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Unit III
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.
Results in a clone, or genetically identical
individual. Rarely, genetic differences occur as
a result of a mutation
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 greater variation; offspring vary
genetically from their siblings and parents.
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 organisms. 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 called the 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.
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
Phenotypic Ratio. 3:1
Genotypic Ratio: 1:2:1
A
a
AA
Aa
Aa
aa
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.
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.
Define random event, and explain why it is significant that allele segregation during meiosis
and fusion of gametes at fertilization are random events.
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.
Law of independent assortment is the independent segregation of each pair of alleles during
gamete formation.
Use a Punnett square to predict the results of a dihybrid cross and state the phenotypic and
genotypic ratios of the F2 generation.
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Phenotypic Ratio: 9:3:3:1
Genotypic Ratio: 1:2:2:4:1:2:1:2:1
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.
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.
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.
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."
One gene affects the other by means that they are all connected to each other in some
which way or form.
Describe how environmental conditions can influence the phenotypic expression of a
character.
The Phenotype is the actual expression of a gene. The environment may cause a mutation
causing there to be change in the physical appearance that isn’t considered “normal”
Given a simple family pedigree, deduce the genotypes for some of the family
members.
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Chapter 15
Define linkage and explain why linkage interferes with independent assortment.
Linkages are genes that reside on the same chromosomes and thus cannot segregate
independently because they are physically connected. It interferes with independent
assortment because homologous chromosomes, and the genes they carry, segregate
independently of the segregation of other chromosome pairs.
Explain how crossing over can unlink genes.
Because individual chromosomes that combine genes inherited from the parents.
Describe sex determination in humans.
The determining factor for sex determination is of the last set of chromosomes in
the Karyotype; XX=GIRL, XY=BOY; Males determine the sex because they carry both
the X and Y-chromosomes
Describe the inheritance of a sex-linked gene such as color-blindness.
Sex linkage refers to a single gene residing specifically on sex chromosomes. A
color-Blindness daughter may be born to a color-blind father whose mate is a carrier.
However, because the sex-linked 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.
Because the X-chromosomes is dominant the Y-chromosomes is too “little”
compared to the X chromosomes
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 mutagens.
Translocations- An aberration in chromosomes structure resulting from as error in
meiosis or from mutagens
Inversion- An aberration in chromosomes structure resulting from as error in meiosis or
from mutagens