Introduction to Genetics & Gregor Mendel

1. Introduction to Genetics & Gregor Mendel

2. Stuff you may not know… • All living things contain deoxyribonucleic acid (DNA). • DNA, in humans, is located in the nucleus of all of our cells.* • The DNA is arranged in the nucleus as organized packets known as chromosomes.

3. Stuff you may not know… • Humans have 46 chromosomes, 23 chromosomes from each parent. • Cells that have the normal number of chromosomes are said to be diploid (i.e. skin cells). • Cells that have half the number of chromosomes are said to be haploid (i.e. egg and sperm cells).

4. Stuff you may not know… • The chromosomes from the parents are the same type, just different variations, so each child has 23 pairs of similar chromosomes. • 22 pairs are known as autosomes that contain important genes. • The last pair are known as the sex chromosomes (X and Y) and they have fewer genes and more of an influence on gender.

5. Stuff you may not know… • On chromosomes are genes, organized sections of DNA that do one of the following: • Code for protein • Aid in the maintenance of an organism’s cells • Control a particular trait

6. Stuff you may not know… • Genes that control traits have different variations called alleles. • Since everyone has two copies of each chromosome, then each person has two alleles for a trait, one from each parent. • The person responsible for the “discovery” of alleles is Gregor Mendel.

7. Gregor Mendel (1822-1884) • Used pea plants to study genetics, heredity and variation. • Looked at 7 different traits that only had two variations. • From his meticulous work he came up with many “key terms” and, more importantly, two generalizations that later became known as Mendel’s Laws.

8. Mendel’s “Key Terms” • Dominant: the variation of a trait, that if present in an individual, will be displayed. (Capital letters when written) • Recessive: the variation of a trait that will only be displayed in an individual if it is the only one present. (Lowercase letters when written) • Remembering that individuals have two copies of a trait, one from each parent, so the only way a recessive trait is displayed is if both parents give the child this variation of the trait.

9. Mendel’s “Key Terms” • Purebred: Individuals that only contain one variation of a trait and therefore can only pass this one variation on to future generations. We now call these individuals homozygous. • Hybrids: Individuals that contain more than one variation of a trait and therefore can pass on more than one variation to future generations. We now call these individuals heterozygous.

10. Mendel’s “Key Terms” • Phenotype: the appearance of the trait in an individual (i.e. blue eyes, brown hair, freckles…) • Genotype: which alleles a person has for a trait. • Every individual has a phenotype and genotype for every trait. • The phenotype is easy to figure out, but occasionally the genotype is hard to determine, especially for dominant traits.

11. Mendel’s 1st Law: Law of Segregation • States that when sex cells (gametes) are formed, they only receive one of each of the parent’s 23 pairs of chromosomes and therefore only one allele for all possible traits.

12. Mendel’s 2nd Law: Law of Independent Assortment • States that the alleles of the different traits assort independently of one another during gamete formation. • In English, this means that if you are able to be dominant for one trait, it will have no influence on whether you will be dominant for another trait.

13. Importance of Mendel • “Mendelian Genetics” makes up one half of the Modern Synthesis Theory of Evolution. • The other half is “Evolution by Natural Selection” proposed by Charles Darwin which we will study in Unit 2. • Even though his work was underappreciated in his day, Mendel’s work has been a cornerstone for genetic theory and evolutionary biology for the past 100 years!

14. Homework • Read pages 123 to 134 • Answer questions on page 135 #1-3 and 6