Year 10 Biology: Genetics, Biotechnology, and Evolution

Comprehensive practice flashcards covering cell biology, DNA replication, protein synthesis, cell division, inheritance, genetic technologies, evolutionary theory, and the fossil record.

What is DNA (deoxyribonucleic acid) and what primary instructions does it contain?

DNA is the genetic material that contains instructions for how an organism develops, maintains itself, and reproduces. These instructions are stored in sections of DNA called genes, which contain the code for making proteins that carry out vital cellular functions.

How does DNA organization and cellular structure differ between prokaryotic and eukaryotic cells?

Prokaryotic cells lack a nucleus and membrane-bound organelles, storing their DNA in the cytoplasm in a region called the nucleoid as $1$ circular DNA molecule (main chromosome) along with plasmids. Eukaryotic cells possess a nucleus surrounded by a nuclear membrane and membrane-bound organelles, storing DNA as multiple linear chromosomes, and usually do not have plasmids.

What is the biological hierarchy of genetic structures from smallest to largest?

$1.$ Gene, $2.$ DNA, $3.$ Chromosome, $4.$ Genome, $5.$ Nucleus, $6.$ Cell.

What is the distinction between a genome and a gene?

A genome is the entire set of genetic instructions found in an organism's cell, comprising the complete set of chromosomes and every single base pair. In contrast, a gene is a specific, small section of DNA containing the instructions to make a single protein or functional molecule.

What is a karyotype and how are chromosomes arranged in one?

A karyotype is an organized display of an individual's chromosomes arranged into matching pairs according to their size, shape, and other features. They are ordered from largest to smallest, with the sex chromosomes placed last as the $23^{\text{rd}}$ pair.

What are the clinical uses and key limitations of a karyotype?

A karyotype allows scientists to determine the total number of chromosomes, identify homologous pairs, examine chromosomal size and structure, and detect chromosomal abnormalities. Its primary limitation is that it does not map out individual genes or show DNA sequences.

What three chemical components comprise a single DNA nucleotide?

$1.$ A phosphate group, which forms covalent bonds linking the $3'$ carbon of one sugar to the $5'$ carbon of the next. $2.$ A deoxyribose sugar ($5$-carbon sugar) acting as the central connector. $3.$ A nitrogenous base (adenine, thymine, cytosine, or guanine).

What are the complementary base pairing rules and hydrogen bonding numbers in DNA?

Adenine ($A$) pairs with Thymine ($T$) by forming $2$ hydrogen bonds ($\text{AT2}$), while Cytosine ($C$) pairs with Guanine ($G$) by forming $3$ hydrogen bonds ($\text{CG3}$).

What roles do helicase, DNA polymerase, and DNA ligase play during DNA replication?

Helicase unwinds the double helix at the replication fork using energy from ATP hydrolysis. DNA polymerase reads template bases in the $3'$ to $5'$ direction and synthesizes new DNA in the $5'$ to $3'$ direction, creating a continuous leading strand and discontinuous Okazaki fragments on the lagging strand. DNA ligase forms covalent bonds to join the Okazaki fragments together.

What four cellular consequences occur if DNA is not replicated before cell division?

$1.$ Apoptosis (programmed cell death), $2.$ Cell cycle arrest (refusal to begin division), $3.$ Incomplete genome (incompatible with life or producing genetic disorders), and $4.$ Tissue and organ failure due to lack of cell replacement.

What key events occur during the four stages of mitosis (PMAT)?

In Prophase, chromosomes condense/thicken and the nuclear membrane breaks down. In Metaphase, chromosomes align along the equator/middle. In Anaphase, spindle fibres pull sister chromatids apart to opposite cell poles. In Telophase, two new nuclear membranes form around the separated chromosomes.

How does meiosis differ from mitosis in rounds of division and cellular outcome?

Meiosis involves $1$ round of DNA replication followed by $2$ successive nuclear divisions, yielding $4$ genetically unique haploid ($n$) gametes with $23$ chromosomes each. Mitosis involves $1$ division yielding $2$ genetically identical diploid ($2n$) daughter cells.

What three meiotic mechanisms contribute to genetic variation, and during which phases do they occur?

$1.$ Crossing over (Prophase I): homologous chromosomes exchange segments to produce new allele combinations. $2.$ Independent assortment (Metaphase I): homologous pairs align in random orientations at the metaphase plate. $3.$ Random segregation (Anaphase I and Anaphase II): random separation of homologous chromosomes and sister chromatids to opposite poles.

What are the comparative advantages and disadvantages of asexual versus sexual reproduction?

Asexual reproduction requires only $1$ parent, is fast, energy-efficient, and preserves successful traits, but lacks genetic variation and is vulnerable to environmental changes. Sexual reproduction requires $2$ parents and high energy, but generates genetic variation, enhancing adaptability, disease resistance, and evolutionary potential.

How does binary fission occur in prokaryotes?

The single circular chromosome unwinds and copies itself from the origin of replication. As the bacterium enlarges, chromosomes migrate to opposite poles. The FtsZ protein forms a ring-like partition at the cell center, a new cross-wall called a septum forms, and the membrane pinches inward to divide the cell into $2$ identical daughter cells.

What are runners and rhizomes, and what plant species utilize each for asexual reproduction?

Runners (stolons) are specialized horizontal stems growing above ground surface from the parent plant that develop nodes with adventitious roots and aerial shoots (e.g., strawberries, spider plants). Rhizomes are modified underground horizontal stems that store nutrients and produce new vertical shoots and roots at intervals (e.g., ginger, turmeric, lilies).

What are three structural and functional differences between DNA and RNA?

$1.$ Strands: DNA is typically double-stranded, whereas RNA is typically single-stranded. $2.$ Nitrogenous bases: DNA contains thymine ($T$), whereas RNA contains uracil ($U$) in place of thymine. $3.$ Function: DNA stores genetic instructions, whereas RNA helps express and decode that information.

What are the individual roles of mRNA, tRNA, and rRNA in protein synthesis?

mRNA (messenger RNA) carries copied genetic instructions from DNA out of the nucleus to the ribosome. tRNA (transfer RNA) carries specific amino acids to the ribosome by matching its anticodon to mRNA codons. rRNA (ribosomal RNA) forms the structural core of ribosomes and helps assemble amino acids into proteins.

What sequential steps occur during transcription in a eukaryotic cell?

RNA polymerase binds to a gene's promoter, forms a transcription bubble by unwinding DNA, disrupts hydrogen bonds to expose the template strand, pairs complementary RNA nucleotides ($A$ with $U$, $T$ with $A$, $C$ with $G$), links nucleotides with phosphodiester bonds, and stops upon reaching a stop sequence, releasing the completed mRNA molecule.

What sequence of events takes place during translation to synthesize a polypeptide?

A small ribosomal subunit and initiator tRNA carrying methionine bind to the start codon ($\text{AUG}$). The large subunit joins to complete the ribosome. tRNAs bind sequentially via complementary codon-anticodon pairing, and the ribosome links adjacent amino acids with peptide bonds. Upon reaching a stop codon, a release factor frees the finished polypeptide chain, which folds into its functional $3\text{D}$ shape.

How do gene mutations differ from chromosomal mutations in scale and type?

Gene mutations affect single nucleotide sequences within a gene via substitutions, insertions, or deletions (insertions and deletions cause frameshifts). Chromosomal mutations affect large segments or whole chromosomes via duplications, deletions, inversions, or translocations (transferring a fragment to another chromosome).

What specific molecular change causes sickle cell anemia and what is its physiological effect?

A point mutation in the HBB gene substitutes Adenine for Thymine, altering the mRNA codon from GAG (glutamic acid) to GUG (valine). This produces abnormal hemoglobin S, which causes red blood cells to become rigid and sickle-shaped under low oxygen, leading to premature cell breakdown, capillary blockages, and tissue anemia.

What beneficial mutation involves the ApoA 1 gene and what health advantage does it confer?

A mutation in the ApoA 1 gene produces an altered ApoA-1 protein that improves the clearance of excess cholesterol from tissues and arterial walls, thereby reducing the risk of atherosclerosis and cardiovascular disease.

What are the three classes of mutagens and how does UV radiation specifically cause melanoma?

Mutagens are classified as physical (UV, gamma rays), chemical (benzene, BPA), or biological (viral insertions, transposons). Excessive UV radiation causes adjacent thymine bases to bond incorrectly into thymine dimers, distorting DNA and triggering replication errors that lead to uncontrolled skin cell proliferation (melanoma).

What is polygenic inheritance and what biological factors influence human skin colour?

Polygenic inheritance occurs when multiple genes exert additive effects on a single trait, creating a continuous bell-curve distribution. Human skin colour is influenced by melanin produced by melanocytes (eumelanin and pheomelanin), where rhodopsin protein receptors detect UV radiation and trigger melanin production to protect DNA.

How do dominant alleles, recessive alleles, genotypes, and phenotypes interact in Mendelian inheritance?

An allele is a version of a gene. Genotype is the combination of alleles present (homozygous if identical, heterozygous if different). Phenotype is the observable physical trait. A dominant allele expresses its phenotype when at least $1$ copy is present, whereas a recessive allele requires $2$ copies to be expressed.

What are the sequential steps of recombinant DNA technology?

$1.$ Identify and isolate the target gene using restriction enzymes or PCR. $2.$ Cut donor DNA and bacterial plasmids with restriction enzymes to produce complementary 'sticky ends'. $3.$ Splice the gene into the plasmid using DNA ligase. $4.$ Introduce the recombinant plasmid into host bacteria via transformation. $5.$ Cultivate the transgenic bacteria in fermenters to express, collect, and purify the target protein.

How is recombinant DNA technology utilized in Bt cotton, and what are its pros and cons?

Insecticidal genes (cry or vip) from Bacillus thuringiensis are inserted into the cotton plant genome. Pros: protects against pests such as button bollworms, reduces chemical pesticide applications, and improves yields. Cons: targeted pests can evolve resistance over time, high seed costs increase dependency on suppliers, and it does not kill non-target pests.

How does the CRISPR-Cas9 gene editing system locate and modify genomic sequences?

Scientists engineer a guide RNA (gRNA) complementary to a specific $20$-nucleotide target sequence in the genome. The gRNA directs the Cas9 protein (acting as molecular scissors) to the precise locus, where Cas9 cleaves phosphodiester bonds to cause double-strand breaks. Cellular DNA repair mechanisms then silence the gene or incorporate a newly supplied sequence.

How is CRISPR-Cas9 applied to treat sickle cell disease?

CRISPR-Cas9 edits a regulatory region of the Bck11A gene in bone marrow blood-forming stem cells, increasing the production of fetal hemoglobin and preventing red blood cells from sickling.

How was Somatic Cell Nuclear Transfer (SCNT) used to rescue the black-footed ferret from inbreeding depression?

Cryopreserved somatic cells from a deceased ferret named Willa were injected into enucleated unfertilized eggs from domestic ferrets. The reconstructed eggs were activated with electrical pulses or chemicals to develop into embryos and implanted into surrogate mothers, producing genetic clones to restore genetic diversity against sylvatic plague.

What is the primary difference in purpose between genetic counseling and population screening?

Genetic counseling is an individualized clinical consultation that assesses a specific person's or family's risk of inheriting or passing on a genetic condition based on family pedigree. Population screening is a public health strategy that tests large groups of asymptomatic individuals (e.g., newborn screening, bowel cancer screening) to detect disorders early.

What are the major ethical and social dilemmas associated with modern genetic technologies?

Key issues include genetic discrimination in employment or health insurance, violations of family privacy through shared DNA findings, stigma devaluing individuals with disabilities, ethical concerns over non-consensual germline editing in human embryos, and socioeconomic inequalities regarding who can afford advanced treatments.

Who formulated the Theory of Evolution by Natural Selection and what are its core steps?

Charles Darwin and Alfred Russel Wallace proposed the theory in $1858$ (published in Darwin's On the Origin of Species in $1859$). Steps: $1.$ Inherited genetic variation exists in a population; $2.$ Overproduction of offspring exceeds environmental capacity; $3.$ Competition for limited resources; $4.$ Natural selection favors individuals with advantageous traits; $5.$ Favorable alleles are inherited and increase in frequency over generations.

How do stabilizing, directional, and diversifying selection differ, and what examples illustrate each?

Stabilizing selection favors intermediate phenotypes against extremes (e.g., robins laying clutch sizes of $4$ eggs). Directional selection shifts the population mean toward one extreme phenotype (e.g., peppered moths shifting from light to dark during the Industrial Revolution). Diversifying selection favors both phenotypic extremes over intermediate forms (e.g., rocky terrain favoring gray and Himalayan rabbits over white rabbits).

What sequence of events causes speciation following geographic isolation?

$1.$ A geographic barrier splits a single population into isolated groups. $2.$ The isolated populations encounter differing environmental selection pressures and independent mutations. $3.$ Natural selection drives distinct morphological and physiological adaptations in each group. $4.$ Over time, reproductive isolation develops, preventing the two groups from interbreeding to produce fertile offspring.

What are the primary divisions of the geological timescale and how do relative and absolute dating differ?

Earth's $4.6\text{ billion years}$ are divided from largest to smallest into eons (Hadean, Archean, Proterozoic, Phanerozoic), eras (Paleozoic, Mesozoic, Cenozoic), and periods. Relative dating uses sedimentary rock layers and index fossils to determine the relative order of events (superposition), whereas absolute dating uses radiometric decay of minerals to determine exact numerical ages.

What three factors explain why the fossil record is inherently incomplete?

$1.$ Early organisms were soft-bodied non-vertebrates lacking exoskeletons, decomposing rapidly without fossilizing. $2.$ Geological processes (erosion, tectonic plate movement, volcanic activity) destroy rock strata. $3.$ The oldest rock layers are buried too deep within Earth's crust to be excavated.

What are the distinct strengths and limitations of analyzing Aboriginal and Torres Strait Islander rock art for paleobiology?

Strengths: rock art provides paleobiological data that skeletons cannot provide, including animal behavior, soft tissue morphology, external colouration/phenotypes, and timelines of human coexistence with extinct megafauna. Limitations: interpretations are subjective, and artwork is subject to taphonomic weathering, pigment oxidization, and potential anatomical inaccuracies.