Unit 5: Heredity

Meiosis I

The first division of meiosis that separates homologous chromosomes

Haploid

A cell with one set of chromosomes (n)

Diploid

A cell with two sets of chromosomes (2n)

Meiosis I

Division where homologous chromosomes separate

Prophase I

Homologous chromosomes pair and crossing over occurs

Genetic recombination (crossing over)

Exchange of DNA between homologous chromosomes

Metaphase I

Homologous pairs line up at the equator

Anaphase I

Homologous chromosomes separate and move to opposite poles

Telophase I

Two haploid cells form after chromosome separation

Meiosis II

Second meiotic division that separates sister chromatids

Prophase II

Chromosomes condense in each haploid cell

Metaphase II

Chromosomes line up at the equator

Anaphase II

Sister chromatids separate

Telophase II

Four genetically unique haploid cells form

Synapsis

Pairing of homologous chromosomes during prophase I

Tetrads

Paired homologous chromosomes (four chromatids)

Linked genes

Genes located close together on the same chromosome

Nondisjunction

Failure of chromosomes to separate properly

Aneuploidy

Abnormal number of chromosomes

Mendelian genetics

Principles of inheritance based on Mendel’s work

Mendel's law of segregation

Alleles separate during gamete formation

Mendel's Law of Independent Assortment

Genes on different chromosomes assort independently

Genotype

Genetic makeup of an organism

Phenotype

Observable traits of an organism

Homozygous

Having two identical alleles

Heterozygous

Having two different alleles

Dominant

Allele expressed when present

Recessive

Allele expressed only when homozygous

Monohybrid cross

Cross involving one trait

Dihybrid cross

Cross involving two traits

Non‑Mendelian genetics

Inheritance patterns that deviate from Mendel’s laws

Linked genes

Genes inherited together because they are close on a chromosome

Map units

Measurement of genetic distance based on recombination frequency

Sex‑linked genes

Genes located on sex chromosomes

Autosomes

Non‑sex chromosomes

Sex chromosomes

Chromosomes that determine biological sex

Sex‑linked genes

Genes found on X or Y chromosomes

Multiple gene inheritance

Traits controlled by several genes (polygenic)

Nonnuclear inheritance

Traits inherited through mitochondrial or chloroplast DNA

Phenotypic plasticity

Ability of one genotype to produce different phenotypes depending on environment