Alleles
We get our physical traits from our mother and father. Two or more variations of genes are called alleles.
Dominant traits
Traits that get expressed even in the presence of one copy different variant of the same type of allele.
Recessive traits
Traits that only get expressed when two copies same variant of an allele are present in a gene.
Co-dominance
Both dominant and recessive allele expresses themselves in an individual. Classic example would be our blood group.
Incomplete Dominance
Dominant and recessive alleles blend in and form a particular phenotype. Results an intermediate between the two alleles.
Explanation: Cross between straight hair genes (homogeneous, SS) and curly hair genes (homogeneous, ss) can result in wavy hair (heterogeneous, Ss).
Example,
- Wavy Hair
- Medium nose
- Medium-sized eyes
Polygenic traits
Condition of features that are expressions by more than just one gene. More than two variations of any subjected character.
Example,
- Body Shape
- Eye colour - Dark brown eyes are dominant over blue and grey eyes
- Hair colour
- Height - dwarfism is dominant over tall stature
- Skin colour - Dark skin is dominant over lighter skin
Sex-linked Traits
1. X-linked Recessive Traits
Male child has one copy of X chromosome. Comes from the mother.
Examples,
- Colour blindness
- Duchenne muscular dystrophy syndrome
- Hemophilia A and B
- Hunter syndrome
- Wiskott-Aldrich syndrome
Related: Dominant vs Recessive Traits: Mendelian inheritance
2. X-linked Dominant Traits
Present on the X chromosome. Inherited from the father. Female child carriers the dominant allele. A male child of the same mother will inherit the trait.
Examples,
- Coffin-Lowry syndrome
- Rett syndrome
- Vitamin D resistant rickets
3. Y-linked Inheritance
Present on the Y chromosome. Inherited only by a male child. Females don't have Y chromosomes, duh!
