1. Mendel’s Peas were ideal for learning about inheritance, but they do not represent the norm… Traits in pea plants are determined by just two alleles In peas, one allele is clearly dominant & the other is clearly recessive However, things aren’t always this clear- cut and simple in the world of genetics.

2. What if Mendel looked at mice?  If a female black mouse and a male white mouse were crossed, what will the offspring look like? GREY - 100% are GREY  If the F1 offspring were crossed, what will there offspring look like? - 25% black - 50% grey - 25% white

3. Incomplete Dominance A cross between two organisms with different traits results in an offspring with a third phenotype that is a blending of the parental traits. It’s like mixing paints: –Red + White = Pink –Red does not totally block (dominate) white, we end up with something in-between.

4. Inheritance in Snapdragons

5. Let’s look at cattle…. This cow resulted from a cross between a cow with red fur and a cow with white fur. This is called ‘roan’ fur; red & white fur together.

6. Codominance Similar to incomplete dominance in that there is a 3 rd phenotype In COdominance, the “recessive” and “dominant” alleles appear together in the phenotype of hybrid organisms. Red x White = red & white

7. Polygenic (Multifactorial) Traits Phenotype is determine by more than one gene Often results in gradations, where each gene has an additive effect Ex) If 10 gene loci are turned on plant will be 20cm tall, if only 5 loci are turned on plant will be 10cm tall Results in a bell-shaped curve –Skin color & Height are examples in humans

8. Phenotype Distribution:Polygenic Traits

9. Full color: CC, Cc ch, Cc h, or Cc Chinchilla: c ch c h, c ch c ch, or c ch cHimalayan: c h c, or c h c h AIbino: cc KEY C = full color; dominant to all other alleles c ch = chinchilla; partial defect in pigmentation; dominant to c h and c alleles c h = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles Multiple Alleles More than 2 alleles for a particular trait

10. ABO Blood Types In addition to having multiple alleles, ABO blood type also exhibits codominance ‘I A’ & ‘I B’ are codominant ‘i’ is recessive

11. ABO Blood Typing GenotypeBlood Type I A I A or I A i I B I B or I B i IAIBIAIB ii

12. What does your ABO blood type mean?  Remember the ‘flags’ on our cell membranes? They help cells to recognize each other.  Some of those flags ‘announce’ your blood type. We call these flags antigens Blood Type Antigen A B AB O

13. ABO Blood Transfusions Blood Type Can receive: A B AB* O*

14. Summary of ABO Blood Types

15. Rh Factor Blood can also be categorized as + or – This refers to the presence (dominant) or absence (recessive) of the Rh antigen PhenotypeGenotype(s)Antigen Rh + Rh -

16. Chromosomal Theory of Inheritance This theory states that genes occupy specific loci on chromosomes and it is the chromosomes that undergo segregation and independent assortment during meiosis.

17. Gene Linkage & Mapping Chromosomes According to the chromosomal theory of inheritance, genes on the same chromosome are more likely to be inherited together Crossing over helps to increased variation, but the closer two genes are on a chromosome the more likely they are to be “linked” The frequency of crossing over between two genes can be used to estimate the relative positions of genes on chromosomes

18. Sex Chromosomes & Autosomes Recall that two of the 46 human chromosomes are known as sex chromosomes, because they determine the individual’s sex. –Females have two copies of an X chromosome. –Males have one X chromosome and one Y chromosome. The remaining 44 chromosomes are known as autosomal chromosomes or autosomes.

19. Sex-Linked Genes Located on one of the sex chromosomes (X or Y) Since the X chromosome is longer, it has many genes not found on the Y chromosome. Most sex-linked genes are X-linked genes.

20. Sex-Linked Genes

21. X-Linked Inheritance Examples: –Hemophilia The protein necessary for normal blood clotting is missing –Colorblindness Defective version of one or all of the 3 genes responsible for color vision –Male Pattern Baldness Hair loss –Duchenne Muscular Dystrophy Weakening and loss of skeletal muscle These traits are recessive & more common in males. Why?

22. Possible Inheritance of Colorblindness Allele

23. Complete the following sex-linked crosses: Eva and Paul just had a son, Michael. Paul is has normal color vision, but Eva’s father was colorblind. What is the likelihood that Michael is colorblind? Laura and Steve are expecting their first child. They are concerned about the chances their child might be hemophiliac because both Steve and Laura’s father are hemophiliac. What is the probability of Laura and Steve having a hemophiliac child?

24. Complete the following pedigrees. Which is for a sex-linked trait? How do you know?