac female
Xh
Xh
Normal male
X
Y
Hemophiliac male
Xh
Y
Other examples of
x-linked
 BALDNESS
 Red/Green Color blindness
 Color vision test
Genetics Vocabulary
1. dominant
2. recessive
3. genotype
4. phenotype
5. allele
6. homozygous
7.heterozygous
8. incomplete dominance
9. co dominance
10. x-linked traits
11. genotypic ratio
12. phenotypic ratio