Alleles

• How many pairs of chromosomes do normal human cells contain?

  23 pairs
• Where does one chromosome in a pair come from?

  From the father
• What are genes?

  Sections of DNA on a chromosome
• What is a key fact about genes in chromosomes?

  There are two copies of every gene
• What are alleles?

  Versions of a gene
• What does the earwax gene control?

  The type of earwax produced
• How many alleles does the earwax gene have?

  Two alleles
• What does the capital letter 'E' represent?

  Wet earwax allele
• What does the lowercase letter 'e' represent?

  Dry earwax allele
• What is the genotype of a person with two copies of the dry earwax allele?

  Lowercase e lowercase e
• What does homozygous mean?

  Having two identical alleles
• What does phenotype refer to?

  The characteristics caused by alleles
• What is the phenotype of a person with two alleles for dry earwax?

  Dry earwax
• What is the genotype of a person with two alleles for wet earwax?

  Capital E capital E
• What is the phenotype of a person with two alleles for wet earwax?

  Wet earwax
• What is the genotype of a person with one allele for wet earwax and one for dry earwax?

  Capital E lowercase e
• What does heterozygous mean?

  Having two different alleles
• What phenotype does a person with one wet earwax allele and one dry earwax allele have?

  Wet earwax
• What is a dominant allele?

  Shows in phenotype with one copy
• What is a recessive allele?

  Shows in phenotype only with two copies
• What is the phenotype of a person with two copies of the dry earwax allele?

  Dry earwax
• What is the difference between single-gene and multi-gene characteristics?

  • Single-gene characteristics: controlled by one gene
  • Multi-gene characteristics: influenced by multiple genes