Alleles

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

  Dominant and recessive alleles, homozygous and heterozygous genotypes, and phenotypes
• Why is it important to learn the definitions presented in the video?

  Because they are fundamental concepts in genetics
• How many pairs of chromosomes do normal human cells contain?


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


  One comes from the father and the other from the mother
• What are genes?


  Sections of DNA on a chromosome
• What does it mean that chromosomes come in pairs?


  It means there are two copies of every chromosome
• What is a key fact about alleles?

  Alleles are different versions of a gene
• What does the earwax gene control?


  The type of earwax a person has
• What are the two alleles for the earwax gene?


  Capital E for wet earwax and lowercase e for dry earwax
• What is the genotype of a person with two copies of the allele for dry earwax?


  Lowercase e lowercase e
• What does the term homozygous mean?


  Having two copies of the same allele
• What does the phenotype of a person indicate?


  The characteristics caused by the person's 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 does it mean if a person has the genotype capital E lowercase e?


  They are heterozygous for the earwax alleles
• What is the phenotype of a person with the genotype capital E lowercase e?


  Wet earwax
• What is a dominant allele?


  An allele that shows in the phenotype even if only one copy is present
• What is a recessive allele?


  An allele that shows in the phenotype only if two copies are present
• How are most characteristics controlled?

  By many genes acting together
• What are the key definitions related to alleles and genotypes?

  • Dominant allele: shows in phenotype with one copy
  • Recessive allele: shows in phenotype with two copies
  • Homozygous: two identical alleles
  • Heterozygous: two different alleles
  • Genotype: the allele composition
  • Phenotype: the observable characteristics
• What will the next video cover?

  Genetic crosses and how alleles are inherited
• Where can you find questions on this topic?

  In the vision workbook linked in the video