Bio Exam 2025

Chromosome

A structure made of DNA and proteins that contains genes.

Chromatin

Unwound DNA found in the nucleus.

Centromere

Region where sister chromatids are joined.

Diploid (2n)

Two sets of chromosomes (e.g., somatic cells).

Haploid (n)

One set of chromosomes (e.g., gametes).

Interphase

Cell grows and prepares for division (90% of cycle).

G1 Phase

Cell grows and performs normal functions.

S Phase

DNA is replicated.

G2 Phase

Organelles duplicate, cell prepares for mitosis.

M Phase

Mitosis + Cytokinesis.

Mitosis

Produces 2 identical diploid somatic cells (used for growth & repair).

Prophase

Chromosomes condense, spindle forms, nuclear envelope breaks down.

Metaphase

Chromosomes align at the cell equator.

Anaphase

Sister chromatids separate and move to opposite poles.

Telophase

Nuclear membranes reform, chromosomes decondense.

Cytokinesis

Cytoplasm divides into two daughter cells.

Meiosis

Produces 4 genetically unique haploid gametes (sperm/eggs).

Homologous chromosomes

Pair up (synapsis), crossing over occurs (Prophase I).

Law of Segregation

Alleles separate during gamete formation.

Law of Independent Assortment

Genes for different traits separate independently.

Gene

A segment of DNA coding for a trait.

Allele

Different forms of a gene (e.g., A or a).

Homozygous

Two identical alleles (AA or aa).

Heterozygous

Two different alleles (Aa).

Dominant

Expressed allele (A).

Recessive

Masked unless two copies are present (a).

Incomplete Dominance

Blended phenotype (e.g., red + white = pink).

Codominance

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

Multiple Alleles

More than two alleles (e.g., A, B, O blood types).

Polygenic Traits

Controlled by multiple genes (e.g., height, skin color).

Sex-linked Traits

Genes located on X or Y chromosomes (e.g., hemophilia, color blindness).

DNA Structure

Double helix made of nucleotides.

Sugar-phosphate backbone

The structural framework of DNA consisting of sugar and phosphate groups.

Nitrogenous bases

Adenine (A), Thymine (T), Cytosine (C), Guanine (G).

Base pairing rules

A pairs with T, C pairs with G.

DNA Replication

Occurs in the S phase of the cell cycle.

Helicase

Enzyme that unzips DNA.

DNA Polymerase

Enzyme that adds complementary nucleotides.

Semi-conservative replication

Each new DNA has one old strand and one new strand.

Transcription

Process where DNA is converted to mRNA in the nucleus.

Translation

Process where mRNA is converted to protein at the ribosome.

Codon

3-base sequence on mRNA (e.g., AUG = start codon).

tRNA

Brings amino acids with anticodons that match codons.

Point Mutation

Change in one base (e.g., substitution).

Frameshift Mutation

Insertion or deletion that shifts the reading frame.

Silent Mutation

A mutation that does not change the amino acid sequence.

Missense Mutation

A mutation that results in a different amino acid.

Nonsense Mutation

A mutation that creates a premature stop codon.

Theory of Evolution

Species change over time through genetic variation and selection.

Natural Selection

Traits that enhance survival are passed on.

Mutation

Random changes in DNA.

Gene Flow

Movement of genes between populations.

Genetic Drift

Random changes in allele frequency (e.g., bottleneck, founder effect).

Allopatric Speciation

Occurs due to geographic isolation.

Sympatric Speciation

Occurs without physical separation.

Fossil Record

Shows changes over time.

Homologous structures

Same origin, different function.

Analogous structures

Different origin, similar function.

Molecular Evidence

Similar DNA and proteins across species.

Embryology

Similar developmental stages across species.