5.3 Mendelian Genetics
Keywords
| English Term | 中文翻译 | Definition & Explanation |
|---|---|---|
| Allele | 等位基因 | Alternative versions of a gene that produce distinguishable phenotypic effects. |
| Genotype | 基因型 | The set of alleles inherited for one or more genes by an individual organism. |
| Phenotype | 表型 | The observable physical and physiological traits of an organism, which are determined by its genetic makeup. |
| Homozygous | 纯合子 | Having two identical alleles for a given gene (e.g., \(AA\) or \(aa\)). |
| Heterozygous | 杂合子 | Having two different alleles for a given gene (e.g., \(Aa\)). |
1. Mendel's Fundamental Laws
Mendel's laws describe how genes are passed from parents to offspring. These laws specifically apply to genes located on different chromosomes.
- Law of Segregation: During gamete formation, the two alleles for a heritable character separate (segregate) from each other and end up in different gametes.
- Law of Independent Assortment: Two or more genes assort independently—that is, each pair of alleles segregates independently of any other pair of alleles—during gamete formation.
2. Fertilization and Genetic Variation
In most cases, fertilization involves the fusion of two haploid (\(1n\)) gametes. * This process restores the diploid (\(2n\)) number of chromosomes. * It increases genetic variation within populations by creating new combinations of alleles in the zygote.
3. The Rules of Probability
Rules of probability can be applied to analyze the passing of single-gene traits from parent to offspring.
The Multiplication Rule (Product Rule)
If two events, A and B, are independent (the outcome of one does not affect the other), the probability that they will both occur is the product of their individual probabilities. $\(P(A \text{ and } B) = P(A) \times P(B)\)$
The Addition Rule (Sum Rule)
If two events, A and B, are mutually exclusive (they cannot happen at the same time), the probability that at least one of them will occur is the sum of their individual probabilities. $\(P(A \text{ or } B) = P(A) + P(B)\)$
4. Predicting Inheritance Patterns
Patterns of inheritance—including whether a trait is autosomal, genetically linked, or sex-linked—can often be predicted from data, including pedigrees.
- Monohybrid Cross: A cross between individuals that involves one pair of contrasting traits (e.g., \(Aa \times Aa\)).
- Dihybrid Cross: A cross between individuals that involve two pairs of contrasting traits (e.g., \(AaBb \times AaBb\)).
- Test Cross: Crossing an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype.
- Punnett Squares: A tool used to predict the genotypes and phenotypes of offspring from a particular cross.