Biology UNIT 4 LG 3 & LG 4

What are homologous chromosomes?

Pairs of chromosomes similar in size, shape and gene content, one inherited from each parent. homologous chromosomes

What is the difference between diploid and haploid?

Diploid (2n) cells have two of each chromosome; haploid (n) cells have one of each chromosome.

What is mitosis?

Cell division producing two genetically identical daughter cells.

What is meiosis and why is it important?

Cell division producing haploid gametes; creates genetic variation through crossing over, independent assortment and random fertilisation. meiosis

What happens in meiosis I vs meiosis II?

Meiosis I separates homologous chromosomes; meiosis II separates sister chromatids.

What are tetrads and chiasmata?

Tetrad = homologous chromosomes aligned together; chiasma = point where crossing over occurs.

How do crossing over and independent assortment create variation?

Crossing over swaps DNA between chromatids; independent assortment randomly distributes maternal/paternal chromosomes.

What is random fertilisation?

Any sperm can fertilise any egg, increasing genetic variation.

What is a karyotype?

Visual display of all chromosomes in a cell, used to identify ploidy and abnormalities.

What are autosomes and sex chromosomes?

Autosomes = non‑sex chromosomes; sex chromosomes = X and Y determining biological sex.

What is spermatogenesis?

Production of sperm through mitosis and meiosis in testes.

What is oogenesis?

Production of ova; meiosis produces one large secondary oocyte and polar bodies.

What is ovulation?

Release of secondary oocyte arrested in metaphase II.

What is fertilisation?

Fusion of haploid sperm and haploid ovum to form a diploid zygote.

What is an allele?

Different versions of the same gene.

What is the difference between homozygous and heterozygous?

Homozygous = same alleles; heterozygous = different alleles.

What is the difference between dominant and recessive alleles?

Dominant alleles are expressed when present; recessive alleles are masked in heterozygotes.

What are genotype and phenotype?

Genotype = genetic makeup; phenotype = observable traits.

What are Mendel’s laws?

Segregation = alleles separate in gametes; independent assortment = allele pairs separate independently if on different chromosomes.

What is a point mutation?

Change in a single nucleotide (silent, missense, nonsense).

What is a silent mutation?

Mutation that does not change the amino acid.

What is a missense mutation?

Mutation that substitutes one amino acid for another.

What is a nonsense mutation?

Mutation that changes an amino acid codon to a stop codon.

What is a frameshift mutation?

Insertion or deletion shifting the reading frame, altering all downstream amino acids.

What is the difference between somatic and germline mutations?

Somatic = non‑heritable; germline = heritable.

What is a mutagen and a carcinogen?

Mutagen = causes DNA changes; carcinogen = causes cancer by altering DNA.

What are block mutations?

Chromosomal changes including deletion, duplication, insertion, translocation and inversion.

What is nondisjunction?

Failure of chromosomes or chromatids to separate in meiosis, causing aneuploidy (e.g., trisomy).

What is the structure of DNA?

Double helix made of nucleotides (phosphate, sugar, base) with complementary base pairing (A–T, C–G). DNA structure

What are introns and exons?

Introns = non‑coding; exons = coding regions of genes.

What is the promoter region?

DNA sequence where transcription begins.

What are histones, heterochromatin and euchromatin?

Histones = DNA‑wrapping proteins; heterochromatin = tightly packed, genes off; euchromatin = loosely packed, genes on.

What are plasmids?

Small circular DNA molecules in bacteria used in genetic engineering.

What enzymes are involved in DNA replication?

Helicase unwinds DNA; DNA polymerase adds nucleotides; ligase joins Okazaki fragments.

What are Okazaki fragments?

Short DNA segments on the lagging strand.

What is transcription?

DNA is copied into mRNA in the nucleus.

What is RNA processing?

5’ cap added, introns removed, poly‑A tail added.

What is translation?

Ribosome reads mRNA codons; tRNA brings amino acids; polypeptide is formed.

What are transcription factors?

Proteins that regulate gene expression by binding promoter regions.

What are epigenetic modifications?

DNA methylation turns genes off; histone acetylation turns genes on. epigenetics

What are HOX genes?

Master regulatory genes controlling body plan and morphology.

What is polygenic inheritance?

Trait controlled by many genes producing continuous variation (e.g., height).

What is multiple‑allele inheritance?

Traits with more than two alleles (e.g., ABO blood groups).

What is recombinant DNA?

DNA formed by combining genes from different organisms using restriction enzymes, plasmids and ligase.

What is PCR?

Technique that amplifies DNA using heating and cooling cycles.

What is gel electrophoresis?

Technique separating DNA fragments by size to create banding patterns.

What is microevolution?

Small genetic changes within a population over time.

What is macroevolution?

Large‑scale changes forming new species.

What processes cause microevolution?

Mutation, gene flow, genetic drift, natural selection.

What are the three types of natural selection?

Stabilising (average favoured), directional (one extreme favoured), disruptive (both extremes favoured).

What is allele frequency?

Proportion of each allele in a population.

What is speciation?

Formation of new species through reproductive isolation (allopatric, sympatric, parapatric).

Why is low genetic diversity dangerous?

Reduces ability to adapt, increasing extinction risk.

What is comparative genomics?

Comparing DNA sequences to determine evolutionary relatedness.

What are cladograms and phylograms?

Cladograms show relationships; phylograms show relationships + genetic distance.

What is evolutionary radiation?

Rapid diversification of species.

What is a mass extinction?

Sudden global loss of many species.