Download Final Review: 2nd Semester Biology Answer Key

Final Review: 2nd Semester Biology Answer Key
DNA is the hereditary material in cells. It is a chain of nucleotides.
2.
A gene is a piece of DNA that controls one trait. Or it is a piece of DNA that is the
information to construct one protein/polypeptide.
3.
A chromosome is a long strand of DNA, composed of many genes. It contains the
information for many traits.
4.
An allele is a form of the gene. For example, the allele for purple flowers and the allele
for white flowers are two different forms of the flower color gene in pea plants.
5.
Heterozygous is an organism that has two different alleles for a trait.
Example: Pp- a purple alleles and a white allele
6.
Homozygous is an organism that has two of the same alleles for a trait.
Examples: PP- homozygous dominant (2 purple alleles)
pp- homozygous recessive (2 white alleles)
7.
Genotype is the two alleles for a gene found in an organism (Example: PP, Pp, or pp)
8.
Phenotype is the expression of a gene in an organism- appearance, existence of a genetic
disease etc. Examples: Brown eyes, freckles, hemophiliac
9.
phenotype … recessive … genotype …. dominant …. homozygous ….heterozygous
A Punnett square is a tool to determine what genotypes/phenotypes are possible offspring
of two parents, and what the probabilities of each genotype/phenotype are.
Each side represents the possible alleles in each of the gametes (egg/sperm) of parents.
Example: If a mother is heterozygous for free ear lobes (a dominant trait) her eggs can
have either a F allele or f allele.
If the father is homozygous recessive for attached ear lobes, his sperm always have the f
allele.
Sperm from father
\
10.
1.
f
f
Eggs from mother
F
f
11.
T
T
t
12.
TT
Tt
A
t
Tt
Phenotype ratio 3:1 (dominant to recessive)
Probability of taster: 75%
Probability of nontaster: 25%
tt
Genotype ratio 1:2:1 (TT:Tt:tt)
Probability of homozygous dominant: 25%
Probability of heterozygous: 50%
Probability of homozygous recessive: 25%
a
a
Aa
aa
a
Aa
aa
Phenotype Ratio : 1:1
Probability of normal pigmentation: 50%
Probability of albino: 50%
13.
A dihybrid cross is a Punnett square that compares the inheritance of two traits.
14.
If the parents are AaBb, their gametes could contain AB, Ab, aB or ab.
15.
on the same chromosome (linked)… independent assortment
16.
SP
Sp
sP
sp
SP
SSPP SSPp SsPP
SsPp
Sp
SSPp SSpp
SsPp
Sspp
sP
SsPP
SSpp
ssPP
ssPp
sp
SsPp
Sspp
ssPp
sspp
Phenotype ratio 9:3:3:1 (standard ratio when both parents heterozygous for both traits)
Fraction Round, Purple: 9/16
Fraction Round, White: 3/16
Fraction Wrinkled, Purple: 3/16
Fraction Wrinkled,White: 1/16
17. If the number of offspring is small, the Punnett square probabilities may not be very
accurate.
18. An X-linked trait is a trait found on the X chromosome.
Red-Green colorblindness, hemophilia and Duchene’s muscular dystrophy are all Xlinked traits.
Men are more likely to have (recessive) sex-linked traits because they only have one X
chromosome.
19.
A man may inherit Red-green colorblindness if his mother is at least a carrier.
A woman must inherit the colorblindness allele from both parents- her mother must
be at least a carrier and her father must be colorblind.
20.
XD
Y
XD
Xd
XDXD XDXd
XDY
Probabilities:
Daughter having MD: O%
Daughter not having MD: 100%
Son having MD: 50%
Son not having MD: 50%
XdY
21. Polygenic is a trait that is controlled by more than one gene. Examples of
polygenic traits include height and skin color. (Polygenic traits are typically traits
that are expressed with a range of various phenotypes.)
22.
Multiple alleles means a trait there is more than 2 possible alleles that can be
inherited for a particular gene. (Each individual only has 2 alleles for the trait.)
ABO blood type is a gene that has 3 possible alleles.
23. A: IAIA or IAi (i represents the recessive O allele)
B: IBIB or IBi
AB: IAIB only
O : ii only
24. Yes, a man with blood type B can father a child with blood type O because his
genotype may be IBi.
25. If a man has blood type AB he can not father a child with blood type O. His
genotype must be IAIB and the child must inherit an i allele from each parent.
26. Trisomy is a condition in which a person inherits an extra copy of a chromosome,
because of nondisjunction (chromosomes not separating properly) during meiosis.
Down’s syndrome is caused by trisomy 21.
27. Independent assortment and crossing over are the two ways that genetic variation
occurs during meiosis. Independent assortment means that each pair of chromosomes
lines up independently during meiosis (I). Crossing over allows genetic variation of
genes on the same chromosome, because nonsister chromatids can exchange segments
during prophase of meiosis I.
28. DNA is a chain of nucleotides.
Each nucleotide is made of 3 parts, a sugar, a phosphate group and a nitrogen base (A, C,
T or G).
29. DNA is a double helix- 2 strands of nucleotides chains that are twisted like a spiral
staircase.
The sugar- phosphate groups form the backbone of the chains and pairs of nitrogen bases
form the “rungs” of the double helix.
30. Adenine always pairs with Thymine
Cytosine always pairs with Guanine
If one side is CATGAG the other side will be GTACTC.
31. DNA replication occurs just prior to cell division.
The enzyme helicase unwinds the double helix, separating the two strands. The enzyme
DNA polymerase constructs the new DNA by adding the complementary nucleotides. In
the end, each of the 2 DNA molecules produced contains one original strand of
nucleotides (that served as the template) and one new strand of nucleotides.
32. Gene expression (producing the protein encoded by a gene) involves transcription and
then translation.
33. DNA nucleotides use the sugar deoxyribose, RNA nucleotides use the sugar ribose.
A DNA molecule is a double strand, mRNA is a single strand.
DNA nucleotides can have the nitrogen bases A, C, G or T. RNA nucleotides have uracil
in place of thymine.
34. Both mRNA and tRNA are chains of nucleotides.
mRNA is a straight chain of nucleotides that serves as a “messenger” . It is a mRNA
copy of a gene.
tRNA is a folded piece of RNA, with an attached amino acid. It serves to transfer the
amino acid encoded by a codon in the mRNA to the protein produced during translation.
35. Transcription is the production of an mRNA copy of a gene. It occurs in the nucleus.
The enzyme RNA polymerase unwinds a section of DNA at the start of a gene, and adds
the complementary RNA nucleotides to the DNA template to make the single stranded
mRNA.
36. AUCGUA (same pairing as within DNA molecule except that adenine pairs with
uracil because thymine not used in RNA molecules)
37.





Translation occurs in the ribosome.
The mRNA is attachs to a ribosome and a start tRNA.
A tRNA with a complementary anticodon to the next codon (series of 3
nucleotides) attaches bringing the corresponding amino acid.
The amino acids are joined together and the mRNA slides down the ribosome,
moving the next codon into the ribosome binding site.
This process continues to build the protein.
38.
All types of organisms translate the codons in the mRNA in the same way (add the
same amino acid). Because of the fact that the genetic code is universal, a gene
from a human, such as insulin, can be inserted into a bacteria and it will produce
the same protein.
39.
A virus contains only hereditary material (DNA or RNA) surrounded by a protein
coat. It does not have any ribosomes, enzymes etc. Therefore, it can not
reproduce on its own. It must take over a host cell and use the host cell’s
ribosomes/enzymes to make new proteins, copy DNA for reproduction.
40.
The lytic cell is when a virus uses a host cell to make many new copies of the
virus, and then lyses(bursts open) the cell, releasing the replicated viruses.
41.
Most viruses can only infect one specific type of host cell. (Examples: polio virus
infects nerve cells, HIV infects white blood cells). The strurcture of the viral
protein coat affects what type of cell it can attach to and infect.
42.
The lysogenic cell is a dormant cycle in which the viral DNA is integrated into the
host DNA. It can later reemerge into the lytic phase. Reoccuring cold sores is an
example of a virus that can be found in the lysogenic phase.
43.
Bacteria are prokaryotic cells, which lack a nucleus and all cell-bound organelles.
44.
An antibiotic is a drug that can kill bacteria. They do not work against viruses.
45.
Antibiotic resistance is when a strain of bacteria are not killed by an antibiotic.
Antibiotic resistance is more likely to develop when an antibiotic is overused. It
can develop by natural selection-if a bacterium (through random mutation) has a
gene that makes it more likely to survive the antibiotic, that gene will increase in
the population.
46.
The nucleus of an egg is removed, the nucleus from the cell to be cloned is added,
(cell division is stimulated by electricity), and the cell is placed in a surrogate
mother.
47.
A recombinant plasmid is a plasmid made from DNA from 2 different sources
(such as a bacteria plasmid with a firefly gene inserted). To make a recombinant
plasmid, both the plasmid and the gene to be inserted are cut with the same
restriction enzyme. Restriction enzymes make cut DNA at specific sequences in a
way that leaves sticky ends (single stranded DNA ends). Complementary sticky
ends (due to being cut by the same restriction enzyme) allow the different types of
DNA to be joined together.
48.
Gene therapy is trying to correct a genetic disease by inserting a correct version of
the gene into the cells that need it.
Genetically modified organisms can be created by inserting the recombinant
plasmid into a fertilized egg. The recombinant DNA can then be passed on into all
the cells in the organism.
In gene therapy, the recombinant vector must be added to all the cells that need it,
in an already existing person.
49. 630 nucleotides, each amino acid is encoded by a codon of 3 nucleotides