Chromosomes Chapter 8

DNA Contain Genetic information Long, thin molecule that consists of three billion nucleotides. If stretched out would be 20 miles long How does it fit into a nucleus?

DNA within a Cell Chromosome Chromatin Rod-shaped structures made of DNA and proteins Visible in a cells nucleus only during cell division Chromatin Less tightly coiled DNA-Protein complex Chromatin structure allows long strands of DNA to be condensed into ordered, accessible arrangements Chromatin coils up to form visible chromosomes during cell division

DNA Packing to form Chromosome Chromosomes are coated with histone and non-histone proteins Histone organize and maintain the shape of chromosomes are responsible for packing the DNA into a compact form. Nonhistone control the activity of specific regions of the DNA

Chromosome Structure Each half of a chromosome is called a chromatid Chromatids are held together by a centromere

Chromosome structure Genes include: Exons-coding regions Introns- non-coding regions interspersed between exons In addition to genes, chromosomes have lots of “non-coding” sequence Complete Eukaryote Chromosome Structure PSSA worksheet together.

Chromosome number DNA of a genome is divided into chromosomes (variable size and number) Diploid 2n Two sets or homologous pairs of chromosomes Haploid n One set or half of a homologous pair Gametes (sperm & egg) Complete Act. #1 Graphing activity

Karyotypes & Medical Genetics Use blood or amniotic fluid to obtain cells. Cells are cultured for three days and stopped during metaphase of mitosis with the drug colchicine. Cultured cells are stained and examined under a microscope. A micrograph of the chromosomes, (metaphasic spread) are arranged by: Length Position of centromere Pattern of bands Humans have 22 autosome pairs and 1 sex chromosome pair! Complete Karyotype Demo

Chromosome- rod-like structure composed of DNA and protein that’s visible only during cell division Chromatid- one of the two strands of a chromosome Chromatin- loosely coiled strands of DNA and protein found in the nucleus of the cell Autosome- any chromosome that is not a sex chromosome Sex chromosome- one of a pair of chromosomes that determine the sex or an individual Haploid- describes a cell, nucleus, or organism that has only one set of unpaired chromosomes;n Diploid- a cell that contains two haploid sets of chromosomes;2n Karyotype- a graphical display that shows an individuals chromosomes Centromere- region of the chromosome that holds the two sister chromatids together Homologous chromosome- chromosomes that have the same sequence of genes and structure that pair during meiosis Histone is not on your vocabulary quiz

Review What is the difference between a chromosome, chromatid, and chromatin? How is all the DNA of an organism crammed into the nucleus of a cell? How is chromosome number related to intelligence? What types of chromosomal traits do scientist look at when completing a karyotype? Handout and Complete Karyotype Activity #2 Don’t forget Vocabulary Quiz #1 is tomorrow!