Name _________________________________________ Class ________ Date ____________
Biology 9
ANSWERS!
Mendelian Genetics Review Packet
Part I: Genotypes & Phenotypes
1. Trait: Pinky shape
Alleles: Bent pinky is dominant (B)
Straight pinky is recessive (b)
Fill in the chart with the correct genotype or phenotype.
Genotype
BB
Phenotype
bent pinky
Bb
BENT PINKY
bb
STRAIGHT PINKY
bb
straight pinky
BB or Bb
bent pinky
2. Trait: Ear lobes
Alleles: Free earlobes (un-attached) is dominant (A)
Attached earlobes is recessive (a)
Fill in the chart with the correct genotype or phenotype.
Genotype
AA
Phenotype
FREE
aa
ATTACHED
Aa
FREE
AA or Aa
free earlobes
aa
attached earlobes
3. Fill in the blanks with DOMINANT or RECESSIVE.
If a person has two copies of the dominant gene, they show the DOMINANT phenotype.
If a person has one copy of the dominant gene and one copy of the recessive gene, they
show the DOMINANT phenotype.
If a person has two copies of the recessive gene, they show the RECESSIVE phenotype.
4. If a person shows the recessive phenotype for a trait, their genotype could be… (circle one
or more)
AA
Aa
aa
If a person shows the dominant phenotype for a trait, their genotype could be… (circle one
or more)
AA
Aa
aa
5. If a person is homozygous dominant, their genotype is AA
6. If a person is homozygous recessive, their genotype is aa
7. If a person is heterozygous, their genotype is Aa and they show the DOMINANT
phenotype.
Check your answers before moving on to Part II!
Part II: Genetics Vocabulary Review
Match the definitions with the words.
dominant
recessive
homozygous
brown hair
alleles
phenotype
Aa
heterozygous
genotype
gene
Word
GENOTYPE
Definition
PHENOTYPE
An organism’s physical characteristics and exhibited traits
Aa
An example of a genotype
The genetic make-up, or combination of alleles, that an organism has
HETEROZYGOUS A genotype that has two different alleles
HOMOZYGOUS
A genotype that has two of the same alleles
BROWN HAIR
An example of a phenotype
DOMINANT
An allele that always shows up (is expressed as a trait) if it is present
An allele that only shows up if no dominant alleles are present (it can be hidden
by a dominant allele)
A section of genetic material (DNA) that holds instructions for one protein or
trait
RECESSIVE
GENE
Different versions of a gene (example: brown eyes vs. blue eyes)
ALLELE
More Words, More Practice:
zygote
gamete
meiosis fertilization
mitosis
Mendel’s Law of Segregation
homologous chromosomes
46
23
Mendel’s Law of Independent Assortment
Word
GAMETE
Definition
FERTILIZATION
The process in which an egg and sperm join together
ZYGOTE
MEIOSIS
A fertilized egg cell that will grow and develop into an offspring
The process of cell division that creates two new cells identical to the
original one; used for growth and repair of tissues
The process of cell division that creates 4 gametes with half the number of
chromosomes as the original cell
46
The number of chromosomes in all human cells except eggs and sperm
23
The number of chromosomes in human egg and sperm cells
Every organism has two alleles for each gene. During meiosis, these
alleles separate into gametes, so every gamete has one allele for each
gene.
During meiosis, alleles for different genes are put into gametes in every
possible combination (Ex: from AaBb, gametes could be AB, Ab, aB, or ab)
MITOSIS
LAW OF
SEGREGATION
LAW OF INDEP.
ASSORTMENT
HOMOLOGOUS
CHROMOSOMES
An egg cell or a sperm cell
A pair of chromosomes that are the same size and shape, and carry the
same genes but not necessarily the same alleles.
Check your answers before moving on to Part III!
Part III: Monohybrid Crosses
(if you are up for a challenge, then skip right to Question 2)
1. In aliens, a certain gene controls the size of the eyes. The allele for bulging eyes (B) is dominant
over the allele for small eyes (b).
Larry is an alien who is heterozygous for the eye gene.
Larry’s genotype is Bb
Larry’s phenotype is bulging eyes
Mary is an alien who is homozygous recessive for the eye gene.
Mary’s genotype is bb
Mary’s phenotype is small eyes
If Larry and Mary have an alien-baby…
Draw a Punnett Square:
b
b
B
Bb
Bb
b
bb
bb
What is the probability that their baby will have bulging eyes? ½ or 50%
2. Challenge Question: In guinea pigs, rough coat (R) is dominant over smooth coat (r). A
homozygous dominant guinea pig is mated with a smooth guinea pig.
a) What is the probability that an offspring will have a rough coat? Show your work
below:
homozygous dominant = RR
smooth guinea pig = rr
R
R
r Rr Rr
r
Rr Rr
b) If two of the offspring mate together to produce a second (F2) generation of offspring,
what is the probability that an F2 offspring would have… (show work below)
A rough coat? ¾ or 75%
Rr x Rr
A smooth coat? ¼ or 25%
R
r
R
r
RR Rr
Rr
rr
Check your answers before moving on to Part IV!
Part IV: Dihybrid Crosses
(if you are up for a challenge, then skip to Question 4)
3. In aliens, a certain gene controls antennae – having antennae (A) is dominant over no antennae (a).
Recall from the previous worksheet that there is also an alien gene for eye size: the allele for
bulging eyes (B) is dominant over the allele for small eyes (b).
a) Consider this cross:
AaBb x AaBb
List the gametes that each alien could make: AB, Ab, aB, ab
Draw a Punnett Square:
AB
Ab
aB
ab
AB
Ab
AABB AABb
AABb AAbb
AaBB AaBb
AaBb Aabb
aB
AaBB
AaBb
aaBB
aaBb
ab
AaBb
Aabb
aaBb
aabb
What is the probability of having a baby with the genotype AaBb? 4/16 = ¼ or 25%
What is the probability of having a baby with no antennae and bulging eyes?
Genotype will be aaBB or aaBb = 3/16
4. Challenge Question: Larry the alien is heterozygous for both antennae and eye size.
Mary the alien is heterozygous for antennae and homozygous recessive for eye size.
What is the probability that they will have a baby with no antennae and small eyes? Show
your work…
Larry = AaBb
Larry’s gametes = AB, Ab, aB, ab
Mary = Aabb
Mary’s gametes = Ab, ab
Ab
ab
AB
Ab
aB
ab
AABb AAbb AaBb Aabb
AaBb Aabb aaBb aabb
Baby with no antennae and small eyes = aabb = 1/8
Check your answers… if you feel 100% confident about everything in this packet,
get a set of Extention Problems!