Biology Chapter 8

Homologous chromosomes

2 chromosomes in a cell that have the same genes (diploid organisms)

Haploid

Cells that contain only 1 type of each chromosome with specific genes (gametes) (the types of chromosomes)

Sister Chromatids

One of the two identical parts of a duplicated chromosome. While joined, two sister chromatids make up one chromosome; chromatids are eventually separated during mitosis or meiosis II.

What process of cell division do prokaryotes use?

Prokaryotes divide using a process called binary fission. "splitting in two"

Diploid

cells with pairs of homologous chromosomes with the same genes (most cells in our body)

What is meiosis? Where does it happen? What is the end product?

• A type of cell division responsible for sexual reproduction, and requires fertilization of an egg and sperm. • 2 cell divisions result in the daughter cells having 1/2 (haploid) number of chromosomes • Where: gonads

What are the 2 types of cell division?

• Asexual reproduction- simple cell division. ‣results in 2 identical daughter cells (with identical genes) ‣no fertilization of an egg by a sperm • Sexual reproduction- requires fertilization of an egg by asperm

What is the function of cell division?

• Function: reproduction of a cell ‣repairs lost or damages cells ‣permits growth ‣allows for reproduction ‣End product: 2 'daughter' cells that are genetically identical to each other and the parent

What are the 2 things that happen during meiosis responsible for genetic variation?

• Offspring from sexual reproduction are genetically different from their parents and each other • Due to independent assortment at metaphase I of meiosis, humans have 8,388,608 different possible chromosome combinations per gamete

What happens in each stage of mitosis?

• Prophase ‣duplicated chromosomes condense ‣spindle fibers form and centrioles move to poles ‣chromosomes caught by spindles ‣nuclear envelope breaks • Metaphase-Duplicated chromosomes line up at the equator of the cell • Anaphase ‣sister chromatids separate ‣unattached spindle fibers lengthen to push poles of cell apart • Telophase ‣when chromosomes reach the poles, the spindle fibers disintegrate ‣nuclear envelope begins to reform ‣the chromosomes unwind • Cytokinesis (in animals) ‣microfilaments form a ring around the equator of the cell and begin to contract ‣cytoplasm divides into 2 cells

Meiosis 1 (separation of homologous chromosomes)

• Prophase 1 ‣Nuclear membrane begins disintegrating ‣Chromosomes condense ‣Centrioles and spindle fibers form ‣Homologous chromosomes pair up ‣Crossing over occurs • Metaphase 1 ‣Homologous pairs line up at the equator ‣Independent assortment homologous- pairs arrange themselves along the equator randomly and independent of other pairs- a type of recombination • Anaphase 1 ‣The spindle fibers shorten and pull apart the chromosomes of the homologous pairs • Telophase 1 and cytokinesis ‣Chromosomes reach the poles ‣Nuclear envelope reappears ‣spindle fibers disappear ‣ Cytoplasm content divides

Meiosis 2 (separation of sister chromatids)

• Prophase 2 ‣Chromosomes condense ‣Centrioles and spindle fibers form and move to poles ‣Nuclear envelope disappears • Metaphase 2 ‣Chromosomes line up at the equator • Anaphase 2 ‣Spindle fibers pull sister chromatids toward poles • Telophase 2 and cytokinesis ‣Chromosomes reach poles ‣Spindle fibers disappear ‣Nuclear envelope reappears ‣Division of the cytoplasm ‣RESULT: 4 haploid cells (1/2 the number of chromosomes as the original cell)

What is mitosis? Where does it happen? what is the end product?

• The type of cell division responsible for asexual reproduction, growth, and maintenance of cells. • Happens in body cells • End products: two daughter cells that are chromosomally identical to the parent.

What happens during interphase?

• cell performs normal functions • cell grows • doubles everything in the cytoplasm • duplicates DNA

What helps DNA coil?

• histones are proteins used to package DNA • nucleosomes consist of DNA wound around histone molecules

Nondisjunction

• when chromosome pairs fail to separate at anaphase • this produces gametes with an incorrect number of chromosomes and disorders due to abnormal amount of genes • can occur during meiosis I or II

What is the difference between DNA, a chromosome, and a chromatin?

•DNA is the main component of chromosomes. •A chromosome is a singular piece of DNA. •Chromosomes consist of chromatin. •Chromatin makes up chromosomes. •Chromatin is the complex of DNA.