Mendelian Genetics

1. Mendelian Genetics Chapter 11

2. What is the definition of genetics? How do we acquire our genes or traits?

3. Inheritance • You get your genes from your parents • In meiosis, half of the chromosomes in a pair come from the Dad, half come from the Mom • What we know about genetics today is based on the work of Gregor Mendel – Austrian monk

4. 1856-1865 Gregor Mendel – studied pea plants in monastery garden – COUNTED the plants and compiled data (QUANTITATIVE approach to science) Paper was published in 1866, but not enough was understood to truly value this work.

5. Key terms to know when talking about Mendel • Allele – each form of a gene for a certain trait (R or r) • Dominant- Allele that is expressed, represented by a capital letter (R) • Recessive- Allele that is masked or hidden, represented by a lower case letter (r) • Gene – sequence of DNA that codes for a protein a thus determines a trait • Genotype – combination of alleles for a given trait (letters) (RR or Rr or rr) • Phenotype – Appearance of trait (physical characteristic) Having Blue Eyes • Homozygous - when you have 2 or the same alleles for a given trait (RR or rr) • Heterozygous – when you have 2 different alleles for a trait (Rr)

6. Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Section 11-1 Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall *Flower color – purple (P) vs. white (p) Seed coat color and flower color are often put in for one another – thus, the EIGHT traits!!! Go to Section:

7. Figure 14.1 A genetic cross

8. Figure 14.5 Genotype versus phenotype

9. Mendel chose to use plants that were true-breeding… • P generation – parentals; true-breeding (On their own create identical offsprings) parents that were cross-pollinated • F1 generation – hybrid offspring of parentals that were allowed to self-pollinate • F2 generation – offspring of F1’s

10. Figure 14.2 Mendel tracked heritable characters for three generations

11. Example…… • Character – flower color • Alleles – Purple (P) and white (p) Note: Purple is dominant with a capital letter and white is recessive shown with a lowercase letter Genotypic combos possible – two dominants: PP (homozygous dominant) two recessives: pp (homozygous recessive) One of each: Pp (heterozygous)

12. Figure 14.4 Mendel’s law of segregation (Layer 2)

13. Punnett Square • Device for predicting the results of a genetic cross between individuals of a known phenotype. • Developed by R.C. Punnett • Rules: 1. must predict possible gametes first 2. male gametes are written across top, female gametes on left side 3. when read Punnett, start in upper left corner and read as if a book 4. WRITE OUT GENOTYPES IN ORDER

14. Phenotypic possibilities – physical appearance • PP – purple • pp – white • Pp – purple (white is masked, but still part of genotype)

15. Monohybrid crosses – only one character considered Steps to do: • Write out genotypes of parents • Write out possible gametes produced • Draw 4 box Punnett square • Put male gametes on top, female on left side • Fill in boxes • Determine genotypes by reading Punnett starting from top left • Determine phenotypes by reading from genotype list Ex. • White flowered plant X Purple flowered plant • Yellow peas X Green peas • Tall plant X short plant Homework: Monohybrid Crosses WS #1

16. From the law of segregation…… • Came the Law of Independent Assortment Genes for different traits can segregate independently during the formation of gametes. In other words….. Just because a seed is round does not mean that it has to be green.

17. Mendel’s 4 ideas… • Alternative versions (alleles) of genes account for variations in inherited characters. • For each character, an organism inherits two alleles, one from each parent. • If the two alleles differ, the dominant allele is expressed in the appearance, and the other, a recessive allele is masked. • The two alleles for each character segregate during gamete production. (Law of Segregation)

18. Dihybrid (Two-Factor)Cross • Because genes separate independently we can determine the possible outcomes of a two-factor cross. • Example: Mendel’s Peas F1 Hybrids for Shape and Color: RrYy Foil – First, Last, Inner, Outer Possible gametes passed on to offspring: RY, ry, rY, and Ry – Place in order (dominant to recessive) RY, Ry, rY, ry then place on cross

19. Beyond Dominant and Recessive • Incomplete Dominance One allele is not completely dominant over the other – something in the middle is expressed Ex. Red and White Snapdragons – Make Pink (Like mixing paints) p. 272 in your book Red – RR White – WW Pink – RW Only one phenotype for each one genotype

22. Beyond Dominant and Recessive • Codominance Both alleles are expressed in the phenotype Ex. Cow Hair Color RR – Red WW – White RW – Roan (Red & White) Homework – Codominance/Incomplete Dominance WS

23. Beyond Dominant and Recessive • Multiple Alleles Genes have more then two alleles Ex. Blood Type Color Coats in Rabbits A and B alleles for blood type are co-dominant

24. More on blood types….. • The blood type determines what antibodies are located within the blood. Type A blood has type B antibodies. If type B blood is put into their bodies, their immune system reacts as if it were a foreign invader, the antibodies clump the blood - can cause death. • Type AB blood has no antibodies, any blood can be donated to them - they are called the "universal acceptors" • Type O blood has no surface markers on it, antibodies in the blood do not react to type O blood, they are called the "universal donors"

27. Chromosomes • How many pairs of chromosomes do humans have? 23 • What is the difference between male and female chromosomes? Pair #23 Male – XY and Females – XX Look at the following karyotype…can you tell the difference?

28. Karyotype – Picture of Chromosomes 1-22 Autosomal 23 Sex Chromosomes

29. What about genes located on the sex chromosomes? • Very few genes are located on the Y chromosome……Most are located on the X • So females carry two genes and males only one. • Doing a punnett square with the sex chromosomes……XX x XY Link the gene to the X only.

30. Sex-Linked Genes • Ex. Colorblindness is carried on the sex-chromosomes • It is a recessive trait – How many genes do females need to express the trait (colorblindness)? 2 How many genes do males need to express the trait (colorblindness)? 1

31. Fig. 8.33

32. Sex-Linked Punnett Square C • C – Normal Vision and c - Colorblind • XY x X X - Normal Male x Carrier Female XY X X C C c C Offsprings: 1 Normal Female 1 Normal (Carrier) Female 1 Normal Male 1 Colorblind Female X X X Y X X X Y C C C C C c c c HW – Sex-Linked Genetics Problems WS

33. Figure 14.3 Alleles, alternative versions of a gene