1. Warm Up Answer the following questions: 1. Chromosomes contain DNA. What is DNA? 2. What do you think is an important function of DNA?

2. Warm Up Answer the following questions: 1. _____________________________ _____________________________ _____________________________ 2. _____________________________ _____________________________

3. Chapter 6 What You Will Learn In sexual reproduction, offspring receive half of their genetic material from each parent. Homologous chromosomes contain the same genes but may have different alleles for each gene. Meiosis results in the production of haploid cells that have half the number of chromosomes that diploid cells do. Section 3 Meiosis

4. Chapter 6 Chromosome Numbers Meiosis and sexual reproduction increase the number of possible genetic combinations in a population. There is a carefully controlled process that ensures sexual reproduction leads to the proper number of chromosomes in the offspring. Section 3 Meiosis

5. Chapter 6 Each species has a normal number of chromosomes in their body cells. Human body cells have 46 chromosomes, corn cells have 20, and dogs cells have 78. Each chromosome in a body cell has a matching pair with the same genes but different alleles. Chromosomes that carry the same sets of genes are called homologous chromosomes. Section 3 Meiosis

6. Chapter 6

7. Cells that have homologous pairs of chromosomes are called diploid. Body cells are diploid. Before sexual reproduction can occur, an organism must make sex cells. The male sex cells are sperm, and the female sex cells are eggs. Section 3 Meiosis Chromosomes in Reproduction

8. Chapter 6 Sex cells do not have homologous pairs and are called haploid. Human sex cells have 23 chromosomes. Sex cells are haploid so that when they combine during fertilization, they produce an individual with the normal number of chromosomes. Human body cells have 46 chromosomes. Section 3 Meiosis

9. Chapter 6 Meiosis Sex cells are made during a process called meiosis. Meiosis is a copying process that produces cells that have half the usual number of chromosomes. When a cell undergoes meiosis, it divides twice. This produces four cells, each with half the number of chromosomes as the parent cell. Section 3 Meiosis

10. Down’s Syndrome

11. Section 3 Meiosis Chapter 6

12. Section 3 Meiosis Chapter 6

13. Meiosis and Mendel Meiosis can help explain the results first observed by Mendel. If the true breeding plant for wrinkled seeds provided the sperm, all of the sperm cells would have the same recessive allele, r. If the true breeding plant for smooth seeds provided the eggs, all of the eggs would have the dominant allele R. Section 3 Meiosis

14. Chapter 6 The only genotype possible in the offspring in this cross is Rr. The only phenotype possible is smooth seeds, since all of the offspring would have the dominant allele. Section 3 Meiosis Meiosis and Mendel, continued

15. Section 3 Meiosis Chapter 6

16. So in sexual reproduction, half of the offspring’s genetic material comes from the mother’s egg, and half comes from the father’s sperm. Mitochondria, which have their own DNA, come from the mother’s egg. So all of the mitochondria in your body can be traced back to your mother. Section 3 Meiosis