B6

• What is the process called when a cell divides to form gametes?

  Meiosis
• How many times does a cell divide during meiosis?

  Twice
• What type of chromosomes do gametes have?

  Single set of chromosomes
• Are all gametes genetically identical?

  No, they are genetically different
• What happens to gametes at fertilization?

  They join to restore chromosome number
• What process follows fertilization in the new cell?

  Mitosis
• What happens as the embryo develops?

  Cells differentiate
• What is DNA made up of?

  Two strands forming a double helix
• What are chromosomes?

  Structures containing DNA
• What is a gene?

  A small section of DNA on a chromosome
• What does each gene code for?

  A particular sequence of amino acids
• What is the genome of an organism?

  The entire genetic material of that organism
• What is the significance of studying the human genome?

  It has great importance for medicine
• What can genome research help with?

  Understanding diseases and tracing migration
• What are some characteristics controlled by a single gene?

  Fur color in mice and color blindness
• How many copies of any gene do humans have?

  Two copies
• What are different forms of a gene called?

  Alleles
• What does genotype refer to?

  The genetic makeup of an organism
• What does phenotype refer to?

  The physical characteristics of an organism
• When is a dominant allele expressed?

  When at least one copy is present
• When is a recessive allele expressed?

  Only when two copies are present
• What is a Punnett square used for?

  • To predict genetic outcomes
  • To visualize allele combinations
  • To determine probabilities of traits
• What is polydactyly?

  Extra fingers or toes due to a dominant allele
• What is cystic fibrosis?

  A cell membrane disorder caused by a recessive allele
• What are the implications of embryo screening?

  • Prepares parents for conditions
  • Informs about potential abortion
  • Identifies if parents passed on disorders
  • May cause distress to families
  • Small risk of miscarriage
• What are the economic concerns of embryo screening?

  • High costs for parents/NHS
  • Expense of multiple screenings
• What are the ethical concerns of embryo screening?

  • False positives leading to unnecessary abortion
  • Religious beliefs against abortion
• How many pairs of chromosomes do human cells contain?

  23 pairs
• What do the first 22 pairs of chromosomes control?

  Characteristics only
• What does the 23rd pair of chromosomes determine?

  The sex of the individual
• What is variation in a population?

  Differences in characteristics among individuals
• What causes variation in a population?

  Inherited genes and environmental conditions
• What is genetic variation within a species caused by?

  Mutations
• What is the effect of most mutations on phenotype?

  Most have no effect
• What can a mutation lead to?

  A new phenotype suited to environmental change
• What is evolution?

  • Change in inherited characteristics over time
  • Process of natural selection
  • May result in new species formation
• What happens when two populations of a species become different in phenotype?

  They may form two new species
• How do plants and animals evolve specific characteristics?

  • Variation occurs due to sexual reproduction
  • Random mutations produce different proteins
  • Organisms with desired traits are more likely to survive and reproduce
  • This is natural selection
• What happens to alleles for desired characteristics over generations?

  They are passed to offspring
• What occurs after many generations of evolution?

  Organisms may no longer reproduce together