Chapter 4 Genetics from genes to genomes Questions with Verified Answers

2n - ANSWERSnumber of chromosomes in a normal diploid cell acrocentric - ANSWERSa chromosome in which the centromere is close to one end amniocentesis - ANSWERSmedical procedure in which a sample of amniotic fluid is taken from a pregnant woman to determine the condition of an unborn baby. A hollow needle is inserted through the woman's abdomen and uterine wall, and the fluid, which contains cells shed by the embryo is drawn off. anaphase 1 - ANSWERSphase of meiosis 1 during which the chiasmata joining homologous chromosomes dissolve, allowing maternal and paternal homologs to move toward opposite spindle poles; the centromeres do not divide so that the chromosome moving toward the poles each consist of two chromatids. anaphase 2 - ANSWERSphase of meiosis 2 when the dismantling of cohesin complexes allows sister chromatids to move to opposite spindle poles. astral microtubules - ANSWERSshort, unstable microtubules that extend out form a centrosome toward the cell's periphery to stabilize the mitotic spindle. autosomes - ANSWERSa chromosome not involved in sex determination. The diploid human genome consists of 46 chromosomes , 22 pairs of autosomes and 1 pair of sex chromosomes. (x & y) bivalent - ANSWERSa pair of synapsed homologous chromosomes during prophase of meiosis 1. cell cycle - ANSWERSrepeating pattern of cell growth, replication of genetic material and mitosis. cell plate - ANSWERSmembrane-enclosed disk that forms inside a plant cell near the equator of the mitotic spindle and grows rapidly outward to divide the cell in two during cytokinesis. centrioles - ANSWERSshort cylindrical structures that help organize microtubules. Two centrioles at right angles to each other form the core of a centrosome. Each centrosome serves as a pole of the miotic spindle. centromere - ANSWERSa specialized chromosome region at which sister chromatids are connected and to which spindle fibers attach during cell division centrosome - ANSWERSmicrotubule organizing centers at the poles of the spindle apparatus. checkpoints - ANSWERSmechanisms that prevent cells from continuing to the next phase of the cell cycle until a previous stop has been successfully complete, thus safeguarding genomic integrity chiasmata - ANSWERSobservable regions in which nonsister chromatids of homologous chromosomes cross over. chromatid - ANSWERSone of two copies of a chromosome that exist immediately after DNA replication. chromatin - ANSWERSthe generic term for any complex of DNA and protein found in a cell's nucleus. chromosome theory of inheritance - ANSWERSthe idea that chromosomes are the carriers of genes. chromosomes - ANSWERSthe self-replicating genetic structures of cells containing the DNA that carries in its nucleotide sequence the linear array of genes. coenocyte - ANSWERSa plant cell containing multiple nuclei condensation - ANSWERScellular process of chromatin compaction that results in the visible emergence of individual chromosomes. contractile ring - ANSWERStransitory organelle composed of actin microfilaments aligned around the circumference of a dividing animal cell's equator; contraction of the filaments pinches the cell in two. crisscross inheritance - ANSWERSinheritance pattern in which males inherit a trait from their mothers, while daughters inherit the trait from their fathers. crossing-over - ANSWERSduring meiosis, the breaking of one maternal and one paternal chromosome, resulting in the exchange of corresponding sections of DNA and the rejoining of the chromosome. This process can result in the exchange of alleles between chromosomes. cytokinesis - ANSWERSthe final stage of cell division, which beins during anaphase but is not completed until after telophase. In this stage, the daughter nuclei emerging at the end of telophase are packaged into two separate daughter cells. diakinesis - ANSWERSsubstage of prophase 1 during which chromosomes condense to the point where each tetrad consists of four separate chromatids; at the end of this substage, the nuclear envelope breaks down and the microtubles of the spindle apparatus begin to form. diploid - ANSWERSzygotes and other cells carrying two matching sets of chromosomes are described as diploid (compare haploid). diplotene - ANSWERSsubstage of prophase 1 during which there is a slight separation of regions of homologous chromosomes but the aligned homologous chromosomes of each bivalent remain tightly merged at chiasmata. division 1 of meiosis/meiosis 1 - ANSWERSthe parent nucleus divides to form two daughter nuclei; during meiosis1, the perviously replicated homologous chromosomes segregate to different daughter cells. divison 2 of meiosis/meiosis 2 - ANSWERSeach of the two daughter nuclei resulting from meiosis 1 divide to produce four nuclei; because the chromosomes do not duplicate at the start of meiosis 2, these four daughter nuclei are haploid. equational dividion - ANSWERScell division that does not reduce the number of chromosomes but instead distributes sister chromatids to the two daughter cells. Mitosis and meiosis 2 are both equational divisions. G0 Phase - ANSWERSin the cell cycle; a resting form of G1. Cells in G0 normally do not divide. G1 Phase - ANSWERSstage of the cell cycle from the birth of a new cell until the onset of chromosome replication at S phase.