Genetics
Genetics
1. What is a chromosome?
A threadlike structure of DNA
and protein that contains
genetic information.
2. Where are chromosomes located?
In eukaryotes chromosomes
are found in the nucleus; in
prokaryotes, they are found
in the cytoplasm
Chromosomes
Genetics
3. What are genes?
Special sequences of
DNA that codes for a
protein and thus
determines a trait.
4. Where are genes found?
Genes are found on
chromosomes.
Genetics
5. What is genetics?
Genetics is the
scientific study
of heredity.
6. Who is considered the
father of genetics?
Gregor Mendel, an
Austrian monk
Mendel’s paper
on genetics
1865
Genetics
7. What kind of organism did Mendel study?
Mendel studied
pea plants
8. What are some of the
traits that Mendel studied?
Seed color and shape;
Pod color and shape;
Flower color and position
Genetics
9. What is an allele?
An allele is one of a number of
different forms of a gene.
Purple
flower
allele
White
flower
allele
For example, the gene for flower
color in peas has two alleles—
purple (P) and white (p).
And the gene for seed pod color
has two alleles—Green (G) and
yellow (g).
Green
Seed Pod
allele
Yellow
Seed Pod
allele
Genetics
10. What is meant by Mendelian
Genetics?
Any traits that are controlled by
a single gene. For example,
flower color is controlled by a
single gene that has two alleles.
11. What is a locus?
The specific location of a
gene on a chromosome.
Locus for
Flower Color
Gene
Locus for
Pod Color
Gene
Genetics
12. What is a true breeding plant?
True breeding plants always
make offspring identical to
themselves. For example,
white flower plants always
produce white flower offspring.
Parents
Offspring
Parents
And purple flower plants
always produce purple
flower offspring.
Offspring
Genetics
13. What is the universal symbol for a male
and female?
Male
Female
14. How many alleles for a single
gene can an organism have? Parents
Two. Offspring inherit one
Alleles P P
allele from the male parent
and the other allele from the
Offspring
female parent. Click once for animation
PP
Genetics
15. State Mendel’s Principle of Dominance?
This principle states that
some alleles are dominant
and others are recessive.
For example, a plant that has a
purple allele (P) and a white
allele (p) will have purple
flowers. This is because the
purple allele is dominant over
the white allele.
Dominant
color
(purple)
Pp
Dominant
allele
(purple)
Recessive
allele
(white)
Genetics
16. Define genotype?
The genotype is the genetic makeup
of an organism. For example, the
possible genotypes for a purple
flower could be PP or Pp.
17. Define phenotype?
The phenotype is the physical
characteristic of an organism. For
example, the phenotype of the
flower shown at right is white.
Genetics
18. Identify the genotype for each flower shown below?
Genotypes =
19. What is the phenotype of each flower?
Phenotypes =
Pp
Purple
PP
Purple
pp
White
Genetics
20. What is a hybrid?
A hybrid is an organism that has two
different alleles for a particular gene.
21. Which of the following is a hybrid?
Pp
Hybrid plant
PP
pp
True breeding plants
Genetics
22. What does homozygous mean
Homo- means “same” and -zygous means “pair.”
Homozygous refers to the fact that two alleles
for a gene are the same. For example
PP
or
pp
23. What does heterozygous mean
Hetero- means “different. Heterozygous refers to
the fact that two alleles for a gene are different.
For example, Pp.
Genetics
24. Match the flower genotypes on the left to the
terms on the right.
Pp
Homozygous recessive
PP
Heterozygous
pp
Homozygous dominant
Genetics
25. How do the alleles get from parents to offspring?
The chromosomes the alleles
reside on are packaged in gametes
(sex cells), like egg and sperm.
When egg and sperm meet,
fertilization occurs, making a
new cell called a zygote.
Egg
Sperm
Fertilization
The zygote will divide by mitosis
and develop into an embryo.
Embryo
Genetics
26. Draw a Punnett square for
the following hybrid cross:
Pp x Pp
a. Since this is a monohybrid
cross, you should have
drawn a 2 x 2 Punnett square.
Genetics
26. Draw a Punnett square for
the following hybrid cross:
Pp x Pp
b. Next, you should have
written the parent
genotypes above the
Punnett square.
Genetics
26. Draw a Punnett square for
the following hybrid cross:
c. Then you should have
placed the sex symbols
on the Punnett square.
Pp x Pp
Genetics
Pp x Pp
26. Draw a Punnett square for
the following hybrid cross:
P
d. After the sex symbols, you
were to determine the
alleles for the sperm and eggs.
P
p
p
Genetics
Pp x Pp
26. Draw a Punnett square for
the following hybrid cross:
e. Finally, you should have
combined the alleles of the
gametes to form zygotes
P
p
P
PP
Pp
p
Pp
pp
Genetics
Punnett Square Review
Pp x Pp
27. Draw squares around the
alleles of the parents
28. Draw ovals around those
alleles found in sperm
29. Draw circles around those
alleles found in eggs.
30. Draw diamonds around the
alleles of the offspring.
P
p
P
PP
Pp
p
Pp
pp
Genetics
Punnett Square Review
Pp x Pp
31. Circle the homozygous
dominant offspring.
32. Put squares around the
heterozygous offspring.
33. Draw a diamond around
the homozygous recessive
offspring.
P
p
P
PP
Pp
p
Pp
pp
Genetics
Punnett Square Review
Pp x Pp
34. Circle the purebred
offspring.
35. Put diamonds around
the hybrid offspring.
36. Why is this called a
monohybrid cross?
P
p
P
PP
Pp
p
Pp
pp
Mono- means “one.” Hybrid refers to having different
alleles for the same gene. Since the cross deals with
only one character (mono-) and each parent is a hybrid,
the cross is described as monohybrid.
Genetics
Punnett Square Review
Pp x Pp
37. What is the genotypic ratio
of the offspring?
PP
1
:
:
Pp
2
:
:
pp
1
38. What is the phenotypic
ratio of the offspring?
Purple
3
:
:
White
1
P
p
P
PP
Pp
p
Pp
pp
Genetics
39. State Mendel’s Principle of Segregation.
Allele pairs separate during gamete formation.
Gametes
Germ cell
Meiosis
Genetics
40. State Mendel’s Principle of Independent
Assortment.
Allele pairs for different traits separate independently
during gamete formation.
Germ cell
Gametes
1
Chromosome
alignment A
2
or
3
Chromosome
alignment B
4
Four
different
types of
gametes
Genetics
41. Study the table below for a pattern. What number
do you think goes in the last space? (Assume genes are on
separate chromosomes and sort independently)
Genotype
Possible number of
unique gametes
1 gene
Aa
2
2 genes
AaBb
4
3 genes
AaBbCc
8
4 genes
AaBbCcDd
16
5 genes
AaBbCcDdEe
32
The formula for
calculating the
number of
possible gametes
is 2n, where 2
equals the
number of
different alleles
and n is the
number of genes.
Genetics
42. Humans have 23 sets of chromosomes. How many
different ways could these chromosomes sort
independently?
Hint: You would use the same formula as was
done for alleles and genes (2n). However, this time
n represents the number of chromosome sets.
2n = 223 = 8,388,608 different combinations
Genetics
43. Draw a Punnett square for
the following dihybrid cross:
AaRr x AaRr
ar
Ar
aR
AR
AARR
AARr
AaRr
AaRr
Ar
AARr
AArr
AaRr
AArr
aR
AaRR
AaRr
aaRR
aaRr
ar
AaRr
Aarr
aaRr
aarr
AR
Since this is a dihybrid
cross, you should have
drawn a 4 x 4 Punnett
square. Each parent will
also be able to produce
4 different kinds of
gametes.
Genetics
44. What is the genotypic frequency of this dihybrid
cross?
AaRr x AaRr
AR
Ar
aR
ar
AR
AARR
AARr
AaRr
AaRr
Ar
AARr
AArr
AaRr
AArr
aR
AaRR
AaRr
aaRR
aaRr
ar
AaRr
Aarr
aaRr
aarr
Genotype Frequency
AARR
1/16
AARr
2/16
AArr
2/16
AaRR
1/16
AaRr
5/16
Aarr
1/16
aaRR
1/16
aaRr
2/16
aarr
1/16
Genetics
45. What is the phenotypic frequency of this dihybrid
A = Axial flowers
R = Round seeds
cross?
A = Terminal flowers r = Wrinkled seeds
AaRr x AaRr
AR
AR
Ar
AARR
AARr
Ar
aR
AARr
AaRr
AArr
AaRr
ar
AaRr
AArr
aR
AaRR
AaRr
aaRR
aaRr
ar
AaRr
Aarr
aaRr
aarr
Phenotype
Frequency
Axial, Round
9/16
Axial, Wrinkled
3/16
Terminal, Round
3/16
Terminal, Wrinkled
1/16