CHAPTER 10 MENDEL AND MEIOSIS WHAT YOU’LL LEARN: **THE BASIC CONCEPT OF GENETICS **THE PROCESS OF MEIOSIS WHY IT’S IMPORTANT: **YOU INHERITED TRAITS FROM YOUR PARENTS. **IF YOU KNOW MEIOSIS YOU WILL SEE HOW TRAITS ARE PASSED TO OFFSPRING.

10.1 MENDEL’S LAWS OF HEREDITY ▸ I. Why Mendel Succeeded –**Mendel lived in a monastery in the mid 1800's –**Heredity - the passing of characteristics from parents to offspring –**Genetics - the study of heredity. –**Traits - the inherited characteristics.

A. Mendel chose his subject carefully ▪1. Mendel chose garden peas. ▪2. Gametes - distinct male and female sex cells ▪3. Pollination - transfer of pollen to pistil ▪4. Fertilization - uniting of male and female ▪ gametes ▪B. Mendel was a careful researcher ▪ He studied one trait at a time to control ▪ variables

II. Mendel’s Monohybrid Crosses ** Hybrid - the offspring of parents that have different forms of a trait **Monohybrid - One trait ▪A. The first generation ▪P + = >

▪B. The second generation ▪F 1

The Rule of United Factors ▸ 1. Each organism has two factors to control each trait. ▸ 2. These factors we call genes they are located on the chromosomes. ▸ 3. Alleles - different forms of the same gene.

The Rules of Dominance ▸ 1. Dominant - Trait expressed without exception ▸ 2. Recessive - Trait that may be hidden by the dominant trait. ▸ 3. Symbols: Capital for Dominant Lower case for recessive. ☺

▪E. The law of Segregation ☺

▪III. Phenotypes and Genotypes ▸ 1. Phenotype - The way an organism looks and behaves. ▸ 2. Genotype - The gene combination an organism contains. ▸ 3. Homozygous - The two alleles for the trait are the same. ( TT or tt ) ▸ 4. Heterozygous - The two alleles for the trait are different. ( Tt )

▪IV. Mendel’s Dihybrid Crosses ▸ Organisms that differ from each other by two traits ▪V. Punnett Squares ▸ A shorthand way of finding the expected proportions of a cross. ▪VI. Probability ▸ The likelihood that a trait will be shown

▪10.2 Meiosis ▸ A. Diploid and haploid cells. –1. Chromosomes are in pairs - one from the mom and one from the dad. –2. Diploid - A cell with two of each kind of chromosome ( 2N ) –3. Haploid - one of each kind of chromosome, these are gametes (N)

▪B. Homologous Chromosomes ▸ Pair of chromosomes that have genes for the same traits. May not be identical alleles.

▪C. Why Meiosis ▸ 1. Produces gametes containing half the number of chromosomes as a parent body cell has. ▸ 2. Male gametes are called sperm. ▸ 3. Female gametes are called eggs. ▸ 4. A zygote results when an Egg and a Sperm unite. This is sexual Reproduction

▪III The phases of Meiosis ▸ A. Interphase –1. Cell replicates its chromosomes => –2. Has two identical sister chromatids

▪B. Prophase I ▸ 1. Each pair of homologous chromosomes comes together ▸ 2. Crossing over - chromosomes can exchange genetic material ▸ 3. In humans the average is two to three crossovers per pair.

▪C. Metaphase I ▸ The Homologous pairs of chromosomes line up along the equator

▪D. Anaphase I ▸ The homologous pairs of chromosomes separate. ☺

▪E. Telophase I ▸ Cytoplasm divides to yield two new cells with half the number of chromosomes

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Meiosis Provides for Genetic Variations ▸ A. genetic recombination - The reassortment of genetic information resulting from crossing over and independent segregation. ▸ B. Meiosis Explains Mendel’s results

▪IV. Mistakes in Meiosis ▸ Nondisjunction - failure of homologous chromosomes to separate properly. ▸ A. Trisomy - one extra chromosome (Downs Syndrome) XXX ▸ B. Monosomy - one less chromosome. In humans most zygotes with Monosomy do not survive. (Turners Syndrome) XO ▸ C. Triploidy - Inherits an additional whole set of chromosomes. ▸ D. Polyploidy - more than the usual sets of chromosomes – rare in animals, many in plants