1. Introduction to Genetics Chapter 11

2. DNA Basics 1.DNA contains the code for making proteins. 2.Proteins control the chemistry of life. Everything that occurs within a living thing is done through chemistry, thus making DNA/proteins vital. 3.DNA is made of base pairs: A-T C-G C-G 4.The sequence of A, T, C, and G determines the construction of the particular protein. 4. The sequence of A, T, C, and G determines the construction of the particular protein. 5. DNA is inheritable. It is passed on from generation to generation.

3. Genes & Chromosomes What is a gene? A segment of DNA that codes for a particular protein (trait). Where are genes found? On a particular location on a chromosome called a locus.

4. Genes & Chromosomes What does diploid mean? Chromosomes come in pairs. 1. Chromosomes come in pairs. The pairs are called homologous chromosomes. 2. The pairs are called homologous chromosomes. - one chromosome came from the mother (maternal chromosome) - the other chromosome came from the father (paternal chromosome) The symbol for diploid is 2N or 2n. 3. The symbol for diploid is 2N or 2n. Sexual reproduction creates diploidy. 4. Sexual reproduction creates diploidy.

5. Genes & Chromosomes What does haploid mean? 1.The chromosomes do not come in pairs. 2.In humans, only the gametes (ovum & sperm cell) are haploid. 3.Meiosis creates haploid cells in a diploid organism.

6. Meiosis Meiosis is also known as reduction division. 1.The daughter cells will have ½ the number of mother cell chromosomes. 2.How is this done? - Replicate the DNA once - Divide twice 3.The 1 st division is known as Meiosis I - crossing-over occurs here 4.The 2 nd division is known as Meiosis II - this is when the reduction occurs

7. Meiosis I What is the coolest thing that occurs during Meiosis I? 1.Homologous chromosomes pair up in a process called synapsis and form a tetrad. 2.The homologous chromosomes exchange portions of their chromatids in a process called crossing-over. 3.This creates a new combination of genes and greatly increases genetic variety. chiasma

8. Meiosis II What occurs during Meiosis II? 1.No DNA replication occurs during Interphase II! 2.When Meiosis II is complete, 4 haploid (n) daughter cells are produced. Meiosis Animation

9. Meiosis What is gametogenesis? It is meiosis that creates gametes. There are two kinds of gametogenesis: 1.Spermatogenesis - creates 4 viable sperm cells 2.Oogenesis - creates 1 viable ovum and 3 unviable polar bodies - this process conserves cytoplasm because the sperm cell contributes no cytoplasm or organelles to the fertilized eggs.

10. Comparing Mitosis & Meiosis

11. Comparison of Mitosis & Meiosis MitosisMeiosis Purpose Start & End # of chromosomes Cells genetically same/not # Cells produced Produce more body cells Produce sex cells/gametes 2N→2N 2N→N Genetically identical Genetically different; crossing over 1 makes 2 1 makes 4

12. Gregor Mendel Who was Gregor Mendel? 1.He is the father of genetics. 2.He was an Austrian monk who lived during the 1800s. 3.He was trained in math & science. 4.While working in his peas garden, he noticed that the plants displayed different traits.

13. Gregor Mendel What pea traits did Mendel study?

14. Mendelian Vocabulary What is a trait? A characteristic of an organism. What is a gene? The genetic code for the trait. What is an allele? An alternative form of a gene Example: Trait = height; Alleles = tall (T) & short (t) * Alleles come in pairs; one from dad, one from mom

15. Mendelian Vocabulary What does homozygous mean? Both parents contributed the same allele. (TT or tt) What does heterozygous mean? Parents contributed different alleles. (Tt) What does dominant allele mean? This allele will always be expressed if present. (TT & Tt are tall). a.k.a. – principle of dominance What does recessive allele mean? This allele will only be expressed is homozygous. (tt = short)

16. Mendelian Vocabulary What does genotype mean? The alleles an organism has. Expressed in terms of recessive/dominant & homozygous/heterozygous. (TT, Tt, tt) What does phenotype mean? Physical expression of the genotype. What an organism actually looks like.

17. Mendelian Vocabulary What does true-breeding (purebred) mean? The organism’s genotype is homozygous. (TT or tt) All of the organism’s gametes will have the same allele. What does hybrid mean? The organism’s genotype is heterozygous. (Tt) The parents were two different purebreds. The organism’s gametes could get either allele.

18. Mendelian Vocabulary Putting it all together: Trait = heightAlleles = tall (T), short (t) Genotypes:Phenotypes: TT (homozygous dominant)Tall Tt (heterozygous)Tall tt (homozygous recessive)Short TT & tt are true-breeding/purebred; Tt is a hybrid.

19. Mendelian Laws The Law of Segregation: The alleles separate during meiosis.

20. Probability & Punnett Squares Probability Probability - The likelihood that an event will occur: In a coin toss, there is a 1 in 2 chance of getting heads with each toss. Punnett Square - Punnett Square - diagram to show possible gene combinations from a genetic cross.

21. Mendel’s Laws The one-factor (monohybrid) cross: 1.Only one trait is studied 2.1 st parental generation (P 1 ) are different true-breeding/purebred genotypes & phenotypes. 3.The first generation of offspring (F 1 ) are all hybrids expressing the dominant phenotype. F= filial (Latin for “son.”

22. Mendel’s Laws The one-factor (monohybrid) cross: 4.Use the F 1 generation as the second set of parents (P 2 ). 5.This cross will create a phenotype ratio of 3:1 (3 dominant phenotype: 1 recessive phenotype). 6.This cross will create a genotype ratio of 1:2:1 (1 homozygous dominant: 2 heterozygous: 1 homozygous recessive).

23. Mendel’s Monohybrid Crosses P Generation F1 Generation F2 Generation

24. Mendel’s Laws The Law of Independent Assortment: 1.This law applies to two-factor (dihybrid) crosses. 2.Alleles for different traits segregate independently of each other 3.FOIL (First, Outside, Inside, Last) 4.Each gamete gets one allele for each trait.

25. Mendel’s Laws The dihybrid cross: 1.The P 2 are heterozygous for both traits 2.This will create a phenotype ratio of 9:3:3:1 9 dominant phenotype for both traits 3 dom. pheno. for 1 st trait; rec. for 2 nd 3 rec. pheno. for 1 st trait; dom. for 2 nd 1 recessive phenotype for both traits

26. Incomplete Dominance Four O’clock Plants : R = red flower allele W = white flower allele Neither allele is dominant or recessive. Genotypes & Phenotypes: RR = red flowers WW = white flowers RW = pink flowers

27. Codominance: both alleles contribute to the phenotype; 2 phenotypes present at same time Human ABO Blood Types display this: I A = type A codominant I B = type B codominant i = type O recessive Genotypes/Phenotypes: I A I A & I A O = type A I B I B & I B O = type B I A I B = type AB (universal recipient) ii = type O (universal donor)

28. Multiple Alleles More than two alleles exists for the trait. Rabbit fur is a good example:

29. Polygenic Traits These traits require the interaction of several genes. Human skin color is a good example.

30. Genes & the Environment The phenotype of an organism is only partially determined by the genotype, the environment can play a key role. The western white butterfly is an example: 1.Springtime hatchlings are darker (shorter days) 2.Summertime hatchlings are lighter (longer days) Spring Hatchling Summer Hatchling