Activity 63: Show Me the Genes! Essential Question: What role do chromosomes play in the inheritance of genes?

Review… In order to produce new cells, humans go through what processes? Asexual reproduction Sexual reproduction Both Explain your selection

Review… Cell Division- Mitosis How is the function of cell division in a single celled organism different from cell division in a multicellular organism? Mitosis

Chromosomes Chromosomes are long, fine strands, like very thin spaghetti in the nucleus of the cell (They contain the organism’s genetic information.) Before the cell divides, it makes copies of its chromosomes so each new cell has a complete set. Chromosomes appear when the nucleus is no longer visible and the cell Each cell in the body contains 46 chromosomes, so during cell division each cell will have 46 pairs of chromosomes

Stopping to Think… What would happen to the number of chromosomes in each cell if copies of them were not make before cell division?

Sexual Reproduction The 46 chromosomes in our human cells are sorted into 23 pairs. Each chromosome looks identical to its partner except pair number 23 (The sex chromosome.) Females have two X chromosomes and Males have an X and a Y chromosome

Cell Division of Sex Cells… Meiosis Sex cells are formed by a type of cell division in which each cell receives copies of half of the chromosomes. Egg and sperm only contain 23 chromosomes When the sperm fertilizes the egg and the new organism is formed it will have 46 chromosomes (Half from mom and half from dad)

Meiosis

Stopping to Think… Why must the number of chromosomes in the sperm and egg be half the number of chromosomes then the other cells of an organism?

Putting it all together Think of 23 pairs of chromosomes as 23 pairs of socks (Egg has 23 and Sperm has its 23 matching socks) The chromosome of each pair carry genes for the same characteristics but the two alleles of any one gene can be different

Stopping to Think Consider two children with the same two parents. Would you expect them to have the same sets of chromosomes? Explain why or why not.

So Many Genes Human cells contain about 30,000 pairs of different genes. Each gene is a small portion of a chromosome. The more complex the trait being studies, the greater the number of different genes which contribute to it. (Ex- Cancer) Genes are part of long molecules called DNA (deoxyribonucleic acid) Each chromosome contains long DNA molecule A mutation is a mistake made in a gene when DNA is copied Some mutations are small and some more significant (Ex- I heer that noise, I fear that noise)

Conclusion Draw a flow diagram (a series of pictures) that shows the locations and relative sizes of DNA, genes, chromosomes, and cells in a human body. Write a paragraph to explain your diagram.