Unit 4: Gene Expression and Inheritance Study Guide 2025 Part B - Meiosis & Genetics

Somatic Cell

A typical human cell containing 46 chromosomes (23 pairs).

Autosomes

Chromosomes other than sex chromosomes, totaling 44 in humans, which resemble each other in length and centromere position.

Sex Chromosomes

Chromosomes that determine an individual's sex; human females have two X chromosomes (XX) while males have one X and one Y chromosome (XY).

Diploid Cells

Cells that contain pairs of homologous chromosomes; in humans, this number is 46 (2n=46).

Haploid Cells

Cells that contain a single set of chromosomes; in humans, this number is 23 (n=23).

Meiosis

A process required for sexual reproduction that reduces the chromosome number by half, producing gametes.

Prophase I

The first stage of meiosis I where homologous chromosomes form tetrads and crossing over occurs.

Metaphase I

The stage of meiosis where homologous pairs line up at the metaphase plate.

Anaphase I

The stage of meiosis where homologous chromosomes are pulled apart to opposite poles of the cell.

Telophase I

The stage where the nuclear membrane reforms and the cytoplasm divides, resulting in two haploid cells.

Nondisjunction

The failure of homologous chromosomes or sister chromatids to separate properly during cell division.

Karyotyping

A laboratory procedure that analyzes the number and structure of chromosomes in a cell.

Deletion

A type of chromosomal alteration where a segment of a chromosome is removed.

Duplication

A chromosomal alteration where a segment of a chromosome is copied and inserted into the homologous chromosome.

Inversion

A chromosomal alteration where a segment of a chromosome is removed and reinserted in the opposite orientation.

Reciprocal Translocation

A chromosomal alteration where segments of two nonhomologous chromosomes swap places.

Homozygous

Having two identical alleles for a given gene.

Heterozygous

Having two different alleles for a given gene.

Dominant Allele

The allele that determines the phenotype when an individual is heterozygous for that gene.

Recessive Allele

The allele that has no noticeable effect on the phenotype when an individual is heterozygous.

Genotype

The genetic makeup of an organism.

Phenotype

The expressed traits of an organism.

Monohybrid Cross

A genetic cross between individuals focusing on a single trait.

Punnett Square

A diagram used to predict the possible genotypes of offspring from a particular cross.

Law of Segregation

Mendel's law stating that allele pairs separate during gamete formation.

Law of Independent Assortment

Mendel's law stating that alleles for separate traits are passed independently of one another.

Incomplete Dominance

A form of inheritance in which the heterozygote expresses an intermediate phenotype.

Codominance

A form of inheritance where both alleles in a heterozygote are fully expressed.

Polygenic Inheritance

A pattern of inheritance where multiple genes influence a trait.

Sex-Linked Genes

Genes located on the sex chromosomes, most often inherited in an X-linked manner.

Pedigree

A diagram that shows the genetic relationships among family members.

Recessive Disorder

A genetic disorder that occurs when an individual inherits two recessive alleles.

Dominant Disorder

A genetic disorder that occurs when an individual has at least one dominant allele.