Summary
Inheritance involves the transmission of genetic information from parents to offspring, determining traits and characteristics.
- Gene — a segment of DNA that codes for a single polypeptide. Example: Agouti gene affects horse coat color.
- Allele — different forms of a gene located at the same locus on a chromosome. Example: Alleles A and a can result in different horse coat colors.
- Genotype — the alleles of a gene that an organism possesses. Example: Genotype AA results in a black coat.
- Phenotype — observable traits of an organism influenced by genotype. Example: Genotype aa results in a chestnut coat.
- Dominant Allele — an allele that expresses its trait even in the presence of a different allele. Example: Dominant alleles are expressed in both homozygous and heterozygous individuals.
- Recessive Allele — an allele that only expresses its trait in the absence of a dominant allele. Example: Recessive alleles manifest in homozygous recessive individuals.
- Codominance — when both alleles express themselves together in the phenotype. Example: Blood type AB in humans.
- Sex Linkage — genes located on sex chromosomes that affect inheritance. Example: Haemophilia is a sex-linked condition.
- Autosomal Linkage — genes located on the same chromosome that do not assort independently. Example: Linked genes remain together during meiosis.
Exam Tips
Key Definitions to Remember
- Gene
- Allele
- Genotype
- Phenotype
- Dominant Allele
- Recessive Allele
- Codominance
- Sex Linkage
- Autosomal Linkage
Common Confusions
- Difference between genotype and phenotype
- Dominance vs. codominance
- Sex-linked vs. autosomal traits
Typical Exam Questions
- What is a gene? A segment of DNA that codes for a single polypeptide.
- How do dominant and recessive alleles differ? Dominant alleles express traits in both homozygous and heterozygous states, while recessive alleles only express in homozygous recessive states.
- What is codominance? When both alleles express themselves together in the phenotype.
What Examiners Usually Test
- Understanding of key genetic terms
- Ability to predict inheritance patterns using Punnett squares
- Differences between types of dominance and linkage