Today is Tuesday, December 15th, 2015

Today is Tuesday, December 15th, 2015
In This Lesson: Codominance, Incomplete Dominance, Blood Type, and Sex-Linked Genes (Lesson 5 of 6) Today is Tuesday, December 15th, 2015 Pre-Class: What’s your blood type? Do you know if it’s positive or negative?

Today’s Agenda Incomplete Dominance Codominance Blood Type
Sex-Linked Genes Where is this in my book? P. 166 and following…

By the end of this lesson…
You should be able to differentiate between codominant and incompetely dominant inheritance patterns. You should be able to analyze sex-linked traits and blood type inheritance using Punnett Squares.

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.

Incomplete Dominance THIRD PHENOTYPE!!!11
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…

Incomplete Dominance Example
The Four O’Clock Plant Flowers can be red or white. Crossing a red and white flower equals… …PINK!

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

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.

Incomplete Dominance Punnett Squares
You can still show incomplete dominance with a Punnett Square (two different ways). Method 1: (same allele letters, less common) Method 2 (different allele letters, more common) R r Rr Pink R W RW Pink

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? R W RW WW R W RR RW WW

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.

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 Punnett Square, and it works in almost the same way as for Incomplete Dominance.

Gratuitous Photo of Cattle

Codominance Punnett Squares
Method 1: (different allele letters) Method 2 (same allele letters and superscripts) R W RW Spots FR FW FRFW Spots

Codominance Practice R W RR RW R W RR RW WW
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 W RR RW R W RR RW WW

R = Red Flowers, r = White Flowers
Table of Phenotypes Complete Dominance Incomplete Dominance Codominance RR Rr rr

R = Red Flowers, r = White Flowers
Table of Phenotypes Complete Dominance Incomplete Dominance Codominance RR Red Rr Pink Red/White Spots rr White

Another Example of Codominance
Human blood type is a codominant trait. 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 i allele)

Blood Type Each red blood cell has two receptors on it called antigens. One is called H (the first floor), and the second one is either A or B. O doesn’t have a second antigen.

Aside: Bombay Type, et cetera
Turns out there’s still another blood type. “Bombay” type individuals have absolutely no antigens. Not even the base level “H.” Also, apes mostly have our blood type: Chimpanzees only have Type A and Type O. Gorillas only have Type B. Other animals don’t have similar blood types. Cats have 3 different blood types, dogs have 12, cattle have 11, pigs have 16, and horses have 34.

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.

What does it mean? Since Type O blood has only H 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.

Blood Compatibility

There’s also this…

Time for a little practice…
Blood Type Worksheet

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. Your immune system’s antibodies bind to it, and in doing so it gets clumpy, a process called agglutination. This helps white blood cells destroy the “invader.” Clumpy blood = ouch/death. You can test unknown blood easily this way. How?

Antibodies and Antigens
To fully understand blood typing, you need to understand antigens and antibodies. Antigens are protein identifiers on the outside of cells. Antibodies (immunoglobulins) are part of the immune system and neutralize pathogens by binding to specific antigens. They’re also proteins. So antigens are antibody generators.

Antibodies and Antigens
Blood Type A These people have A antigens on their blood cells and will generate B antibodies to defend against B invaders. Blood Type B These people have B antigens on their blood cells and will generate A antibodies to defend against A invaders. Blood Type AB These people have A and B antigens on their blood cells and will not generate antibodies. Blood Type O These people have type no antigens on their blood cells and will generate A and B antibodies to defend against A/B invaders.

A Little More About Blood
We often say blood is “O negative” or “A positive.” This (positive) means that their blood also 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…

Rh Factor Rh+ Blood These people have Rh antigens (D) on their blood cells and will not not generate Rh antibodies. Rh- Blood These people have no antigens on their blood cells and will generate Rh antibodies to defend against invaders.

Blood Donation So, Rh+ blood will prompt an immune response when inside people that have Rh- blood. Therefore, you can’t give + to -. However, - can be given to +.

Rh Factor In pregnancy, blood sometimes “leaks” between the fetus’s circulatory system and the mother’s. The baby may have a different blood type from the mother. If the baby is Rh+ (means it makes this D antigen) and the mother is Rh- (means she doesn’t), the leakage of blood may cause the mother to make antibodies. Her body sees this D antigen and treats it like an invader (pathogen).

Rh Factor Normally, this wouldn’t matter; the fetus and mother should have separate blood vessels. Sometimes, however, mom’s blood “leaks” back across the placenta into the baby. Mom’s D antibodies (the “police” of her blood) attack the baby’s blood. This is called erythroblastosis fetalis or hemolytic disease in the newborn. RhoGAM® is a drug available to treat Rh incompatibility.

? Back to Blood Tests A B Rh Imagine a sample of unknown blood.
You also have known samples of antibodies for Blood Type A, Blood Type B, and Rh Factor. Take the unknown blood and mix it with the antibodies. A B Rh ? If the blood clumps in A, it’s A. 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 B, it’s B. If it clumps in here, it’s positive.

Antiserum Actual blood typing kits, like in the game we’re about to play, use an antiserum (not actual blood). An antiserum is the stuff that contains antibodies for different blood types. For example, B antiserum contains B antibodies and 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. Confused? Just remember this: With actual blood, clumping occurs with incompatibility. With antiserum, clumping occurs when there is a match.

Blood Type Game Nobel Prize website for blood typing and transfusions:
Drag above the test tubes to add the drawn blood. Drag the syringe to the patient’s arm to draw blood. No match for B Match for A Match for Rh (+)

Blood Type Game (New Version)
Beware – lots of blood: Match for B No match for A No match for Rh

Blood Type Game Donor Match Game (Are You My Type?)
See accompanying worksheet.

A Look at Global Blood Types

Back to Blood Type Genetics
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 i i genotype, which we call Type O blood. Any other allele (IA or IB) will override the i allele.

Blood Types Here’s a table to summarize: Parent 1 Parent 2 Offspring
Type O (i) Type O (i i) Type A (IA) Type A (IA IA) Type B (IB) Type B (IB IB) Type A (IA i) Type B (IB i) Type AB (IA IB)

My Blood Type Punnett Square
[Write this down] Dad has Type A Blood (IA i). Heterozygous. Mom has Type O Blood (i i) Set up the Punnett Square. What are the chances of a child: With Type A blood? With Type B blood? With Type AB blood? With Type O blood? (that’s me!)

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

Another Blood Type Punnett Square
Dad has Type A- Blood (IA i). Heterozygous. Mom has Type AB+ Blood (IA IB) Set up the Punnett Square. What are the chances of a child: With Type A blood? With Type B blood? With Type AB blood? With Type O blood?

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

Rh Factor in Punnett Squares
For Rh Factor, positive (+) is dominant, negative (-) is recessive. Someone with Rh+ blood could be ++ or +-. If you don’t know what they are, you have to assume they’re +- (heterozygous): - + +- --

Putting It Together Cross AB+ and A-
IA- i- IA+ IAIA+ IAi+ IAIA- IAi- IB+ IAIB+ IBi+ IB- IAIB- IBi-

Aside: What Makes Red Blood Cells?
Bone marrow!

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)

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.

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.

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…

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 (carrier for colorblindness) for normal vision would be XN Xn. A woman homozygous recessive (colorblind) would be Xn Xn.

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 or Y-linked. They’re passed from father to son.

Colorblind Male → Xn Y Normal (Heterozygous) Female ↓ XN XNXn Normal (heterozygous) female XNY Normal male XnXn Colorblind female (RARE!) XnY Colorblind male

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.

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

Normal Male → XN Y Normal (Heterozygous) Female ↓ XNXN Normal (homozygous) female XNY Normal male Xn XNXn Normal female (carrier) XnY Colorblind male 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.

Colorblindness in America
By the way, in this country, estimates show that 7% of males are colorblind in the most common way (red/green colorblind). On the other hand, only 0.4% of females are red/green colorblind. Why? Because it’s a sex-linked (X-linked) gene!

Colorblindness To have a female that is colorblind, her mother must have been at least a carrier, and her father had to have been colorblind too. To have a male that is colorblind, all that’s needed is a mother that’s at least a carrier. Last thing: If you are a colorblind male, it was an allele passed from your Mom. Dad gave you the Y chromosome, remember?

Practice Now let’s put it all together in one of my favorite activities: Who Gets the Money?

“Skipping a Generation”
Some traits appear to “skip a generation.” In other words, they’ll appear in a child and his grandparents, but not his parents. This is usually a result of sex-linked genes, and frequently can be traced via the maternal (mother) side of the family. It’s also usually from a recessive allele.

Imagine colorblindness (again). A colorblind male (we’ll call him Grandpa) has children with an unaffected female. 50% Chance of Carrier Daughter 50% Chance of Unaffected Son Let’s watch one of the carrier daughters.

She grows up. She then has children with an unaffected male. 25% chance of unaffected son. 25% chance of unaffected daughter. 25% chance of carrier daughter. 25% chance of affected son.

Sex-Linked Traits Virtual Lab

Types of Inheritance Complete Dominance Incomplete Dominance
R = Red, r = White, Rr = Red Incomplete Dominance R = Red, W = White, RW = Pink Codominance R = Red, W = White, RW = Red AND White Sex-Linked Traits that appear on the X or Y chromosome. Colorblindness or hemophilia. They may also display some form of complete dominance, incomplete dominance, or codominance.

Types of Inheritance Multiple Alleles Polygenic
R = Red, w = White, b = Blue, p = Purple Individuals still have only two alleles at a time, but more than two alleles exist. Eye color is a good example. Polygenic Controlled by more than one gene Hypertension (high blood pressure) is not one gene – it’s controlled by many (some for obesity, some for metabolism, some for kidney function, and perhaps others).

Which type of inheritance?
Codominance Codominance

Complete dominance Complete Dominance

Sex-linked Sex-Linked

Incomplete dominance Incomplete Dominance

Complete Dominance Complete Dominance

Codominance/multiple alleles Codominance and Multiple Alleles

Now for some new ones… These are some of the other forms of inheritance (there are quite a few in the biology world).

Sex-linked/codominance Codominance and Sex-Linked

Calico Cats “Calico” is just a name for a color pattern involving orange, black, and white on cats. Cats with these colors are nearly always female because the gene for orange or black fur is X-linked. Thus, males can have either the allele for orange OR black, but not both. Females can have both. The gene for the white fur is not X-linked.

Parthenogenesis However, there are cases in biology in which reproduction among only females can take place. Parthenogenesis is reproduction by use of egg cells without fertilization. This can be artificially done in mammals but is generally a reptile, insect, fish, bird, or lower animal process.

Parthenogenesis Egg cells are produced by meiosis which then develop into an adult sans fertilization. The adults can be haploid in some creatures (honeybees notably) but in other cases the polar body will fuse with the egg making a diploid individual. Due to crossing over already happening prior to formation of the egg, they are NOT clones. However, many times the offspring are homozygous for every gene. Even sex chromosomes.

XY and ZW? What? One last thing…
In humans and other animals, the sperm determines the sex of the offspring. This is the XY sex-determination system. Males XY, Females XX In some species, the egg determines the sex of the offspring. This is the ZW sex-determination system. Males ZZ, Females ZW. Depending on which sex-determination system is used by the species, parthenogenesis will either produce all females (XX) or all males (ZZ).

XY and ZW? What? TED: Aaron Reedy – Sex Determination More Complicated Than You Thought

Multiple Alleles Multiple Alleles and [maybe] Incomplete Dominance

Multiple alleles/codominance Multiple Alleles and Codominance

Multiple Alleles Multiple Alleles and Polygenic

Polygenic Polygenic

Closure and Homework Who Gets the Money?
It’s a murder-mystery (well, accident-and-inheritance-mystery) involving genetics. You and a partner (of your choosing) will solve the case and figure out who gets the money.

Today is Tuesday, December 15th, 2015

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