Genetics Practice Questions:
1. Define the following Vocabulary Words:
 Fertilization –fusion of a haploid nucleus of an egg cell and a haploid nucleus of a sperm cell
 haploid-- a nucleus containing a single set of unpaired chromosomes (e.g. sperm and egg)
 diploid -- a nucleus containing a double set of unpaired chromosomes (e.g. sperm and egg)
 chromosomes -- chromosome is a thread of DNA, made up of a string of genes
 Test cross an individual that might be heterozygous or homozygous dominant is crossed with an individual
that is homozygous recessive
 Meiosis -- Define meiosis as reduction division in which the chromosome number is halved from
diploid to haploid (details of stages are not required)
 Gametes – haploid cells/ sex cells/ example: sperm and egg
 inheritance the transmission of genetic information from generation to generation
 phenotype -- • phenotype as the physical or other features of an organism due to both its genotype
and its environment (e.g. tall plant or green seed)
 genotype -- as genetic makeup of an organism in terms of the alleles present (e.g. Tt or GG)
 allele -- as any of two or more alternative forms of a gene
 gene -- as a length of DNA that is the unit of heredity and codes for a specific protein. A gene may be
copied and passed on to the next generation
 homozygous – homozygous as having two identical alleles of a particular gene (e.g. TT or gg). Two identical
homozygous individuals that breed together will be pure-breeding
 heterozygous - as having two different alleles of a particular gene (e.g. Tt or Gg), not pure-breeding
 recessive allele as an allele that is only expressed when there is no dominant allele of the gene
present (e.g. t or g)
 dominant allele -- as an allele that is expressed if it is present (e.g. T or G)
 co-dominant -- two alleles may be expressed in the phenotype at the same time. That is, NO allele is truly
dominant or recessive.
 Sex-linked gene -- a gene located on the sex chromosomes (usually the X chromosome)
 Non-sex-linked gene – a gene that is NOT located on the sex chromosome
 independent assortment -- genes on separate chromosomes will independently assort into different
gametes
1. How are a chromosome, DNA, and a gene interrelated. Draw a picture to support your answer.
Chromosomes are made of DNA, DNA are made of Genes.
2. Below Given the Haploid number of chromosomes write down the diploid number of chromosomes:
Haploid Number
Diploid Number
60
30
24
12
14
7
3. What type of cells have a haploid number?
Gametes/ Sex Cells/ Sperm and egg.
4. What type of cells have a diploid number? Non-sex cells/ example: skin cells, heart cells, muscle cells.
5. What type of cells a formed through the process of meiosis?
Gametes/ Sex Cells/ Sperm and egg..
6. How many chromosomes does human sperm cell contain?
23
.
7. Cross two heterozygous tall plants.
T=tall
t=short
i.
Write the cross described above. __Tt___X___Tt___
ii.
Draw a Punnett Square to represent the cross.
T
t
iii.
iv.
v.
T
TT
Tt
T
Tt
Tt
What percent of the offspring will be tall? __75% ________
If T= Tall plant and t= short plant what would be the phenotype for a heterozygous plant?
_______________Tt____
Organisms that have 2 identical genes such as TT or tt are said to be___Homozygous______________.
8. W=Widow’s peak, w=No widow’s peak
i.
What is the genotype for a person that is heterozygous? What is the phenotype?
a. Genotype ______Ww_____
b. Phenotype __ Widow’s peak __________
9. In corn, dark kernels are dominant to light. Show the cross between a heterozygous plant and a pure homozygous
dominant plant. Please include the following: the symbols, the cross, , the Punnet square, and the genotypic and
phenotypic ratios.
a. The symbols _D=dark d=light
b. The cross _ Dd x DD
c. The Punnet square:
D
D
D
DD
DD
d
Dd
Dd
d. What percent are dark? 100%
10. In rabbits, brown fur is dominant to white fur and long ears are dominant to short. Cross two brown long-eared
rabbit that are heterozygous for both traits. Include the following: the symbols, the cross, the Punnet square, and
the phenotypes of the offspring.
a. The symbols _B=brown b= white; L=long l= short
b. The cross __BbLl x BbLl__________
c. The Punnet square:
BL
Bl
bL
bl
BL
BBLL
BBLl
BbLL
BbLl
Bl
BBLl
BBll
BbLl
Bbll
bL
BbLL
BBLl
BbLL
bbLl
bl
BbLl
Bbll
bbLl
bbll
d. The phenotypes: 9 brown long: 3 brown short: 3 white Long: 1 short white
.
11. Hemophilia is a sex-linked trait. Write the cross for a hemophiliac man and a woman that is a carrier.
a. The Cross:_XhY x XHXh__
b. Make the punnet square:
H
X
Xh
Xh
XH Xh
Xh Xh
Y
XH Y
XhY
c. What percent of the males do you expect to be hemophiliacs? _50%__
d. What percent of the females do you expect to be hemophiliacs? _50%____
e. What percent of the females do you expect to be carriers? ___50%_____
Pedigree Practice
12. Which members of the family above are afflicted with Huntington’s Disease?
I-1, II-2, II-3, II-7, III-3
**
13. There are no carriers for Huntington’s Disease- you either have it or you don’t. With this in mind, is Huntington’s
disease caused by a dominant or recessive trait? **
DOMINANT
14. How many children did individuals I-1 and I-2 have? **
SIX= 6
15. How many girls did II-1 and II-2 have?
2** How many have Huntington’s Disease? 1
16. The pedigree to the above shows the passing on of Hitchhiker’s Thumb in a family. Is this trait dominant or
recessive? **
Recessive
17. How do you know? **
you know because III-4 & III-5 both don’t have hitchhikers thumb, but they both pass it on to their children (IV-2
and IV-4) Thus they both must carry the allele,but they don’t show it because it is recessive
18. How are individuals III-4 and III-5 related? **
III-4 is III-5 are cousins
19. Name 2 individuals that have hitchhiker’s thumb. **
IV-2 & IV-4
20. Name 2 individuals that were carriers of
hitchhiker’s thumb. ** III-4 & III-5
21. Is it possible for individual IV-3 to be a carrier? Yes *Why? She could have inherited the recessive allele from her
mother or father.
22. The pedigree to the above shows the passing on of colorblindness. What sex can ONLY be carriers of
a. colorblindness? **
FEMALES
23. Why does individual IV-7 have colorblindness? **
She inherited the recessive allele from both her mother and father.
24. Why do all the daughters in generation II carry the colorblind
gene? **
Because they all inherit an X chromosome from their dad and his X
chromosome contains the allele for color blindness
25. List 2 IV generation colorblind males. **
IV-1, IV-5
26. What is a test cross? Select the best answer below:
A.
Crossing a possible heterozygote with a homozygous recessive
B.
Any genetic cross to determine genotype
C.
Crossing a possible homozygote with a homozygous dominant
D.
Crossing a possible heterozygote with another heterozygote
27. A parent organism of unknown genotype is mated in a test cross. Half of the offspring have the same phenotype as the
parent. What can be concluded from this result?
A.
The parent is homozygous dominant for the trait.
B.
The trait being inherited is polygenic.
C.
The parent is heterozygous for the trait.
D.
The parent is homozygous recessive for the trait.
28. A woman has a heterozygous genotype for blood group B. She is expecting a baby with a man who is
homozygous Group A. What are the possible blood groups for their baby? SHOW YOUR WORK/ PUNNET
SQUARE (genetic diagram)
Symbols: IB = Type B i = Type O IA = Type A
Cross: IB i X IA IA
A
I
IA
IB
IA IB
IA IB
i
IAi
IAi
Type A or Type AB
29. If a man has blood group O and a woman has blood group AB, what is the probability that their child will be
blood group O? SHOW YOUR WORK/ PUNNET SQUARE (Genetic Diagram)
Symbols: IB = Type B i = Type O IA = Type A
Cross: i i X IA IB
IA
IB
i
IA i
IB i
i
IAi
IBi
0% of their children can become type O blood