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Chapter 16 ­ Genetics and Heredity
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Title: Chapter 16 (1 of 212)
Section 16.1 ­ Genetics of Inheritance
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Title: 16.1 (2 of 212)
Homework : Preparation Assignment
Read pages 522­528, and take notes on these pages.
Define what is meant by the following terms:
Traits
Heredity
Genetics
Gene
Allele
Variations
Purebred
True Breeding
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Homework Review
Define what is meant by the following terms:
Traits:
Heredity:
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Homework Review
Define what is meant by the following terms:
Genetics:
Gene:
Allele:
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Homework Review
Define what is meant by the following terms:
Variations:
Purebred:
True Breeding:
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Monohybrid Cross
Read Pages 529­530, and define the following terms:
Timed Activity:
P Generation
F1 Generation
F2 Generation
Dominant
Recessive
Homozygous
Heterozygous
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Definitions
Two important terms in genetics are genotype and phenotype.
Genotype refers to the genetic makup of an organism. In our mice, for example, a white mouse will always have the genotype bb. A black mouse may have the genotype BB or BB.
Phenotype refers to the physical appearance of a trait in an organism. For example, a mouse may be heterozygous for fur color, with the genotype Bb, but the phenotype will be that the mouse is black.
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Alleles
Pea plants have several traits that are easy to identify. For example, the plants may be either tall or short.
This characteristic is controlled by a single gene, which has two alleles.
Tall is the dominant characteristic, so we use the notation:
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Tall allele :
T
Short allele:
t
Homozygous
A true breeding tall plant will be homozygous tall.
TT (both genes carry the dominant allele)
A short plant will be homozygous short.
tt (both genes carry the recessive allele)
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Heterozygous
A heterozygous plant carries one of each allele.
Tt
Because the allele for tall is dominant, the tall characteristic is still expressed.
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Monohybrid Cross
Describe what is meant by the Principle of Dominance and the
Law of Segregation.
Principle of Dominance:
Law of Segregation:
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Principle of Dominance
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Law of Segregation
T
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t
Monohybrid Cross
What are the possible results?
T t
T t
X
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Punnett Squares
A Punnett Square is a convenient way to organize the possible combinations of alleles in a crossing.
T t
T t
X
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Monohybrid Cross
Use a diagram to outline the following hypothetical crossing.
One species of mouse may be either black or white, with fur color being controlled by a single gene. The allele for black fur is dominant to the allele for white fur.
If a purebred black mouse is bred to a purebred white mouse, what will the physical color of the offspring be? What will their genetic makeup be?
Use a diagram to explain your answer!
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All offspring of this cross will be heterozygous (genotype) and have black fur (phenotype)
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Monohybrid Cross
Use a diagram to outline the following hypothetical crossing.
If two F1 mice from the previous example are crossed, what ratio of physical characteristics and genetic makeup would you expect to find in the offspring?
Use a Punnett square to explain your answer!
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Monohybrid Cross ­ Solution
This cross will result in two phenotypes, with 75% being black and 25% being white. However, there are three possible genotypes:
25% homozygous black; 50% heterozygous (but still having black fur, the dominant trait); and 25% homozygous white
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Punnett Squares
In the previous example using mice, the Punnet square allows us to easily see the possible results of an F 1 cross.
Female gametes are generally placed across the top
Male gametes are generally placed down the left side
You need to know the genotype
of both parents to fill in the possible
gametes.
B
B
Since the F1 mice are all heterozygous,
they could each produce a B or a b b
gamete (ie: a gamete carrying either the dominant or recessive allele)
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b
Punnett Squares
Fill in the square, and analyze the results.
By filling in the possible combinations, you can see that:
1/4 offspring are BB, or homozygous dominant, and will have black fur
2/4, in other words 1/2, are Bb, or heterozygous , and will have black fur
1/4 offspring are bb, or homozygous recessive , and will have white fur
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Sample Problem
Use Punnet Squares to solve the following problem:
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In fruit flies, red eyes are dominant over white eyes.
Show the F1 generation results of a cross between a purebreeding red­eyed fly and a purebreeding white­eyed fly. Describe the ratio of phenotypes and genotypes in this generation.
Then, show the F2 generation results, and describe the ratio of phenotypes and genotypes in this generation.
Give about 5 minutes to complete this question, then review the solution on the following pages.
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Sample Problem ­ Solution
Because both parents are pure­breeding , they are both homozygous .
As a result, each gamete from either parent will carry the same allele.
Therefore, all offspring in the F 1 generation are heterozygous , and will display the dominant trait ...in this case, red eyes.
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Sample Problem ­ Solution
100% of the F1 offspring will display the red­eyed phenotype, and be heterozygous (genotype)
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Sample Problem ­ Solution
When you cross two of the F 1 flies, both parents are heterozygous .
In the F 2 generation, you get a distinct pattern of phenotypes, with 75% showing the dominant trait and 25% showing the recessive trait . However, when you look at the genotypes, you see that only 25% are homozygous dominant; 50% are heterozygous ; and 25% are homozygous recessive .
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Sample Problem ­ Solution
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TestCross
What is the genotype of a white­eyed fruit fly?
How do you know?
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TestCross
What about a red­eyed fly?
What are the possible genotypes?
How would you determine the genotype of a red­eyed fly?
Perform a test­cross.
What phenotype would you use to cross the red­eyed fly with? Why?
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TestCross
Outline the possible results of the testcross, and how you would interpret them. What results would indicate the red­eyed fly was homozygous?
What results would indicate the red­eyed fly was homozygous?
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Homework
Complete the Sample Problem activity on page 533
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In Class Assignment and Homework
Review Section 16.1, pages 526­534
Complete Questions #8, 10, 11, 13, and 15 on page 535
Bring two quarters to class on Thursday
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Determining Genotypes ­ Test Cross
If you look at a fruit fly, can you determine the genotype for eye coloe by observing the phenotype?
You can if the fly is white­eyed, because the white­eye allele is recessive...so the only way a fly could have white eyes would be if it was homozygous.
rr
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Determining Genotypes ­ Test Cross
But what if the fly has red eyes?
There are two possible genotypes that produce red eyes:
RR
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Rr
Determining Genotypes ­ Test Cross
In this case, the genotype can be determined by performing a test cross.
This involves crossing the fly with a fly which is homozygous recessive for the trait being observed. By observing the phenotypes of the offspring, you can then determine the genotype of the unknown parent.
Use Punnett squares to predict the percentages of phenotypes if a white­
eyed (homozygous recessive) female fly is crossed with a red eyed male.
You will need to create one Punnett square to show the results if the male is homozygous, and one to show the expected results if the male is heterozygous.
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Determining Genotypes ­ Test Cross
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Sample Problem
In cats, long hair is recessive to short hair. 1)
A true­breedingshort­haired male is mated to a true­breeding
long­haired female. What will their kittens look like?
2)
If you performed a test cross on a short­haired female cat, what
phenotype should the male cat have? Why?
3)
If the testcross resulted in eight kittens, what ratios of phenotypes
would you expect if the female was homozygous? Heterozygous?
4) What if the testcross resulted in seven short­haired kittens, and one long­haired kitten? How can you explain these results?
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Determining Genotypes ­ Test Cross
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Homework
Any questions on any of the homework problems?
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Section 16.2 ­ Complex Inheritance Patterns
Return to Contents
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In pairs, complete the mini­lab on page 531.
Write the answers to questions #1­3 in the lab.
Any questions?
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Complex Patterns of Inheritance
Multiple Traits
It is possible to look at more than one trait at a time.
For example, in pea plants you could look at both color and the shape of the seed.
Color is controlled by a single gene with two alleles, Y (yellow) and y (green)
Shape is controlled by a single gene with two alleles, R (round) and r (wrinkled)
What are the results of crossing a true­breeding yellow, round plant with a true­breeding green, wrinkled plant?
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Yellow Round Plant
*This is the phenotype
*What is the genotype?
*What alleles will all gametes contain?
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Green Wrinkled Plant
*This is the phenotype
*What is the genotype?
*What alleles will all gametes contain?
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Give the results of this cross:
This is the generation.
Phenotype:
Genotype:
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Sample Problem:
Chickens can have brown or white feathers, with brown color dominant.
They can also have long or short tail feathers, with short feathers dominant.
What are the phenotypes and genotypes of chickens produced by crossing a brown, short­tailed male with a white, long­tailed female? (Assume both parents are true­breeding for both traits.)
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Give the results of this cross:
F1 Generation
Phenotype:
Genotype:
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What if homozygous white, long­tailed male was crossed with a homozygous brown, heterozygous short­tailed female?
What gametes could be produced by these parents?
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Multiple Traits
Example from yesterday's class:
In pea plants color is controlled by a single gene with two alleles, Y (yellow) and y (green)
Shape is controlled by a single gene with two alleles, R (round) and r (wrinkled)
What are the results of crossing a true­breeding yellow, round plant with a true­breeding green, wrinkled plant?
First, you have to determine the possible parent gametes.
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Multiple Traits
True­breeding yellow, round plant
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True­breeding green, wrinkled plant
YYRR
yyrr
YR
yr
Multiple Traits
yr
What are the genotypes of the F1 plants?
100% heterozygous for both traits
What are their phenotypes?
100% yellow, round (the dominant trait is displayed)
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YR
YyRr
Multiple Traits
What percentages of phenotypes and genotypes would you expect in the F
2 generation if you crossed two plants from the F1 generation?
Again, the first step is to determine the possible alleles.
What are the possible gametes that the F1 plants could form?
YyRr
F1 Genotype:
Possible Gametes:
YR
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Yr
yR
yr
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Law of Independent Assortment
Inheritance of alleles for one trait does not affect the inheritance of alleles for another trait.
In other words, alleles for different characteristics are passed on to the offspring independently of one another, so that the offspring may have combinations that are different from either of the parents.
What process in cell division allows for this to happen?
Can you think of a situation where it would be more likely that alleles would be kept together?
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B ­ black fur
b ­ brown fur
Law of Segregation
R
t
r
T
R ­ rough coat
r ­ smooth coat
T ­ long tail
t ­ short tail
b
B
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Multiple Traits
Create a Punnett square to determine the phenotypes and genotypes of the F
2 generation in the pea plant example.
Remember, the F1 plants
were heterozygous for both traits, and there are four possible gametes
formed from each parent.
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Sample Problem:
Yesterday, we looked at this sample problem:
Chickens can have brown or white feathers, with brown color dominant.
They can also have long or short tail feathers, with short feathers dominant.
When a brown, short­tailed male is crossed with a white, long­
tailed female, what are the phenotypes and genotypes of the F 1 offspring? (Assume both parents are true­breeding for both yesterday's solution...
traits.)
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Sample Problem:
BbSs
F1 Genotype:
F1 Phenotype:
All offspring will be brown with short tail feathers
What are the possible gametes that the F1 chickens could form?
Possible Gametes:
BS
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Bs
bS
bs
Create a Punnett square to determine the phenotypes and genotypes of the F2 generation resulting from crossing two of the F1 chickens.
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Sample Problem:
In guinea pigs, the allele for dark fur is dominant to the allele for white fur.
The allele for rough coats is dominant to the allele for smooth coats.
Find the genotype and phenotype ratios of the offspring resulting from a cross of a dark, rough coated male with a white, smooth coated female.*
*(Both of these parent guinea pigs are true­breeding for both traits)
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First, determine the genotypes of both parents:
Male
Female
Possible Gametes:
Male
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Female
Give the results of this cross:
F1 Generation
Phenotype:
Genotype:
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Determine the results of a cross between two F1 individuals.
First, determine the genotypes of both F1 parents:
Male and Female Possible Gametes:
Male and Female
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Create a Punnett square to determine the phenotypes and genotypes of the F2 generation resulting from crossing two of the F1 guinea pigs.
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Homework:
1.
A dihybrid cross is made of pea plants. Purple flowers (P) are dominant
and white flowers (p) are recessive. Tall plants (T) are dominant and
and short plants (t) are recessive. Both parents are heterozygous for
both traits. Prepare a Punnett square to determine the phenotypic
ratios of the offspring. What Mendelian law does this ratio demonstrate?
Solution:
What is the genotype of both parents?
PpTt
What possible gamets are formed?
PT
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Pt
pT
pt
Homework
1)
Solution
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Homework
Complete the homework assignment sheet. Use Punnett squares where appropriate. Be sure to answer all questions.
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Test Cross with Multiple Traits
A test cross when looking at multiple traits is the same as in a single trait. The only difference is, you will cross your unknown genotype with an individual that is homozygous recessive for both of the characteristics you are investigating.
How can you tell an individual has a homozygous recessive genotype?
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Test Cross with Multiple Traits
What are the possible genotypes of a yellow, round pea plant? (Remember, yellow peas are dominant to green peas, and round peas are dominant over wrinkled peas.) *Hint: there are four possibilities!
What would the results of each testcross be? (Since there are four See results...
possibilities, there will be four possible testcross results.)
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Test Cross with Multiple Traits
Testcross of round, yellow pea plant.
What are the results if the genotype is YYRR?
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Test Cross with Multiple Traits
Testcross of round, yellow pea plant.
What are the results if the genotype is YYRr?
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Test Cross with Multiple Traits
Testcross of round, yellow pea plant.
What are the results if the genotype is YyRR?
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Test Cross with Multiple Traits
Testcross of round, yellow pea plant.
What are the results if the genotype is YyRy?
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Multiple Traits Sample Problem
In cats, black color is dominant to a special gene which produces cream­colored cats with dark legs, faces and tails (Siamese cats, in case you don’t recognize it). Length of fur is controlled by a single gene with two alleles; long hair is dominant to short hair.
What are the F 1 expected results of a cross between a true­breeding long­haired black cat and a true­breeding short­haired Siamese colored cat?
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Multiple Traits Sample Problem
If two F 1 cats are crossed, what genotype and phenotype ratios would you expect in the F 2 offspring?
bl
bL
Bl
BL
BL
BBLL
BBLl
BbLL
BbLl
Bl
BBLl
BBll
BbLl
Bbll
bL
BbLL
BbLl
bbLL
bbLl
bl
BbLl
Bbll
bbLl
bbll
Black, Long: 9
Black, Short: 3
Siamese, Long: 3
Siamese, Short: 1
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Multiple Traits Sample Problem
How could you determine the phenotype of a long­haired black cat?
Show all possible combinations, and the expected results?
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Multiple Traits Sample Problem
Solution:
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Incomplete Dominance
Not all traits are completely dominant or recessive. In some cases, neither allele is dominant...in these cases, a heterozygous individual will display a blending of the two traits. This is called incomplete dominance.
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Incomplete Dominance
For example, some flowers have petal color controlled by a single gene with two alleles: one coding for red color, the other for white. If the individual is homozygous for either allele, this is the petal color that will be displayed.
Phenotype:
Phenotype:
Genotype:
Genotype:
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Incomplete Dominance
However, if the individual is heterozygous, neither of these traits is displayed...instead, the flower shows a blending of red and white, resulting in pink petals.
Phenotype:
Genotype:
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Codominance
Codominance is similar to incomplete dominance, except both traits are dominant. In this case, homozygous individuals display one trait, while heterozygous individuals display both traits, not as a blending of the two, but showing both characteristics partially.
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Codominance
For example, color in one type of cow is controlled by a single gene with two alleles, one coding for brown fur and one for white fur.
Homozygous cows are either brown or white.
Phenotype:
Phenotype:
Genotype:
Genotype:
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Codominance
However, heterozygous cows will display brown and white patches, rather than being light brown all over.
Phenotype:
Genotype:
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Multiple Alleles
Not all traits are controlled by genes with only two alleles; some have multiple alleles.
In humans, for example, the A, B and O blood types are determined by three alleles, two of which are co­dominant and one of which is recessive.
The IA allele results in blood type A; the IB allele results in blood type B; and the i allele, being recessive, results in blood type O.
Remember that the blood types are determined by antigens on the surface of blood cells. These antigens are proteins, so the gene codes for the production of these antigens...in type O, the gene does not code for production of an antigen.
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Multiple Alleles
List all possible genotypes which could result in the following phenotypes (blood types).
Blood Type
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Genotype
Homework
Review Section 16.2, and complete Questions #2­4 on page 544
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Homework
Page 544 #1­2
1)
A dihybrid cross is made of pea plants. Purple flowers (P) are
dominant and white flowers are recessive. Tall plants (T) are
dominant and short plants are recessive. Both parents are heterozygous for both traits. Prepare a Punnett square to
determine the phenotype ratios of the offspring.
What Mendelian law does this ratio demonstrate?
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Homework
1)
Solution
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Homework
2)
A rose­combed rooster is mated with two rose­combed hens.
Hen A produces 14 chicks, all rose­combed.
Hen B produces 9 chicks, 7 of which are rose­combed and
2 single­combed.
What are the likely genotypes of the parent birds?
Rose comb
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Single comb
Homework
2)
Solution
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Homework
2)
Solution
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Homework
2)
Solution
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Sample Problem
You know that one type of flower has petal color determined by a single gene with two alleles, red or white, and they display incomplete domininance. If a red flower is crossed with a white flower, what are the genotypes and phenotypes of the F 1 generation offspring?
What are the expected genotypes and phenotypes of the F 2 offspring if two pink flowers are cross pollinated?
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Sample Problem
Solution
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Sample Problem
Solution
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Assignment: Inheritance of Coat Color in Rabbits
Complete theThinking Lab on page 543. Be sure to answer all questions completely, including the Punnett squares.
white
chinchilla
Darkgrey
Himalayan
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Assignment: Inheritance of Coat Color in Rabbits
1) List all the possible genotypes for a:
(a) Dark grey rabbit
(b) Chinchilla rabbit
(c) Himalayan rabbit
(d) White rabbit
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Assignment: Inheritance of Coat Color in Rabbits
2) Predict the phenotype of a rabbit with the following genotypes.
Explain your answers.
(a) c h cch
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(b) C c h
Assignment: Inheritance of Coat Color in Rabbits
3) Would it be possible to obtain white rabbits if one parent is white
and the other is chinchilla? Explain.
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Assignment: Inheritance of Coat Color in Rabbits
4) Would it be possible to obtain chinchilla rabbits if one parent is
Himalayan and the other is white? Explain.
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Assignment: Inheritance of Coat Color in Rabbits
5) A chinchilla rabbit is mated with a Himalayan. Some of the offspring
are white. What are the parents' genotypes?
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Assignment: Inheritance of Coat Color in Rabbits
5) A chinchilla rabbit is mated with a Himalayan. Some of the offspring
are white. What are the parents' genotypes?
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Assignment: Inheritance of Coat Color in Rabbits
Extension Question:
A male chinchilla rabbit and a female dark grey rabbit are crossed.
The resulting litter contains 11 kits; 6 are dark grey, and 2 are
chinchilla. However, 3 of the kits are Himalayan! Show how this
is possible.
Is there any way for this cross to produce white rabbits?
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Assignment: Inheritance of Coat Color in Rabbits
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Assignment: Inheritance of Coat Color in Rabbits
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Testcross Question
If you had a brown cow and wanted to know its genotype, how would you perform a testcross?
A testcross is not necessary if traits show incomplete or co­
dominance...because the phenotype tells you the genotype!
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Rabbit Question
You crossed a dark grey male rabbit and a Himalayan female rabbit, with 6 kits produced:
2 dark gray
3 white
1 Himalayan
What are the genotypes of the parents?
Which parent genotype is it impossible to know for sure?
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Rabbit Question
You crossed a dark grey male rabbit and a Himalayan female rabbit, with 6 kits produced:
2 dark gray
3 white
1 Himalayan
What are the genotypes of the parents?
Which parent genotype is it impossible to know for sure?
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Assignment: Human Blood Types
Complete the Sample Problem on page 542.
Check yourself against the solution on page 811.
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Class Assignment: Oompa Loompa Genetics
Complete the assignment sheet on Oompa Loompa genetics.
Be sure to show all work, including Punnett squares, for all problems!
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Homework
Read Section 16.3, pages 545­553, taking notes on this section.
Define the following terms in your own words!
Sex­linked inheritance
Barr body
Polygenic inheritance
Modifier genes
Deletion error
Inversion error
Duplication error
Translocation error
Nondisjunction
Monosomy
Down Syndrome
Fragile X Syndrome
What is the result of the following genotype: XO
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XXY
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Section 16.3 ­ Chromosomes and Heredity
Return to Contents
Title: 16.3 (177 of 212)
Chromosomes and Heredity
Mendel did his work by esperimentation, before scientists knew what chromosomes or DNA were. Still, he was able to conclude that characteristics were determined by pairs of "factors", and that one factor was donated to an offspring by each parent. He also stated that inheritance of one factor did not affect the inheritance of other factors; this became the Law of Independent Assortment.
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Chromosomes and Heredity
It wasn't until the 1900s that scientists were able to determine that Mendel's "factors" were located on chromosomes. Walter Sutton and Theodor Boveri made the connection while studying the behavior of chromosomes during meiosis. They noticed that chromosomes occur in pairs, and that during meiosis, the chromosome pairs align at the cell's equator, and are then segregated (separated) independently. This meant that each gamete receives one chromosome from each pair, and this one does not influence which other chromosomes end up in the gamete. This allowed them to come up with the Chromosome Theory of Inheritance.
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Chromosomes Theory of Inheritance
The theory contains two main points:
1)
Mendel's factors of inheritance, or genes, are carried
on the chromosomes
2)
The segregation and independent assortment of
chromosomes during meiosis accounts for the patterns
of inheritance.
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Chromosomes Theory: Independent Assortment
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Linked Traits
Not all characteristics follow the law of independent assortment completely.
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Chromosomes Theory: Linked Traits
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Sex­Linked Traits
Characteristics which occur on the X or Y chromosomes are called
sex­linked traits.
For example, the gene for eye color on fruit flies is located on the X chromosome. The "wild type" or red eyes are dominant; white eyes are recessive.
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Chromosomes Theory: Sex Linked Traits
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Problem
If you cross a homozygous red­eyed female fruit fly with a white­eyed male, what will the phenotype ratios of the offspring be?
Remember, the gene for eye color on fruit flies is located on the X chromosome, and the white­eyes allele is recessive.
First, determine the parent (P) genotypes:
Male Genotype
XrY
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Female Genotype
XRXR
Problem
Fill in the Punnett square.
XR
Xr
Y
XRXr
XRY
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XR
XRXr
XRY
In the F1 Generation:
50% of the young are female, and all of the females have red eyes. (However, all carry the recessive white­eyed allele)
50% of the young are male, and all of the males have red eyes. (However, they only carry the red­
eyed allele on the X chromosome.)
Problem
What about the F 2 Generation? If you crossed one of these males with one of the females, what would the F 2 results be?
XR
XR XRXR
Y
XRY
Xr
In the F2 Generation:
XRXr
50% of the young are female, and all of the females have red eyes. (However, half carry the recessive white­eyed allele)
XrY
50% of the youndg are male, and half of the males have red eyes, while the other half have white eyes. Because eye color is carried on the X chromosome, which parent do the males inherit eye color from?
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Homework
Read Section 16.3, pages 545­549.
Complete Questions #1, 5­9 on page 554.
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Review of Tests
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Virtual Fruit Fly Lab
http://www.sciencecourseware.org/vcise/drosophila/
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Virtual Fruit Fly Lab 2
http://www.biologylabsonline.com/protected/FlyLab/
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Section 16.4 ­ Human Genetics
Return to Contents
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Attachments
Endrocrine Gland Function.wpd
codontable2[1]