Download Genetics Study Guide Key

Genetics Study Guide
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8-1 The Origin of Genetics
1) Genetics is the branch of biology that studies…? Heredity
2) What is meant by the term “genetic cross”? mating
3) Why were Gregor Mendel’s studies different from T.A. Knight’s?
a. Gregoor Mendels studies were detailed, well documented, and analyzed statistically. TA Knights
were informal
4) What are some reasons that the garden pea was a good choice for genetic studies?
a. Small, easy to breed, contain both male and female reproductive organs within the same lower,
short generation times, produce many offspring
5) How did Mendel create the P generation?
a. By self-pollinating plants untile they became true breeding for a trait
6) How did Mendel create the F1 generation? By cross pollinating the p-generation
a. How did Mendel control breeding while cross pollinating the P generation? By cutting off the
male reproductive organs to prevent self pollination
7) What is a monohybrid cross? A cross looking at only 1 contrasting trait
8) Give an example of a trait with two contrasting forms.
a.
b.
c.
d.
e.
Flower color (purple/white)
Plant height (tall/ short)
Seed color (yellow/ green)
Seed shape (round/ wrinkled)
Pod shape (inflated/constricted)
9) In regards to flower color, what colors were…
a. The P generation Purple & White
b. The F1 generation  Purple
c. The F2 generation  75% Purple & 25% white
10) How did Mendel explain the disappearance and reappearance of the white flower color?
a. Mendel said that organisms must carry 2 copies of each trait, and if those copies differ you will
only see the dominant one in the organisms appearance
11) In addition to flower color, what are some examples of other traits that Mendel studied?
a. Seed shape, pod shape, plant height, flower location
12) In every F2 generation, the ratio of contrasting traits was approximately…?
a. 3 dominant: 1 recessive
8-2 Mendel’s Theory
1) Mendel concluded that…
a. Each individual has __2____ copies of a gene.
b. There are different versions of the genes that today we call _alleles___.
c. When two different alleles combine one may be __Dominant/ fully______ expressed while the
other has no ____noticeable____ effect on the organism.
d. When gametes are formed the alleles from each gene __separate__.
2) What is the difference between genotypes and phenotypes?
a. Genotypes refer to the collection of alleles an organism has for a trait, phenotype refers to the
physical appearance of the organism
3) Use the letters A and a to write examples of genotypes that are…
a. Homozygous dominant AA
b. Homozygous recessive  Aa
c. Heterozygous  aa
4) For pea plants, what phenotypes are expressed by the following genotypes?
a. PP  purple flowers
b. Pp  purple flowers
c. Pp  white flowers
5) Mendel’s Law of Segregation states that…
a. Organisms have 2 alleles for each gene and they separate during gamete formations so that each
gamete receives only 1 copy. This involves the behavior of homologous chromosomes
6) Mendel’s Law of Independent Assortment states that…
a. Inheritance of one trait has no effect on inheritance of different traits. This involves the behavior
of nonhomologous chromosomes
7) Mendel’s Law of Independent Assortment is only accurate for genes located on different_______
chromosomes
8) Genes found close together on a chromosome are usually _linked_____.
9) How does gene linkage affect the number of possible genetic combinations?
a. Gene linkage reduces or limits the number of possible gene combinations
8-3 Studying Heredity
1) Who created the Punnett square? Reginald Punnett
2) What does a Punnett square predict? Punnett squares predict the probability of having an offspring
with a particular genotype & phenotype
3) Where are gametes placed in a Punnett square? Along the top and side
4) What process occurs inside each box in a Punnett square? Fertilization to form a zygote
5) Use the letters T and t to cross a tall homozygous dominant pea plant with a short plant.
T
t
t
T
Tt
Tt
Tt
Tt
a. Genotype? All offspring will have the genotype Tt
b. Phenotype? All offspring will be tall
6) Cross two heterozygous tall pea plants.
T
T
t
a. Genotype ratio?
t
TT
Tt
Tt
tt
1TT: 2Tt:1tt
b. Phenotype ratio? 3 Tall: 1 Short
c. What is the probability that an offspring from the cross will be short? Write your answer as a
fraction and a percentage.
i. ¼ will be short, or 25%
7) Who discovered sex-linked traits? Thomas Hunt Morgan
8) What is a sex-linked trait? A trait found on one of the sex chromosomes, usually the X
9) Use the alleles R and r to cross a heterozygous red-eyed female fruit fly with a white-eyed male (sexlinked recessive).
XRXr * XrY
XR
Xr
Xr
Y
XRXr
XRY
XrXr
XrY
a. Genotype ratio?
1 XRXr :1 XrXr :1 XRY :1 XrY
b. Phenotype ratio?
male
1 red eyed female: 1 white eyed female: 1 red eyed male: 1 white eyed
10) Use the alleles C and c to cross a heterozygous female with normal vision and a color blind male (sexlinked recessive).
XCXc * XcY
Xc
Y
XC
Xc
XCXc
XCY
XcXc
XcY
a. Genotype ratio? 1 XCXc :1 XcXc :1 XCY :1 XcY
b. Phenotype ratio? 1 color vision female: 1 color blind female: 1 color vision male: 1 color
blind male
c.
d. What chromosome does a male offspring receive from his male parent? The Y chromosome
e. Does a male offspring inherit the allele for color blindness from his mom or dad?  Mom
11) If an x-linked trait is caused by a dominant allele, how many alleles will a female offspring need to
inherit in order to have the trait? Just 1
a. For a female offspring, this allele may come from which parent(s)? mom or dad
b. For a male offspring, this allele may come from which parent(s)? mom
12) Test crosses are used to determine the _genotype______ of dominant phenotypes.
a. What two dominant genotypes could cause purple flower color?
i. Homozygous  PP
ii. Heterozygous  Pp
b. In a test cross, which dominant genotype would produce offspring that are all purple?
i. Homozygous  PP would produce all purple offspring
13) How do you determine the probability of multiple events?
a. Multiply the probability of each individual event
14) What is the probability that a coin will land heads up five times consecutively?
a. ½ * ½ * ½ * ½ * ½ = 1/32
15) In a pedigree…
a. What shape are females? Circles
b. What shape are males? Squares
c. How are affected individuals shown? Their shape is shaded in
d. What indicates offspring? Vertical (up & down) lines
e. What indicates death from a trait? A crossed out shape
16) For an autosomal recessive trait, what genotype will unaffected parents of an affected offspring have?
Create and label a simple pedigree below.
OR
a. They will be heterozygous so Aa
17) For an autosomal dominant trait, what two genotypes may an affected individual have? AA or Aa
a. What will always be true of one of the affected individual’s parents? One of the parents will
have the disease
18) For a recessive sex-linked trait, which sex is affected more often? Males
a. So which pedigree symbol will be shaded more often for a recessive-sex linked trait? Squares
b. What are heterozygous females called? carriers
8-3 Continued…Dihybrid Punnett Squares
1) What is a dihybrid cross? A cross involving 2 contrasting traits
2) If R = round seeds, r = wrinkled seeds, Y = yellow seeds and y = green seeds, write the genotypes and
gametes formed for the following plants….
a. homozygous dominant for both seed shape and color
i. genotype  RRYY
ii. Gametes  F RY
O  RY
I  RY
L RY
b. heterozygous for both seed shape and color
i. genotype  RrYy
ii. Gametes  F RY
O  Ry
I  rY
L ry
c. homozygous recessive for both seed shape and color
i. genotype  rryy
ii. Gametes  F ry
O  ry
I ry
L ry
d. heterozygous for seed shape, but homozygous recessive for seed color
i. genotype  Rryy
ii. Gametes  F Ry
O  Ry
I  ry
L ry
3) Create a dihybrid punnett square that crosses two plants that are heterozygous for seed shape but
homozygous recessive for seed color (#2d above)
Rryy*Rryy
Ry
Ry
ry
ry
Ry
Ry
RRyy
RRyy
RRyy
Rryy
Rryy
ry
Rryy
ry
Rryy
Rryy
Rryy
rryy
rryy
rryy
rryy
RRyy
Rryy
Rryy
Genotype ratio: 4 RRyy: 8 Rryy: 4 rryy
a. Phenotype ratio? 12 round green: 4 wrinkled green
b. What is the probability that an offspring from the cross will inherit wrinkled and green seeds?
i. 4/12 or 1/3
c. What is the probability that an offspring from the cross will inherit wrinkled and yellow seeds?
i. 0/16
4) When individuals heterozygous for two traits are crossed, what ratio is always produced by a dihybrid
punnett square?
a. 9 Dominant/Dominant: 3 Dominant/ Recessive: 3 recessive/ dominant: 1 recessive/recessive
b. 9:3:3:1
8-4 Complex Patterns of Heredity
1) What is polygenic inheritance? When inheritance of 1 trait is controlled by 2 or more different
genes
a. What are some examples of human traits that are governed by polygenic inheritance?
i. Hair color
ii. Eye color
iii. Skin color
iv. Height
v. weight
b. If graphed, what kind of pattern does polygenic inheritance display…what does this pattern
indicate?
i. All polygenic traits display a bell shaped curve. For example
2) What happens to a heterozygous offspring as a result of incomplete dominance? They have a
phenotype different from both parents
a. Relate this to flower color in snapdragons  a red flower crossed with a white flower would
make pink flowers
3) What happens to a heterozygous offspring as a result of codominance? The heterozygous offspring
express BOTH parental phenotypes
a. Relate this to feather color in chickens.  a black chicken crossed with a white chicken has
black & white checkered offspring
4) Describe multiple allelic inheritance. This is when there are 3 or more alleles for a given trait
a. What are the three alleles that govern the ABO blood types?
IA
IB
i
5) Write down the genotype that will determine the following phenotypes.
a.
b.
c.
d.
Blood type A  IA IA or IA i
Blood type B IB IB or IB i
Blood type AB IA IB
Blood type O ii
6) Why is blood type O- considered a universal donor? Because type O blood does not have any surface
markers (antigens) that would be recognized by a persons immune system, so anybody with any
blood type can receive this blood type in a transfusion
7) Why is blood type AB+ considered a universal acceptor? Because people with AB+ makes all surface
markers (antigens) naturally, their immune system recognizes them as “self” and does not launch
an attack against any of the markers. Therefore, these people can receive blood from any other
blood type.
8) Why is blood type AB an example of codominance? Because heterozygotes express both the A and B
markers, and so show both parental phenotypes
9) Create a Punnett square crossing a female with blood type O and a male homozygous dominant for
blood type B.
IB
IB
i
IB i
IB i
i
IB i
IB i
a. Possible blood type of offspring? All the offspring will be heterozygous for type B blood
10) Create a Punnett square crossing a female with blood type O and a male heterozygous for blood type B.
IB
i
i
IB i
ii
I
IB i
ii
a. Possible blood types offspring? 50% will have type B blood and 50% will have type O
11) What kind of alleles, dominant or recessive, are responsible for most genetic disorders?
12) The alleles associated with genetic diseases produce ___defective____ proteins.
13) Identify the symptoms of the following genetic disorders…
a. Cystic fibrosis: accumulation of thick mucus in the lungs, liver, pancreas, and intestines
making it hard to breath and causing individuals to be malnourished eventually leading to
premature death (most common in Caucasians)
b. Tay Sach’s disease: nervous system, especially the brain, breaks down causing paralysis,
blindness, and death (most common in Jewish populations)
c. Sickle Cell anemia: Red Blood cells take on a sickle shaped appearance and aren’t able to
carry oxygen as well. This leads to tissue damage, clogging and rupture of blood vessels,
and premature death (most common in African Americans and Africans)
d. Hemophilia: Blood doesn’t clot (most common in boys)
e. Huntington’s disease: the nervous system breaks down initially causing slurred speech,
irritability, and forgetfulness and eventually causing muscle spasms, paralysis, and death.
Symptoms start between the age of 30-40
14) Why is sickle cell disease also an example of codominance…what benefit do heterozygotes have?
a. Heterozygotes have both normal hemoglobin and sickle hemoglobin
15) Which disease above is caused by a dominant allele? Huntingtons disease
a. Why is it so easily passed on in families? Because symptoms don’t start until later in life (3040 yrs old) so most people have already had children
16) Analyze the following disease and determine why their inheritance pattern is different from a disease
like cystic fibrosis or hemophilia.
a. Down syndrome- Trisomy 21
b. Klinefelter’s syndrome – XXY
c. Turner syndrome – X0 (missing X chromosome in females)
All of the above diseases are due to incorrect chromosome numbers. Diseases like cystic
fibrosis and hemophelia, however, are due to mutations in the DNA sequence
17) How can genetic testing and counseling help the following individuals…
a. An infant with PKU? They can help determine a diet that keeps the child healthy
A couple in which one member has Huntington’s disease? They can help them determine the
likelihood of passing the Disease onto a a child so they can decide if they want to have children
18) What does gene therapy involve? Replacing a defective gene with a healthy one
19) How is recombinant DNA formed? Using a restriction enzyme to cut out a copy of the healthy gene
and put it into a vector
20) Why does the virus named AAV seem to be a good candidate for use in gene therapy? Because its not
easily recognized by the immune system and doesn’t cause disease