Meiosis, DNA Replication, and Genetic Variability Key Concepts

Crossing over

Process that occurs during Prophase I in which pieces of nonsister chromatids of homologous chromosomes are exchanged resulting in new genetic combo of chromosomes.

Synapsis

Pairing of homologous chromosomes in prophase 1 of meiosis.

Chiasmata

The site of crossing over of nonsister chromatids of homologous chromosomes.

Homologous chromosomes

Chromosomes of the same shape/ size that contain genes for the same traits.

Spermatogenesis

Process of sperm production in males.

Oogenesis

Process of egg production in females.

Sexual reproduction variability

Introduces variability through crossing over, independent alignment of paired chromosomes, and random fertilization.

Meiotic errors

Occur because of nondisjunction, the failure of homologous chromosomes to separate in meiosis I or sister chromatids in meiosis II.

Aneuploidy

Condition in which 1 or more chromosomes or pieces of chromosomes are lacking or in excess.

Down syndrome

Genetic abnormality caused by Trisomy 21, which is an extra chromosome.

Prophase I

Duplicated chromosomes condense, homologous chromosomes pair up, and crossing over occurs.

Metaphase I

Paired homologous chromosomes line up along the equator of the cell.

Anaphase I

Homologues separate, one member of each pair goes to each pole of the cell.

Telophase I

Spindle microtubules disappear, nuclear envelope reforms, resulting in two haploid daughter nuclei.

Prophase II

Chromosomes recondense and spindle microtubules re-form.

Metaphase II

Chromosomes line up along the equator with sister chromatids attached to spindle microtubules.

Anaphase II

Chromatids separate into independent daughter chromosomes.

Telophase II

Nuclear envelopes reform and chromosomes become extended again.

Four haploid cells

Cytokinesis results in four haploid cells, each containing one member of each pair of homologous chromosomes.

DNA's antiparallel

Refers to 3'/5' ends of DNA, where the 3' end is the end that grows.

Histone proteins

Proteins DNA wraps around to make chromatin.

DNA Replication

Process in which an identical copy of DNA is produced in a cell.

Semiconservative process

At the end of DNA replication, the new DNA molecule will contain 1 original parent strand and 1 new daughter strand.

Primer

Starter strand of DNA or RNA needed for replication.

DNA helicase

Enzyme responsible for unwinding/unzipping DNA during replication.

DNA polymerase

Enzyme responsible for formation of DNA strand from a template.

DNA ligase

Enzyme that unites Okazaki strand fragments of lagging strand during DNA replication.

Leading strand

The daughter strand in DNA replication that is synthesized continuously.

Lagging strand

The daughter strand in DNA replication that is synthesized discontinuously.

Replication bubble

Opens in DNA to replicate, and two replication forks form.

Erwin Chargaff's rule

The number of purines is equal to the number of pyrimidines in DNA.

Hershey-Chase experiment

Used viruses to determine DNA, not protein, was genetic material.

Watson and Crick

Used Rosalind Franklin's x-ray diffraction photograph of DNA to build a model of DNA.