Year 10 Genetics, Cell Division, and Evolution

Comprehensive vocabulary flashcards covering the molecular structure of DNA, cell division (mitosis and meiosis), Mendelian and sex-linked inheritance, genetic mutations, and mechanisms and evidence for evolution.

Genetics

The scientific study of inherited characteristics and traits passed down from parents to offspring.

Inheritance

The passing down of genes and genetic information from parents to their offspring.

Allele

A different version or alternative form of the same gene, located at the same position on homologous chromosomes.

Genotype

The combination of alleles or letter symbols possessed by an organism for a specific trait (e.g. $RR$, $Rr$, or $rr$), representing its genetic makeup.

Phenotype

The physical appearance or observable characteristic displayed by an organism as determined by its genotype.

Dominant Trait

A trait that is expressed in the phenotype whenever at least one dominant allele is present, masking the presence of a recessive allele.

Recessive Trait

A trait that is only physically expressed when an organism inherits two copies of the recessive allele, remaining masked if a dominant allele is present.

Homozygous

A genotype possessing two identical copies of an allele for a particular trait, either homozygous dominant (such as $RR$) or homozygous recessive (such as $rr$).

Heterozygous

A genotype possessing two different alleles for a particular trait (such as $Rr$).

Pure-breeding

The breeding of organisms carrying only one type of allele for a trait through repeated self-fertilisation or selective crosses so all subsequent generations show the same trait.

Test-cross

A cross-breeding experiment where a pure-bred organism that is homozygous dominant for a trait is mated with a pure-bred organism that is homozygous recessive.

Punnett Square

A diagrammatic grid used to calculate and predict the mathematical probabilities of offspring genotypes and phenotypes from parents with known genotypes.

Sex-linked Genes

Genes located specifically on the sex chromosomes (the 23rd pair in humans, predominantly on the $X$ chromosome), such as those causing colour-blindness or haemophilia.

Pedigree

A family tree diagram used to chart and identify the pattern of inheritance of a specific trait or genetic disorder across multiple generations.

Down Syndrome

A chromosomal abnormality caused by an extra copy of chromosome 21 (trisomy 21), resulting from an error during meiotic cell division.

Klinefelter Syndrome

A chromosomal condition in males resulting from an extra $X$ chromosome in the 23rd pair, characterized by a $47,XXY$ karyotype.

Mutation

A permanent change in the base sequence of a DNA molecule resulting from errors during replication or damage from radiation, chemical, or biological factors.

Silent Mutation

A base substitution in the DNA sequence that does not alter the amino acid sequence or the structure of the protein produced, having no physical effect on the individual.

Missense Mutation

A mutation that changes a codon to produce a different amino acid, resulting in an altered protein that may fail to function correctly and cause disease (e.g. sickle-cell anaemia).

Nonsense Mutation

A mutation that causes the cell to stop reading the genetic message prematurely, producing an incomplete, non-functional protein (e.g. cystic fibrosis, beta thalassaemia).

Frameshift Mutation

A mutation caused by the insertion or deletion of one or more base pairs, shifting the reading frame and jumbling all downstream genetic information (e.g. Tay-Sachs disease).

Carcinogen

A chemical, physical, or biological agent capable of inducing DNA mutations that lead to cancer and uncontrolled cell multiplication.

DNA (Deoxyribonucleic Acid)

A macromolecule composed of two nucleotide strands coiled into a double helix that contains the chemical blueprints and instructions for cellular function and inherited traits.

Nucleotide

The repeating structural unit of nucleic acids, consisting of a phosphate group ($\text{PO}_4^{3-}$), a deoxyribose sugar, and one of four nitrogenous bases ($A$, $T$, $C$, or $G$).

Complementary Base Pairing

The specific chemical pairing across the DNA double helix where adenine ($A$) only pairs with thymine ($T$), and cytosine ($C$) only pairs with guanine ($G$).

Histones

Protein spools around which long DNA strands wind compactly to form chromatin fibers and condense into chromosomes.

Karyotype

A photographic or diagrammatic image showing the complete set of an organism's homologous chromosomes arranged in numerical order.

Gene

A specific physical section of DNA along a chromosome that possesses a unique nitrogenous base sequence coding for the synthesis of a specific protein.

Chargaff's Rule

The biochemical observation that in DNA, the amount of adenine equals thymine ($A = T$), the amount of guanine equals cytosine ($G = C$), and total purines equal total pyrimidines ($A + G = T + C$).

Gene Pool

The complete collection of all genetic information and every allele copy present within a reproducing population of a species.

Allele Frequency

The proportion or percentage representing the number of copies of a specific allele relative to the total number of all alleles for that gene in a population.

Gene Flow

The transfer of alleles into or out of a population resulting from the immigration or emigration of breeding individuals.

Genetic Drift

A random change in allele frequencies from generation to generation driven by chance events rather than natural selection, acting most strongly in small populations.

Bottleneck Effect

A form of genetic drift resulting from a sharp, random reduction in population size, producing a surviving population that carries only a small, unrepresentative sample of alleles.

Modern Synthesis

The unified biological framework integrating Darwin's concept of natural selection with Mendelian genetics, mutation, and population genetics.

Homologous Structures

Anatomical features in different species that share an underlying skeletal design due to common ancestry, modified over time for different functions (e.g. vertebrate forelimbs).

Analogous Structures

Structures in different species that perform similar functions but evolved independently through convergent evolution without a shared structural origin (e.g. shark fin and dolphin flipper).

Vestigial Structures

Reduced anatomical remnants inherited from evolutionary ancestors where the structure previously had a larger, fully developed function (e.g. human coccyx, plica semilunaris).

Romer's Gap

An approximate $15\text{ million-year}$ gap in the fossil record spanning the late Devonian and early Carboniferous periods containing relatively few discovered early tetrapod fossils.

Trace Fossil

A geological fossil recording the activity, movement, or behavior of an ancient organism, such as footprints, tracks, burrows, or fossilised faeces.

Carbon Dating

A radiometric dating method measuring the radioactive decay of carbon-14 in organic materials, useful for samples up to about $50\,000\text{ years}$ old.

Zygote

A single diploid cell formed immediately following the fertilisation of an ovum (egg cell) by a sperm cell.

DNA Replication

The biological process occurring during interphase in which an existing double-stranded DNA molecule unzips and replicates to produce two identical DNA molecules.

Helicase

The enzyme responsible for unzipping the DNA double helix during replication by breaking the hydrogen bonds holding nitrogenous base pairs together.

Chromatin

The relaxed, unwound form of DNA strands coiled around histones found in the cell nucleus during interphase prior to chromosome supercoiling.

Mitosis

The division of the cell nucleus in eukaryotic cells that produces two genetically identical diploid daughter cells for body growth and cellular repair.

Cytokinesis

The final stage of cell division involving the physical pinching off and division of the cytoplasm and cell membrane into two distinct daughter cells.

Diploid ($2n$)

A cellular state containing two complete sets of homologous chromosomes, representing $46$ chromosomes ($2n = 46$) in normal human somatic cells.

Haploid ($n$)

A cellular state containing only one set of unpaired chromosomes, representing $23$ chromosomes ($n = 23$) in human gametes (sperm and egg cells).