1. Mendelian Genetics

2. By the end of this class you should understand: The Mendelian model of genetics and Punnett squares How the structure and function of genes influences phenotypes The different modes of inheritance and expression of genes The concept of a pedigree chart and how to read one

3. Gregor Mendel Austrian Monk (1822- 1884) Discovered the modern principles of genetics working in a pea garden His work was not widely acknowledged until the 20 th century

4. Why Pea Plants? All animals and plants use the same DNA and chromosome structure  Plants complain much less when you force them to mate with particular individuals and take their children away for a breeding program Many traits with different alleles at a given locus

5. Allele An allele is a particular version of a gene –How do different versions come about? There are many alleles for almost all genes –Many of them are functionally identical –Sometimes the function is different for different alleles –Some alleles are defective!

6. Alleles In Mendelian genetics (simplified case) there are only two alleles, one is capitalized and the other is lowercase In reality there are many alleles and any symbol can stand for any of them

7. Terminology The matching genes at the same locus are on homologous chromosomes Having two of the same allele for a gene is called homozygous Having two different alleles for one gene is called heterozygous

8. Mendel's Findings Mendel studied seven traits and started with true-breeding specimens  Are true-breeding individuals homozygous or heterozygous?

9. Mendel's Discoveries Mendel discovered that when he crossed true-breeding peas for opposite traits (P generation), all the offspring had only one of the traits (F1 generation) When these offspring were self- crossed or crossed with other F1 plants, the F2 plants had a 3:1 ratio One trait was dominant over the other

10. Pattern of Inheritance All seven of the listed traits follow the same pattern

11. Dihybrid Crossing What if a true- breeding yellow smooth pea is crossed with a true-breeding green wrinkled pea? According to Mendel's work the traits are not linked but sort randomly

12. Dihybrid Cross Analysis

13. Chromosomal Inheritance Half your chromosomes come from each parent (via meiosis) Each parent randomly passes on 1 of the 2 chromosomes s/he has This means each gene your parent has, you have a 50% chance of having – This fits Mendel's model!

14. Probability Table A table of which genes get passed on is called a Punnett Square Mother's possible genes go on one axis, father's possible genes go on the other

15. Phenotype When an organism has two different alleles, how are they expressed? – The phenotype is what is actually expressed What if two different organisms look the same but have different alleles? – They have different genotypes

16. One of these green peas is not like the other....

17. Dominant/Recessive “Dominant” and “Recessive” are relative terms Much like “taller” and “shorter” One allele may dominate over another Sometimes two alleles do not have a dominant/recessive relationship If both are equally expressed they are called codominant If the phenotype is a blend between the two this is called incomplete dominance

18. Incomplete Dominance The phenotype is a blending of the two This means there are red proteins and white proteins here This is very common in more complex traits Height, etc

19. “Blending theory” Mendel's work disproved earlier ideas of “blending theory” Blending theory states you are a literal mix of your parents Blending theory gained support because many of your genes are codominant or incompletely dominant alleles from your parents Developmental genes control your height, body type, facial structure, etc

20. Dominant/Recessive Many genetic disorders and diseases are recessive Only found in people who are homozygous for the allele that causes the disease Albinism, cystic fibrosis, phenylketonuria, Tay- sachs disease, etc These disease come from a lack of a specific enzyme or other protein

21. “Recessive” Typically a “recessive” gene is a defective gene Blue eyes are a defect in an allele for coloring the eye This means blue eyes are recessive and parents with brown eyes can be carriers for blue eyes

22. Example: Cystic Fibrosis A gene called CFTR produces a protein channel that pumps chloride ions onto the surface of mucus membranes Through osmosis, water follows the chloride ions out Failure to produce this protein or have it be expressed means mucus builds up in the respiratory tract and can become fatal Cystic Fibrosis

23. Example: Albinism The protein melanin is the pigment for our skin and is present in our hair and eyes as well If one allele is defective and one is normal, what is the genotype? What is the phenotype? If both alleles are defective, what is the genotype? What is the phenotype?

24. Carriers How many copies of a working blueprint do you need to make the enzyme? Just 1! Having 1 working and 1 defective allele means you are healthy

25. Pedigree Chart A pedigree chart, or just pedigree, shows family history for a particular condition Can be for hair color, eye color, etc Most commonly for a genetic disorder Can be used to determine the nature of the inheritance

26. Example: Recessive Disorder Often “skips” generations When both parents are carriers, about 1 in 4 offspring are affected When one parent has the condition: 1 in 2 offspring are affected and other half are carriers OR all are carriers

27. Multi-Allele Genes There are three alleles for a marker on our red blood cells: A, B, and O A and B markers are large and can be detected by the immune system O marker is small and cannot be detected As though it weren't there What allele is recessive?

28. ABO blood type Six possibilities for genotype: AA AO BB BO AB OO

29. Codominance Since A and B are both fully expressed, they are codominant O is recessive because it is only expressed when there are no other alleles present

30. Why does this matter? We have an immune system! Your immune system will attack any markers that were not in your body when you were a fetus This includes A and B markers O type blood is the universal donor!

31. See you in lab! Coming soon to a lab near you: more genetics!