Chromosomes -janine.ppt

Heredity: Inheritance and Variation

Why we look somewhat like our parents, but not exactly.

 Chromosomes are very small.  Here is what they look like when you see

them through a microscope.

Chromosome smear

 A karyotype is when chromosomes are

grouped from largest to smallest.

 They are also grouped by the centromere position

and the banding patterns.

Compare the karyotypes for a

male and a female.

A female karyotype

A male karyotype

 Chromosomes are thread-like structures

located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique.

A typical mitotic chromosome at metaphase

Centromere  The

constricted region of linear chromosomes is known as the centromere. Although this constriction is called the centromere, it usually is not located exactly in the center of the chromosome and, in some cases, is located almost at the chromosome's end. The regions on either side of the centromere are referred to as the chromosome's arms.

Centromeres help to keep chromosomes properly aligned during the complex process of cell division. As chromosomes are copied in preparation for production of a new cell, the centromere serves as an attachment site for the two halves of each replicated chromosome, known as sister chromatids

Telomeres Telomeres are repetitive stretches of DNA located at the ends of linear chromosomes. They protect the ends of chromosomes in a manner similar to the way the tips of shoelaces keep them from unravelling. In many types of cells, telomeres lose a bit of their DNA every time a cell divides. Eventually, when all of the telomere DNA is gone, the cell cannot replicate and dies.

Telomeres also play a role in cancer.

The chromosomes of malignant cells usually do not lose their telomeres, helping to fuel the uncontrolled growth that makes cancer so devastating.

White blood cells and other cell types with the capacity to divide very frequently have a special enzyme that prevents their chromosomes from losing their telomeres. Because they retain their telomeres, such cells generally live longer than other cells.

 The code for traits is contained in the nucleus of each cell of our body.  Inside the nucleus are chromosomes which are made of

DNA. This is the code to make you you. Nucleus

Cell

Chromosome

DNA: One section of DNA is a gene

Assessment 1. What contains specific instruction that make each type of living creature unique. A. Chromosome C. Cell B.DNA D. RNA 2. It is the structure which keeps the chromosomes properly aligned during cell division? A. Centromeres C. Spindle Fiber B. Telomeres D. Nucleus

3. DNA is a long molecule made up of units called nucleotides. Which of the following consists a nucleotide? a. a nitrogen base b. a nitrogen base and a sugar c. a nitrogen base, sugar, and phosphate d. two nitrogen bases, a sugar, and a phosphate

4. Which sequence of nucleotides would

bond with the DNA sequence TATGA? a. TATGA b. ATACT c. GCGTC d. CGCAC

5. Which of the following DOES NOT describe the structure of DNA? a. double helix b. nucleotide polymer c. sugar phosphate background d. d. contains adenine – uracil pairs