Summary
Inheritance is the transmission of genetic information from generation to generation.
- Chromosome — a thread of DNA, made up of a string of genes. Example: Humans have 23 pairs of chromosomes.
- Gene — a length of DNA that is the unit of heredity and codes for a specific protein. Example: A gene might code for a protein like collagen.
- Allele — any of two or more alternative forms of a gene. Example: Alleles for eye color can be blue or brown.
- Haploid nucleus — a nucleus containing a single set of unpaired chromosomes. Example: Sperm and egg cells are haploid.
- Diploid nucleus — a nucleus containing two sets of chromosomes. Example: Body cells are diploid.
- Mitosis — nuclear division giving rise to genetically identical cells. Example: Mitosis is used for growth and repair.
- Meiosis — reduction division in which the chromosome number is halved from diploid to haploid. Example: Meiosis produces gametes like sperm and eggs.
- Genotype — the genetic makeup of an organism in terms of the alleles present. Example: Tt or GG.
- Phenotype — the physical or other features of an organism due to both its genotype and its environment. Example: Tall plant or green seed.
- Homozygous — having two identical alleles of a particular gene. Example: TT or gg.
- Heterozygous — having two different alleles of a particular gene. Example: Tt or Gg.
- Dominant — an allele that is expressed if it is present. Example: T or G.
- Recessive — an allele that is only expressed when there is no dominant allele of the gene present. Example: t or g.
Exam Tips
Key Definitions to Remember
- Inheritance: transmission of genetic information from generation to generation
- Chromosome: thread of DNA, made up of a string of genes
- Gene: length of DNA that codes for a specific protein
- Allele: alternative form of a gene
- Haploid: nucleus with a single set of unpaired chromosomes
- Diploid: nucleus with two sets of chromosomes
- Mitosis: nuclear division for genetically identical cells
- Meiosis: reduction division for gametes
Common Confusions
- Mixing up amino acid and base sequences in DNA and RNA
- Differences between mitosis and meiosis
- Haploid means half the normal number of chromosomes
- Writing genotypes with the dominant allele first
Typical Exam Questions
- What is the difference between mitosis and meiosis? Mitosis results in identical cells, meiosis results in genetic variation.
- How is sex determined in humans? By the XX or XY chromosomes.
- What is a genotype? The genetic makeup of an organism in terms of alleles.
What Examiners Usually Test
- Understanding of key definitions
- Ability to differentiate between mitosis and meiosis
- Predicting outcomes of monohybrid crosses
- Interpreting pedigree diagrams