Chapter 8 Part B; Meiosis, Crossing Over, and Chromosome Alterations

Homologous chromosomes

Chromosomes paired with identical gene loci.

Diploid cells

Cells containing two sets of chromosomes (2n).

Haploid cells

Cells with a single set of chromosomes (n).

Meiosis

Cell division reducing chromosome number to haploid.

Crossing over

Exchange of segments between homologous chromosomes.

Sister chromatids

Identical copies of a chromosome after duplication.

Gametes

Reproductive cells: eggs and sperm.

Zygote

Fertilized egg, diploid (2n = 46).

Interphase

Phase where chromosomes duplicate before meiosis.

Meiosis I

First division separating homologous chromosomes.

Meiosis II

Second division separating sister chromatids.

Tetrad

Structure formed by paired homologous chromosomes.

Centromere

Region where sister chromatids are joined.

Locus

Specific location of a gene on a chromosome.

Spindle microtubules

Structures that separate chromosomes during division.

Metaphase plate

Equatorial plane where chromosomes align during metaphase.

Telophase

Final stage of cell division, nuclear envelope reforms.

Cytokinesis

Division of cytoplasm following mitosis or meiosis.

Somatic cells

Body cells, typically diploid with 46 chromosomes.

Mitosis

Cell division producing two identical diploid cells.

Fertilization

Union of sperm and egg to form zygote.

Chromatin

Uncondensed form of DNA in the nucleus.

Mitosis

Process producing two identical diploid cells.

Meiosis I

First division of meiosis, reduces chromosome number.

Prophase I

Homologous chromosomes pair and crossing over occurs.

Metaphase I

Homologous chromosomes align at the metaphase plate.

Anaphase I

Homologous chromosomes separate, sister chromatids remain attached.

Telophase I

Nuclear membranes form around separated homologous chromosomes.

Meiosis II

Second division of meiosis, separates sister chromatids.

Prophase II

Chromosomes condense, spindle apparatus forms again.

Metaphase II

Sister chromatids align at the metaphase plate.

Anaphase II

Sister chromatids separate and move to opposite poles.

Telophase II

Nuclear membranes form around four haploid cells.

Nondisjunction

Failure of chromosomes to separate during meiosis.

Gametes

Haploid reproductive cells formed by meiosis.

Crossing Over

Exchange of segments between nonsister chromatids.

Chiasma

Point where homologous chromosomes cross over.

Independent Orientation

Random arrangement of chromosomes during metaphase I.

Genetic Recombination

New combinations of genes due to crossing over.

Haploid Cells

Cells with half the number of chromosomes.

Diploid Cells

Cells with two sets of chromosomes.

Sexual Reproduction

Process producing genetically unique offspring.

Asexual Reproduction

Process producing genetically identical offspring.

Nondisjunction

Failure of chromosomes to separate properly during meiosis.

Karyotype

Photographic inventory of an individual's chromosomes.

Trisomy 21

Extra copy of chromosome 21 causes Down syndrome.

Polyploidy

Organisms with extra sets of chromosomes.

Chromosome Breakage

Can lead to deletions, duplications, inversions, translocations.

Philadelphia Chromosome

Abnormal chromosome linked to chronic myelogenous leukemia.

Somatic Cells

Body cells that are not gametes.

Gametes

Reproductive cells, either sperm or eggs.

Diploid Cells

Cells containing two complete sets of chromosomes.

Haploid Cells

Cells containing one complete set of chromosomes.

Meiosis

Cell division producing gametes with half chromosome number.

Mitosis

Cell division resulting in two identical daughter cells.

Cytokinesis

Division of the cytoplasm during cell division.

Sister Chromatids

Identical copies of a chromosome connected at centromere.

Homologous Chromosomes

Chromosome pairs, one from each parent.

Cell Cycle

Series of events leading to cell division.

Chemical Growth Factors

Substances that regulate cell division.

Anchorage Dependence

Requirement for cells to be attached to a substrate.

Cell Density

Influence of cell population on cell division.

Chromosomal Abnormalities

Alterations in chromosome number or structure.

Down Syndrome Symptoms

Physical and cognitive impairments due to trisomy 21.

Evolution of New Species

Can arise from errors in cell division.