Pattern Of Inheritance
Review
Define the Following
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Gene
Alleles
Locus
Homozygous
Heterozygous
Dominant
Recessive
Phenotype
Genotype
Monohybrid cros
Definition
• A. gene - the unit of heredity; a section of DNA sequence encoding
a single protein
B. alleles - two genes that occupy the same position on homologous
chromosomes and cover the same trait
C. locus - a fixed location on a strand of DNA where a gene or one
of its alleles is located
D. homozygous - having identical genes (one from each parent) for
a particular characteristic
E. heterozygous - having two different genes for a particular
characteristic
F. dominant - the trait that appears in the heterozygous condition
G. recessive - the trait that is masked in the heterozygous condition
H. phenotype - appearance
I. genotype - genetic makeup
J. monohybrid cross - cross involving a single pair of genes, one trait
Useful Links
• http://www.life.umd.edu/classroom/bsci124/l
ec10.html
Which of the following is a
heterozygous genotype? (1 point)
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a) HHbb
• B) HH
• C) Hh
• D) hh
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• If black hair (B) is completely dominant over
brown hair (b), which of the following will
produce brown hair? (1 point)
A) BB
• B) Bb
• C) bb
• D) Both A and B
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In a plant, the tall characteristic (T) is dominant
over the short (t). In a monohybrid cross, two
tall plants produce 3 tall and 1 short offspring.
What are the genotypes of the parents?
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(A) TT, tt
(B) TT, Tt
(C) Tt, Tt
(D) tt, tt
With incomplete dominance, when a red flowered
plant is crossed with a white flowered plant, the
offspring will be
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(A) red
(B) pink
(C) white
(D) all of these
State the Laws of Mendel
• The inheritance of one pair of factors (genes)
is independent of the inheritance of the other
pair.
• Law of Independent assortment
The "father of genetics" is (1 point)
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Gregor Mendel.
Isaac Newton.
Carl Sagan.
Charles Darwin.
Hint: Think of a test cross
• Tongue rolling (the ability to roll your tongue) is a dominant
trait in humans. A woman who CAN roll her tongue is
married to a man who CANNOT roll his tongue. They have
four children, only two of whom CAN roll their tongues.
Which of the following describes the genotypes of the
parents (woman x man)? (1 point)
a) Rr x rr
• B) RR x rr
• C) Rr x RR
• D) Rr x Rr
• What are the chances of a child being
homozygous recessive for a trait if both parents
are heterozygous? (1 point)
a) 25%
• B) 50%
• C) 75%
• D) 100%
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• Which of the following crosses will only
produce homozygous recessive offspring?
(1 point)
a) RRYY x RRYY
• B) RRYY x rryy
• C) RrYy x rryy
• D) rryy x rryy
• In leopard frogs, black spots (B) are dominant over
brown spots (b). A homozygous recessive male frog
mates with a heterozygous female frog. What
percentage of the offspring will have black spots?
(1 point)
a) 0%
• B) 25%
• C) 50%
• D) 100%
• In Australian Shepherds (a breed of dog), black fur (FB) is
codominant with white fur (FW). The heterozygous
phenotype is spotted fur--both black and white. A
homozygous male with black fur mates with a spotted
female. What percentage of the offspring from this cross
are expected to be white? (1 point)
a) 0%
• B) 25%
• C) 50%
• D) 75%
• Which of the following correctly lists all of the
possible gametes that could be produced by a
parent with the genotype BbNn? (1 point)
a) Bb, Nn
• B) BN, Bn
• C) BN, Bn, bb, nn
• D) BN, Bn, bN, bn
Pedigree analysis
Multiple alleles
• A man with blood type O marries a woman with blood
type A. All of there seven children have blood type A.
What is the woman's most likely genotype? (1 point)
a) IAIA
B) IAIB
c) IAi
d) ii
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• In pea plants, round peas (R) are dominant over
wrinkled peas (r). A cross between two plants yielded
the following results: ROUND: 148
WRINKLED: 51
• Based on this information, which of the following
crosses represents the most likely genotypes of the
parents? (1 point)
a) RR x RR
• b) RR x Rr
• C) Rr x Rr
• D) Rr x rr
• The sex-linked allele for colorblindness is located
on (1 point)
a) chromosome 21.
• B) the X chromosome only.
• C) the Y chromosome only.
• D) both the X chromosome and the Y
chromosome.
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• Colorblindness is more common in males than in females
because (1 point)
a) fathers pass the allele for colorblindness to their sons
only.
• B) the allele for colorblindness is located on the Y
chromosome.
• C) males who are colorblind have two copies of the allele
for colorblindness.
• D) the allele for colorblindness is recessive and located on
the X chromosome.
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• The genetic make up of an organism
_________
• The physical characteristics of on organism
_____
Practice Genetics Problems
• Solve the genetics problems in the following
slides based on the concepts of monohybrid
cross, dihybrid cross, incomplete dominance,
multiple alleles, sex-linked inheritance,
autosomal dominant and recessive
inheritance.
Genetic Problems
• Most individuals of a certain wild flower have white petals,
but a few are blue. Crosses have shown that the blue color
is due to a recessive allele. Use "W" for white and "w" for
blue.
• a. What is the genotype of a blue-flowered plant and what
gametes would it produce as a result of meiosis?
d. If a blue-flowered plant is crossed with its whiteflowered parent, what fraction of their offspring would
have the genotype "ww"?
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e. If two blue-flowered plants cross, what fraction of their
offspring will be blue? White?
Incomplete Dominance
• Four o'clocks exhibit incomplete dominance.
Thus, if a plant with red flowers is crossed
with a plant with white flowers, the offspring
will all produce pink flowers.
• What offspring would you expect if you
crossed a red-flowered plant with a pinkflowered plant?
Dihybrid Cross
• In peas, the gene for tall plants (T) is dominant
over the gene for dwarf plants (t) and round
seed (R) is dominant over wrinkled seed (r). If
one crosses a homozygous tall, wrinkledseeded plant with a homozygous dwarf,
round-seeded plant, what is the phenotype of
the F1? The genotype of the F1? The
phenotypic ratio of the F2?