1. LET’S TAKE SOME NOTES! Mendelian Genetics

2. Mendel’s Law of Segregation Definition: The idea that, of the two copies of each gene everyone carries, only one of the two alleles (letters) gets put into each gamete  Each parent puts a single set of instructions for building a particular trait into every sperm or egg it makes  You may get a “A” allele or “a” allele from each parent, for example  The trait observed in an individual depends on the two copies (alleles) it inherits from both its parents

3. Punnett Square Practice Mom is heterozygous for pigmented skin, whereas dad displays albinism. What are the genotypic ratios and phenotypic ratios of the offspring?  Draw a punnett square in your notes Use the example above to explain Mendel’s law of segregation.

4. Mendel’s Law of Independent Assortment Mendel got lucky. Each of the 7 traits he studied in pea plants were located on their own chromosomes. Thus, they did not get inherited together!  In other words, pea flower color was not influenced by plant height or pea color and vice versa. Definition: Neither trait influences the inheritance pattern for the other trait; all traits are inherited independently of each other

5. Law of Independent Assortment (continued) Is Mendel’s law of independent assortment always true?  Example: Most redheads have pale skin and freckles. Mendel’s 2 nd law is not true for every pair of traits. Sometimes the alleles for two genes are inherited together and expressed as a package.  Linked Genes = when genes of different traits are close or right next to each other on a chromosome and are often inherited together  Example: Skin pigmentation and hair color

6. Dihybrid Cross Definition = a cross between individuals that involves two pairs of contrasting traits  More complicated than “monohybrid crosses” because there are more possible combinations of alleles to work out  Dihybrid Cross Example: A homozygous dominant purple flowered, wrinkly seeded pea plant is crossed with a heterozygous purple flowered pea plant that is also heterozygous for smooth round seeds. Complete the cross.  What are the genotypic and phenotypic ratios?

7. It isn’t as simple as we thought… Unfortunately, the world in which each trait is coded for by a single gene with two alleles- one completely dominant and one recessive- and no environmental effects at all doesn’t quite capture the complexity of the world beyond Mendel’s pea plants.

8. Incomplete Dominance Definition = The phenotype of a heterozygote is intermediate between the phenotypes of the two homozygotes Flower color in four o’clocks shows incomplete dominance, where both the allele for red flowers (R) and the allele for white flowers (r) influence the phenotype  What would a heterozygote four o’clock flower look like?

9. Codominance Definition = occurs when both alleles for a gene are expressed in a heterozygous offspring  Neither allele masks the effect of the other  A mom blue fish (BB) is crossed with a dad red fish (RR). Fish color displays codominance.  What color would the offspring be?  What would their genotype be?

10. Codominance

11. Which flowers exhibit codominance and which exhibit incomplete dominance? What would complete dominance look like for homozygous dominant, heterozygous, and homozygous recessive flowers?

12. http://www.ansci.cornell.edu/usdagen/codominance.html

13. Transfusion Reaction Clumped blood cells clog arteries Hemolysis Lack of oxygen Organ damage or failure Death

14. Red Blood Cells

15. Blood Types Multiple allelism- when a single gene has more than two alleles (letters)  An example of this is blood type in which there are 3 alleles  Each individual still carries only two alleles- one from mom and one from dad

16. Blood Types Three alleles:  A  B  O The A and B alleles are completely dominant to O, but are codominant to each other.  Thus A and B are equally strong but overpower O, which is recessive.

17. Blood Types An individual’s blood type alleles carry instructions that direct construction of antigens that protrude from every red blood cell. Antigens are proteins that stick out of a cell surface and play a role in defense. Phenotypes:  Type A instructs for A antigens to be made  Type B instructs for B antigens to be made  Type O does not instruct for any type of antigen  If a person has blood type AB, they make both A and B antigens on their red blood cells

18. Blood Types

19. If a red blood cell with the wrong antigens enter your bloodstream, your immune system will attack it. This can cause destruction of red blood cells, low blood pressure, and even death. Under normal conditions your immune system will not encounter a red blood cell with foreign antigens.  When may this occur?

20. Blood Types This is why matching blood types is very important! Type A individuals would attack Type B blood cells and vice versa. What about Type AB individuals? What about Type O individuals?

21. Blood Types

22. Polygenic Traits Definition = traits that are influenced by many different genes Polygenic traits may have additive effects when the effects of alleles from multiple genes all contribute to the ultimate phenotype

24. Are there traits that are influenced by both our genetics and our environment? Complex traits are influenced by both genetics and the environment. Nature versus Nurture Give a few examples! Wow, this is getting complex !

25. Sex-Linked Genes Sex-linked traits- traits caused by genes located on the sex chromosomes (x or y) There are more X-linked than Y-linked traits.  What do you notice about the size of the X and Y chromosomes? X and Y chromosomes do not have all of the same genes. Since a male has an XY chromosome combination, if the X chromosome carries a recessive allele for a trait, then the male will show the recessive phenotype.  What??? Explain why!

26. Sex-Linked Genes www.ksu.edu/biology/pob/genetics/xlinked.htm Red-green colorblindness is a recessive X lined disorder Brain Games on National Geographic