Alternate Patterns Alternate Patterns of Inheritanceof Inheritance

The simple rules of The simple rules of Mendelian inheritance Mendelian inheritance

(complete dominanance) (complete dominanance) do not always apply…. do not always apply….

there are exceptionsthere are exceptions

1. Co-Dominance1. Co-Dominance

BOTH alleles are dominantBOTH alleles are dominant

In a heterozygous individual, BOTH are In a heterozygous individual, BOTH are expressed in original formexpressed in original form

Results in having characteristics of Results in having characteristics of BOTH parentsBOTH parents

Co dominanceCo dominance

Example Example Red flowers + white flowers Red flowers + white flowers

red/white flowersred/white flowers

Co dominanceCo dominance

Examples in humans: Examples in humans: Blood typesBlood types

Sickle Cell AnemiaSickle Cell Anemia

2. Incomplete 2. Incomplete DominanceDominance

NEITHER allele is dominant (equal)NEITHER allele is dominant (equal)

In a heterozygous individual In a heterozygous individual NEITHER original trait can be seenNEITHER original trait can be seen

Results in a combined phenotype, Results in a combined phenotype, or blendor blend

Incomplete dominanceIncomplete dominance

ExampleExample Red flowers + white flowers Red flowers + white flowers pink pink

flowersflowers Example in humans: Skin colorExample in humans: Skin color

3. Sex-linked traits3. Sex-linked traits

Sex-linked gene is located on the X Sex-linked gene is located on the X chromosomechromosome

The X chromosome is longer and The X chromosome is longer and has more genes than yhas more genes than y

Therefore, sex-linked traits are Therefore, sex-linked traits are always always x-linkedx-linked

X-linked traitsX-linked traits

Result Result Females will have 2 copies of the sex-Females will have 2 copies of the sex-

linked traitlinked trait Males only have one copy of this geneMales only have one copy of this gene

Even if the gene is recessive, males Even if the gene is recessive, males only need one gene to get the traitonly need one gene to get the trait

Therefore males exhibit some traits Therefore males exhibit some traits more frequently than femalesmore frequently than females

Example of Example of x-linked traits x-linked traits

HEMOPHILIAHEMOPHILIA Recessive disorderRecessive disorder Missing a trait that codes for a protein Missing a trait that codes for a protein

essential to blood clottingessential to blood clotting Bleeders disease – bleed very easilyBleeders disease – bleed very easily Females can get the disease, but Females can get the disease, but

usually act as a carrier (have the usually act as a carrier (have the gene/not the disorder)gene/not the disorder)

HEMOPHILIAHEMOPHILIA PHENOTYPEPHENOTYPE

Normal femaleNormal female

Female carrierFemale carrier

Hemophiliac femaleHemophiliac female

Normal maleNormal male

Hemophiliac maleHemophiliac male

GENOTYPEGENOTYPE

XX XX

XXhh XX

XXhh XXhh

XX YY

XXhh YY

Other examples ofOther examples of x-linked x-linked

BALDNESS

Red/Green Color blindness  Color vision test

Genetics Vocabulary

1. dominant2. recessive3. genotype4. phenotype5. allele6. homozygous7.heterozygous

8. incomplete dominance

9. co dominance10. x-linked traits11. genotypic ratio12. phenotypic ratio