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Today is Monday, December 16 th , 2013

In This Lesson: Codominance , Incomplete Dominance, Blood Type, and Sex-Linked Genes (Lesson 5 of 6). Today is Monday, December 16 th , 2013. Pre-Class: What’s your blood type? Do you know if it’s positive or negative?. Today’s Agenda. Incomplete Dominance Codominance Blood Type

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Today is Monday, December 16 th , 2013

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  1. In This Lesson: Codominance, Incomplete Dominance, Blood Type, and Sex-Linked Genes (Lesson 5 of 6) Today is Monday,December 16th, 2013 Pre-Class: What’s your blood type? Do you know if it’s positive or negative?

  2. Today’s Agenda • Incomplete Dominance • Codominance • Blood Type • Sex-Linked Genes • Where is this in my book? • P. 272 and following…

  3. Tell me honestly… • Did you really think this would be that simple? • Of course not. But we all hoped, right? • What Mendel studied, and what we’ve covered so far, is a system of inheritance called complete dominance. • Complete dominance is when one trait is completely expressed over another. • In other words, with a heterozygous Pp plant, the flowers were just purple. Not light purple or purple with white spots.

  4. Incomplete Dominance • Some flowers don’t end up either purple or white. Sometimes…there’s a… • THIRD PHENOTYPE!!!11 • …that is typically a blend of the other two. • Here’s an example or two…

  5. Incomplete Dominance Example • The Four O’Clock Plant • Flowers can be red or white. • Crossing a red and white flower equals… • …PINK! http://www.britannica.com/EBchecked/topic-art/214994/5550/Four-oclock

  6. Incomplete Dominance Example • Remember hair texture from the Making Babies activity? • Curly is dominant (H) • Straight is recessive (h) • If you inherit one of each allele, you have neither curly nor straight hair. You have wavy hair. • Curly = HH • Straight = hh • Wavy = Hh

  7. Incomplete Dominance • So…what is incomplete dominance? • Incomplete dominance occurs when two parents with different phenotypes reproduce to create offspring with a third phenotype that is a blend of the parents’. • One very important note here… • Incomplete dominance results in a different phenotype from the parents’. • If we were to get a red flower with white spots, that would be something different, which we will learn about in two slides.

  8. Incomplete DominancePunnettSquares • You can still show incomplete dominance with a PunnettSquare (two different ways). • Method 1: (same allele letters, less common) • Method 2 (different allele letters, more common) r W r W Pink Pink Pink Pink R R Pink Pink Pink Pink R R

  9. Incomplete Dominance Practice • Imagine a cross of a pink individual with a white individual. What are the possible offspring? • Imagine a cross of a pink individual with a pink individual. What are the possible offspring? W R W W R R W W

  10. Codominance • Two slides ago I told you we would learn about how you can combine a red flower and a white flower to get a red one with spots. • This is called codominance. • Codominance occurs when two parents with different phenotypes reproduce to create offspring with a third phenotype in which both parents’ phenotypes are visible at the same time.

  11. Codominance Example • Cattle. • Some species of cattle have three phenotypes (really two and a combination). One is white hair. One is red hair. One is…? • Red and white hair (called roan) • We can still use a PunnettSquare, and it works in almost the same way as for Incomplete Dominance.

  12. Gratuitous Photo of Cattle http://www.ck12.org/ck12/images?id=149175

  13. CodominancePunnettSquares • Method 1: (different allele letters) • Method 2 (same allele letters and superscripts) Spots Spots Spots Spots Spots Spots Spots Spots W FW W FW FR R FR R

  14. Codominance Practice • Imagine a cross of a red individual with a roan individual. What are the possible offspring? • Imagine a cross of a roan individual with a roan individual. What are the possible offspring? R R R W R R W W

  15. R = Red Flowers, r = White Flowers

  16. R = Red Flowers, r = White Flowers

  17. Another Example of Codominance • Human blood type is a codominanttrait. • The allele used for blood type is I or i. • I is dominant (in my font). • i is recessive (in my font). • There are four types of human blood but only three alleles each coding for a particular protein on the blood cells: • A (has the IA allele) • B (has the IB allele) • O (has the iallele - no protein)

  18. Blood Type • Each red blood cell (except O) has a specific kind of receptor on it (in this case called an antigen). http://lomalindahealth.org/health-library/graphics/images/en/19450.jpg

  19. How is it inherited? • IA and IB are both dominant. i is recessive. • So, anyone receiving two IA alleles or an IA and i allele will have Type A blood. • The same goes for IB alleles producing Type B blood. • Type O blood is produced by the ii genotype. • The last blood type, AB, is produced by one IA allele and one IB allele, since they’re codominant.

  20. What does it mean? • Since Type O blood has no antigens on it, it can be given to anyone. • We call it the Universal Donor (O-, technically). • Type O blood is also the most common, believe it or not. • Since Type AB blood has both A and B antigens, people with type AB blood can receive any type. • We call it the Universal Acceptor (AB+, technically). • Type AB blood is also the least common.

  21. Blood Compatibility http://upload.wikimedia.org/wikipedia/commons/thumb/5/51/Blood_Compatibility.svg/230px-Blood_Compatibility.svg.png

  22. There’s also this…

  23. Time for a little practice… • Blood Type Worksheet #1

  24. What If We Mix Blood? • Well, a little mixed blood won’t hurt you, but getting a blood transfusion with the wrong type can be a big problem. • Basically what happens is your body sees the wrong antigens on the cell and treats it like an invader, a pathogen. • The body destroys it, but in doing so it gets clumpy, a process called agglutination. • Clumpy blood = ouch/death. • You can test unknown blood easily this way.

  25. A Little More About Blood • We often say blood is “O negative” or “A positive.” • This (positive) means that their blood expresses a particular Rh (Rhesus) antigen called D. • Negative means they don’t express it - about 15% of people. • Here’s why it’s important…

  26. Blood Donation • People that have Rh+ blood produce a substance called D (it’s also an antigen). People that are Rh- don’t produce D. • So, Rh+ blood will prompt an immune response when inside people that have Rh- blood. • Therefore, you can’t give “positive” blood to people that have “negative” blood. • However, “negative” blood can be given to “positive” blood people because the blood is not treated like an invader. http://nobelprize.org/educational_games/medicine/landsteiner/readmore.html

  27. Blood Tests • Imagine a sample of unknown blood. • Now imagine you have known samples of Blood Type A, Blood Type B, and Rh Factor (-). • Take the unknown blood and put it in the known blood. A B Rh ? If the blood clumps in A and B, it’s AB. If the blood clumps in neither, it’s O. If the blood clumps in A, it’s not A. If the blood clumps in B, it’s not B. If it clumps in here, it’s positive.

  28. Blood Type Game • Nobel Prize website for blood typing and transfusions: • http://www.nobelprize.org/educational/medicine/landsteiner/blood.swf Drag the syringe to the patient’s arm to draw blood. Drag above the test tubes to add the drawn blood. Match for A Match for Rh (+) No match for B

  29. Blood Type Game (New Version) • Beware – lots of blood: • http://www.nobelprize.org/educational/medicine/bloodtypinggame/game/blood_loader.swf No match for A No match for Rh (-) Match for B

  30. Wait, what? • You may be wondering why matches seem to clump – shouldn’t it be the other way around? • Well, yes and no. • In actual blood typing kits like what is simulated, they use an antiserum, which is blood designed to react to the blood type for which you’re testing. • For example, you use B antiserum, which is designed to clump in the presence of B antigens. • Put B antigens in there (as in, B blood cells) and you’ll get agglutination, which is a match.

  31. Blood Type Game • Donor Match Game (Are You My Type?) • http://www.redcrossblood.org/donating-blood/donor-zone/games/blood-type • See accompanying worksheet.

  32. A Look at Global Blood Types http://en.wikipedia.org/wiki/Blood_type#ABO_and_Rh_distribution_by_country

  33. A Look at Global Blood Types http://en.wikipedia.org/wiki/Blood_type#ABO_and_Rh_distribution_by_country

  34. Blood Types • The i allele is recessive here, and if it is paired with another i it produces blood type O. • If it is paired with anything other than another i, it is “hidden,” or not expressed. The other allele is expressed. • That person becomes a “carrier”of the recessive (i) allele. • If you get an i allele from your mom and an i allele from your dad, you wind up with the ii genotype, which we call Type O blood. • Any other allele (IA or IB) will override the i allele.

  35. Blood Types • Here’s a table to summarize:

  36. My Blood Type Punnett Square • [Write this down] • Dad has Type A Blood (IAi). • Heterozygous. • Mom has Type O Blood (i i) • Set up the PunnettSquare. • What are the chances of a child: • With Type A blood? • With Type B blood? • With Type AB blood? • With Type O blood? http://www.thetech.org/genetics/ask.php?id=71

  37. IAi x ii [ignore Rh] IA i Chances of A: 50% Chances of B: 0% Chances of AB: 0% Chances of O: 50% i i

  38. Another Blood Type Punnett Square • Dad has Type A Blood (IAi). • Heterozygous. • Mom has Type AB Blood (IA IB) • Set up the PunnettSquare. • What are the chances of a child: • With Type A blood? • With Type B blood? • With Type AB blood? • With Type O blood? http://www.thetech.org/genetics/ask.php?id=71

  39. IAi x IAIB [ignore Rh] IA i Chances of A: 50% Chances of B: 25% Chances of AB: 25% Chances of O: 0% IA IB

  40. Aside: What Makes Red Blood Cells? • Bone marrow! http://www.nlm.nih.gov/medlineplus/magazine/issues/summer11/images/boneAnatomy-lg.png http://sicklecellbodypolitics.files.wordpress.com/2011/04/bonemarrow2.jpg

  41. Sex-Linked Genes • Sex-linked genes are genes found on the sex chromosomes (you know, X and X/Y). • They are not necessarily related to gender. • Most appear only on the X chromosome. • As a result, sometimes these traits/genes are called X-linked. • The X chromosome has about 140 genes, but only a few are related to sex-characteristics. • The Y chromosome has nearly only male sex-related genes (and about 40 genes). • Examples: • Colorblindness • Hemophilia (disorder where blood doesn’t clot easily)

  42. Male Sex-Linked Alleles • X and Y are not equal chromosomes. • Most genes on the X chromosome are not duplicated on the Y chromosome. • Therefore only one allele is present. • Only one allele necessary for a dominant or recessive phenotype. http://www.chessieinfo.net/user/cimage/XY.jpg

  43. Sex-Linked Genes • To put it another way, suppose I had you playing a game. • The goal of the game is to flip a coin and get heads. • Males get to flip once; females twice. • Who’s more likely to lose? • The same goes for sex-linked traits. • Males, with only one X chromosome, get only one shot at dodging sex-linked disorders. Females get two.

  44. Sex-Linked Genes and Punnett Squares • To do a Punnett Square with a sex-linked gene, pick an allele letter just like normal, but put it on the appropriate sex chromosome. • Example next slide…

  45. Sex-Linked Genes and Punnett Squares • Having normal vision (N) is dominant to having colorblind vision (n). • A woman homozygous dominant for normal vision would be XN XN. • A woman heterozygous for normal vision would be XN Xn. • A woman homozygous recessive (colorblind) would be XnXn.

  46. Sex-Linked Genes and Punnett Squares • Having normal vision (N) is dominant to having colorblind vision (n). • A man that is normal would be XNY. • A man that is colorblind would be XnY. • Fun fact: Because men don’t have two alleles, they’re called hemizygous (either affected or not). • Other fun fact: Genes found on the Y chromosome are holandric. • They’re passed from father to son.

  47. Sex-Linked Genes and Punnett Squares

  48. Sex-Linked Genes and Punnett Squares • If this couple had a child, it would have a: • 25% chance (1/4) of being a normal female. • But a carrier of the colorblindness allele. • 25% chance (1/4) of being a colorblind female. • Rare because it takes two recessive alleles as a female. • 25% chance (1/4) of being a normal male. • 25% chance (1/4) of being a colorblind male. • More common than colorblind females because even just one recessive allele leads to colorblindness.

  49. Let’s try another… • Try crossing a normal vision female (heterozygous) with a normal vision male (hemizygous unaffected).

  50. Sex-Linked Genes and Punnett Squares Notice: Neither parent is colorblind, but one in four children (one in two males) from this couple will be colorblind, and it is an allele passed from Mom.

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