Mike Donvito and Gerri Jesse

Biology 113

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.

What and where are chromosomes?

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.

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.

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

A – helix DNAB – sheet RNA

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.

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?

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.

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. TreesB. Shoelace tipsC. Fingerprints D. Steps

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 yardsB. 10 feetC. 6 feetD. 78 inches

Presented by Mike Donvito and Gerri Jesse

Biology 113