1. Chapter 8 Section 2: Mendel’s Theory Grade 10 Biology Spring 2011

2. Bell Ringer Does a tall plant plus a short plant equal a medium plant? ◦ Blending

3. Objectives Describe the four major hypotheses Mendel developed Define the terms homozygous, heterozygous, genotype, and phenotype Compare Mendel’s two laws of heredity

4. A Theory of Heredity Mendel’s results did not support blending hypothesis Mendel concluded each pea plant has two separate “heritable factors” for each character- one from each parent Fig. 4 page 166

5. Mendel’s Hypotheses Mendelian theory of heredity: 1. For each inherited character, an individual has 2 copies of the gene- one from each parent 2. There are alternative versions of genes (alleles)

7. Mendel’s Hypotheses 3. When two different alleles occur together, one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance 4. When gametes are formed, the alleles for each gene in an individual separate independently for one another. Thus, gametes carry only one allele for each inherited character. When gametes unite during fertilization, each gamete contributes one allele.

8. Mendel’s Hypotheses Alleles: different versions of a gene ◦ Purple or white flower

9. Mendel’s Hypotheses Dominant: expressed form of the character ◦ Purple flower Recessive: trait that was not expressed when the dominant form of the character was present ◦ White flower

10. Mendel’s Findings in Modern Terms Dominant = AA Recessive = aa Homozygous: if 2 alleles of a particular gene present in an individual are the same ◦ Ex. AA or aa Heterozygous: if the alleles of a particular gene present are different ◦ Ex. Aa

11. Mendel’s Findings in Modern Terms Genotype: set of alleles that an individual has for a character ◦ Ex. Aa, aa, AA Phenotype: physical appearance of a character ◦ Ex. Brown hair, purple flowers Are phenotype and genotype related?

12. The Laws of Heredity Law of Segregation: the two alleles for a character segregate (separate) when gametes are formed

13. The Laws of Heredity Dihybrid Cross: cross that considers two pairs of contrasting characters ◦ Flower colour and plant height

14. The Laws of Heredity Law of Independent Assortment: the alleles of different genes separate independently of one another during gamete formation ◦ Only applies to genes that are located on different chromosomes or far apart on the same chromosome

16. The Laws of Heredity Units of heredity are portions of DNA called genes, which are found on the chromosomes that an individual inherits from its parents