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Chapter 13
-Explain why organisms only reproduce their own kind, and why offspring more closely
resemble their parents than unrelated individuals of the same species.
Reproduction is an emergent property associated with life. The fact that organism
produce their own kind is a consequence of heredity. Heredity is the continuity of biological traits
from one generation to the next. This results from the transmission of genes from parents to
offspring. Because they share similar genes, offspring most closely relate to their parents or close
relatives than unrelated individuals of the same species.
-Distinguish between asexual and sexual reproduction.
Asexual Reproduction
Single individual is the sole parent.
Single parent passes on all its genes to its
offspring.
Offspring are genetically identical to the parent.
Sexual Reproduction
Two parents give rise to offspring.
Each parent passes on half its genes, to its
offspring.
Offspring have a unique combination of genes
inherited from both parents.
Results in a clone, or genetically identical Results in a greater variation; offspring vary
individual. Rarely, genetic differences occur as genetically from their siblings and parents.
a result of a mutation
-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.
The human life cycle follows the same basic pattern found in all sexually producing
organisms. Meiosis and fertilization result in alternation between the haploid and diploid condition.
Somatic cells are any other cells other than a sperm or an egg. Zygotes are diploid cells that result
from the union of two haploid gametes. Meiosis occurs during gamete production. Fertilization
produces a diploid zygote that divides by mitosis to produce a diploid multicellular animal.
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-Distinguish among the life cycle patterns of animals, fungi, and plants.
Animals: In animals, including humans, gametes are the only haploid cells. Meiosis occurs
during gamete production. The resulting gametes undergo no further cell division before
fertilization. Fertilization produces a diploid zygote that divides by mitosis to produce a diploid
multicellular animal.
Fungi and some protists: in many fungi and some protests, the only diploid stage is the
zygote. Meiosis occurs immediately after the zygote forms. Resulting haploid cells divide by
mitosis to produce a haploid multicellular organims. Gametes are produced by mitosis from the
already haploid organism.
Plants and some algae: plants and some species of algae alternate between multicellular
haploid and diploid generations. This type of life cycle is called an alternation of generations. The
multicellular diploid stage is calle da sporophyte, or spore producing plant. Meiosis in this stage
produces haploid cells called spores. Haploid spores divide mitotically to generate a multicellular
haploid stage called a gametophyte, or gamete producing plant. Haploid gametophytes produce
gametes by mitosis. Fertilization produces a diploid zygote which develops into the next
sporophyte generation.
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-List the phases of meiosis I and meiosis II and describe the events characteristic of each
phase.
Prophase I: The nucleolus disappears, chromatin condenses into chromosomes, the
nuclear envelope breaks down, and the spindle apparatus develops. Metaphase I: homologous
pairs of chromosomes are spread across the metaphase plate. Anaphase I: begins when
homologues within tetrads uncouple as they are pulled to opposite poles. Telophase I: the
chromosomes have reached their respective poles, and a nuclear membrane develops around
them. Prophase II: the nuclear envelope disappears and the spindle develops. Metaphase II: the
chromosomes align singly on the metaphase plate. Anaphase II: begins as each chromosome is
pulled apart into two chromatids by the microtubules of the spindle fiber apparatus. Telophase II:
the nuclear envelope reappears at each pole and cytokineses occurs.
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-Describe the process of synapsis during prophase I, and explain how genetic
recombination occurs.
In mitosis, every daughter cell is exactly like the parent cell. Meiosis and sexual
reproduction, however, result in a reassortment of the genetic material. This reassortment, called
genetic recombination, originates from three events during the reproductive live cycle. Crossing
over, which happens during prophase I, independent assortment of homologues and the random
joining of gametes.
-Describe key differences between mitosis and meiosis; explain how the end result of
meiosis differs from that of mitosis.
Meiosis is a reduction division. Cells produced by mitosis have the same number of
chromosomes as the original cell, whereas cells produced by meiosis have half the number of
chromosomes as the parent cell. Meiosis creates genetic variation. Mitosis produces two
daughter cells genetically identical to the parent cell and to each other. Meiosis produces four
daughter cells genetically different from the parent cell and from each other. Meiosis is two
successive nuclear divisions. Just one nuclear division, on the other hand, characterizes mitosis.
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-Explain how independent assortment, crossing over, and random fertilization contribute to
genetic variation in sexually reproducing organisms.
Crossing Over: As a result each homologue no longer entirely represents a single parent.
Independent assortment of homologues: During metaphase I, tetrads of homologous
chromosomes separate into chromosomes that go to opposite poles. Which chromosomes goes to
which pole depends upon the orientation of a tetrad at the metaphase plate. This orientation and
subsequent separation is random for each tetrad. For some chromosome pairs, the chromosome
that is mostly maternal may go to one pole, but for another pair, the maternal chromosome may go
to the other pole.
Chapter 14
-State, in your own words, Mendel's law of segregation.
Mendel’s Law of Segregation: Allele pairs segregate during gamete formation (meiosis),
and the paired condition is restored by the random fusion of gametes at fertilization.
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-Use a Punnett square to predict the results of a monohybrid cross and state the phenotypic
and genotypic ratios of the F2 generation.
Father
A
a
A
a
AA
Aa
Aa
aa
Phenotypic Ratio. 3:1
Genotypic Ratio: 1:2:1
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-Distinguish between genotype and phenotype; heterozygous and homozygous; dominant
and recessive.
Genotype is the genetic makeup of an organism, and phenotype is just the appearance
of it. Organisms having two different alleles for character are heterozygous while an organism
having a pair of identical alleles for a character homozygous. A dominant allele in a heterozygote,
is the allele that is fully expressed in the phenotype, and the recessive allele is completely masked
in the phenotype.
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-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. Such an organism could be either homozygous for the
dominant allele or heterozygous. The most efficient way to resolve the genotype is to cross the
organism with an individual; expressing the recessive trait. Since the genotype of the white
flowered parent must be homozygous, we can deduce the genotype of the purple- flowered parent
by observing the phenotypes of the offspring.
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-Define random event, and explain why it is significant that allele segregation during
meiosis and fusion of gametes at fertilization are random events.
Random joining of gametes: which sperm fertilizes which egg is to a large degree a
random event. In many cases, however, this event may be affected by the genetic composition of
a gamete. For example, some sperm may be faster swimmers and have a better chance of
fertilizing the egg. It is important that these are random events because then if it were not like that
then all the organisms would look the same.
-State, in your own words, Mendel's law of independent assortment.
During metaphase I, tetrads of homologous chromosomes separate into chromosomes
that go to opposite poles. Which chromosome goes to which pole depends upon the orientation of
a tetrad at the metaphase plate. This orientation and subsequent separation is random for each
tetrad. For some chromosome pairs, the chromosome that is mostly maternal may go to one pole,
but for another pair, the maternal chromosome may go to another pole.
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-Use a Punnett square to predict the results of a dihybrid cross and state the phenotypic
and genotypic ratios of the F2 generation.
Phenotypic Ratio: 9:3:3:1
Genotypic Ratio: 1:2:2:4:1:2:1:2:1
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-Give an example of incomplete dominance and explain why it is not evidence for the
blending theory of inheritance.
Incomplete dominance is when the F1 hybrids have an appearance somewhere in between
the phenotypes of the two parental varieties. For instance, when red snapdragons are crossed with
whit , all the F1 hybrids have pink flowers. We should not regard incomplete dominance as
evidence of the blending theory, which would predict that the red or white traits could never be
retrieved from the pink hybrids. The segregation of the red and white alleles in the gametes
produced by the color are heritable factors that maintain their identity in the hybrids; that is,
inheritance is particulate.
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-Explain how the phenotypic expression of the heterozygote is affected by complete
dominance, incomplete dominance and codominance.
In complete dominance, the phenotypes of the heterozygote are indistinguishable.. This
represents one extrame of a spectrum in the dominance/recessiveness relationship of alleles. At
the other extreme is codominance, in which both alleles are separately manifest in the phenotype,
and in incomplete dominace the F1 hybrids have an appearance somewhere in between the
phenotypes of the two parental varieties.
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-Describe the inheritance of the ABO blood system and explain why the IA and IB alleles are
said to be codominant.
The ABO blood groups in humans are one example of multiple alleles of a single
gene.Four blood groups result from various combinations of three different alleles of one gene,
symbolized as IA (for the carbohydrate), IB (for B), and I (giving rise to neither A nor B). Both the
IA and the IB alleles are dominant to the I allele. Thus, IAIA and IAi individuals have A blood, and
IBIB and IBi individuals have type B. Recessive homozygotes, ii, have type O blood, because
neither the A nor the B substance is produced. The IA and IB alleles are codominant; both are
expressed in the phenotype of the IAIB heterozygote, who has type AB blood.
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-Define and give examples of pleiotropy.
Pleiotropy is the ablitity of a single gene to have multiple effects. For example, alleles
that are responsible for certain hereditary diseases in humans, including sickle-cell disease, usually
cause multiple symptoms.
-Explain, in their own words, what is meant by "one gene is epistatic to another."
Epistatis is the interaction between two nonallelic genes in which one modifies the
phenotypic expression of the other. If one gene suppresses the phenotypic expression of the
other, the first gene is said to be epistatic to the other.
-Describe how environmental conditions can influence the phenotypic expression of a
character.
Environmental conditions can influence the phenotypic expression of a gene, so that a
single genotype may produce a range of phenotype. This environmentally induced phenotypic
range is the norm of reaction for the genotype.
-Given a simple family pedigree, deduce the genotypes for some of the family members.
Please refer to the following website:
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Chapter 15
- Define linkage and explain why linkage interferes with independent assortment.
Linked genes are genes that are located on the same chromosome and that tend to be
inherited together. Linked genes do not assort independently, because they are on the same
chromosome and move together through meiosis and fertilization. Since independent assortment
does not occur, a dihybrid cross following two linked genes will not produce an F 2 phenotypic ratio
of 9:3:3:1.
- Explain how crossing over can unlink genes.
Crossing over is the shuffling of the genes. In this process, the linked genes can be
unlinked. If genes are totally linked, some possible phenotypic combinations should not appear.
However, sometimes, the unexpected recombinant phenotypes do appear. This was shown by
T.H. Morgan in his experiment with flies.
- Describe sex determination in humans.
Sex is an inherited phenotypic character usually determined by the presence or absence of
special chromosomes. The mother is a female, thus she has two X chromosomes. The father is a
male, thus he has an X and a Y chromosome. When they are both united, all that the female has
to offer are two Xs. Since the sperm carries either an X or a Y, it is up to the male to determine the
gender of the child.
-Describe the inheritance of a sex-linked gene such as color-blindness.
Sex linked genes have unique patterns of inheritance. Some genes on sex
chromosomes play a role in sex determination, but these chromosomes also contain genes for
other traits. In humans, the term sex-linked traits usually refers to x linked traits. A color-Blindness
daughter may be born to a color-blind father whose mate is a carrier. However, because the sexlinked allele for color blindness rare, the probability that such a man and woman will come together
is very low.
-Explain why a recessive sex-linked gene is always expressed in human males.
Most sex-linked traits are linked to the X chromosomes. Females have two X
chromosomes and, thus, are able to cancel the sex-linked diseases better than males. On the
other hand, males have an X and a Y chromosome. The Y chromosome is much shorter than the
X. Scientists have identified a specific area of the X chromosome that contains the sex-linked
disorders. Since males lack one X chromosome, they are not able to cancel off any sex-linked
disorder.
-Distinguish among nondisjunction, aneuploidy, and polyploidy; explain how these major
chromosomal changes occur and describe the consequences.
Nondisjuction: The Chromosomes do not properly separate. Aneuploidy: A chromosomes
aberration in which certain chromosomes are present in extra copies or are deficient in
number. Polyploidy: A chromosomes alteration in which the organism possesses more than two
complete chromosomes sets
-Distinguish among deletions, duplications, translocations, and inversions.
Deletions: A deficiently in a chromosomes resulting from the loss of a fragment through
breakage. Duplication: An aberration in chromosomes structure resulting from an error in meiosis
or mutants. Translocations: An aberration in chromosomes structure resulting from as error in
meiosis or from mutants. Inversion: An aberration in chromosomes structure resulting from as error
in meiosis or from mutants