1. It’s All In Your Genes Introduction to Genetics and Punnett Squares Developed By: Stephanie Shirley Senior Graduate Student MD Anderson Cancer Center Science Park Research Division

2. Background Inherit - to receive from a parent or ancestor by genetic transmission Genetics - the study of inheritance Gregor Mendel –1822-1884 –Pea plants –“Father of Genetics”

3. Mendel’s Laws The Law of Segregation –Alternative versions of genes account for variations in traits –For each trait, two copies of a gene are inherited; one from each parent. –The two copies of a gene segregate during reproduction Eggs have one copy of each gene Sperm have one copy of each gene Offspring have two copies of each gene The Law of Independent Assortment –The inheritance of one trait will not affect the inheritance of another The genes that end up in gametes are randomly sorted from all possible combinations of maternal and paternal genes Because the gametes end up with a random mix of genes, they assort independently (any combination is possible) Mom Dad Children

4. Definitions Genes - sequence of DNA coding for a protein –units of inheritance Allele - different forms of a gene Genotype - the genetic makeup of an individual Phenotype - an observable trait in an organism Homozygous - having two copies of the same allele Heterozygous - having one copy of two different alleles

5. Dominant and Recessive Alleles Remember that Mendel’s Laws state that some traits aren’t seen in the offspring but can still be passed on to the next generation Traits that require two alleles to be seen are called recessive –Phenotype of aa is different from both AA and Aa Traits that require only one copy to be seen are called dominant –Phenotype of Aa is the same as AA Even one copy of a dominant allele will cover up a recessive trait

6. Can genetics be predicted? Probability - chance of something happening Punnett Square - diagram used to predict probability of genotype

7. Gummy Bear Genetics Each bear has 2 genes –one from Mom and one from Dad Possible Combinations: –A and A = Red –A and a = Red –a and a = Yellow Mom Dad A A A a a

8. A a Gummy Bear Genetics Test Crosses What Genotype is Dad? AaAa AA or Aa ?

9. Harry Potter and the Recessive Allele Craig JM, Dow R, Aitken M. Nature. 2005 Aug 11;436(7052):776.

10. How Are Wizards Made ? Wizarding ability and muggleness are observable traits i.e. phenotypes All humans including wizards and muggles receive one allele from each parent So, being a wizard or a muggle is all decided by genetics i.e. a person’s genotype

11. How Are Wizards Born ? The allele for wizarding ability is m Wizards have the genotype mm The allele for muggleness is M Muggles have the genotype MM or Mm

12. Lucius Malfoy ( mm ) Narcissa Malfoy ( mm ) Draco Malfoy ( ) m m The Malfoys All their ancestors are wizards so they must have the alleles mm m m m m m m 4/4 = 100% mm

13. The Potters Both Harry’s parents had magical ability so they must both have been mm Lily Potter ( mm ) James Potter ( mm ) Harry Potter ( ) mm m m m m m m 4/4 = 100% mm

14. Hermione is a witch so she must be mm Both her parents are muggles so they must be Mm so they can give her a m allele each M mM m M mM m mm M m M MM Mm m Mm mm 1/4 MM 1/2 Mm 1/4 mm 3/4 Muggle 1/4 Magic

15. Tom Riddle is a ‘half blood’. His mother was a witch ( mm ) and his father was a muggle His father must have had the alleles Mm so he could give him the other m allele m M mM m mm M m m Mm mm 2/4 Mm - Muggle 2/4 mm - magic

16. What wizarding alleles would Ron and Hermione’s children have ? Ron (mm) Hermione (mm)

17. Hermione X Ron Hermione m m m m m Ron m m m All kids will be mm = wizard/witch 4/4 = 100 % mm homozygous

18. Dominant and Recessive Alleles Which allele is recessive? Which allele is dominant?

19. AA aa Aa Intermediate Concepts Incomplete dominance –The heterozygote (Aa) has a phenotype intermediate to that of the two homozygotes (AA or aa) Orange Gummy Bears Pink snapdragn flowers Codominance –The heterozygote has a phenotype distinguishable from both homozygotes and both alleles are separately manifest in this phenotype. Blood type in humans (proteins A and B are both expressed on surface of blood cells in AB individuals) Multiple alleles –A group of individuals may have more than two different alleles for a given gene (but only two are inherited, one from each parent) ABO blood group system in humans –3 alleles: A, B or O. A and B are codominant and both A and B are dominant to the O allele. So, there are 4 blood group phenotypes: »A: AA and AO »B: BB and BO »AB: AB »O: OO O A B AB

20. Intermediate Concepts (cont) Genetic Variation –Phenotypic polymorphism Qualitative differences in phenotype as a result of genetic variation –Eye color variation in humans - two major eye color genes with multiple minor genes –DNA polymorphisms Minisatellites and microsatellites - variable number of tandem repeats SNP - single nucleotide polymorphisms –Antigenic polymorphism Sequence differences in a molecule due to gene rearrangement –MHC - major histocompatibility complexes

21. Intermediate Concepts (cont) Genetic variation continued: –Mutation Myostatin gene AD genes OB gene Crustacyanin gene Melanin gene Fd gene

22. Summary Genes Genetics Genotype and phenotype Predict Inheritance using Punnett Squares Dominant vs. recessive alleles Example: A or a for bear color Example: M or m for wizard or muggle Mom Dad Children Mom Dad A A A a a

23. Short tail with brown coat SS BB (1) Ss BB (2) SS Bb (2) Ss Bb (4) Short tail with white coat SS bb (1) Ss bb (2) Long tail with brown coat ss BB (1) ss Bb (2) Long tail with white coat ss bb (1) 9 3 3 1 Short tail (S) White coat (b) Long tail (s) Brown coat (B)