Download KEY - mybiologyclass

1/17
2009-2010 CP2 GENETICS UNIT PACKET
FOR COMPLEX INHERITANCE
MA STATE Frameworks: (This is what the state of MA says you need to be able to do on your MCAS test)
Broad Concept: Genes allow for the storage and transmission of genetic information. They are a set of instructions
encoded in the nucleotide sequence of each organism. Genes code for the specific sequences of amino acids that
comprise the proteins that are characteristic of that organism.
3.3 Explain how mutations in the DNA sequence of a gene may or may not result in phenotypic change in an
organism. Explain how mutations in gametes may result in phenotypic changes in offspring.
3.4 Distinguish among observed inheritance patterns caused by several types of genetic traits (dominant, recessive,
incomplete dominance, codominant, sex-linked, polygenic, and multiple alleles).
3.5 Describe how Mendel’s laws of segregation and independent assortment can be observed through patterns of
inheritance (such as dihybrid crosses).
3.6 Use a Punnett Square to determine the probabilities for genotype and phenotype combinations in monohybrid
crosses.
2/17
GENETICS: INCOMPLETE AND CODOMINANCE (10.3)
Exploring Life concept 10.3: There are many variations of inheritance patterns
TOPICS:




Incomplete Dominance
Codominance
Blood Typing
Sickle Cell Anemia
OBJECTIVES:
_________ 9. Explain the difference between complete dominance, incomplete dominance and codominance, and
solve genetics problems of each type of inheritance.
_________ 10. Explain what sickle cell anemia is and how it is inherited. Also explain its link to malaria.
_________ 11. Use Punnett squares to predict possible blood types from a cross.
_________ 12. Differentiate between the 4 major blood types; determine blood types of artificial blood (lab).
KEY TERMS:
Antigen: identifying molecule found on the surface of cells
Antibody: protein in blood plasma that attaches to a particular antigen
Codominance: inheritance pattern in which a heterozygote expresses the distinct traits of both
alleles
Intermediate inheritance: (also known as Incomplete dominance) neither allele for a trait is
dominant
Polygenic inheritance: combined effect of two or more genes on a single character
3/17
NOTES: Incomplete Dominance (Otherwise known as “Intermediate Inheritance”)
•
•
•
•
•
In incomplete dominance, neither allele is dominant over the other
In the heterozygous individual, the phenotypes are blended.
The letter “C” is used to label the petal color gene.
Two different capital letters are used as superscript to show that neither color is dominant.
Do not use lower-case letters when demonstrating incomplete dominance.
Example of Incomplete Dominance
• In flowers, petal color is sometimes inherited through incomplete dominance.
Genotype
CRCR (sometimes seen as RR)
CWCW (sometimes seen as WW)
CWCR (sometimes seen as WR)
Phenotype
Red
White
Pink
NOTES: Sickle Cell Disease (An example of Incomplete Dominance)
•
•
•
People with sickle cell disease have red blood cells that contain an abnormal type of hemoglobin.
Sometimes these red blood cells become sickle-shaped (crescent shaped) and have difficulty passing
through small blood vessels.
When sickle-shaped cells block small blood vessels, less blood can reach that part of the body and it will
eventually become damaged from lack of oxygen.
Example of incomplete dominance in humans
Shape of red blood cells
• CR CR - all round (normal)
• CS CS - all sickle shaped (sickle cell disease)
• CR CS – cells are sort-of sickle, sort-of round (called
“sickle cell trait”) (a carrier)
Sickle Cell Disease
• In people with sickle cell disease, all red blood cells are
shaped like sickles (all SS)
• Serious health problems: blood can’t carry enough
oxygen to cells/ tissues/ organs
– Severe pain, Stroke, Chronic renal (kidney)
failure, Anemia (deficiency of hemoglobin), Etc…
• Individuals that are heterozygous (CR CS) have only mild health problems.
• But…they and individuals that are CS CS
• are protected against malaria!
• Sickle cell is therefore more common in areas with tropical climates.
Why are people with sickle protected against malaria?
• People with one or two alleles of the sickle-cell disease (CS CS OR CR CS) are resistant to malaria
because the sickle red blood cells are not conducive to the parasites
• In areas where malaria is common there is a survival value in carrying the sickle-cell genes.
• The malaria parasite (plasmodium) has a complex life cycle and spends part of it in red blood cells.
• People with sickle trait and sickle cell disease are not able to carry as much oxygen in the blood as those
who do not have the trait or the disease.
• The malaria parasite can not live in this low-oxygen environment.
4/17
What is Incomplete Dominance?
1. FIGURE A: The crossing of pure red (CRCR) and pure white (CWCW) four-o’clock
flowers
2. Fill in the Punnett square next to figure A
3. The offspring of crossed pure red and pure white four-o’clock flowers are
a. Only red
c. Only pink
b. Only white
d. Both red and white
4. In four-o’clock flowers,
a. Neither red nor white is
dominant
b. Red is dominant over white
c. Pink is dominant over red
d. White is dominant over red
5. Pink is a blend of which two colors? Red and White
6. Blended four-o’clock flowers have
a. Only genes for the color red
b. Only genes for the color white
c. Genes for both red and white
d. Only pink genes
7. Just by looking at the chart in figure A, how can you tell that there is incomplete
dominance?
There are two different capital letters being used to represent alleles of one trait (a W and an
R). With complete dominance, we use one letter – either uppercase for dominant, or
lowercase for recessive.
FIGURE B: The crossing of pure black (CBCB) and pure white (CWCW) Andalusian
chickens
8. Fill in the Punnett
square next to figure B
5/17
9. The offspring of crossed pure black and pure white Andalusian chickens are
a. Only white
c. Only black
b. A blend of black and white
d. Black and white
10. In Andalusian chickens
a. Both black and white are
dominant
b. White is dominant over black
c. Neither black nor white is
dominant
d. Black is dominant over white
11. What color are the offspring of black and white chickens? Gray
12. Gray is a blend of which two colors? Black and White
13. Blended Andalusian fowl have
a. Only genes for the color white
b. Only gray genes
14. Blended Andalusian fowl are…Choose:
c. Genes for both black and white
d. Only genes for the color black
pure / hybrids
15. FIGURE C: The crossing of pure red (CRCR) and pure white (CWCW) Shorthorn cattle
16. Complete the Punnett square in Figure C
17. The offspring of crossed pure red and pure white shorthorn cattle are:
a. Red and white
c. Only red
b. Only white
d. A blend of red and white
18. In shorthorn cattle,
a. pink is dominant over white
b. there is incomplete dominance
of red and white colors
19. What are red and white blended cattle called? Roan
c. white is dominant over red
d. red is dominant over white
6/17
20. Roans have
a. Only genes for the color white
b. Genes for both white and red
21. Roans are…Choose:
c. Only genes for the color red
d. Only pink genes
pure / hybrids
Complete each statement using a term or terms from the list below. Write your
answers in the spaces provided
Blending, roan calf, recessive, white, dominant, red, eye, skin, pure, hybrid,
strong, pink four-o’clock flower, incomplete dominance
22. A “hidden trait” is called a recessive trait
23. Not all genes are completely recessive nor completely dominant Some are equally
strong
24. An individual that has only dominant or recessive genes for a trait is pure for that trait.
25. An individual that has both dominant and recessive genes for a trait is hybrid for that
trait.
26. A condition where the genes for a given trait are equally strong is called incomplete
dominance
27. A combination of genes in which a mixture of both traits shows up is called hybrid
28. Two examples of offspring of incomplete dominance are pink four-o’clock flower and
the roan calf
29. In four-o’clock flowers and roan cattle, neither the color red nor the color white is
dominant.
30. Incomplete dominance produces offspring with hybrid / blending genes for the given
trait.
31. Examples of incomplete dominance in humans are found in eye and skin color.
7/17
INCOMPLETE DOMINANCE MONOHYBRID
CROSS PRACTICE PROBLEMS #1
1. Flower color in snapdragons is a trait showing incomplete dominance. It is governed by two alleles, C R and
CW, for red and white pigment production, respectively. Identify the expected phenotypic results (%) of the
progeny (offspring) from crossing:
1. Two pink flowered plants
25% red
50% pink
25% white
2. Two white flowered plants
100% White
3. A pink flowered plant and a white flowered plant
50% White
50% Pink
2. Radish roots are long, round, or oval. When long-rooted radishes are crossed to round ones, the offspring all
have oval roots.
Symbols:
RL = Long
RD = Round
a. What type of inheritance is this? Incomplete Dominance
b.
c. If oval-rooted radishes are crossed together, what will be the phenotypes and genotypes of the
offspring, and in what proportion?
Genotypes
RD RD
RD RL
RL RL
%
25%
50%
25%
Phenotypes
Round
Oval
Long
%
25%
50%
25%
8/17
3. In cattle, red is incompletely dominant to white. When the two colors are crossed, the resulting cow is a pinkcolor called “roan.”
Symbols:
CR = Red
CW = White
a. A rancher has some roan cattle in his herd. He likes the color so well that he would like all his
cattle to be that color. Is it possible to develop a pure roan herd? Complete the Punnett square
below for two roan cows, and then explain your answer.
No, you would not be able to develop a pure roan herd
permanently. You could develop a roan herd by mating
red cows with white. However, when the roan cows bred,
they would produce:
25% Red cows
50% Roan cows
25% White cows
Yes, you could sell or give away the red and white cows. But, it is not possible for roan cows
to produce calves that are only roan.
4. Sickle-cell anemia is a human hereditary condition in which the red blood cells, normally round, become
abnormally shaped. The problem is in the structure of the hemoglobin molecule. The red blood cells are
smaller and transport less oxygen than normal. They also tend to jam up in capillaries, causing hemorrhage
and thus anemia.
Symbols:
CRCR = normal hemoglobin and red blood cells
CSCS = high proportion of sickled cells and severe anemia
CRCS = some sickled cells and mild anemia
a. When two CRCS people marry, what are the expected genotypes and phenotypes of their children?
Complete the Punnett square below, and fill in the phenotype and genotype charts.
Genotypes
CRCR
CSCS
CRCS
%
25%
25%
50%
Phenotypes
No Sickle Cell (Normal)
Mild Sickle Cell (Sickle Trait)
Sickle Cell Anemia
%
25%
50%
25%
9/17
NOTES: CODOMINANCE




In codominance, BOTH alleles are equally dominant
In the heterozygous individual, BOTH phenotypes are expressed.
An Example of Codominance
o In flowers, petal color is sometimes inherited through codominance.
o The letter “C” is used to label the petal color gene.
Two different capital letters are used as superscript to show that each color is equally dominant. Do not use
lower-case letters when demonstrating codominance.
Genotype
CRCR
CWCW
CRCW
Phenotype
Red
White
Red AND White
Name: __________________________________________________________ Date: ____________ Class:______
WS: CODOMINANCE MONOHYBRID
CROSS PRACTICE PROBLEM #1
In “pink pufferbelly pigs” spot color is inherited through codominance. Some pink pufferbelly pigs have pink skin with
green spots (SG). Some pink pufferbelly pigs have pink skin with purple spots and SP)
1. List the three possible genotypes and phenotypes for pink pufferbelly pig spot color below:
Genotype:
SG SG
SG SP
SP SP
Phenotype:
Pink Skin, Green Spots
Pink Skin, Green and Purple Spots
Pink Skin, Purple Spots
2. Show the results (genotypes, phenotypes and their percentages) of a cross between two pink pufferbelly pigs
heterozygous for the spot color gene.
Genotype:
SG SG
SG SP
SP SP
%
25%
50%
25%
Phenotype:
Pink Skin, Green Spots
Pink Skin, Green and Purple Spots
Pink Skin, Purple Spots
%
25%
50%
25%
10/17
NOTES: BLOOD TYPES (An Example of Codominance in Humans)




Blood types are determined by the presence or absence of a molecule on the surface of the red blood cells.
This molecule is called an “antigen”
“I” is the letter designated for the gene for blood type.
There are three possible alleles for this gene: IA
IB
i
Dominance of Alleles
 IA and IB are co-dominant to each other
 Both A and B are dominant over i
The Blood Types
 There are four blood types: A, AB, B, and O
 A person with type A blood could have the following genotypes:
 A person with type B blood could have the following genotypes:
 A person with type AB blood could have the following genotype:
 A person with type O blood could have the following genotype:
IAIA
IBIB
IAIB
ii
OR
OR
IAi
IBi
Antigens and Their Antibodies (see next page for chart)
 Blood Type A produces surface antigens for molecule A and B antibodies
 Blood Type B produces surface antigens for molecule B and A antibodies
 Blood Type AB produces surface antigens for molecules A and B and NO antibodies
 Blood Type O produces NO surface antigens and A and B antibodies
Makeup of Blood Types In the World
 Blood Type O: 45%
 Blood Type A: 40%
 Blood Type B: 11%
 Blood Type AB: 4%
Rh Factor
 Named after the Rhesus monkey where it was first identified.
 It is another blood antigen
 If you are Rh+, you have the antigen
 If you are Rh- you do not have the antigen
 Rh- individuals will produce antibodies against Rh+ blood if introduced.
 If an Rh- mother becomes pregnant with an Rh+ baby, the mother will produce antibodies against the Rh
antigen.
 This is not a problem during the 1st pregnancy.
 However, her blood will attack her baby’s blood if she becomes pregnant with another Rh+ baby in the future.
 Rh- mothers are given a drug called “Rho-gam” to neutralize the Rh+ in the baby’s blood.
11/17
12/17
Name: ____________________________________________________ Date: ____________ Class: ______
Blood Typing Problems #2
1.
What are the possible blood types of the offspring of a cross between individuals that are type AB
and type O?
2.
What are the possible blood types of the offspring of a cross between individuals that are type A
and type O?
3.
What are the possible blood types of the offspring of a cross between individuals that are both
type A?
Type A
4.
Type A
Types A and O
A brother and sister who have the same parents have the following blood types: Judy is blood
type A, and Mark is blood type O. What are the possible blood types of their parents?
Judy: Type A (IA IA or IA i)
Mark: Type O (ii)
You need to figure out how you can get Judy’s blood
type AND Mark’s blood type in ONE Punnett square.
(Either is possible). Do this by putting the kids in the
Punnett square, then figure out what parents can make
those combinations (there might be more than one
right answer!
OVER:
The parents could be:
-Blood types: A and A
-Blood types: A and O
- Blood types: A and B
13/17

14/17
WS G2E: Blood Type Mystery!
Geneticists are often called upon to solve mysteries using some of the tools you have become familiar with in this
chapter. Using genetic clues, give a possible solution for each problem below.
PROBLEM: Four newborn babies in the delivery room of the hospital at the same time were mixed up by the person
who typed the wristbands. The blood types of the four babies were known to be AB, O, A and B. How did the doctors
eventually find out which baby belongs to which set of parents? Parents #1 had blood types O and AB; Parents #2
had blood types AB and B; Parents #3 both had blood type O; Parents #4 had blood types O and A.
Possible Solution: Use Punnett Squares to determine possible genotypes of offspring.
1) Children’s blood types:
a) Children of parents #1 could be these blood types: A
B
b) Children of parents #2 could be these blood types: A
B
c) Children of parents #3 could be these blood types: O
d) Children of parents #4 could be these blood types: A
2) Baby with type AB blood belongs to: Parents 2
3) Baby with type B blood belongs to: Parents 1
4) Baby with type A blood belongs to: Parents 4
5) Baby with type O blood belongs to: Parents 3
O
AB
15/17
Name: _______________________________________ Date: _____________Class: _______
Blood Typing Problem #3
Human blood type is determined by codominant alleles. There are three different alleles, known as IA, IB,
and i. The IA and IB alleles are codominant, and the i allele is recessive.
The possible human phenotypes for blood group are type A, type B, type AB, and type O. Type A and B
individuals can be either homozygous (IAIA or IBIB, respectively), or heterozygous (IAi or IBi,
respectively).
Complete Punnett squares below to show all of the crosses of a woman with type A blood and a man with
type B blood and use your Punnett squares to answer the following questions.
Blood type A genotypes: IAIA IAi
Blood type B genotypes: IBIB IBi
You can make these matings: IAIA x IBIB
IAIA x IBi
You will need to make all of these Punnett squares.
IAi x IBIB
IAi x IBi
There are 16 boxes total.
Type: AB (4/16)
AB (2/16)
A (2/16)
AB (2/16)
B (2/16)
AB (1/16)
A (1/16)
B (1/16)
O (1/16)
1. What is the % chance that each of these children will be born to this couple:
Type A blood
3/16 (18.75%)
Genotype IAIB 9/16 (56.25%)
Type B blood
3/16 (18.75%)
Genotype IAi
3/16 (18.75%)
Type AB blood 9/16 (56.25%)
Genotype IB i
3/16 (18.75%)
Type O blood
Genotype IBIB 0/16 (0%)
1/16 (6.25%)
Genotype IAIA 0/16 (0%)
Genotype ii
1/16 (6.25%)
16/17
Name: ______________________________ Date: ____________Class: __________
Blood Typing Problems #4
A nurse at a hospital removed the wrist tags of three babies in the maternity ward.
She needs to figure out which baby belongs to which parents, so she checks their
blood types. Using the chart below, match the baby to its correct parents. Show the
crosses to prove your choices.
Parents
Blood Types
Baby
Blood type
Mr. Hartzel
O
Mrs. Hartzel
A
Jennifer
O
Mr. Simon
AB
Rebecca
A
Mrs. Simon
AB
Holly
B
Mr. Peach
O
Mrs. Peach
O
17/17
2. A child has type A blood. What are ALL the possible blood types of its parents.
Show each cross to prove that it is possible.
The only parents that can produce a child with type A blood are:
AxA
AxB
A x AB
AxO
B x AB
AB x AB
AB x O