Mike Donvito and Gerri Jesse Biology 113 Chromosomes Provide handouts to class and handout/notes to Professor Skinner. Mike Donvito and Gerri Jesse Biology 113

What and where are chromosomes? Chromosomes are thread-like structures found inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). DNA contains the hereditary information specifying cell structure and function. DNA contains the specific instructions that make each type of living creature unique.

How were chromosomes discovered? In the late 1800s, scientists first observed chromosomes viewed with a microscope. In the early 1900s, Thomas Hunt Morgan gave researchers a much better understanding. Morgan's pioneering studies made the link between chromosomes and inherited traits by relating X chromosomes to gender and eye color. Morgan used fruit flies.

Do all living things have the same types of chromosomes? Chromosomes vary in number and shape. Circular chromosomes can be found in bacteria. Linear chromosomes in humans and other animals and plants have linear arrangement in pairs in the nucleus of the cell. Prokaryotic DNA organization– bacteria for example are single circular. Gametes are the only human cell that do not contain pairs of chromosomes, they only carry just one copy of each chromosome. Eukaryotes’ DNA is divided into multiple linear arrangements.

What and where are centromeres? The constricted region of linear chromosomes is the centromere. It’s usually not located exactly in the center. The regions on either side of the centromere are called arms. The centromeres keep proper alignment of chromosomes during cell division The short arm of the chromosome is labeled the “p arm” and the long arm is labeled the “q arm”. The centromere is where the cell divides the chromosome into two sections or “arms”. The location of the centromere on each chromosome can be used to help describe the location of specific genes.

Shape determines function: A – helix DNA B – sheet RNA Blow by this for time factor.

What are telomeres? Telomeres are repetitive stretches of DNA found at the end of linear chromosomes. They protect the ends of chromosomes to keep them from unraveling. Telomeres lose DNA each time a cell divides. When all of the telomere DNA is gone, the cell cannot replicate and dies. Composed of specific DNA. Not made by the replicated complex.

How many chromosomes? Each species of plants and animals has a set number of chromosomes. Humans have 23 pairs totaling 46 chromosomes. Fruit fly – four pairs. Rice plant – twelve pairs. Dog – 39 pairs.

How are chromosomes inherited? One copy of each chromosome is inherited from the female parent and the other from the male parent. Females have two X chromosomes in their sex cells. Males have one X and one Y chromosome.

What are problems with chromosomal abnormalities? Down’s Syndrome is a good example. The extra copy of chromosome 21 identifies above.

Chromosomes are a key part that ensures DNA is accurately copied and distributed. Mistakes do occur on rare occasions. Changes in number and structure may lead to serious problems. In humans, one type of leukemia and some other cancers are caused by defective chromosomes that are made up of joined pieces of broken chromosomes. If egg and sperm do not have the right structure the offspring may fail to develop properly.

Chromosomes within mitochondria Mitochondria contain their own DNA. This is carried by humans and other complex organisms. The chromosome is circular (similar to bacteria). The mitochondria are found outside the nucleus. Mitochondria can be considered a “cell-within-a-cell.”

Skinner-style question no. 1 The ends of chromosomes (telomeres) resemble what? A. Trees B. Shoelace tips C. Fingerprints D. Steps B. Also known as an aglet.

Skinner-style question no. 2 DNA is tightly wound around histones (spool-like proteins). If all of the DNA molecules in a single human cell were unwound and placed end to end, how long would they stretch? A. 3 yards B. 10 feet C. 6 feet D. 78 inches Answer: c

Presented by Mike Donvito and Gerri Jesse Biology 113 Chromosomes Provide handouts to class and handout/notes to Professor Skinner. Presented by Mike Donvito and Gerri Jesse Biology 113 15