Alleles

• What are the terms you should describe related to alleles?

  Homozygous, heterozygous, genotype, phenotype
• 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 the gene that controls earwax?

  The earwax gene
• How many copies of every gene do humans have?

  Two copies
• What are alleles?

  Versions of a gene
• What does the allele for wet earwax symbolize?

  Capital E
• What does the allele for dry earwax symbolize?

  Lowercase e
• What is the genotype for a person with two copies of dry earwax?

  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 for a person with two alleles for dry earwax?

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

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

  Wet earwax
• What is the genotype for 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 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 are present
• What is the phenotype for a person with two copies of the allele for dry earwax?

  Dry earwax
• How are most characteristics controlled?

  • By many genes acting together
  • Example: Height
• What will the next video cover?

  • Genetic crosses
  • Inheritance of alleles