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 x- linked

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 Normal female Female carrier Hemophiliac female Normal male Hemophiliac male  GENOTYPE XXXXXXXX Xh XXh XXh XXh X Xh XhXh XhXh XhXh Xh XY XY XY XY XhYXhYXhYXhY

Other examples of x-linked   BALDNESS   Red/Green Color blindness   Color vision testColor vision test

Genetics Vocabulary 1. dominant 2. recessive 3. genotype 4. phenotype 5. allele 6. homozygous 7.heterozygous 8. incomplete dominance 9. 9.co dominance x-linked traits 11. genotypic ratio 12. phenotypic ratio