Comprehensive Guide to AP Biology Unit 5: Heredity

Meiosis

A specialized form of cell division that produces gametes with half the number of chromosomes as the parent cell.

Gametes

Sex cells (sperm and egg) that contain half the chromosome number.

Diploid (2n)

A cell containing two full sets of chromosomes, one set from each parent.

Haploid (n)

A cell containing only one set of chromosomes.

Homologous Chromosomes

A pair of chromosomes that are similar in size, shape, and genetic content.

Loci

Positions on a chromosome where specific genes are located.

Sister Chromatids

Identical copies of a chromosome formed during the S-phase of Interphase.

Prophase I

The phase in Meiosis I where homologous chromosomes condense and synapse to form tetrads.

Synapsis

The pairing of homologous chromosomes during Prophase I.

Tetrads

Groups of four chromatids formed during synapsis.

Crossing Over

The exchange of genetic material between non-sister chromatids at chiasmata.

Independent Assortment

The random orientation of homologous pairs during Metaphase I.

Anaphase I

The phase where homologous pairs separate and move to opposite poles in Meiosis I.

Telophase I

The phase where two haploid daughter cells form after Meiosis I.

Meiosis II

The second round of meiotic division that separates sister chromatids.

Prophase II

The phase in Meiosis II where the spindle apparatus reforms.

Recombinant Chromosomes

New chromosomes that carry genes from both parents as a result of crossing over.

Genetic Variation

The differences in DNA sequences among individuals, crucial for evolution.

Chi-Square Goodness of Fit Test

A statistical test to determine if observed data match expected data.

Null Hypothesis

The assumption that there is no significant difference between observed and expected frequencies.

Allele

Alternative versions of a gene.

Genotype

The genetic makeup of an individual.

Phenotype

The observable physical traits of an organism.

Dominant Allele

An allele that is fully expressed in the phenotype of a heterozygote.

Recessive Allele

An allele whose phenotypic effect is not observed in a heterozygote.

Law of Dominance

In heterozygotes, the dominant allele masks the recessive allele.

Law of Segregation

The separation of two alleles during gamete formation.

Law of Independent Assortment

Genes for distinct traits segregate independently during gamete formation.

Multiplication Rule

The probability that two independent events will occur together.

Addition Rule

The probability that any one of two or more mutually exclusive events will occur.

Incomplete Dominance

Heterozygotes show a blend of the two alleles.

Codominance

Heterozygotes express both alleles simultaneously and separately.

Multiple Alleles

More than two allele options exist for a gene.

Polygenic Inheritance

A single trait controlled by two or more genes.

Mitochondrial Inheritance

Traits inherited maternally from mitochondria in the egg.

Phenotypic Plasticity

The ability of one genotype to produce more than one phenotype based on environmental conditions.

Pedigree Analysis

A chart that tracks a trait through generations.

Aneuploidy

Abnormal number of chromosomes due to errors in meiosis.

Nondisjunction

The failure of chromosomes to separate properly during cell division.

Trisomy

Three copies of a chromosome due to nondisjunction.

Monosomy

One copy of a chromosome due to nondisjunction.

Barr Bodies

Inactivated X chromosomes in female mammals.

Recombination Frequency (RF)

The percentage of recombinant offspring in a genetic cross.

Map Units (Centimorgan)

A unit measuring genetic linkage, equivalent to a 1% recombination frequency.

Mitochondrial Myopathy

A disorder stemming from mutations in mitochondrial DNA.