Nt1310 Unit 1 Writing Assignment

Joyce Balingit

BIOL 196 - 1006

Instructor: Austin McKenna

30 October 2015

Writing Assignment #3

Part A

In meiosis, the cell goes through the same stages as mitosis twice. The stages of Meiosis I are: prophase I, metaphase I, anaphase I, and telophase I. The stages of Meiosis II are: prophase II, metaphase II, anaphase II, and telophase II. Meiosis generates four haploid cells, which begins with the division of one diploid cell. Diploid means having two sets of chromosomes, and haploid means having half the number of genetic information as diploid (or one set). To begin, late interphase is the phase when the DNA in the diploid parent cell is replicated. Then, in prophase I, the chromatin condenses and the chromosomes become visible. The homologous

In which case, the nuclear envelope is visible again and the DNA uncoil into chromatin. No DNA replication occurs during interphase II. In prophase II, the nuclear envelope disintegrates again, and the chromosomes stay in sister chromatid form (if they unraveled into chromatin during interphase II they condense again). In metaphase II, spindle fibers from opposing poles of the cell attach to the centromeres of each sister chromatid. Sister chromatids are two identical copies/strands connected by one centromere that results from the replication of a chromosome during the S phase. The sister chromatids line up alone the equatorial line. During anaphase II, each sister chromatid begins to move to its respective pole thus the pairs begin to separate. In telophase II, the sister chromatids reach their respective poles. Cytokinesis takes place, and the nuclear envelope becomes visible, resulting in four haploid

Sadava, Richard W. Hill, and Mary V. Price. Principles of Life. 2nd ed. Sunderland: Sinauer Associates, 2014. Print.

• Andres, Andrew. Biology 196: Principles of Modern Biology I Laboratory Manual. Minneapolis: Bluedoor, LLC, 2015. Print.

Part B – Down’s Syndrome

In 1866, John Langdon Down, a British physician, identified a group of people whose symptoms were very similar. These were: eyes that were upwardly slanting, a flattened back of the head, and fissured and poorly controlled tongues. The term “mongolism” was coined to describe these people with Down’s Syndrome. In 1959, Jerome Lejeune identified the disorder as a chromosomal condition. He saw that those with the condition had 47 chromosomes in their cells instead of the normal 46. Later it was discovered that it was the result of an extra copy of chromosome 21. The nondisjunction that results in an extra copy of chromosome 21 occurs during anaphase I in meiosis I. The genetic mutation is trisomy 21 (3 copies of chromosome 21). The characteristic phenotypic occurrences that are distinct to the disorder: poor muscle tone, stout neck, flat face, small head, mouth, and ears, eyes slanting upwardly, Brushfield spots, and stout fingers and