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segment of DNA that transmits information from parent to offspring


a rod-shaped structure that forms when a single DNA molecule and its associated proteins coil tightly before cell division


the two copies of each chromosome, formed prior to cell division


the protein disk in the center of a chromosome where the two chromatids are attached

Homologous Chromosomes

the two copies of each chromosome, which are similar in size and shape and have similar gene information


when a cell contains two homologues of each chromosome


egg cells and sperm cells


when a cell contains only one homologue of each chromosome


a fertilized egg cell; first cell of a new individual


a condition where a diploid cell has an extra chromosome


the collection of chromosomes found in an individual's cells

Down Syndrome

the traits produced by having an extra copy of chromosome 21


when each chromosome and its homologue fail to properly separate; one cell will receive both chromosomes while another cell receives no chromosomes


when a physician uses a needle and syringe to remove a small amount of fluid from the amnion, the sac that surrounds the fetus

Chorionic villi sampling

a physician analyzes a karyotype made using cells grown from a sample of the chorionic villi, fingerlike extensions of placenta that grow into the mother's uterus


changes in an organism's genetic material


when a fragment of a chromosome breaks off, it can be lost when the cell divides


the chromosome fragment attaches to its homologous chromosome, which will carry two copies of a certain set of genes


when a fragment of a chromosome breaks off and reattaches to the original chromosome in reverse orientation


when a fragment of a chromosome breaks off and joins a non-homologous chromosome


the 22 pairs of chromosomes that are the same in both males and females

Sex Chromosomes

the chromosomes that differ between males and females

Binary Fission

a form of asexual reproduction that produces identical offspring

Cell Cycle

a repeating sequence of growth and division that is completed by many eukaryotic cells


when the cytoplasm divides


a period of time where the cell does a great deal of growing while carrying out normal cell processes

Spindle Fiber

made of microtubules (long narrow tubes of protein) that help move the chromosomes apart in cell division


a disk of protein that serves as a platform for assembling the microtubules that extends out from the centromere


the mechanism that halves the number of chromosomes in cells as a form of cell division


haploid cells in plants that later lead to the production of gametes


the process in the beginning of meiosis 1 where homologous chromosomes pair up next to each other

Skipping Replication

there is only one replication of DNA but two divisions, halving the number of chromosomes in each new cell

Reduction Division

when each new cell after meiosis 1 contains half the number of chromosomes of the original cell

Genetic Recombination

the formation of new combinations of genes

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