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AP Biology Genetics/ DNA Flashcard Review
Translocation:
A translocation moves a segment from one chromosome to a nonhomologous chromosome. In a
reciprocal translocation, the most common type, nonhomologous chromosomes exchange fragments.
In a nonreciprocal translocation, which is less common, a chromosome transfers a fragment without
receiving a fragment in return. This occurs during meiosis.
Describe and diagram the process of mitosis and cytokinesis:
I like this one, very helpful ^^
Explain what gene duplication mutation is, and describe its potential effects:
This is very likely to occur during meiosis, during crossing over. Often occurs in conjunction with
deletion, in which a gene is removed from a chromosome and added to another, often a sister
chromatid, or to a nonsister chromatid. In this case, the duplicated segments are not identical because
the homologs could carry different alleles of certain genes. They are a common cause of many types of
cancer and are a source for evolutionary change.
Example of epistatic inheritance: In roosters, the shape of the comb is an epistatic trait. It is affected
by the interaction of genes at several different loci. In a dihybrid cross, the ratios of comb shape
phenotypes come out different from 9:3:3:1 because both genes affect the comb shape.
How does meiosis explain Mendel's laws? Mendel's first law (law of segregation) states that when a
cell produces gametes, each gamete only gets on allele of a gene. This is caused by sister chromatids
dividing in meiosis to leave each cell with half the necessary genetic material. Mendel's second law
(law of independent assortment) states that genes for separate traits are passed down the generation
independently of other genes for other traits. This is caused by the randomness of chromosomes
aligning in meiosis: each gamete could get either allele of every single gene, and no chromosome
alignment affects any others.
Codominance: Two alleles of a particular gene both a re expressed without one overpowering the
other. Ex.: In blood, I(a) and I(b) are codominant as both are expressed together when present as AB
blood type.
translocation is when two nonhomologous chromosomes trade parts of
their genes. In order for this to occur, a ribosome is needed to
facilitate the process. The two chromosomes now have a different make
up from the other homologue but the genes themselves haven't changed.
The phenotype can be expressed differently because a gene's
expression can be influenced by its neighbors, and with the new
neighbors, devastating changes can occur.
Meiosis is the process that makes sexual reproduction possible.
Sexual reproduction is driven by variation, and meiosis has enough
steps that cause variation for it to be the cellular division process
for the job. Of the three areas of variation, (crossing over,
independent assortment of chromosomes, and random mating) the first
two are from meiosis. Crossing over occurs in prophase I and
independent assortment occurs in metaphase and anaphase I and II.
Both of these parts cause a great amount of variation, and coupled
with random mating, makes sexual reproduction successful.
When DNA is ready to be duplicated, a helicase enzyme attaches the
DNA strand and unzips the molecules by breaking the bonds between the
base pairs. A primase molecule then moves onto the 3' strand and lays
down an RNA primer strand attached to the DNA. Next, DNA pol III adds
more bases to finish replicating the DNA sequence, match up the pairs
and attaching them to the original sequence. As the DNA pol III moves
down the DNA strand, the helicase continues to unzip the DNA so the
DNA pol III can continue to move. This all happens very quickly until
the whole strand of DNA is replicated.
Polar Bodies: cells that result from the asymmetric division of an oocyte
Law of Segregation: the two coexisting alleles of an individual for each trait segregate during gamete
formation so that each gamete receives one of the two alleles
Co-dominance Inheritance Patterns: form of gene expression wherein individuals heterozygous for a
trait display characteristics of both alleles; eg. sickle cell
Transcription: It is the process of transcribing or making a copy of genetic information stored
in a DNA strand into a complementary strand of RNA (messenger RNA or mRNA) with the aid
of RNA polymerases.
Although RNA polymerase traverses the DNA template strand from 3' → 5', the coding (nontemplate) strand is usually used as the reference point. Hence, the process proceeds in the 5'
→ 3' direction, like in DNA replication. However, unlike DNA replication, transcription does not
need a primer to start and it uses base pairing to create an RNA copy containing uracil instead
of thymine.
In prokaryotes transcription occurs in the cytoplasm whereas in eukaryotes it takes place
primarily in the nucleus before the mRNA is transported into the cytoplasm for translation or for
protein synthesis.
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Translocation Mutation: A type of gene mutation wherein the deletion (as well as addition) of
(a number of) nucleotide(s) causes a shift in the reading frame of the codons in the mRNA,
thus, may eventually lead to the alteration in the amino acid sequence at protein translation..
Mutations involving the genes are of two major types:
base-pair substitution
frameshift mutation or addition/deletion mutation
Silent Mutation: A form of point mutation resulting in a codon that codes for the same or a
different amino acid but without any functional change in the protein product.
Silent mutations do not cause changes in the amino acid sequence and hence the protein is
still functional. Because of that they are regarded as though they are evolutionarily neutral.
Explain how to use the Chi Square Test...
The Chi-Square Test is a statistical test used to compare observed data with data we would expect to
obtain according to a specific hypothesis. The equation for the test is as follows:
Describe an experiment that compares DNA or proteins from two individuals...
There are a few ways a scientist can compare DNA or proteins from several individuals. In forensics,
PCR (polymerase chain reaction) testing is more commonly
used than RFLP testing. PCR uses regions of DNA sequences to compare the same regions that are on
other DNA sequences. PCR uses two short pieces of DNA called primers that serve as starting points for
copying a region of DNA.
Effects of proto-oncogenes and tumor suppressor genes...
A proto-oncogene codes for proteins that help to regulate cell growth and differentiate. however, once
the proto-oncogene is activated it becomes an oncogene, a tumor-inducing agent. Proto-oncogenes
activated by mutations, increased protein concentration, or chromosomal translocation. Fir example, a
proto-oncogene called the MYC gene is implicated in Burkitt's Lymphoma, which gets activated by
chromosomal translocation.
Unlike oncogenes, Tumor-suppressor genes allow both alleles that code for a specific gene to be
affected before an effect is manifested. That way if one allele is damaged, the second allele can still
produce a corrected protein. Tumor-suppressor genes have a dampening or repressive effect on the cell
cycle or promote apoptosis.
transgenic organism...
a transgenic organism is a genetically modified organism (GMO) that has genetic material from another
species that provides a useful
Explain what a nonsense mutation is and describe its potential effects.
--- it is a point mutation in a sequence of DNA that often results in a useless protein product. Nonsense
mutations can cause a genetic disease by damaging a gene responsible for a specific protein
Describe a human autosomal chromosome abnormality.
---Down syndrom is an example and is a mild to severe form of mental retardation accompanied by
distinctive physical traits. People with Down syndrome have an irregularity with autosome pair 21. In
most cases, there is an extra chromosome.
homologous
---are chromosome pairs of approximately the same length,centromere position, and staining pattern,
with genes for the same characteristics at corresponding loci.
transposon- small, mobile dNA sequences that can replicate and insert copies at random sites within
chromosomes. They have nearly identical sequences at each end, oppositely oriented repeats and code
for the enzyme, transposase, that catalyses their insertion. (Transposons can jump to different locations
on the genome. This gives them the common name of "jumping genes")
transduction- Transfer of genetic material or characteristics from one bacterial cell to another by the
incorporation of bacterial DNA into a bacteriophage. Transduction and specialized transduction are
especially important because they explain how antibiotic drugs become ineffective due to the transfer of
resistant genes between bacteria.
translocation- a chromosome abnormality caused by rearrangement of parts between nonhomologous
chromosomes. Cancer, infertility and Down's Syndrome are often the effects of translocation.
Avery, McCarty, MacLeod ExperimentsThey were able to identify DNA as Griffiths transforming principle through the following
experiment.
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took extract (from heated smooth bacteria) and treated it with DNAase (digests DNA) - then
mixed with rough bacteria and injected into rats -> the rats lived
in other side of experiment, treated extract with protease (digests proteins) -then mixed with
rough bacteria and injected into rats -> rat died
This showed that DNA, not protein, has ability to transform cells
Transcription Factor
 Protein that binds to specific DNA sequences
 Controls the flow (or transcription) of genetic information from DNA to mRNA.
Give an example and explain a simple dominance and recessive inheritance pattern
 Each individual has 2 alleles which make one gene and will receive
A
A
one allele (50%) from the
A
a
father and one allele (50%)
A
AA
AA
A
AA
Aa
from the mother. Alleles can
A
AA
AA
A
AA
Aa
either be dominant usually
indicated by a capital letter (A) or recessive usually indicated by small letter (a). For instance
the color black is dominant (A) over the color red which is a recessive color (a), so whenever the
black allele is present in the gene controlling color, then the animal will be black in color. Since
the recessive trait is unknown or hidden it often produces unhealthy or undesirable
traits. Sometimes it provides desirable traits.
Possible Punnett Square examples:
Homozygous AA
Heterozygous Aa
Homozygous aa
Free from illness and not carrier. Both
parents have given the dominant allele A
Free from symptoms but carrier. One
parent has given the dominant allele A and
the other the recessive allele a. Since A is
dominant over a the offspring will not
show the trait for a.
Will show the recessive trait and pass it on
to its offspring. Both parents either are
homozygous for a or are a carrier
(heterozygous) for a.
Give an example and explain a polygenic inheritance pattern
 Inheritance of quantitative traits, traits which are influenced by multiple genes, not just one.
 EX: Human skin color
o Assume that three "dominant" capital letter genes (A, B and C) control dark
pigmentation because more melanin is produced. The "recessive" alleles of these three
genes (a, b & c) control light pigmentation because lower amounts of melanin are
produced.
o Genotype with all "dominant" capital genes (AABBCC) has the maximum amount of
melanin and very dark skin. A genotype with all "recessive" small case genes (aabbcc)
has the lowest amount of melanin and very light skin. Each "dominant" capital gene
produces one unit of color, so that a wide range of intermediate skin colors are
produced, depending on the number of "dominant" capital genes in the genotype. For
example, a genotype with three "dominant" capital genes and three small case
"recessive" genes (AaBbCc) has a medium amount of melanin and an intermediate skin
color.
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transfer RNA: an RNA molecule that functions as an interpreter between nucleic acid and
protein language by picking up specific amino acids and recognizing the appropriate codons in
the mRNA
Give an example and explain an incomplete dominance inheritance pattern: In some genes,
neither allele is completely dominant and the F1 hybrids have a phenotype somewhere between
those of the two parental varieties.
o Example: When red snapdragons are crossed with white snapdragons, all the F1 hybrids
have pink flowers
Describe the experiments by TH Morgan that determined that genes are chromosomes:
While examining fruit flies, Morgan noticed that one fly had white eyes as opposed to the normal
bright-red color of the species. Curious, he chose to do a simple breeding analysis to observe the
transmission of genes through successive generations. After observing thousands of flies under a
magnifying glass, Morgan and his colleagues confirmed the chromosomal theory of inheritance:
that genes are located on chromosomes and that some genes are linked.
Explain what a gene inversion mutation is and describe its potential effects.
A gene inversion is a mutation in which a segment of DNA is broken away from its chromosome,
inverted from end to end, then re-inserted into the breakage site. There are two types of such inversions:
paracentric and pericentric. In paracetric inversions, the break occurs in the arm of the chromosme and
the centromere is not involved. Pericentric inversions include the centromere, involving a breaking site
in each arm. Inversions usually do not cause abnormalities as longs as the amount of genetic information
is not changed. However, individuals heterozygous for an inversion may produce abnormal chromatids,
causing some gametes to be produced unbalanced. In rare cases, inversions can cause genetic diseases or
make the invidual a carrier. Genetic testing and counseling is necessary for such individuals.
Give an example and explain a pleiotropic inheritance pattern.
Pleiotropy occurs when a single gene has several phenotypic effects. Pleiotropy is causes by the
complex molecular and cellular interactions within organisms. This is especially common among
hereditary diseases, explaining why some have so many symptoms. Sickle-cell disease is one such
hereditary disease. In this disease, one amino acid in hemoglobin is replaced. However, the symptoms
are much greater. The disease causes red blood cells to take a sickle-like shape. This can cause
weakness, pain, clogging, organ damage, and even paralysis. The multiple effects are an example of
pleiotropy.
Translocation in Plants
Translocation is the transport of soluble organic material made during photosynthesis. It is mainly
performed by phloem, the vascular tissue responsible for transporting organic nutrients like sugars
throughout plants.
Q: Explain heterozygote advantage. Give an example.
A: Heterozygote advantage means that the heterozygote genotype has a higher fitness than the
homozygote dominant and homozygote recessive genotype. For example, the allele for sickle-cell
anemia offers resistance to malaria. If a person is heterozygous for sickle-cell anemia, the resistance
they have to malaria outweighs the disadvantage of having heterozygous sickle-cell anemia; humans
who are homozygous for sickle shaped cells will suffer from a near fatal condition.
Q: Electrophoresis
A: Electrophoresis is the movement of particles in a gel or fluid under the influence of an electric field.
Particles with a positive charge go to the cathode and particles with a negative charge go to the anode. It
could also be a technique for separating the components of a mixture of charged molecules (proteins,
DNAs, or RNAs) in an electric field within a gel or fluid.
Q: Explain the relationship between the haploid and diploid stages in an animal cell.
A: During meiosis I, a diploid cell that contains two copies of each chromosome, divides into two
haploid cells. During meiosis II, the two haploid cells divide into two more cells, resulting in four
identical daughter cells, each with half the number of chromosomes as the parent cell. During metaphase
I, homologous chromosomes line up at the equator, and during anaphase I, the homologous pairs
separate, so each cell contains one copy of each chromosome. During metaphase II, chromosomes line
up at the equator, and during anaphase II, the sister chromatids pull apart, resulting in all four cells
containing one copy of each chromatid.
Explain how energy molecules are used in DNA replication: Energy is used in DNA syntheses by the
enzyme polymerase as it attached individual nuclides but removing 2 of the three phosphates as each
new base is added.
Explain how an organism’s phenotype is dependent on genetics and environment: The genotype
dose not always strictly influences the phenotype; instead it provides a range called the norm of reaction.
This allows certain factors like altitude to effect a person’s red blood count level. The norm of reaction
for certain a characteristic like blood type is extremely narrow and for multifactorial characteristic like
skin color is very wide.
Deletion: A genetic mutation in which a single nucleotide is missing or a section of chromosome is
removed, this can cause server problems as the organisms grow and sometimes cause automatic cell
death.
Homozygous: organisms that have two of the same alleles for a particular trait. Ex RR for homozygous
dominant and rr for homozygous recessive.
Differences of Mitosis and Meiosis:
1.
Synapsis and crossing over normally do not occur in mitosis
2.
At metaphase I, paired homologous chromosomes (tetrads) are positioned on the metaphase
plate, rather than individual replicated chromosomes, as in mitosis.
3.
At anaphase I, duplicated chromosomes of each homologous pair move toward opposite
poles, but the sister chromatids of each duplicated chromosome stay attached. In mitosis, the
chromatids separate
4.
2 Divisions in meiosis, 1 in mitosis
5.
Meiosis results in 4 haploid daughter cells (genetically differ from parent cell) why mitosis
results in 2 diploid daughter cell (genetically same as parent cell)
6.
Meiosis used for production of sex cells, mitosis used for cellular growth.
Commonalities of Mitosis and Meiosis:
1.
Both have chromosome replication before the processes begins.
2.
Both have cytokinesis that occurs during telophase.
3.
Both use spindle fibers (microtubules) to separate the chromatids from each other.
Describe the four sex-chromosome abnormalities and their effects.
1.
Turner syndrome - occurs when females inherit only one X chromosome. If they survive to
birth, these girls have abnormal growth patterns. They are short in stature, averaging 4 foot 7
inches as adults, and often have distinctive webbed neck. However, treatments of hormones
allow Turner syndrome women to appear relatively normal.
2.
Triple-X syndrome - occurs in women who inherit three X chromosomes--their genotype is
XXX or more rarely XXXX or XXXXX. They generally are an inch or so taller than average with
unusually long legs and slender torsos but otherwise appear normal. They usually have normal
development of sexual characteristics and are fertile. They may have slight learning difficulties
and are usually in the low range of normal intelligence.
3.
Klinefelter syndrome – Males that inherit one or more extra X chromosomes--their genotype
is XXY or more rarely XXXY. They have relatively high-pitched voices, asexual to feminine body
contours as well as breast enlargement, and comparatively little facial and body hair. They are
sterile and as a result, they produce relatively small amounts of testosterone.
4.
XYY syndrome - males inherit an extra Y chromosome--their genotype is XYY. They generally
appear and act normal. However, they produce high levels of testosterone. They are usually
fertile and lead ordinary lives as adults. Many, if not most, are unaware that they have a
chromosomal abnormality.
Explain what a deletion mutation is, describe its potential effects, and give an example.
Mutations that result in missing DNA are called deletions. These can be small, such as the removal of
just one "word," or longer deletions that affect a large number of genes on the chromosome. Deletions
can be caused by errors in chromosomal crossover during meiosis, leading to several serious genetic
diseases. Deletions can also cause frameshift mutations.
If for example, a gene coded for alanine, with a genetic sequence of C-G-G, and the cytosine nucleotide
was deleted, then the alanine amino acid would not be able to be created, and any other amino acids that
are supposed to be coded from this DNA sequence will also be unable to be produced because each
successive nucleotide after the deleted nucleotide will be out of place.
Examples:
Original
Deletion
The fat cat ate the wee rat.
The fat ate the wee rat.
Give an example and explain a sex-linked inheritance pattern.
Sex-linkage is another common alternative-inheritance pattern. In sex-linked traits, such as colorblindness, the gene for the trait is found on the X chromosome (a sex chromosome). Sex-linked traits
affect primarily males, since they have only one copy of the X chromosome (male genotype: XY).
Females, who have two copies of the X chromosome, are affected only if they are homozygous for the
trait. Females can, however, be carriers for sex-linked traits, passing their X chromosomes on to their
sons. Sex-linked inheritance works as follows: if a female carrier and a normal male give birth to a
daughter, she has a 1 in 2 chance of being a carrier of the trait (like her mother). If the child is a son, he
has a 1 in 2 chance of being affected by the trait (for example, colorblindness). If a female carrier and an
affected male give birth to a daughter, she will either be affected or be a carrier. If the child is a son, he
will either be affected or be entirely free of the gene. See the following Punnett squares (The letters X
and Y represent their respective normal chromosomes; X underlined represents the colorblindness
allele).
Another example of a sex-linked trait is hemophilia, made famous by the "Queen Victoria pedigree" of
the European nobility. Beginning with Queen Victoria of England (in whom it was probably a
spontaneous mutation), the hemophilia gene spread quickly throughout the European rulers (who
intermarried as a matter of course). The disease, which prevents blood from clotting properly and
renders a minor injury a life-threatening event, claimed several young men of the royal line. Especially
since male heirs were preferred over female as successors to the thrones of Europe, the spread of such a
debilitating disease was a major problem.
Transcription
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Transcription is the synthesis of mRNA from a DNA template.
It is like DNA replication in that a DNA strand is used to synthesize a strand of mRNA.
Only one strand of DNA is copied.
A single gene may be transcribed thousands of times.
After transcription, the DNA strands rejoin.
Steps involved in transcription
1. RNA polymerase recognizes a specific base sequence in the DNA called a promoter and binds to
it. The promoter identifies the start of a gene, which strand is to be copied, and the direction
that it is to be copied.
2. RNA polymerase unwinds the DNA.
3. RNA polymerase assembles bases that are complimentary to the DNA strand being copied. RNA
contains uracil instead of thymine.
4. A termination code in the DNA indicates where transcription will stop.
5. The mRNA produced is called a mRNA transcript.
Cytotoxic T cell
A cytotoxic T cell is a type of white blood cell and can induce the death of infected somatic
or tumor cells. They kill cells that are damaged or infected with viruses. T cell receptor
genes have high genetic variability, which creates many different T cells with many different
T cell receptors. This helps the immune system respond to almost any protein invader.
Continuity and Change: Explain what an addition mutation is and describe its
potential affects.
An addition mutation is an addition of a nucleotide that causes a shift in the reading frame
of the codons in mRNA. This may lead to a change in the amino acid sequence at protein
translation. It can create the wrong amino acid, a stop codon, or a nonsense codon.
Continuity and Change: Describe the process of crossing over.
Crossing over is the reciprocal exchange of genetic material between nonsister chromatids
and occurs durring meiosis I. The chiasmata, an x-shaped, microscopically visible region
where homologous nonsister chromatids have exchanged genetic material through
crossing over, forms. Crossing over also increases genetic variability by producing
recombinant chromosomes. At metaphase II, chromosomes that contain one or more
recombinant chromatids can be oriented in two different ways, which increases the number
of genetic types of daughter cells that can result from meiosis.
Science as a Process: Describe an experiment that tests linkage of two genes.
Bateson and Punnett conducted an experiment with sweet peas that later led them to
believe flower color and shape of pollen grain where linked genes. They performed a
dihybrid cross between pure purple flowers with long pollen grains and red flowers with
round pollen grains. Their results were 284 purple flowers with long pollen grains, 21 purple
flowers with round pollen grains, 55 red flowers with round pollen grains, and 21 red flowers
with long pollen grains. Bateson and Punnett expected that their results would follow a
9:3:3:1 ratio, but this was not the case. Their expected results would have been 215 purple
flowers with long pollen grains, 71 purple flowers with round pollen grains, 24 red flowers
with round pollen grains, and 71 red flowers with long pollen grains. The fact that their
observed results were not consistent with their expected results led Bateson and Punnett to
predict that the alleles were coupled in parents and did not sort independently into
gametes.
Describe Mendel's 2nd law of hereditary- Otherwise known as the Law of Independent Assortment,
this states that separate genes for separate traits are passed independently from one another from
generation to generation.
Explain what a missense mutation is, describe its potential effects, and give an example- A point
mutation in which a single gene is altered. This may change a codon, which codes for a certain amino
acid, which may make the overall protein nonfunctional. One example is one type of sickle cell anemia.
Heterozygote- Having two different forms of the same gene.
Inversion: an aberration in chromosome structure resulting from reattachment of a chromosomal fragment in a
reverse orientation to the chromosome from which it originated. Even though all the genes are still present,
there can be a change in the phenotype if the gene’s expression is influenced by location.
Continuity and Change
Describe and diagram the process of meiosis and cytokinesis
Meiosis I
Prophase I: The nuclear envelope breaks down, the chromosomes begin to condense, and they
connect to their homologs. While they are in synapsis, crossing over occurs.
Metaphase I: The homologous chromosomes line up at the metaphase plate. The chromatids of each
chromosome are attached to the microtubules at the kinetochores.
Anaphase I: Homologs move toward opposite poles
Telophase I & Cytokinesis: A cleavage furrow or cell plate forms, creating two haploid cells. Each
chromosome consists of two sister chromatids. No replication occurs between Meiosis I and Meiosis II.
Meiosis II
Prophase II: Spindle apparatus forms and chromosomes will recondense.
Metaphase II: The chromosomes realign at the metaphase plate. The sister chromatids are not
genetically identical due to the crossing over in prophase 1.
Anaphase II: Chromatids separate and move to opposite poles of the cell.
Telophase II & Cytokinesis: Nuclei form, the chromosomes begin to decondense and cytokinesis
produces four daughter cells that are genetically distinct from each other.
Continuity and Change
Explain what a frameshift mutation is and describe the potential effects.
A frameshift mutation is a mutation that occurs when the number of nucleotides inserted or deleted is
not a multiple of three and results in the improper grouping of the subsequent nucleotides into
codons. This usually results in nonfunctional proteins and other serious problems.
Barr Body: The condensed, inactive, single X-chromosome found in the nuclei of somatic cells of most
female mammals and whose presence is the basis of sex determination tests that are performed, for
example, on athletes.
Fertilization: the union of haploid gametes to produce a diploid zygote.
Fred Griffith’s experiments supporting the transforming principle: in 1928, Griffith preformed one of
the first experiments suggesting that bacteria are capable of transferring genetic information through a
process known as transformation. He took 2 strains of pneumococcus and tested the smooth-coated
and the uncoated bacteria effects on mice. Type III-S had a smooth, polysaccharide coating that
protected it from the mouse’s immune system, where the type II-R did not have the protective coating.
The type III-S strain was injected into the mouse and resulted in killing the mouse, but the type II-R
strain had no effect in the mouse. Another sample of III-S was heated until the bacteria were
destroyed, then the sample was injected into a mouse. There was no effect from the heated bacteria.
The final mouse was injected with a small sample of heated III-S and a small sample of live II-R. In the
end, the mouse died from what Griffith hypothesized as the transforming principle. We know that
transforming principal was the DNA from the III-S strain bacteria which had survived the heating
process and was taken up by the II-R strain. That DNA had the gene for the protective protein coating
that allowed the bacteria to survive the immune system attacks, and as a result allows the II-R strain to
become a II-S strain. The bacteria now have the smooth coating and accumulate in the mice, resulting
in their deaths.
Explain how meiosis creates variation: During meiosis (the production of gametes) crossing over
occurs. Crossing over is when the DNA from one homologue is cut and exchanged with an exact portion
of DNA from the other homologue. Basically, a small part of DNA from one parent is exchanged with
the DNA from the other parent. By having crossing over occur, parts of DNA from each parents is given
to the offspring. This process of recombination allows for genetic variation.
Explain nondisjunction and how it leads to chromosomal abnormalities: Nondisjunction occurs
when the members of a pair of homologous chromosomes do not separate properly during meiosis I, or
sister chromatids don’t separate properly during meiosis II. As a result of nondisjunction, one gamete
receives two copies of the chromosome, while the other gametes receives none. When the faulty
gametes progress to fertilization, the offspring will have an incorrect chromosome number (aneuploidy).
Translation: the synthesis of protein from RNA. Hereditary information is contained in the nucleotide
sequence of DNA in a code. The coded information from DNA is copied faithfully during transcription
into a form of RNA known as messenger RNA, which is then translated into chains of amino acids.
Amino acid chains are folded into helices, zigzags, and other shapes to form proteins and are sometimes
associated with other amino acid chains.