Genetic diagrams and crosses
| English | Chinese | Pinyin |
|---|---|---|
| Punnett square | 庞纳特方格 | páng nà tè fāng gé |
| monohybrid cross | 单基因杂交 | dān jī yīn zá jiāo |
| dihybrid cross | 双基因杂交 | shuāng jī yīn zá jiāo |
| multiple alleles | 复等位基因 | fù děng wèi jī yīn |
| sex linkage | 伴性遗传 | bàn xìng yí chuán |
| epistasis | 上位性 | shàng wèi xìng |
| chi-squared test | 卡方检验 | kǎ fāng jiǎn yàn |
Genetic crosses
- A genetic diagram shows how alleles pass to offspring.
- The handiest tool is the Punnett square 庞纳特方格 — a grid of all gamete combinations.
- Then we meet the special cases.
A Punnett square is used to predict the offspring genotypes and ratios of a genetic cross.
It combines every possible pairing of the parents' gametes.
The Punnett square
- A monohybrid cross 单基因杂交 follows one gene; a dihybrid cross 双基因杂交 follows two at once.
- Some genes have multiple alleles 复等位基因 (more than two versions in a population), like human blood groups.
Genetic crosses
Aa × Aa → 3 : 1
Pick the parents' genotypes and read the offspring ratios straight from the Punnett square.
In a Tt × Tt cross (T dominant), the offspring ratio is:
The Punnett square gives TT, Tt, Tt, tt — three with a dominant T (tall) to one tt (short).
In a Tt × Tt cross, what fraction of the offspring (as a decimal) are expected to be short (tt)?
One of the four boxes (TT, Tt, Tt, tt) is tt, so 1/4 = 0.25 are short.
Match each genetics term to its meaning.
Mono = one gene, di = two; a sex-linked gene is on the X; the Punnett square works out the ratios.
A cross that follows the inheritance of a single gene is a ______ cross.
A monohybrid cross follows one gene; a dihybrid cross follows two genes together.
Special inheritance patterns
- sex linkage 伴性遗传: the gene is on the X chromosome, so results differ for males and females.
A sex-linked gene sits on the X chromosome, so sons and daughters inherit it differently
- linkage: genes on the same chromosome tend to be inherited together.
- epistasis 上位性: one gene affects how another gene is shown.
Sex linkage means that:
A sex-linked gene sits on the X chromosome, so inheritance differs between the sexes.
The chi-squared test 卡方检验
- The chi-squared test compares the numbers you actually counted with those you expected.
- It tells you whether the difference is small enough to be chance, or large enough to mean something else is going on.
The chi-squared test is used to:
Chi-squared tests whether the gap between observed and expected counts is small enough to be chance.
You've got it
- a Punnett square shows all gamete combinations (Tt × Tt → 3 : 1)
- monohybrid (one gene) vs dihybrid (two genes); multiple alleles = >2 versions
- sex linkage (gene on X), linkage (same chromosome, inherited together), epistasis (one gene affects another)
- chi-squared compares observed vs expected — is the difference just chance?