Non-Mendelian Genetics
| English | Chinese | Pinyin |
|---|---|---|
| incomplete dominance | 不完全显性 | bù wán quán xiǎn xìng |
| codominance | 共显性 | gòng xiǎn xìng |
| multiple alleles | 复等位基因 | fù děng wèi jī yīn |
| polygenic | 多基因 | duō jī yīn |
When 3 : 1 breaks down
- Mendel's simple dominant-and-recessive rules explain a lot, but not everything.
- Some traits blend; some show two versions at once; some depend on many genes.
- These patterns are called non-Mendelian inheritance.
- They make the living world far more varied than a simple 3 : 1.
Incomplete dominance
- In incomplete dominance 不完全显性, neither allele fully wins.
- The heterozygote is a blend of the two.
- A red flower crossed with a white one gives pink offspring.
- The two alleles mix, rather than one masking the other.
In incomplete dominance, a red and a white flower can give offspring that are…
In incomplete dominance neither allele fully dominates, so the heterozygote is a blend — pink.
Codominance
- In codominance 共显性, both alleles show fully, at the same time.
- Neither blends and neither hides — you see both.
- In blood group AB, both the A and the B alleles are expressed.
- The result shows each allele clearly, side by side.
In codominance, both alleles…
In codominance both alleles are fully expressed together — like the A and B in blood group AB.
Some genes, like the human blood group gene, have more than two possible alleles.
The ABO gene has three alleles (A, B, O) — an example of multiple alleles.
Multiple alleles and polygenic traits
- Some genes have multiple alleles 复等位基因 — more than two versions in a population.
- The blood-group gene has three: A, B, and O.
- A polygenic 多基因 trait is controlled by many genes together.
- Height and skin colour are polygenic, giving a smooth range of values.
Which inheritance pattern?
Sort each example by the non-Mendelian pattern it follows.
A trait controlled by many genes together, like skin colour, is called ____.
A polygenic trait is shaped by many genes adding together, giving a smooth range of values.
Select all true statements about non-Mendelian inheritance.
Many traits do not follow the simple 3:1 pattern. The other three are correct.
Simple dominant-and-recessive is just one pattern, not the whole story. Do not force every trait into a 3 : 1 ratio — many follow incomplete dominance, codominance, multiple alleles, or polygenic inheritance instead.
The ABO blood groups:
- The gene has three alleles: A, B, and O.
- A and B are codominant — someone with both shows blood group AB.
- O is recessive to both — so type O needs two O alleles. Several patterns in one gene.
Not all inheritance is simple dominant-and-recessive. In incomplete dominance the heterozygote is a blend; in codominance both alleles show fully; some genes have multiple alleles; and polygenic traits are shaped by many genes together. These non-Mendelian patterns add huge variety.