NCEA Level 1 Biology and Chemistry: Genetic Variation and Inheritance

Comprehensive practice flashcards covering genetics, DNA structure, meiosis, pedigree analysis, cystic fibrosis, Huntington's disease, and New Zealand conservation case studies (kākāpō, hoiho, Old Man's Beard) for NCEA Level 1 Chemistry and Biology.

What is the structural composition of a DNA molecule?

DNA is a large molecule coiled into a double-helix structure, composed of a sugar-phosphate backbone (ribose/sugar and phosphate) and four nitrogenous bases that pair specifically ($A$ with $T$ and $G$ with $C$).

How are chromosomes, genes, alleles, and DNA biologically related?

Chromosomes are long strands of DNA coiled around proteins. A gene is a specific section of that DNA sequence coding for a trait or protein, and an allele is an alternative form or version of that specific gene.

What is the biological definition of a mutation?

A mutation is a permanent change in the base sequence of a DNA strand, which acts as the primary source of new alleles and genetic variation.

What distinguishes a somatic mutation from a gametic mutation regarding inheritance?

A somatic mutation occurs in body cells, affects only the individual, and cannot be passed to offspring. A gametic mutation occurs in sex cells (sperm or egg) and can be inherited by future generations, being copied into every cell of the offspring.

What is the difference between an organism's genotype and its phenotype?

Genotype is the specific combination of alleles an organism possesses at a particular locus on a chromosome (e.g., $FF$, $Ff$, or $ff$), whereas phenotype is the observable physical expression or characteristic resulting from the genotype interacting with the environment.

How do heritable and non-heritable variation differ?

Heritable variation results from mutations or allele combinations in gametes that are passed down genetically to offspring (e.g., kākāpō beak colour). Non-heritable variation results from environmental influences on somatic cells (e.g., muscle development from exercise or body condition from food availability) and cannot be inherited.

What causes cystic fibrosis at the genetic level, and what are its physiological symptoms?

Cystic fibrosis is caused by a recessive mutant allele ($f$) of the CFTR gene located on chromosome 7. Homozygous recessive individuals ($ff$) produce thick, excessive mucus in the body, leading to difficulty breathing and digestive issues.

What are the possible genotypes and corresponding phenotypes for the CFTR gene in humans?

Homozygous dominant ($FF$) and heterozygous ($Ff$) individuals both express the normal phenotype (no cystic fibrosis). Homozygous recessive ($ff$) individuals express the cystic fibrosis phenotype.

In a pedigree chart for cystic fibrosis, why must unaffected parents with affected children be heterozygous ($Ff$)?

Because an affected child has the homozygous recessive genotype ($ff$), they must inherit one recessive allele ($f$) from each parent. Unaffected parents must also carry a dominant allele ($F$), making their genotype $Ff$.

How can the genotype of an unaffected individual (such as Individual 7) be definitively confirmed as heterozygous ($Ff$)?

Individual 7 is unaffected (carrying at least one dominant allele $F$) but has affected children with genotype $ff$, proving that Individual 7 must carry and pass on a recessive allele ($f$), confirming their genotype as $Ff$.

Why can an unaffected individual with a family history of cystic fibrosis (like Individual 4) have an unconfirmed genotype of either $FF$ or $Ff$?

Individual 4 does not show symptoms, meaning they possess at least one dominant $F$ allele, but because their offspring are also unaffected, it cannot be determined whether they inherited an $F$ or an $f$ allele from heterozygous parents without direct genetic testing.

What is the primary medical and reproductive purpose of tracking cystic fibrosis alleles in families?

Tracking determines whether prospective parents are carriers ($Ff$), helping them assess the probability of having a child with cystic fibrosis, make informed reproductive decisions (such as using IVF with embryo screening), and guide targeted medical healthcare.

How can the recessive $f$ allele increase in frequency within a population without increasing the frequency of the cystic fibrosis phenotype?

Because the dominant $F$ allele completely masks the recessive $f$ allele in heterozygotes ($Ff$), the number of carrier individuals can increase (increasing $f$ allele frequency) while the homozygous recessive ($ff$) phenotype frequency remains low or unchanged.

What selective advantage might the heterozygous ($Ff$) CFTR genotype provide in human populations?

Heterozygotes may have increased resistance to certain infectious bacterial diseases, such as cholera or typhoid, conferring higher reproductive success and survival in environments where these diseases are prevalent.

What causes Huntington's disease, and on which chromosome is the gene located?

Huntington's disease is an inherited genetic disorder caused by a dominant mutation in the $HTT$ gene on chromosome 4.

What is the molecular mutation associated with the mutant $HTT$ allele, and what are its symptoms?

The mutant $HTT$ allele contains expanded CAG repeats ($>20$ base pairs), coding for a longer abnormal protein. Symptoms usually appear in adulthood (after age 30) and include uncontrollable movements, cognitive decline, and emotional disturbances.

Why has the dominant mutant $HTT$ allele not increased significantly in frequency within the general human gene pool?

Although it is dominant and passed on before late-onset symptoms appear, its frequency remains low due to negative natural selection against severe debilitation and family tracking/reproductive management that reduces transmission.

How does meiosis produce genetically different gametes?

Meiosis produces four genetically non-identical daughter cells through crossing over (exchange of genetic material between homologous chromosomes) and independent assortment (random alignment and separation of homologous chromosomes).

What is crossing over in meiosis?

Crossing over is the process during meiosis where homologous chromosomes pair up and exchange segments of genetic material, creating new and unique combinations of alleles on each chromosome.

What is independent assortment in meiosis?

Independent assortment occurs when homologous chromosome pairs line up randomly along the centre of the cell before separating into daughter cells, ensuring random combinations of maternal and paternal chromosomes in gametes.

How does random fertilisation contribute to genetic variation in sexually reproducing species?

Fertilisation randomly combines the unique genetic sets of two separate haploid gametes (one sperm and one egg), resulting in a genetically unique diploid zygote with novel combinations of parental alleles.

What is non-random mating, and what is its consequence in small populations?

Non-random (selective) mating occurs when individuals choose mates based on specific traits rather than by chance. In small populations, it often leads to inbreeding among close relatives, increasing homozygosity and the expression of harmful recessive alleles.

What historical population bottleneck did the kākāpō experience between 1995 and 2022?

The kākāpō population declined to a low of just 51 birds in 1995, but conservation management raised the population to approximately 252 birds by 2022.

Why is low genetic variation a severe risk to the survival of the kākāpō population?

Low genetic variation means individuals share nearly identical alleles. If an environmental change or new disease (such as a fungal infection) strikes, there is a high risk that no individuals possess resistant alleles, potentially killing the entire population.

What are genetic markers, and how do conservationists use them in kākāpō recovery?

Genetic markers are specific variable DNA sequences used to identify relatedness and individual differences. Conservationists use them to manage breeding pairs, minimise inbreeding, and increase genetic diversity in future generations.

In kākāpō beak colour inheritance, what are the phenotypic and genotypic outcomes of crossing a heterozygous male ($Bb$) with a homozygous recessive female ($bb$)?

The possible offspring genotypes are $50\%$ $Bb$ (heterozygous) and $50\%$ $bb$ (homozygous recessive). The resulting phenotypes are $50\%$ dark beaks and $50\%$ light beaks.

Why can three different genotypes produce only two distinct phenotypes in kākāpō beak colour?

Because the dark beak allele ($B$) is completely dominant over the light beak allele ($b$), both the homozygous dominant ($BB$) and heterozygous ($Bb$) genotypes express the dark beak phenotype, while only $bb$ expresses the light beak phenotype.

Why is understanding genotypes more advantageous for conservation management than merely observing phenotypes?

Observing phenotypes cannot distinguish between homozygous dominant ($BB$) and heterozygous carriers ($Bb$). Knowing genotypes enables conservationists to predict offspring outcomes accurately, avoid pairing carriers of deleterious recessive alleles, and preserve rare genetic diversity.

What ecological threat does Old Man's Beard (Clematis vitalba) pose to native New Zealand forests?

Old Man's Beard is an invasive woody vine that spreads rapidly, climbing over and smothering host trees (such as cabbage trees, Cordyline australis), blocking sunlight and severely limiting their ability to photosynthesise.

How does repeated application of glyphosate herbicide lead to an increase in resistant Old Man's Beard plants?

Pre-existing random mutations in the plant genome confer glyphosate resistance. Repeated herbicide applications kill susceptible weeds, allowing resistant individuals to survive, reproduce, and pass their resistance alleles on, thereby increasing the resistant allele frequency over generations.

What population decline has the yellow-eyed penguin (hoiho, Megadyptes antipodes) experienced on the Otago Peninsula?

The hoiho population on the Otago Peninsula has declined by $75\%$ since the mid-1990s, with current trends indicating it could completely disappear from the area within the next 40 years.

What contribution does the Yellow-eyed Penguin Trust habitat make to the overall hoiho population?

The Trust manages a protected area containing more than 48 breeding pairs, representing over $10\%$ of the total hoiho population across New Zealand and the sub-Antarctic islands.

What gene tracking methodologies are applied in hoiho conservation programmes?

Scientists utilise DNA sequencing, DNA profiling, and pedigree analysis to assess relatedness, monitor gene flow, and guide selective breeding strategies.

What are the score thresholds (cut scores) for NCEA Level 1 Chemistry and Biology assessment 92022?

The cut scores are: Not Achieved ($0-7$ marks), Achievement ($8-12$ marks), Achievement with Merit ($13-18$ marks), and Achievement with Excellence ($19-24$ marks).