Chromosomes What are chromosomes Chromosomes are tiny structures

Chromosomes What are chromosomes? Chromosomes are tiny structures inside cells made from DNA, RNA, and protein. The information inside chromosomes act like a recipe that tells cells how to function and replicate. Every form of life has its own unique set of instructions, including you. Your chromosomes describe what color eyes you have, how tall you are, and whether you're a boy or a girl. Inside the Cell Chromosomes are found in the nucleus of every cell. Different forms of life have a different number of chromosomes in each cell. Humans have 23 pairs of chromosomes for a total of 46 chromosomes in each cell. Can we see them? Normally we can't see chromosomes. They are so small and thin, we can't see them even with a powerful microscope. However, when a cell gets ready to divide, the chromosomes wind themselves up and become tightly packed. With a high powered microscope, scientists can see chromosomes. They are usually in pairs and look like short little worms. Different Chromosomes Different chromosomes carry different types of information. For example, one chromosome may contain information on eye color and height while another chromosome may determine blood type. Genes Within each chromosome are specific sections of DNA called genes. Each gene contains the code or recipe to make a specific protein. These proteins determine how we grow and what traits we inherit from our parents. The gene is sometimes called a unit of heredity. Human Chromosomes As we mentioned above, humans have 23 different pairs of chromosomes for a total of 46 chromosomes. We all get 23 chromosomes from our mother and 23 from our father. Scientists number these pairs from 1 to 22 and then an extra pair called the "X/Y" pair. The X/Y pair determines if you are a boy or a girl. Girls have two X chromosomes called the XX, while boys have an X and a Y chromosome called the XY. Chromosomes in Different Animals Different organisms have different numbers of chromosomes: a horse has 64, a rabbit 44, and a fruit fly has 8.

Heredity Patterns The Basics Gene - Inside the DNA molecule are sections of information called genes. Each gene tells the cell how to make a certain protein which may determine a trait such as the color of the eyes. Allele - While the section of DNA is called a gene, a specific pattern in a gene is called an allele. For example, the gene would determine the hair color. The specific pattern of the hair color gene that causes the hair to be black would be the allele. Dominant and Recessive Genes Each child inherits two genes for each trait from their parents. Some genes are more dominant than others. For example, brown eyes are dominant over blue eyes. If someone has a brown eyed gene and a blue eye gene, they will have brown eyes. They will only have blue eyes if both genes are blue. The brown eyed gene is called the dominant gene and the blue eyed gene is the recessive gene. Writing out the Genes In order to write out the specific allele a person has for a gene, you write a letter representing the gene from the mother and a letter for the gene from the father. Dominant genes are written with capital letters and recessive genes with lower case letters. Here is an example: We use the capital letter "B" to represent the dominant brown-eyed gene and a lower case "b" to represent the recessive blue-eyed gene. Bb - one brown gene, one blue gene (this person will have brown eyes) BB - both brown genes (this person will have brown eyes) bb - both blue genes (this person will have blue eyes) Punnet Square The main way to figure out the pattern of inheritance that could come from two parents is using a Punnet square. A Punnet square shows all the possible combinations of genes from the parents. We will use the example of a plant that could have a purple flower or a white flower. The purple gene is dominant and we write it "P. " The white gene is recessive, so we write it "w. " Here is an example of a Punnet square where one parent has two purple genes "P" and the other parent has two white "w" genes. Each child has the same gene pattern "Pw". They all have the dominant P gene and will all have purple flowers. Here is another example where each parent has a purple gene and a white gene (Pw): P P W Pw Pw