LEVEL 1 BIO

NCEA Level 1 Chemistry and Biology: Genetic Variation

Assessment Details and Key Concepts

• Achievement Standard: $92022$ (Chemistry and Biology $1.3$).

• Assessment Mode: Online examination worth $5$ credits.

• Examination Schedule: Thursday $19$ November $2026$ at $2:00\text{ pm}$.

• Requirements: Demonstrate understanding of genetic variation in relation to identified characteristics (e.g., $CFTR$ or $CCR5$ gene mutations).

• Core Topics for Excellence:

  • DNA & Alleles: Relationships between base sequences, genes, and alleles.

  • Sources of Variation: Introduction of new alleles via permanent mutations and new combinations through sexual reproduction (meiosis and fertilization).

  • Gene Tracking: Use of pedigree charts and Punnett squares to determine phenotypes and track alleles across generations.

  • Population Advantages: The importance of genetic variation for survival and adaptability in changing environments.

The Molecular Structure of DNA

• Definition: DNA (Deoxyribonucleic acid) is the molecule inside cells containing genetic information responsible for an organism's development and function. It allows information to be passed between generations.

• Length and Scale:

  • In a single cell, DNA is approximately $2\text{m}$ long.

  • The total DNA in a human body is estimated at $16\text{ billion kilometers}$ ($16,000,000,000\text{ km}$), a distance equivalent to traveling to Pluto and back.

  • Human DNA shares $99.9\%$ similarity with other humans, $99.1\%$ with chimpanzees, and $50.0\%$ with bananas.

• Physical Structure:

  • DNA is a nucleic acid described as a double-helix or a "twisted ladder."

  • It is comprised of two strands made of repeating units called nucleotides.

• Nucleotide Components:

  • Phosphate group.

  • Sugar group (ribose/deoxyribose).

  • Nitrogenous base (Adenine, Thymine, Cytosine, or Guanine).

• Base Pairing Rules:

  • Nitrogenous bases pair via hydrogen bonds.

  • Adenine ($A$) always bonds with Thymine ($T$).

  • Guanine ($G$) always bonds with Cytosine ($C$).

  • The sugar and phosphate groups link to form the solid vertical "backbone" of the DNA strand.

• Genetic Facts:

  • Humans possess approximately $25,000$ different genes.

  • The first human genome sequence cost $2.7\text{ billion dollars}$; today, it costs roughly $1000\text{ dollars}$.

  • The genome contains about $700\text{ Terabytes}$ ($700,000\text{ Gigabytes}$) of data.

  • DNA is damaged over $1000$ times daily; unrepaired damage can lead to cancer.

  • Approximately $8\%$ of human DNA originates from ancient viruses.

Relationships Between DNA, Chromosomes, Genes, and Alleles

• DNA: The genetic material used to code for traits.

• Chromosomes: Long, wound-up lengths of DNA that contain many genes. Human body cells typically contain $46$ chromosomes ($23$ pairs).

• Genes: Distinct sections of a chromosome (or DNA) that code for a specific protein and physical characteristic/trait (e.g., eye color).

• Alleles: Alternate or different versions of a gene (e.g., the allele for blue eyes vs. the allele for brown eyes).

• Locus: The specific physical location of a gene on a chromosome.

• Gene Expression Sequence: DNA (Gene) → Triplet/Codon → Amino Acids → Polypeptide Chain → Folded Protein → Physical Trait.

• Inheritance Logic: Individuals have two alleles for every gene, inheriting one from the mother (egg) and one from the father (sperm).

Karyotypes and Genetic Disorders

• Definition: A karyotype is a diagram showing the complete set of chromosomes in the nucleus of a cell, arranged by size and shape.

• Biological Sex Determination:

  • The last pair are the sex chromosomes.

  • Biological human females: $XX$.

  • Biological human males: $XY$.

• Autosomes: The non-sex chromosomes ($22$ pairs in humans).

• Karyotyping Purposes: Used to detect missing, extra, or broken chromosomes.

  • Down Syndrome (Trisomy $21$): Caused by an extra chromosome at pair $21$.

  • Turner Syndrome: Caused by a missing $X$ chromosome ($X0$ genotype).

  • Klinefelter Syndrome: Characterized by extra sex chromosomes (e.g., $XXY$).

  • Methemoglobinemia: A rare disorder ($0.035\%$ global prevalence) where blood carries less oxygen, appearing brown and causing skin to look blue.

• Test Sources: Amniotic fluid, blood, bone marrow, or placental tissue.

• Species Differences:

  • Dogs: $78$ chromosomes ($39$ pairs).

  • Cows: $60$ chromosomes ($30$ pairs).

Types of Variation: Continuous vs. Discontinuous

• Variation: The differences between individuals of the same species.

• Continuous Variation:

  • Variation that has a range of values.

  • Examples: Height, foot length, hand span.

• Discontinuous Variation:

  • Variation that has distinct categories or limited possible outcomes.

  • Examples: Gender, blood group ($A, B, AB, O$), ability to roll tongue, left vs. right-handedness.

Inheritable vs. Non-Inheritable Variation

• Inheritable Variation:

  • Caused by an individual's genetics/DNA.

  • Can be passed on to offspring because the genetic information is in the gametes.

  • Example: Natural eye color, dimples.

• Non-Inheritable Variation:

  • Caused by environmental factors.

  • Affects only somatic (body) cells and cannot be passed to offspring.

  • Example: Scars, dyed hair color, lung damage from infection (e.g., $COVID-19$), sun-tanned skin.

• Phenotype Equation: The physical appearance (phenotype) is determined by the combination of the genotype (genetic makeup) and the environment.

Mutations as a Source of Variation

• Definition: A permanent and random change in the base sequence of DNA.

• Impact: Can lead to the creation of a new allele for a gene by changing the protein produced.

• Types of Mutations:

  • Beneficial: Provides a survival advantage (e.g., antibiotic resistance in bacteria, super-strong bones).

  • Harmful: Discourages survival or causes disease (e.g., cancer, sickle cell anemia).

  • Silent: Has no observable effect.

• Mutagens: Physical or chemical agents that increase the frequency of mutations (e.g., $UV$ light, certain chemicals).

• Inheritance of Mutations:

  • Somatic Mutations: Occur in body cells; impact the individual during their lifetime (e.g., cancer) but are not passed on.

  • Gametic Mutations: Occur in gametes (sperm or egg); can be passed to the next generation if that specific gamete is used in fertilization.

Cell Division: Mitosis and Meiosis

• DNA Replication: The process of copying a double-stranded DNA molecule before cell division. It is semi-conservative, meaning each new DNA molecule contains one original parent strand and one new strand.

• Mitosis:

  • Purpose: Growth and repair of tissues; replacement of old cells.

  • Location: Occurs in all somatic (body) cells.

  • Outcome: Two genetically identical diploid daughter cells ($46$ chromosomes in humans).

  • Variation: Does not increase variation.

• Meiosis:

  • Purpose: Production of gametes (sex cells).

  • Location: Occurs in the gonads (Testes/Ovaries in animals; Anther/Ovary in plants).

  • Outcome: Four genetically unique haploid daughter cells ($23$ chromosomes in humans).

  • Variation: Significantly increases variation.

• Mechanisms of Variation in Meiosis:

  • Crossing Over: Homologous chromosomes (maternal and paternal) line up and swap segments of DNA/alleles.

  • Independent Assortment: Chromosome pairs line up randomly on the cell equator before being separated, creating unique combinations in gametes.

Sexual vs. Asexual Reproduction

• Asexual Reproduction:

  • Requires only one parent.

  • Process: Uses mitosis to create clones.

  • Advantages: Rapid population growth, energy-efficient (no mate needed), successful traits guaranteed.

  • Disadvantages: Zero genetic variation; highly vulnerable to environmental changes or disease; negative traits always inherited.

  • Examples: Strawberry runners, potato tubers, yeast budding, starfish regeneration, parthenogenesis in honeybees.

• Sexual Reproduction:

  • Requires two parents (fusion of male and female gametes).

  • Process: Uses meiosis and fertilization.

  • Advantages: High genetic variation; high chance of species survival during environmental changes due to diversity.

  • Disadvantages: Slower process; high energy cost to find a mate; unique individuals may inherit undesirable traits.

Genetic Terminology and Predicative Tools

• Dominant Allele: Represented by a capital letter (e.g., $B$); always expressed in the phenotype if present.

• Recessive Allele: Represented by a lowercase letter (e.g., $b$); only expressed if the dominant allele is absent.

• Genotype: The specific combination of alleles an individual possesses (e.g., $BB, Bb, bb$).

• Phenotype: The observable physical characteristic (e.g., brown eyes).

• Homozygous (Purebred): Possessing two of the same alleles for a trait (e.g., $BB$ or $bb$).

• Heterozygous: Possessing two different alleles for a trait (e.g., $Bb$).

• Punnett Square: A grid used to predict the mathematical probability of genotypes and phenotypes in offspring resulting from a cross.

• Test Cross: A method used to determine an unknown dominant genotype (is it $BB$ or $Bb$?) by crossing the individual with a homozygous recessive ($bb$) partner.

  • If any recessive offspring appear, the unknown parent must be heterozygous.

  • If all offspring show the dominant trait after many crosses, the parent is likely homozygous dominant.

Tracking Genetic Lines

• Pedigree Charts: Diagrams showing the inheritance of a trait across multiple generations of a family. Circles represent females; squares represent males; shaded symbols indicate the presence of the trait.

• Phylogenetic Trees: Diagrams representing the evolutionary history and relationships between different species.

  • Nodes: Branching points indicating a common ancestor.

  • Proximity: Species with a more recent common ancestor are more closely related.

Population Genetics and Evolution

• Gene Pool: The sum of all alleles present in a population.

• Population: A group of organisms of the same species breeding together in the same place and time.

• Factors Affecting Diversity:

  • Natural Selection: Organisms with advantageous phenotypes are more likely to survive, reproduce, and pass on favorable alleles. This changes allele frequencies over time (e.g., Peppered moths, Giraffe neck length).

  • Migration (Gene Flow): The movement of alleles into (immigration) or out of (emigration) a population.

  • Population Size and Genetic Drift: Small populations are highly vulnerable to random events.

    • Bottleneck Effect: A random disaster (e.g., volcano, hunting) drastically reduces population size and diversity.

    • Founder Effect: A small group establishes a new population with limited genetic variation.

  • Non-Random Mating: Selection of mates based on specific criteria (e.g., peacocks selecting bright tails) or proximity, which can reduce variation over time.

• Human Origins: The "Out of Africa" theory suggests modern humans appeared in Africa and spread globally. Evidence includes the highest rates of genetic variation being found in African populations due to the length of time mutations have accumulated.

Real-World Applications of Genetics

• Genomics: The study of the entire genome of an organism.

• Human Genome Project: An international research effort ($1990\text{--}2003$) that sequenced all $3\text{ billion}$ base pairs of human DNA.

• Medical Interventions: Testing for genes like $CDH1$ (stomach cancer) or $BRCA$ (breast cancer) allows for preemptive surgeries.

• Conservation: Using DNA sequencing to manage breeding programs for endangered species (e.g., K\u0101k\u0101p\u014d, Cheetahs) to maximize genetic diversity.

• Forensics: Matching DNA from crime scenes to suspects or determining paternity by checking genetic markers.

• Biological Heritage: Investigating specific NZ variants, such as the white variant of the Kermadec p\u014dhutukawa ($Metrosideros kermadecensis$) or winglessness in the Kiwi ($Apteryx$).