Biology Inheritance, Variation and Evolution

What is DNA and what is its function?

• DNA (Deoxyribonucleic Acid) is the genetic material found in all living organisms.

• It carries instructions for making proteins.

• Found in the nucleus, coiled into chromosomes.

What is the structure of DNA?

• A double helix made of two strands.

• Contains nucleotide bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).

• A pairs with T, and C pairs with G (complementary base pairing).

What is a gene?

• A small section of DNA coding for a specific protein.

• Different genes determine different characteristics.

What is a genome?

• The entire genetic material of an organism.

• The Human Genome Project mapped all human genes.

What are chromosomes?

• Long strands of coiled DNA found in the nucleus.

• Humans have 46 chromosomes (23 pairs).

What is an allele?

• A different version of a gene.

• Can be dominant or recessive.

What is meant by homozygous and heterozygous?

• Homozygous: Two identical alleles for a trait.

• Heterozygous: Two different alleles for a trait.

What is genotype vs. phenotype?

• Genotype: The genetic makeup (e.g., BB, Bb, bb).

• Phenotype: The physical characteristics expressed (e.g., brown eyes).

What is a dominant allele?

• An allele that is always expressed in the phenotype.

• Represented by a capital letter (e.g., B for brown eyes).

What is a recessive allele?

• An allele that is only expressed if two copies are present.

• Represented by a lowercase letter (e.g., b for blue eyes).

What is a Punnett square?

A diagram used to predict the probability of offspring inheriting certain traits.

What is a carrier in genetics?

An individual who has one copy of a recessive allele but does not show symptoms.

What is mitosis?

• Cell division for growth and repair.

• Produces two identical diploid cells.

What is meiosis?

• Cell division that produces gametes (sperm and egg cells).

• Produces four genetically different haploid cells.

Why is meiosis important?

• Maintains chromosome number across generations.

• Creates genetic variation.

What is sexual reproduction?

• Requires two parents.

• Produces genetically diverse offspring.

• Uses meiosis.

What is asexual reproduction?

• Requires one parent.

• Produces clones (genetically identical offspring).

• Uses mitosis.

What are some advantages and disadvantages of each?

• Sexual reproduction:
  ✅ Genetic variation (helps survival).
  ❌ Slower and requires two parents.

• Asexual reproduction:
  ✅ Fast and efficient.
  ❌ No genetic variation (risk from diseases).

What is variation?

Differences within a species caused by:

• Genetic factors (different alleles).

• Environmental factors (diet, climate).

What is a mutation?

• A change in the DNA sequence.

• Can be harmful, beneficial, or neutral.

What is evolution?

• A gradual change in a species over time.

• Driven by natural selection.

What is natural selection?

Survival of the fittest—organisms best adapted survive and reproduce.

Who proposed the theory of evolution?

Charles Darwin in his book On the Origin of Species.

What evidence supports evolution?

• Fossil records (show gradual changes over time).

• Comparative anatomy (similar structures in different species).

What is selective breeding?

• Humans choose organisms with desired traits to breed.

• Examples:

  • Disease-resistant crops.

  • High-yield cows.

What is genetic engineering?

• Direct modification of an organism’s DNA.

• Example: GM crops (resistant to pests/diseases).

What are the benefits and risks of genetic engineering?

✅ Increases crop yield and reduces disease.
❌ May have unknown long-term effects.

How does antibiotic resistance occur?

• Overuse of antibiotics leads to resistant bacteria.

• Example: MRSA (a superbug).

Why is antibiotic resistance a problem?

• Infections become harder to treat.

• Need for new antibiotics.

How are living things classified?

• Traditional system: Kingdom, Phylum, Class, Order, Family, Genus, Species.

• Modern system: Three Domains (Bacteria, Archaea, Eukaryota).

What is binomial naming?

A two-part scientific name:

• Genus (capitalized) + Species (lowercase).

• Example: Homo sapiens.

What is speciation?

• The formation of a new species due to evolution.

• Often caused by geographic isolation.

What causes extinction?

• Environmental changes (climate change, habitat loss).

• New predators or diseases.

• Competition for resources.

What do neutral mutations do?

Turn genes on or off.

How do three bases code for an amino acid?

• Every three DNA bases (triplet) form a codon.

• Each codon codes for one amino acid.

• A chain of amino acids forms a protein.

What are nucleotides made of?

• A phosphate group.

• A sugar (deoxyribose).

• A nitrogen base (A, T, C, G).

What is the process of protein synthesis?

• Transcription: DNA is copied into mRNA in the nucleus.

• mRNA leaves the nucleus and goes to the ribosome.

• Translation: Ribosomes read mRNA and assemble amino acids.

• Amino acids join to form a protein.

What are three functions of proteins?

• Enzymes: Speed up chemical reactions (e.g., amylase).

• Hormones: Send signals (e.g., insulin).

• Structural proteins: Build body parts (e.g., collagen).

What is cystic fibrosis?

• A recessive disorder (need two faulty alleles).

• Causes thick mucus buildup in lungs and digestive system.

• Leads to breathing and digestive problems.

• Carriers have one normal and one faulty allele but no symptoms.

What is polydactyly?

• A dominant disorder (only need one faulty allele).

• Causes extra fingers or toes.

• Can be inherited from one affected parent.

How does cutting and grafting clone plants?

• A piece of plant (cutting) is taken and replanted.

• Grows into an identical clone.

How does tissue culture clone plants?

• Small plant cells grown in a lab using a nutrient-rich medium.

• Produces many clones quickly.

What is embryo cloning?

• Embryo cells are split before specialization.

• Each cell develops into an identical clone in a surrogate.

What is adult cell cloning?

• Remove the nucleus from an adult body cell.

• Insert it into an empty egg cell.

• Use an electric shock to trigger division.

• The embryo is implanted into a surrogate.

What are fossils and how do they form?

• Fossils are remains of ancient organisms.

• They form by:

  • Mineralization: Bones turn into rock.

  • Casts & impressions: Organisms leave imprints.

  • Preservation: In amber, ice, or peat bogs (no decay).

Why is the fossil record incomplete?

• Many organisms decompose before fossilizing.

• Fossils may be destroyed by geological activity (earthquakes, erosion).

• Soft-bodied organisms rarely leave fossils.