Pre-AP Genetics Review
KEY
1. What is a trait?
A characteristic an organism has such as hair color
(inherited) or riding a bike (learned)
2. What is a dominant trait?
The stronger trait that masks the other (hides) represented
by a capital letter in the genotype. Example T=tall
3. What is a recessive trait?
The weaker trait that is masked by the other (hidden)
represented with a lower case letter in the genotype.
Example t= short
4. What is a genotype?
The genetic makeup of an organism; each trait is
represented by 2 alleles in the genotype. Example Tt not
visible, what’s inside
5. What is a phenotype?
The physical appearance or action that can be observed in
an organism. Example rolling your tongue or tall plant
6. If blue eyes are dominant to green eyes, what genotypes
would give someone blue eyes? What genotypes would give
someone green eyes?
B=blue b=green
BB =blue Bb=blue bb=green
The only way to see the (green eyes) is homozygous
recessive genotype (bb).
7. How many genes do we have for each trait?
1 gene for each trait
8. How many alleles do we get for each trait from each parent?
Each gene is made of 2 alleles: one from mom and one from
dad.
For questions 9, 10, and 11, tall is dominant to short.
Tall=T short=t
9. What would a heterozygous genotype be? What would its
phenotype be?
Tt would be tall because it has at least one dominant allele
10. What would a homozygous dominant genotype be? What
would its phenotype be?
TT would be tall because it has at least one dominant allele
11. What would the homozygous recessive genotype be? What
would its phenotype be?
tt would be short because there is no dominant allele
12.What is the difference between a purebred and a hybrid?
Purebred genotypes has either two dominant or two
recessive alleles (TT or Tt=homozygous), hybrid genotypes
have one dominant and one recessive allele (tt=heterozygous)
13.Why do we use a Punnett square in genetics?
To predict the probability of offspring traits (genotypes and
phenotypes from 2 parents –sexual reproduction
14. Determine the probability that two parents who are
heterozygous for eye color will have a blue-eyed child.
Brown eyes are dominant to blue eyes.
Brown=B blue=b
Bb X Bb
Genotypes
BB=25%
Bb=50%
bb=25%
Phenotypes
Brown
Blue
there is a 25% chance of blue
eyes in the offspring
15.A homozygous black rabbit is crossed with a heterozygous
white rabbit. White is dominant to black. Set up the
Punnett square cross. Show all your work. Then use the
Punnett square to fill out the genotypes and phenotypes, and
probability of each. Don’t forget the KEY.
White=W
w
w
Black=w
W
Ww
Ww
w
ww
ww
Ww X ww
Genotypes:
Ww
50%
ww 50%
Phenotypes: white 50%
black =50%
16. What are the base pairs in DNA and how do they go
together?
Adenine-Thymine (A-T) and Cytosine-Guanine (C-G)
17. Where is DNA found in an organism?
In the nucleus of a cell wrapped into a chromosome
18. What is the function of DNA?
It encodes information needed to create and direct the
chemicals that produce the diversity of living organisms
19. What does DNA look like? Make a sketch in the space
below (hint: how did we make the ladder).
Sugar and phosphate sides to the ladder and base pair rungs
This ladder shape is then twisted
.
20. Compare and contrast asexual and sexual reproduction.
Include 2-3 facts about each one and 2 examples of each.
asexual reproduction
sexual reproduction
one parent
two parents (egg and sperm)
identical (replica of parent)
more diversity in offspring
faster
more time invested in offspring
21. What are the levels of organization from organism to gene?
Organism-organ system-organ-tissue-cell-nucleus-chromosomedna-gene
22. Red coat color in cattle is codominant with white coat color.
Roan cattle show both characteristics. What are the
genotypes of:
a. a red cow: RR
b. a roan cow: RW
c. a white cow: WW
Cross two roan cattle and list the genotype and phenotype
results for the offspring.
R
R
RR
W
RW
W
RW
WW
RR: 25%
RW: 50%
WW: 25%
Red: 25%
Roan: 50%
White:25%
23. White color and black color are both dominant in sheep. A
grey sheep is the result of a hybrid of these two. Make a
key to show the genotypes. Cross a grey sheep with a white
sheep.
B- Black Sheep
W
B
W
W
BW
BW
WW
WW
W- White Sheep
BW- Grey sheep
BW x WW
24. What is the difference between how you get a contagious
disease compared to a genetic disorder?
You get contagious diseases such as the flu, by coming in contact
with someone that has the disease. You come in contact with the
virus, bacteria, or whatever carries the “bug”. In a genetic
disorder, the problem is in the genetic makeup carried through
genes (chromosomes/dna) of the parents and inherited by the
offspring through their parents.