General Biology 2: Unit 5 - Beyond Mendelian Inheritance

(02-14-2026)

•Traits are controlled by one gene

• Only two alleles exist

•One allele is completely dominant

•Traits are inherited independently

What do the Mendel’s Laws assume?

Incomplete Dominance

• Neither allele is completely dominant.

•The offspring shows a blended phenotype.

•Example:

Red flower × White flower → Pink flower

Curly hair × Straight hair → Wavy hair

Codominance

Both alleles are fully expressed in the phenotype.

•Example:

•AB blood type (both A and B antigens are present)

•Black chicken × White chicken → Black and white feather

Multiple Alleles

•A gene has more than two alleles.

•An individual still inherits only two alleles, but more exist in the population. •Example:

•Human blood types: A, B, AB, O

Polygenic Inheritance

•Traits controlled by two or more genes.

•Results in continuous variation.

•Example:

• Height

• Skin color

•Eye color

Sex-Linked Traits

•Traits controlled by genes located on the X or Y chromosome.

• More common in males because they have only one X chromosome. •Example:

•Color blindness

• Hemophilia

Environmental Influence on Traits

•Genes interact with the environment to affect traits.

•Example:

•Skin tanning due to sunlight

•Plant height affected by soil nutrients