Alleles

• What are dominant and recessive alleles?

  Types of alleles affecting traits
• What does homozygous mean?

  Having two identical alleles for a trait
• What does heterozygous mean?

  Having two different alleles for a trait
• What is the difference between genotype and phenotype?

  Genotype is the allele combination; phenotype is the trait
• 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, one from the mother
• What are genes?

  Sections of DNA on a chromosome
• What are alleles?

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

  The type of earwax produced
• What are the two alleles for the earwax gene?

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

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

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

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

  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 it mean if a person is heterozygous for the earwax alleles?

  They have one allele for each type of earwax
• What is the phenotype for a person with one allele for wet earwax and one for dry earwax?

  Wet earwax
• What is a dominant allele?

  An allele that shows in the phenotype with one copy
• What is a recessive allele?

  An allele that shows only if two copies are present
• What are the key definitions related to alleles and genotypes?

  • Dominant allele: shows in phenotype with one copy
  • Recessive allele: shows only with two copies
  • Homozygous: two identical alleles
  • Heterozygous: two different alleles
  • Genotype: allele combination
  • Phenotype: observable traits
• How do single-gene traits differ from polygenic traits?

  • Single-gene traits: controlled by one gene (e.g., earwax)
  • Polygenic traits: controlled by multiple genes (e.g., height)
• What will be covered in the next video?

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

  In the vision workbook