Study Guide for Genetics Test
1. Where do the alleles of the offspring come from?
Hint: 1 from Mom and 1 from Dad
2. How would you write a dominant allele? What does dominant mean?
With a capital letter, the dominant trait is the one that is shown, stronger.
3. How would you write a recessive allele? What does recessive mean?
With a lower case letter, the recessive trait is hidden when a dominant
one is present.
4. If a person has 1 allele for dimples and 1 for no dimples, what trait will show up?
The dominant trait for dimples will show up.
5. Write the 2 alleles for homozygous dominant. For heterozygous. For homozygous recessive. (Use
whatever letter you would like)
DD is homozygous dominant, Dd is heterozygous and dd is homozygous
recessive.
6.
Can a person with no dimples ever be heterozygous? Why or why not? (Remember…dimples is
dominant and no dimples is recessive)
They cannot be heterozygous because the dominant allele will be shown
so they will have dimples.
Define:
7. Phenotype – physical
8. Genotype –
appearance like dimples, brown hair, or A blood
genes or alleles for a trait, like Dd or AA (we use letters)
9. Homozygous – same
form of the trait like DD or dd
10. Heterozygous – different
forms of the trait like Dd
11. Co-dominance – when
two traits are dominant like A and B in blood types are
both dominant so a person with genes AB will have AB blood.
12. When you flip a coin, and you got a heads the first time, does that mean that you have less of a chance
of getting a heads they second time? Why or why not?
Each time you flip a coin you still have a 50 % chance of getting either
heads or tails. What happens the first time does not influence what
happens during later events.
13. Give an example of a phenotype and a genotype.
Phenotype = freckles
genotype = Ff
t = CAN’T taste PTC
14. T = CAN taste PTC
a.
b.
c.
d.
e.
T
t
T
TT
Tt
t
Tt
tt
Tt x
Tt
What is the probability of TT? 25%
What is the probability of Tt? 50%
What is the probability of tt?
25%
What is the probability you can taste PTC? 75%
What is the probability you can’t taste PTC? 25%
15. Cross an AB blood type mother with a homozygous B blood type father:
A
B
AB x B
B
B
a)
b)
c)
d)
e)
AB
BB
AB
BB
What blood type(s) do the offspring have?
AB and B blood
Are the offspring heterozygous or homozygous? 50 % heterozygous and 50% homozygous
Are the parents homozygous or heterozygous? AB heterozygous and B homozygous
What is the co-dominance? When two traits are both dominant they both show
Which blood type shows co-dominance? AB shows co-dominance
16. Make a Punnet square for dimples crossing
D = Dimples
d = no dimples
a)
b)
c)
d)
e)
D
D
d
Dd
Dd
d
Dd
Dd
DD x dd
What is the probability of a person having dimples? 100%
What is the probability of a person having no dimples? 0 %
What is the probability of a person being DD? 0 %
What is the probability of a person being Dd? 100 %
What is the probability of a person being dd? 0 %
18. How many chromosomes do humans have in each body cell?
Humans have 46 chromosomes
19. How many pairs of chromosomes do humans have in each body cell?
Humans have 23 pairs of chromosomes
20. How many chromosomes are in human sex cells? (I.E. Sperm and Egg cells)
In human sex cell there are 23 chromosomes for egg and 23 for sperm
𝟏
( from each parent)
𝟐
21. Write the symbols for the chromosomes that these people have: Men:
`
22. Which chromosome is smaller, X or Y?
XY
Women:
XX
The Y chromosome is smaller than the X chromosome.
23. All eggs carry an
X chromosome.
24. ½ the sperm carry an X chromosome and the other ½ carry a Y
25. Explain the difference between identical and fraternal twins. Use a diagram if helpful.
Identical twins = 1 egg & 1 sperm = splits into 2 babies = same gender
Fraternal twins = 2 eggs & 2 sperm = 2 separate babies = can be different
genders
26. List 3 characteristics that are inherited.
1) natural hair and eye color
2) cleft chin
3) dimples
27. List 3 characteristics that are acquired.
1) ear piercing
2) reading and speaking
3) scars or tattoos
28. Explain the difference between acquired and inherited traits.
Inherited traits are the ones you are born with that come from genes from
your parents.
Acquired traits are the ones you learn or practice or get after you are born
from the environment.