Alleles

• What is the significance of DNA in chromosomes?

  • DNA is found in chromosomes
  • Normal human cells have 23 pairs of chromosomes
  • Each pair consists of one chromosome from each parent
• How many copies of every chromosome do normal human cells contain?

  Two copies
• What do genes represent on a chromosome?

  Sections of DNA
• What is a key fact about chromosomes in pairs?

  One comes from the father, one from the mother
• What are alleles?

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

  Earwax characteristics
• How many alleles does the earwax gene have?

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

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

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

  Lowercase e lowercase e
• What does homozygous mean?

  Two copies of the same allele
• What does phenotype refer to?

  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?

  Two different alleles
• What phenotype does a heterozygous person for earwax alleles have?

  Wet earwax
• What is a dominant allele?

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

  Shows in phenotype only if two copies present
• How are most characteristics controlled?

  • Most characteristics result from many genes
  • Genes act together to influence traits