Operons, Meiosis, Inheritance, and Population Genetics

Promoter

DNA sequence where RNA polymerase binds to begin transcription.

Operator

DNA region where a repressor binds to regulate transcription.

Genes (in operons)

Structural genes transcribed as a unit in an operon.

Repressible operon

Usually on; can be turned off by a repressor (e.g., Trp operon).

Inducible operon

Usually off; turned on by an inducer (e.g., Lac operon).

Negative control

A repressor protein blocks transcription.

Positive control

An activator protein increases transcription.

Activator (CAP)

Binds cAMP to stimulate transcription in the Lac operon.

Cyclic AMP (cAMP)

A signaling molecule that activates CAP in low glucose.

Eukaryotic gene expression stages

Includes transcription, RNA processing, translation, post-translational modifications.

Alternative splicing

Process that creates different mRNAs from the same gene.

Polymerase (RNA polymerase)

Enzyme that synthesizes RNA from a DNA template.

Lac operon

Inducible operon turned on by lactose, regulated by glucose.

Trp operon

Repressible operon turned off by tryptophan.

Lactase

Enzyme that breaks down lactose into glucose and galactose.

Lactose

Sugar that acts as an inducer in the Lac operon.

Glucose

Preferred sugar; its absence leads to cAMP increase.

Negatively induced

A repressor is removed by an inducer (e.g., Lac operon).

Negatively repressed & positively activated

Describes Lac operon: repressed by repressor, activated by cAMP-CAP.

Homologous chromosomes

Chromosomes with the same genes but possibly different alleles.

Sister chromatids

Identical copies of a chromosome connected at the centromere.

Centromeres

Region where sister chromatids are joined.

Synapsis

Pairing of homologous chromosomes during Prophase I.

Bivalent

A pair of homologous chromosomes during synapsis.

Meiosis

Cell division that reduces chromosome number by half.

Cytokinesis

Division of the cytoplasm after mitosis or meiosis.

Crossing over

Exchange of genetic material between homologs in Prophase I.

Independent assortment

Random distribution of homologous chromosomes during meiosis.

Chiasmata

Point where chromatids cross over and exchange DNA.

Synaptonemal complex

Protein structure that forms between homologs during synapsis.

Homolog

One of two chromosomes in a homologous pair.

Kinetochore

Protein structure on centromere where spindle fibers attach.

Daughter cells

Cells produced at the end of meiosis.

Parent cells

Original cell before meiosis begins.

Chromosome

Structure of DNA and proteins carrying genetic information.

Ploidy

Number of chromosome sets in a cell (e.g., diploid or haploid).

Haploid

Cell with one set of chromosomes (n).

Diploid

Cell with two sets of chromosomes (2n).

Somatic cells

Body cells that are diploid.

Gametes

Reproductive cells (sperm/egg), haploid.

Fertilization

Fusion of gametes to form a zygote.

Zygote

Fertilized egg, diploid cell formed from two gametes.

Incomplete dominance

Heterozygous phenotype is a blend (e.g., red + white = pink).

Codominance

Both alleles are fully expressed (e.g., AB blood type).

Recessive

Allele expressed only when homozygous.

Recessive pattern

Trait only appears when both alleles are recessive.

Dominant

Allele that masks the effect of a recessive allele.

Alleles

Different versions of a gene.

Genotype

Genetic makeup (e.g., AA, Aa, aa).

Phenotype

Physical trait expressed (e.g., brown eyes).

Heterozygous

Two different alleles for a trait (e.g., Aa).

Homozygous

Two identical alleles for a trait (e.g., AA or aa).

Blood types

Determined by alleles A, B, and O (e.g., AB = codominant).

Law of Independent Assortment

Alleles of different genes assort independently.

Law of Segregation

Allele pairs separate during gamete formation.

Hardy-Weinberg equation

p² + 2pq + q² = 1; predicts genotype frequencies.

Equilibrium

No evolution; allele frequencies remain constant.

Genotypic frequency

Proportion of each genotype in a population.

Allele frequency

Proportion of each allele (A or a) in a population.

Natural selection

Process where advantageous traits increase in frequency.