Alleles

• What should you be able to describe by the end of the video?

  Dominant and recessive alleles
• What do homozygous and heterozygous refer to?

  Types of genotypes based on alleles
• What is a key fact about human chromosomes?

  • Normal human cells contain 23 pairs of chromosomes
  • Each pair consists of one chromosome from the father and one from the mother
• What are genes?

  Sections of DNA on a chromosome
• How many copies of every gene do humans have?

  Two copies of every gene
• What is the gene that controls earwax?

  The earwax gene
• 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 of a person with two copies of the allele for dry earwax?

  Lowercase e lowercase e
• What does homozygous mean?

  Having 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?

  Having 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 with two copies
• How are most characteristics controlled?

  • Most characteristics result from many genes acting together
  • Example: Height is influenced by multiple genes
• What will the next video cover?

  Genetic crosses and allele inheritance
• Where can you find questions on this topic?

  In the vision workbook