Hon. Bio. Final

Sister chromatids

Identical chromosomes in a pair.

Homologous chromosomes

Carries the same genes (NOT SAME ALLELES), inherited from parents.

Recombinant chromatids

Sister chromatids which go through recombination during prophase 1

Synapsis

Homologous chromosomes pair up.

Tetrads

Each made of 2 homologous chromosomes, 4 chromatids total.

Chiasmata

Crossing over occurs between non-sister chromatids .

Meiosis

Reduces chromosome number from diploid (2n) to haploid (n).

Gene

Segment of DNA that codes for a trait.

Allele

Different versions of a gene.

Genotype

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

Phenotype

Physical expression of a trait.

Homozygous

Two identical alleles (AA or aa).

Heterozygous

Two different alleles (Aa).

Dominant allele

Expressed if present.

Recessive allele

Only expressed if both alleles are recessive

Law of Segregation

Alleles separate during gamete formation.

Law of Independent Assortment

Genes for different traits assort independently during meiosis.

Monohybrid cross

Involves one gene (e.g., Aa × Aa).

Dihybrid cross

Involves two genes (e.g., AaBb × AaBb), 9:3:3:1 ratio typical.

Incomplete dominance

Heterozygous phenotype is a blend (e.g., red × white → pink).

Codominance

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

Multiple alleles

More than two possible alleles in population (e.g., ABO blood group).

Polygenic inheritance

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

Pleiotropy

One gene affects multiple traits.

Epistasis

One gene masks or alters expression of another gene.

X-linked traits

More common in males (e.g., color blindness, hemophilia).

Punnett square

Predicts offspring genotypes and phenotypes.

Pedigree chart

Tracks inheritance of traits through generations.

Test cross

Cross with homozygous recessive to determine unknown genotype.

Point mutation

Change in one nucleotide.

Shift mutation

Insertion/deletion alters reading frame.

Chromosomal mutations

Deletion, duplication, inversion, translocation.

Nondisjunction

Failure of chromosomes to separate in meiosis (e.g., trisomy 21).

Autosomal disorders

Involve non-sex chromosomes.

Sex-linked disorders

Usually involve recessive alleles on the X chromosome.

Evolution

Change in allele frequencies in a population over time.

Natural selection

Pressure from environment to increase fitness.

Population

Group of interbreeding individuals of the same species.

Gene pool

All the alleles present in a population.

Allele frequency

Proportion of a specific allele in the gene pool.

Natural Selection

Individuals with favorable traits have higher reproductive success

Directional selection

Favors one extreme.

Stabilizing selection

Favors average traits.

Disruptive selection

Favors both extremes over the average.

Genetic Drift

Random changes in allele frequencies due to chance.

Bottleneck effect

Population sharply reduced in size.

Founder effect

Small group colonizes new area.

Gene Flow

Movement of alleles between populations (e.g., migration).

Mutation

Random changes in DNA; source of new alleles.

Speciation

Formation of new species.

Prezygotic barriers

Before fertilization (e.g., behavioral, temporal, mechanical).

Postzygotic barriers

After fertilization (e.g., infertile offspring).

Allopatric speciation

Geographic isolation.

Sympatric speciation

No physical barrier; often via polyploidy or niche differentiation.

Homologous structures

Same structure, different function (common ancestry).

Analogous structures

Same function, different origin (convergent evolution).

Adaptive radiation

One species evolves into many to exploit different niches.

Convergent evolution

Unrelated species evolve similar traits.

Coevolution

Two species evolve in response to each other.

Hardy-Weinberg equilibrium

No evolution if certain conditions are met (no selection, mutation, migration, drift, random mating).

Plasmid

Small, circular piece of DNA.

Bacterial Transformation

Can be transferred between bacteria via conjugation. This contributes to horizontal gene transfer.