Download genetics: typical test questions

GENETICS: TYPICAL TEST QUESTIONS
[Look at the underlined words and select the word that correctly completes each statement by circling it.]
1. In mitosis/meiosis, the haploid / diploid parent cell undergoes a process in which one /two/ four cells are
produced that are smaller but identical to the parent cell. In mitosis/meiosis, the haploid /diploid parent cell
undergoes a process in which one /two / four cells are produced that are not identical to the parent cell.
Fill in the blanks:
2. Humans have ______23 Pairs of_____ chromosomes, __ 23_(half)__ of which are provided by the female and
_____23_(half)_ of which are provided by the male. Thus we get _two_ copies of every gene, which is why every
gene has ___two_____ alleles.
3. In humans, chromosome pair # 23 are the sex chromosomes because it is the pair that determines weather a
child will be male or female. In males, the chromosome pair is identified as: ___Xy________; in females, as
_____XX_____.
Matching. Match the phrase in the column on the left with the correct word(s) in the column on the right. Write
the letter to the left on the number on this paper.
4._ I Outward appearance on inherited traits
A. incomplete dominance
5.__E
B. meiosis
Variations of a gene that can be passed on
6.__L Both alleles phenotypes are seen individually in the organism C. gene
7.__F The allele whose phenotype is expressed in heterozygous individuals
D. trait
8.__N When a person has two different alleles controlling a trait
E. allele
9.__M Pair of identical alleles
F. dominant
10._O The first generation produced in a breeding experiment
G. recessive
11._H
H. genotype
The genetic makeup of an individual
12._G The form of a trait that is not seen in heterozygous individuals
I. Phenotype
13.__J The passing of traits from parents to the offspring
J. heredity
14._A Both alleles blend together to create a phenotype
K. genetics
15._K The study of how genotypes affect phenotypes in organisms L. codominance
M. homozygous
N. heterozygous
O. F1 Generation
MULTIPLE CHOICE. Choose the single, best answer to complete each question and circle it.
16. In a Punnett square a capital letter (like “T” or “E”) stands for which type of allele?
a. dominant
c. recessive
b. heterozygous
d. sex-linked
17. For every trait, there is at least one type of gene and ______ allele(s) that control that trait.
a. one
c.
four
b. two
d.
as many as eight
18. The combination Tt represents a ______ genotype.
a. heterozygous
c.
b. homozygous
d.
codominant
sex linked
19. Explain how genes are passed down from each parent to the off spring. Think back to your skittle lab.
Ans. Both Parents have 23 pairs of chromosomes. Those chromosomes carry our genes and those genes
determine what traits we outwardly show (phenotypes). Each chromosome pair has the same set of genes but the
version of each gene may differ (alleles). We receive one of each of Mom’s pairs of chromosomes, and one of
each of our Dad’s 23 pairs of chromosomes. (Look back at your notes when we drew out mitosis and meiosis with
colored pencils.) Some of the mom’s body cells go through Meiosis to create eggs that contain half a set of 23
chromosomes and the dad’s body cells go through meiosis to create sperm containing only ½ a set of chromosomes.
Therefore, when one of Mom’s eggs joins with one of Dad’s sperm, we have a new human with its own unique set of
23 chromosome pairs.
20. In the, “Bunny Evolution Lab”, why did the frequency of the dominant allele (F) increase even though the
amount of F alleles in the population remained the same after each generation.
Ans. The lab began with 50 F alleles (black beans) and 50 f alleles (white beans). Rabbits were born when mother
nature put two random alleles together. (She pulled two beans from the bag. This represents two possible alleles
that could end up together after two rabbits from the current population mated. Each rabbit provides one allele
from his sperm or egg.) Bunnies who were FF, or Ff had fur and bunnies who were ff did not have fur. Furless
bunnies died during the winters and thus the frequency of the f allele went down because the f alleles from the ff
bunnies were no longer able to be passed on the following spring during mating season (dead bunnies can’t pass on
genes). As the proportion of f alleles grew smaller the proportion of F alleles available during mating season
increased.
21. Brown hair and long eyelashes are examples of:
a.
alleles.
b.
phenotypes
c. genotypes.
d. genes.
22. According to the law of Incomplete Dominance, if red carnations (RR) are crossed with white carnations (WW),
the offspring will be:
a.
red.
c. pink
b.
white.
d. red and white
SHORT ANSWER. Complete sentences are not required. PTC tasting (T) is dominant over not tasting.
Dimples (D) are dominant over no dimples. Show Punnett in the blank space provided below each question.
23. Make a Punnett Square to show all possible combinations of offspring that could result from a parent who is
homozygous dominant for PTC tasting and a parent who is homozygous recessive for the same trait.
a.
What is the written (not abbreviated) genotype of the offspring? Tt
b.
List all possible phenotypes of the F1 generation. PTC tasting
TT x tt
t
t
T
Tt
Tt
T
Tt
Tt
24. Simple Dominance: Fill in the Punnett Square to show all possible combinations of offspring that could result
from two parents who are both heterozygous (hybrid) for dimples.
What percent of the offspring will have the same genotype as the parents?
a. What percent of the offspring will have the same phenotype as the parents? 75%
b. What fraction of the offspring will be homozygous recessive? 25%
c. What fraction of the offspring will have the ability to pass on the recessive trait? 75%
D
d
D
DD
Dd
d
Dd
dd
25. Incomplete Dominance: Black color (BB) is incompletely dominant over white (WW) in pig fur colors, resulting in
the color gray. Fill in the Punnett Square to show all possible combinations of offspring that could result from two
parents who are both gray.
a. List all possible genotypes and phenotypes in the resulting offspring. Geno (BB, BW, WW)
Pheno(Black, Gray, White)
b. What percent of the offspring will have the same phenotype as the parents? 50%
c. What fraction will be black? 25%
B
W
B
BB
BW
W
Bw
WW
26. Codominance: Explain the difference between incomplete dominance and codominance.
Give an example.
Codominance: Two alleles such as Red – R and White – W are expressed independently in the phenotype of
an individual that is heterozygous for that trait. If a flower that is RW – you would see red and white dots for
example. Incomplete Dominance yields a phenotype that is a mix of the two individual alleles. A flower that is RW
would have a pink phenotype in this case.
27. Two-Factor Cross: In pea plants, the “tall” allele is dominant over the short one, and yellow is dominant over
green. Cross two plants that are hybrid for both traits. Show the Punnett Below
(Review the Gene Interactions Hwk to find the correct punnett square and answers)
a. List all possible genotypes and phenotypes.
b. What is the ratio of resulting phenotypes? 9 Tall Yellow: 3 Tall green: 3 Short Yellow: 1 short green
c. What fraction of the offspring will be homozygous recessive for both traits? 1/16
d. What fraction of the offspring will be tall and yellow? 9/1
RrYy
RY
Ry
RY
Ry
rY
ry
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYy
F generation
2
rY
RrYY
RrYy
rrYY
ry
RrYy
Rryy
rrYy
rrYy
Figure 3. If the genes f or
two traits are not linked,
then they will undergo
independent assortment.
This results in new
combinations of the traits.
rryy
28. Sex-Linked Traits: Hemophilia is a sex-linked trait. Show a cross between a woman who is a carrier and a man
who has hemophilia. (Save this for test review day if you don’t know how to d this punnett.)
a. What percent of the female offspring will be carriers of the disease? 50%
b. What percent of the female offspring will have hemophilia? 50%
c. What percent of the male offspring will have hemophilia? 50%
h
X
y
XH
XH Xh
XH y
Xh
Xh Xh
Xh y
Emphasize that a carrier is a person who is heterozygous and thus does not HAVE the disease, but they are CARRYING the
disease as a recessive allele that can be passed down to their kids. A person who has the disease is not called a carrier. A male
either has the disease or does not have the disease because the disease is linked onto the X chromosome and males only have
one X chromosome.
29. Polygenetic Inheritance: Tail length in cats is determined by more than one gene. Show all possible offspring
resulting from the mating of an individual with an average length tail (AAbb) and an individual with a longer-thanaverage tail (aaBb).
No tail = AABB
Short tail = AaBB or AABb
Average tail = AaBb or AAbb or aaBB
Longer-than-average tail = Aabb or aaBb
Very long tail = aabb
a. What fraction of the offspring will have tails that are shorter than their parents’ tails? -0%
b. What fraction of the offspring will have the same genotype as the parent with the longerthan-average length tail? 0%
c. What fraction of the offspring will have the same phenotype as the parent with the longerthan average length tail? 1/2
P: AAbb x aaBb
Ab
Ab
Ab
Ab
aB
AaBb
ab
Aabb
aB
AaBb
ab
Aabb
30. DNA is composed of nitrogenous bases – adenine, thymine, guanine and cytosine – phosphate and sugar
(deoxyribose). It forms strands that link together in a predictable manner, forming a twisted ladder shape called a
double helix. If one side of the DNA strand is AGGTTAC, what is the nitrogenous base order for the
complementary strand?
S-A T-S
P
P
S-G C-S
P
P
S-G C-S
P
P
S-T A-S
P
P
S-T A-S
P
P
S-A T-S
P
P
S-C G-S
31. Why is it necessary for the nitrogenous bases to break apart during DNA replication?
The nitrogenous bases/nucleic acids (ATCG) must break apart so the cell can use each strand as a template or
guide indicating what new bases should be added to make two complete double helixes. See number 33 for further
explanation.
32. As discussed in the film “What Darwin Never Saw”, what are the most important factors that cause evolution?
Explain how these factors contribute to the evolution of a species.
A change in the environment occurs, creating a natural selection event, that renders some traits more successful
than others. (Example – Winter makes Fur on bunnies preferable to bunnies with no fur.) Thus, successful traits
are passed on to the next generation at a higher frequency than the others. This changes the genetic makeup of
the species. (As the no fur alleles were purged from the bunny population as those bunnies homozygous for ff died
each winter, less and less f alleles were present in the future generations. This changed the population of bunnies
from a mix of those with no fur and fur to a species with only fur.)
33. Describe and draw a diagram of the structure of DNA
DNA Structure
S-A T-S
P
P
S-G C-S
P
P
S-G C-S
P
P
S-T A-S
P
P
S-T A-S
P
P
S-A T-S
P
P
S-C G-S
Description of the Structure.
The backbone of both sides of the helix are composed of sugars (S) and phosphates (P).
Attached to each sugar is a nucleic acid (A-Adenine, T- thymine, C-cytosine, or G-Guanine).
A always pairs with a T and C always pairs with a G.
The DNA forms into the shape of a double helix.
The nucleic acids (ATCG) on each side of the helix are stuck together via hydrogen bonds.
34. Explain how DNA replicates. Include a diagram.
1. The two sides of the helix separate as a molecular machine moves through and breaks the hydrogen bonds
between them.
S-A T-S
P
P
S-G C-S
P
P
S-G C-S
S-A
P
S-G
P
S-G
T-S
P
C-S
P
C-S
2. Now each of the separated strands can act as a template or guide that the cell can use to put in the
complimentary bases for the missing strand.
S-A
P
S-G
P
S-G
S-A T-S
P
P
S-G C-S
P
P
S-G C-S
Fill in the missing strand
T-S
P
C-S
P
C-S
S-A T-S
P
P
S-G C-S
P
P
S-G C-S
The new strands of DNA are in red.
3. The cell will place a C across from every G and a T across from every A. This will complete each missing strand
of DNA and create two double helices.
35. Compare and Contrast Natural and Artificial Selection, Give examples to support your answer.
Natural Selection occurs when some traits are more successful than others and thus, those genes are passed on at
a higher frequency than the less successful genes. Ex. Slow rabbits are eaten more often than fast rabbits, thus
more fast rabbit genes are passed on than slow rabbit genes. This creates a generation of rabbits with more fast
alleles than the previous generation,
In Artificial Selection, humans breed animals so the next generation exhibits the traits we have selected. Ex.
Humans breeding dogs with big ears together and not allowing dogs with small ears to contribute their genes to the
next generation.
Humans can contribute to both artificial and natural selection. For example, humans cutting down only pine trees is
NATURAL SELECTION as we are inadvertently affecting the gene pool of those trees by our selections. It is not
a purposeful breeding or mating of those trees by us. It is similar to a cheetah eating the slowest gazelles. The
cheetah is affecting the genes passed on to future generations and that is natural. The cheetah putting the slow
gazelles into cages and only allowing those gazelles to mate would be artificial selection by the cheetah.