EXTENSION OF MENDELIAN GENETICS (NON-MENDELIAN
GENETICS)
Protein - provide structure and support for cells.
Wild-type alleles - prevalent alleles in a population; most frequent; dominant.
- These encode proteins that
- function normally
- made in the right amounts
Mutant alleles - rare in natural population; alleles that have
been altered by mutation; recessive.
These tend to be
- cause a reduction in the amount or function of the encoded protein
- prevents the allele from producing a fully functional protein
(Example in relation with Mendel’s experiment)
Wild-type (dominant) allele Mutant (recessive) allele
Purple flowers White flowers
Axial flowers Terminal flowers
Yellow seeds Green seeds
Round seeds Wrinkled seeds
Smooth pods Constricted pods
Green pods Yellow pods
Tall plants Short plants
1. Dominance Relations
- The various ways in which pair of alleles can affect the phenotype.
- Alleles can show different degrees of dominance and recessiveness in relation to
each other.
▪ Incomplete Dominance - the heterozygote exhibits a phenotype that is
intermediate between the corresponding homozygotes.
Example:
• Flower color in the four o’clock plant
• Two alleles
C = wild-type allele for red flower color
R
CW = allele for white flower color
• A red snapdragon (four o’clock plant) is crossed with a white snapdragon
and the resulting offspring will all be pink
• Results in a blending of the two alleles
- In this case, 50% of the CR protein is not enough to produce the
red phenotype.
- 1:2:1 phenotypic ratio NOT the 3:1 ratio observed in simple
Mendelian inheritance
GENETICS)
Protein - provide structure and support for cells.
Wild-type alleles - prevalent alleles in a population; most frequent; dominant.
- These encode proteins that
- function normally
- made in the right amounts
Mutant alleles - rare in natural population; alleles that have
been altered by mutation; recessive.
These tend to be
- cause a reduction in the amount or function of the encoded protein
- prevents the allele from producing a fully functional protein
(Example in relation with Mendel’s experiment)
Wild-type (dominant) allele Mutant (recessive) allele
Purple flowers White flowers
Axial flowers Terminal flowers
Yellow seeds Green seeds
Round seeds Wrinkled seeds
Smooth pods Constricted pods
Green pods Yellow pods
Tall plants Short plants
1. Dominance Relations
- The various ways in which pair of alleles can affect the phenotype.
- Alleles can show different degrees of dominance and recessiveness in relation to
each other.
▪ Incomplete Dominance - the heterozygote exhibits a phenotype that is
intermediate between the corresponding homozygotes.
Example:
• Flower color in the four o’clock plant
• Two alleles
C = wild-type allele for red flower color
R
CW = allele for white flower color
• A red snapdragon (four o’clock plant) is crossed with a white snapdragon
and the resulting offspring will all be pink
• Results in a blending of the two alleles
- In this case, 50% of the CR protein is not enough to produce the
red phenotype.
- 1:2:1 phenotypic ratio NOT the 3:1 ratio observed in simple
Mendelian inheritance
