ADN


 * Inheritance**
 * Created by Juan Valencia**

__Objective:__


 * Students will be learning about DNA and the importance of it.
 * Students will learn how different characteristics are passed from one organism to another.
 * Students will complete different virtual labs about heredity.
 * Students will complete a virtual lab about Punnet squares.

__Introduction to DNA and heredity__

In order for us to understand what DNA is and how it plays an important role in the inheritance of traits, we ought to review what cells are and what the differences are between them. Go to the following animation and then come back and answer the following questions: What are the main differences between plant and animal cells? and where is the DNA located in eukaryotic and prokaryotic cells? Cells differences


 * Have you ever wondered how traits are passed from one person to another? Well read the following article and find it by yourself.

The genes for certain traits are passed down in families from parents to children. This has been known for thousands of years--even in Biblical times--and has allowed farmers to breed better crops and animals. For example, parents with black hair will likely give birth to children with black hair, just as parents with long noses will have kids with long noses. Once in awhile, though, this doesn’t work and parents with black hair will give birth to a blond. This discrepancy can be explained by the principle of segregation, first noted by Austrian monk Gregor Mendel over 100 years ago. The principle has three parts: **1.** Hereditary traits are determined by specific genes. **2.** Individuals carry two genes for each trait, one from the mother’s egg and one from the father’s sperm. ** 3. ** When an individual reproduces, the two genes split up (segregate) and end up in separate gametes. The principle of segregation applies to all organisms, including humans. **1.** Hereditary traits are determined by specific genes. Within the DNA molecule, genes exist that specify a certain, single characteristic; there is a gene for height, a gene for weight, and a gene for eye color, etc. Variations of the gene relating to the same trait are called alleles. **2.** Individuals carry two genes for each trait, one from the mother’s egg and one from the father’s sperm. One of these two genes is dominant over the other. The dominant allele will mask the other, called the recessive allele. For example, if the father gives a tall allele of the height gene, and the mother gives a short allele, the offspring will be tall. This is because tall is dominant and short is recessive. The British mathematician/biologist R.C. Punnett devised a method of picturing this concept on a graph called a Punnett Square. Punnett Squares graph the father’s genotype (the genetic information concerned with a specific trait: for example, two alleles for tall, or two for short, or one for each) crossed with the mother’s. Punnett Squares show the probability of having children who have a certain trait. · Dominant alleles are shown by a capital letter. · Recessive alleles are shown by the lowercase of the same letter.
 * || [[image:http://library.thinkquest.org/19037/media/basics/punnman.gif width="67" height="67" caption="Dad"]] ||
 * [[image:http://library.thinkquest.org/19037/media/basics/punnwoman.gif width="67" height="67" align="center" caption="Mom"]] ||  ||   || ** t ** || ** t ** ||
 * ** T ** || ** Tt ** || ** Tt ** ||
 * ** t ** || ** tt ** || ** tt ** ||  ||

This graph is a cross between a mother who is a hybrid or heterozygous for tall (meaning she has one allele (T) for tallness and one (t) for shortness). Physically she is tall because T is dominant and masks the shortness genes from the father. Half of their offspring will therefore be short (tt) and half will be tall hybrids (Tt; a pure tall offspring would be TT). This means that the parents have a 2/4 or 50% chance of having tall children and a 2/4 or 50% chance of having short children. This is a 1:1 ratio. //More examples:// **· 50%** will be pure
 * ||  || [[image:http://library.thinkquest.org/19037/media/basics/punnman.gif width="67" height="67" caption="Dad"]] ||
 * [[image:http://library.thinkquest.org/19037/media/basics/punnwoman.gif width="67" height="67" align="center" caption="Mom"]] ||  ||   || ** T ** || ** T ** ||
 * ** T ** || ** TT ** || ** TT ** ||
 * ** t ** || ** Tt ** || ** Tt ** ||  ||   || All kids will be tall: ** 4:0 ratio **

· **50%** will be hybrids ||

**· 75%** chance of being tall
 * ||  || [[image:http://library.thinkquest.org/19037/media/basics/punnman.gif width="67" height="67" caption="Dad"]] ||
 * [[image:http://library.thinkquest.org/19037/media/basics/punnwoman.gif width="67" height="67" align="center" caption="Mom"]] ||  ||   || ** T ** || ** t ** ||
 * ** T ** || ** TT ** || ** Tt ** ||
 * ** t ** || ** Tt ** || ** tt ** ||  ||   || 3 of 4 kids will be tall: ** 3:1 ratio **

· **25%** chance of being pure tall

**· 50%** chance of being hybrid tall

**· 25%** chance of being short ||

Now that you have learn about how traits are passed from one person to another, I want you to go to the following site and complete the virtual lab about inheritance:

virtual lab about inheritance

After completing the virtual lab about inheritance, I want you to create different combinations of alleles in the following link:

Punnet Squares

After completing the previous activities please feel free to visit any of the following sites where you can find a lot of information about heredity. Brainpop movie heredity Heredity and variation Quiz about heredity DNA Replication