How Does DNA Control Traits? Lesson 3 pg. A52 Ms. Lourdes Martinez 6th Grade

Unique DNA A giraffe belongs to a species that is different from the species that the zebras belong to. Each animal has all the physical characteristics, or traits, of the species to which it belongs. How do the traits of these giraffes and zebras differ?

Inside the nucleus of each giraffe cell is a set of instructions for building the giraffe’s body. You’ve already learned that chromosomes are the parts of a cell’s nucleus that carry information that controls all the cell’s activities. Chromosomes contain a substance called DNA (deoxyribonucleic acid). The DNA determines the kind of organism that the cell belongs to, in this case a giraffe.

Down Syndrome Most people have 23 pairs of chromosomes, for a total of 46. But a baby with Down syndrome has an extra chromosome (47 instead of 46) or one chromosome has an extra part. This extra genetic material causes problems with the way their bodies develop.

The DNA of a chromosome is divided into sections called genes. Each gene controls how a certain trait will develop. For example – a gene might control the color of a giraffe’s hair. The body of the giraffe will look a certain way because of a particular gene. No two living things that are produced by sexual reproduction (except identical twins) have exactly the same genes.

Structure of DNA The shape of the DNA molecule lookslike a long twisted ladder. The ladder has millions of rungs made of four kinds of smaller molecules called bases. The four bases are represented by the letters A,T,G, and C. Bases have shapes that allow them to fit together only in certain combinations.

Using DNA Information Humans contains at least 100,000 genes organized into 46 chromosomes.

Lesson 3 Review pg.A Why is every organism unique? 2.-What are chromosomes? 3.- What does DNA stand for? 4.- Where can we find DNA? 5.- People who are born with Down Syndrome have how many chromosomes? In what pair of chromosomes does this problem occur? 6.- The DNA of a chromosome is divided into sections. What are these sections called?

How Do Organisms Inherit Traits? Lesson 4 pg.A62

Variation Family Picture

The process by which traits are passed from parent to offspring- from generation to generation- is called heredity. Remember that DNA in the egg cell combines with DNA in the sperm cell during fertilization. Then a single cell – the zygote – forms.

Organisms that are produced as a result of sexual reproduction receive, or inherit, at least two genes for every trait. One gene is inherited from the mother. The other gene is inherited from the father. Not every child in a family receives the same set of genes from the mother and father. Each egg cell of the mother contains a different combination of genes. Each sperm cell of the father also contains a different combination of genes. *The appearance of each child in the family results from the particular combinations he or she received during fertilization.

Dominant and Recessive Genes