Mitosis, Meiosis, and Sexual Selection – Exam Prep Notes bsci 160 9/17/25

Vocabulary flashcards covering key terms from the lecture on mitosis, meiosis, genetic diversity, and sexual selection.

Mitosis

A cell division process that copies DNA and divides the cell into two genetically identical diploid daughter cells; chromosome number remains the same.

Prophase

First stage of mitosis where chromosomes condense, the nuclear envelope breaks down, and the spindle apparatus begins to form.

Metaphase

Stage in mitosis where chromosomes align along the center of the cell (metaphase plate) and attach to spindle fibers at kinetochores.

Anaphase

Stage in mitosis when sister chromatids are pulled apart to opposite poles, becoming separate chromosomes.

Telophase

Stage in mitosis where chromosomes arrive at poles, de-condense, and the nucleus begins to reform.

Cytokinesis

Division of the cytoplasm, resulting in two separate daughter cells; in plants a cell plate forms, in animals the cell pinches apart.

Chromosome

Package of DNA wrapped around histones; duplicated chromosomes consist of two sister chromatids held at the centromere.

Sister chromatids

Two identical copies of a chromosome connected at the centromere, formed after DNA replication.

Centromere

Region of a chromosome where sister chromatids are held together and where spindle fibers attach during division.

Diploid (2n)

An organism or cell containing two sets of chromosomes, two of each type.

Haploid (n)

A cell containing a single set of chromosomes; gametes are haploid.

Homologous chromosomes

Pairs of chromosomes that contain the same genes (one from each parent) and may carry different alleles.

Meiosis

Cell division that produces haploid gametes through two rounds of division, reducing chromosome number and increasing genetic diversity.

Meiosis I

First division that separates homologous chromosomes, reducing from diploid to haploid; produces two haploid cells that are still duplicated.

Meiosis II

Second division that separates sister chromatids, yielding four haploid, unduplicated gametes.

Prophase I

Meiosis I stage where homologous chromosomes pair (synapsis) and crossing over occurs, forming tetrads; synaptonemal complex forms.

Metaphase I

Meiosis I stage where homologous chromosome pairs align at the center; orientation is random (independent assortment).

Anaphase I

Meiosis I stage where homologous chromosomes are pulled to opposite poles; sister chromatids remain attached.

Telophase I

Meiosis I stage where nuclei may reform; cytokinesis produces two haploid cells with duplicated chromosomes.

Prophase II

Meiosis II stage where a new spindle forms in each haploid cell and chromosomes condense again.

Metaphase II

Meiosis II stage where sister chromatids align at the center and attach to the spindle.

Anaphase II

Meiosis II stage where sister chromatids separate to opposite poles, becoming individual chromosomes.

Telophase II

Meiosis II stage where nuclei reform and cytokinesis yields four haploid, unduplicated gametes.

Recombinant chromosome

A chromosome that contains DNA from both parents due to crossing over between non-sister chromatids.

Crossing over

Exchange of genetic material between non-sister chromatids during prophase I, creating new allele combinations.

Synaptonemal complex

Protein structure that forms between homologous chromosomes during prophase I to facilitate pairing and crossing over.

Chiasmata

Points where crossing over occurs between homologous chromatids during prophase I.

Law of Segregation

Mendelian principle that offspring inherit one allele from each parent for each gene, randomly.

Law of Independent Assortment

Mendelian principle that the orientation of homologous chromosome pairs during metaphase I is random, increasing variety.

Random fertilization

The concept that any sperm can fertilize any egg, contributing to genetic diversity.

Genetic diversity

Variation in a population resulting from crossing over, independent assortment, and random fertilization.

Gamete

A haploid sex cell (sperm or egg) produced by meiosis.

Zygote

Diploid cell formed when a sperm fertilizes an egg; contains a complete set of chromosomes.

Allele

Variant form of a gene.

Karyotype

A display or arrangement of an organism's chromosomes, typically showing homologous pairs.