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Basallo, Jacqueline
Chapter 13 - (SELF MONITOR) Objectives
1. Explain why organisms only reproduce their own kind, and why offspring more closely
resemble their parents than unrelated individuals of the same species.
Life's most exclusive distinction is the ability of organisms to reproduce their own kind. Like
begets like. Only oak trees produce oaks, and only elephants make elephants. Offspring more
closely resemble their parents than unrelated individuals of the same species because parents
pass on to their offspring discrete genes that retain their identity generation after generation.
2. Explain what makes heredity possible.
The gene idea makes heredity possible. According to this model, parents pass on discrete
heritable units that retain their separate identities in offspring. An organism's collection of genes
can be sorted and passed along, generation after generation, in diluted form.
3. Distinguish between asexual and sexual reproduction.
Asexual Reproduction: type of reproduction involving only one parent that produces genetically
identical offspring by budding or by the division of a single cell or the entire organism into two
parts or more.
Sexual Reproduction: type of reproduction in which two parents give rise to offspring that have
unique combinations of genes inherited from the gametes of two parents.
4. Diagram the human life cycle and indicate where in the human body that mitosis and meiosis
occur; which cells are the result of meiosis and mitosis; and which cells are haploid.
Figure 12.3, Page 228
The human life cycle. In each generation, the doubling of chromosome number that results from
fertilization is offset by halving of chromosome number that results from meiosis. For humans, the
number of chromosomes in a haploid cell is 23 (n=23); the number of chromosomes in the diploid
cell zygote and all somatic cells arising from it is 46 (2n=46).
5. Distinguish among the life cycle patterns of animals, fungi, and plants.
6. List the phases of meiosis I and meiosis II and describe the events characteristic of each
phase.
I understand the concepts of Meiosis and the events that take place during each phase.
7. Recognize the phases of meiosis from diagrams or micrographs.
I can recognize the phases of meiosis from diagrams or micrographs.
9. Describe the process of synapsis during prophase I, and explain how genetic recombination
occurs.
During Prophase 1 of meiosis, the duplicated chromosomes pair with their homologues, a
process called synapsis. The four closely associated chromatids are visible in the light
microscope as tetrads.
10. Describe key differences between mitosis and meiosis; explain how the end result of meiosis
differs from that of mitosis.
The key differences between mitosis and meiosis is:
* Mitosis has one division, consisting of prophase, metaphase, anaphase and telophase.
Meiosis has two divisions each consisting of prophase, metaphase, anaphase and telophase;
DNA replication does not occur between the two divisions, and the homologous chromosomes
synapse and form tetrads.
*Mitosis has 2 daughter cells, each diploid and genetically identical to the mother cell.
Meiosis has four daughter cells, each containing half as many chromosomes as the mother cell
and they genetically un-identical to the mother cell and to each other.
The end of meiosis differs from the end of mitosis in the at the end of meiosis, there is a
production of gametes, the chromosome number reduces by half and it introduces genetic
variability in the gametes. Mitosis develops of a multi-cellular adult from zygote and allows for the
production of cells for growth and tissue repair.
11. Explain how independent assortment, crossing over, and random fertilization contribute to
genetic variation in sexually reproducing organisms.
The sexual processes that contribute to genetic variation in a population are independent
assortment of chromosomes during meiosis 1, crossing over between homologous chromosomes
during meiosis 1, and random fertilization of an ovum by a sperm. In independent variation, the
positioning of each homologous pair of chromosomes is a matter of chance. This arrangement of
chromosomes determines which chromosomes will be packed together in the haploid daughter
cells. Crossing over is a process which produces individual chromosomes that combine genes
inherited from two parents. Crossing over gives rise to individual chromosomes that have some
combination of DNA originally derived from two different parents.
12. Explain why inheritable variation was crucial to Darwin's theory of evolution.
Darwin’s theory of evolution was based on natural selection, in which the importance of
genetic variation was recognized. This natural selection results in adaptation, the accumulation of
those genetic variations that are favored by the environment.
13. List the sources of genetic variation.
Sources of genetic variation are
*independent assortment of homologous chromosome pairs during meiosis 1.
*crossing over between homologous chromosomes during prophase 1 of meiosis 1.
*Random fertilization of an ovum by a sperm.
Chapter 14 - (SELF-MONITOR) Objectives
1. Describe the favored model of heredity in the 19th century prior to Mendel, and explain how
this model was inconsistent with observations.
The favored model of heredity in the 19th century prior to Mendel was the blending
model, which was the idea that genetic material contributed by the two parents mixes in a manner
analogous to the way blue and yellow paints blend to make green. This predicts that mating a
blue parakeet with a yellow would for generations result in green offspring. The actual results of
parakeet breeding contradict such prediction as well as also fails to explain other phenomena of
inheritance, such as traits skipping a generation.
2. Explain how Mendel's hypothesis of inheritance differed from the blending theory of
inheritance.
An alternative to the blending model is Mendel’s gene idea. According to this model,
parents pass on discrete heritable units that retain their separate identities in offspring. An
organism's collection of genes can be sorted and passed along, generation after generation, in
diluted form.
3. List several features of Mendel's methods that contributed to his success.
Mendel began breeding garden peas in order to study inheritance. He chose to work with
peas because they are available in many varieties. The use of peas also gave Mendel strict
control over which plants mated with which. Mendel was careful to track the inheritance of only
categorical variations, after cross pollination, making sure he started his experiments with
varieties that were true-breeding.
4. List four components of Mendel's hypothesis that led him to deduce the law of segregation.
1. Alternative versions of genes account for variations in inherited characters
2. For each character, an organism inherits two alleles, one from each parent
3. If the two alleles differ, then one, the dominant allele is fully expressed in the
organisms appearance, the other , the recessive allele, has no noticeable affect on
the organisms appearance.
4. The two alleles for each character segregate during gamete production.
5. State, in their own words, Mendel's law of segregation.
Two alleles for a character are packaged into separate independent gametes as each
organism inherits one allele.
6. Use a Punnett square to predict the results of a monohybrid cross and state the phenotypic
and genotypic ratios of the F2 generation.
P
P
PP
Pp
p
Pp
pp
p
7. Distinguish between genotype and phenotype; heterozygous and homozygous; dominant and
recessive.
phenotype: an organism’s appearance
genotype: an organism’s genetic material
homozygous: an organisms having a pair if identical alleles for a character
heterozygous: an organism having a pair of two different alleles for a character
dominant: the allele fully expressed in the organism’s appearance
recessive: the allele that has no noticeable effect on the organism’s appearance
8. Explain how a testcross can be used to determine if a dominant phenotype is
homozygous or heterozygous.
A testcross is designed to reveal the genotype of an organism that exhibits a dominant
trait, such as purple flowers in pea plants. The most efficient way to resolve the genotype is to
cross the organism with an individual expressing the recessive trait. Since the genotypes of the
white flowered plants, for example, must be homozygous, we can deduce the genotype of the
purple-flowered parent by observing the phenotypes of the offspring.
9. Define random event, and explain why it is significant that allele segregation during meiosis
and fusion of gametes at fertilization
are random events.
10. Use the rule of multiplication to calculate the probability that a particular F2 individual will be
homozygous recessive or dominant.
The probability of an F2 plant having the genotype YYRR is 1/16 (1/4 chance for a YR
ovum X 1/4 chance for a YR sperm.
11. Given a Mendelian cross, use the rule of addition to calculate the probability that a particular
F2 individual will be heterozygous.
We can calculate the probability of an F2 heterozygote as 1/4 +1 /4 = 1/2
12. Describe two alternate hypotheses that Mendel considered for how two characters
might segregate during gamete formation, and explain how he tested those hypotheses.
1. For each character, an organism inherits two alleles, one from each parent.
2. Two alleles for each character segregate during gamete production.
One test of Mendel’s segregation hypothesis is whether or not it can account for the 3:1
ratio he observed in the F2 generation of his numerous monohybrid crosses. When alleles
segregate, half the gametes receive a purple-flower allele, while the other half get a white-flower
allele. Using the Punnet square, a useful tool for showing all possible combinations of alleles in
the offspring, each square represented an equally probable product of fertilization. This model
accurately explains the 3:1 ratio that he observed in the F2 generations.
14. Use a Punnett square to predict the results of a dihybrid cross and state the phenotypic and
genotypic ratios of the F2 generation.
YR Yr yR yr
YR
YYRR
YYRr
YyRR
YyRr
Yr
YYRr
YYrr
YyRr
YyRr
Yr
YYRr
YYrr
YyRr
Yyrr
YR
YYRR
YYRr
yYRR
YyRr
16. Give an example of incomplete dominance and explain why it is not evidence for the blending
theory of inheritance.
An example of incomplete dominance is when red snapdragons are crossed with white
snapdragons. TheF1 hybrids have pink flowers. Segregation of alleles into the gametes of the F1
plants result in an F2 generation with a 1:2:1 ration for both genotype and phenotype.
17. Explain how the phenotypic expression of the heterozygote is affected by complete
dominance, incomplete dominance and co-dominance.
The phenotypic expression of the heterozygote is affected by incomplete dominance by
the F1 hybrids having an appearance somewhere in the middle of the phenotypes of the two
parental varieties. In complete dominance, the phenotypic expression of the heterozygote is
affected by the phenotype of the parental varieties being indistinguishable. In codominance, both
alleles are separately manifested in the phenotype f the heterozygote.
18. Describe the inheritance of the ABO blood system and explain why the IA and IB alleles are
said to be codominant.
19. Define and give examples of pleiotropy.
Pleitropy is the ability of a gene to affect an organism in many ways. Alleles that are
responsible for certain hereditary diseases in humans, including sickle cell anemia diseases,
usually causing multiple symptoms are examples of Pleitropy.
20. Explain, in their own words, what is meant by "one gene is epistatic to another."
By “one gene is epistatic to another” it is meant that a gene a specific region in a
chromosome will alter the phenotypic expression of a gene on another region, thus, following an
independent assortment.
23. Describe how environmental conditions can influence the phenotypic expression of a
character.
The environment can influence the phenotypic expression of a character by influencing
quantitative characters. The environment affects the range of phenotypic possibilities over which
there may be variation. Geneticists refer to these characters as multi-factorial, meaning that many
factors, both genetic and environmental, collectively influence the phenotype.
24. Given a simple family pedigree, deduce the genotypes for some of the family members.
I am familiarized with deducing the gentoypes for the family members of a family with a
simple pedigree.
Chapter 15 (SELF-MONITOR) Objectives
4. Define linkage and explain why linkage interferes with independent assortment.
Genes located on the same chromosome tend to be inherited together in genetic crosses
because they are a part of a single chromosome that is passed along as a unit. These are known
as linked genes. Linked genes do not assort independently because they are located on the
same chromosomes and tend to move together through meiosis and fertilization.
6. Explain how crossing over can unlink genes.
Crossing over accounts for the recombination of linked genes. A crossover between
homologous chromosomes breaks linkages in the parental chromosomes to form recombinant
chromosomes that may bring together alleles in new combinations.
10. Describe sex determination in humans.
The male carries X and Y chromosomes while the female carries two X chromosomes.
When fertilization occurs, if a male's X chromosome unites with a female's X chromosome, the
union produces a female. If this occurs with a male's Y chromosome, a male is produced.
11. Describe the inheritance of a sex-linked gene such as color-blindness.
With color-blindness for example, a color-blind daughter may be born to a color-blind
father whose mate is a carrier. However, because the sex-linked allele for color blindness is rare,
the probability that such a man and woman will come together is very low. Sex-linked traits refers
to X-linked traits. A mother may pass the gene to both her son and daughter while the father may
only pass it on to their daughters. Females will only express the phenotype if homozygous
recessive for the trait while any male receiving the trait from his mother will express the trait.
12. Explain why a recessive sex-linked gene is always expressed in human males.
Recessive sex-linked genes are always expressed in human males because males lack
the other X chromosome allowing them to be carriers of the genes. Whether recessive or
dominant, the slight presence of a gene from a heterozygote mother would result in the male
expressing the phenotype for the trait.
14. Distinguish among nondisjunction, and uploidy, and polyploidy; explain how these major
chromosomal changes occur and describe the consequences.
Nondisjunction is an accident of meiosis or mitosis, in which both members of a pair of
homologous chromosomes or both sister chromatids fail to move apart properly.
Aneuploidy is a chromosomal aberration in which certain chromosomes are present in
extra copies or are deficient in number.
Polyploidy is a chromosomal alteration in which the organism possesses more than two
complete chromosome sets.
16. Distinguish among deletions, duplications, translocations, and inversions.
Deletion is
(1) a defficiency in a chromosome resulting from the loss of a fragment through a
breakage,
2) a mutational loss of a nucleotide from a gene.
Duplication is an aberration in chromosome structure resulting from an error in meiosis or
mutagens; duplication of a portion of a chromosome resulting from fusion with a fragment
from a homologous chromosome.
Translocation is an aberration in chromosome structure resulting from an error in meiosis
or from mutagens; attachment of a chromosomal fragment to a nonhomologous
chromosome. (2) During protein synthesis, the third stage in the elongation cycle when
the RNA carrying the growing polypeptide moves from the A site to the P site on the
ribosome. (3) The transport via phloem of food in a plant
Inversion is an aberration in chromosome structure resulting from an error in meiosis or
from mutagens; reattachment in a reverse orientation of a chromosomal fragment to the
chromosome from which the fragment originated.