Genes

Study Notes

Genes are heritable factors consisting of DNA that influence specific characteristics and occupy a specific position on a chromosome called the locus. Alleles are different forms of the same gene, differing by a few bases, and mutations can create new alleles. The genome is the complete set of genetic information in an organism, and the Human Genome Project mapped the entire human genome.

• Gene — a heritable factor consisting of a length of DNA that influences a specific characteristic.
  Example: The gene for eye color.
• Locus — the specific position on a chromosome where a gene is located.
  Example: The locus of the gene for eye color on chromosome 15.
• Allele — alternative forms of a gene that occupy the same locus.
  Example: Alleles for blue and brown eyes.
• Mutation — a permanent change in the base sequence of DNA, forming new alleles.
  Example: A base substitution mutation causing sickle cell anemia.
• Genome — the entire base sequence of an organism's DNA.
  Example: The human genome consists of 46 chromosomes.
• Human Genome Project — an international project that sequenced the entire human genome.
  Example: Mapping the number and location of human genes.

Exam Tips

Key Definitions to Remember

• Gene: A heritable factor consisting of DNA that influences a specific characteristic.
• Allele: Alternative forms of a gene that occupy the same locus.
• Mutation: A permanent change in the base sequence of DNA.
• Genome: The entire base sequence of an organism's DNA.

Common Confusions

• Confusing genes with alleles; remember, alleles are different forms of the same gene.
• Thinking all mutations are harmful; some are neutral or even beneficial.

Typical Exam Questions

• What is a gene?
  A heritable factor consisting of DNA that influences a specific characteristic.
• How do alleles differ from each other?
  By one or only a few bases.
• What was the purpose of the Human Genome Project?
  To sequence the entire human genome.

What Examiners Usually Test

• Understanding the difference between genes and alleles.
• The role of mutations in forming new alleles.
• The significance of the Human Genome Project.