BIOL 2019 Exam 1 + Quizzes 2021

Labrador retriever dogs have two genes that affect coat color. One gene, the B locus, codes for the intensity of eumelanin production in the dog's coat. It has two alleles that produce either a black pigment (B) or a brown pigment (b). Another gene, the E gene, is epistatic to the B gene. The dominant E allele causes eumelanin to be deposited along the length of the dog's hair shafts. The recessive e allele blocks the deposition of eumelanin in the hair, so only the yellow producing phaeomelanin pigment is deposited, resulting in yellow dogs. If you cross parents with the following genotypes, Bbee x bbEe, what phenotypic ratio do you expect in their offspring?

1 black: 1 brown: 2 yellow

1. What does the duplication of cells require? In order to make a new cell, it is necessary to do 3 main things:

1. Replicate genetic material. In eukaryotic cells this means the duplication of all chromosomes (each consisting of a single DNA molecule).2. Accurate segregation of each duplicated chromosome to each daughter cell. This ensures that the two new cells each have the same number and kind of chromosomes.3. Division of the cytoplasm such that each daughter cell receives all the subcellular organelles needed to maintain cellular life.

In the following cross upper case letters indicate a dominant allele and lower case letters the recessive allele. The alleles all assort independently. When the cross Aa Bb Cc x Aa bb cc is made, what is the probability of getting all phenotypically recessive offspring?

1/16

When one of the dog's cells from above is in telophase 1 of meiosis, how many chromatids would the cell contain?

156

A true-breeding round seed pea is crossed to a true-breeding wrinkled seed pea. The progeny are all round. If one of the F1 progeny is test-crossed, what phenotypic ratio would you expect in the offspring?

2 round : 2 wrinkled

If an individual's genotype is AaBBCcDD, this individual has

4 loci and 6 different alleles.

Which of the following characterizes a kinetochore?

A kinetochore serves as the spindle fiber attachment point on a chromosome.

2. What is a locus? How is this related to a gene, and an allele?

A locus is the physical location of a gene on a chromosome. Genes are the physical units of inheritance. Traditionally, genes are defined as a segment of DNA that codes for a protein, but we will define genes in different ways throughout the semester. Alleles are the different forms of a gene that can exist. The copies of genes found on different chromosomes can be different alleles of that gene. This refines the idea of locus to be the site of the particular allele of a gene that is carried on a chromosome. This will become even more important later when we see how we can genetically map loci.

After genetic counseling Abby and Abe were told that the baby they were expecting had a 50% chance of having type A blood and a 50% chance of having type B blood. What are the most likely blood types of Abby and Abe?

AB and O

3. What are centromeres and kinetochores and what are their roles in the function of chromosomes? What is the function of cohesion?

Centromeres are the constrictions seen in chromosomes, often in the center of the chromosome (so-called metacentric chromosomes). Kinetochores are the proteins found at the centromere that function as microtubule attachment sites during mitosis. The attachment of polar microtubules to the kinetochores of sister chromatids is necessary for accurate segregation of chromosomes. Centromeres can be thought of as genetic entities: they are DNA sequences and their behavior can be followed genetically by following the behavior of traits that are tightly linked (see next section on genetics for information on linkage). Kinetochores are cell biological entities that are found at the physical location of centromeres. Both are necessary for the proper functioning of this structure during mitosis. Cohesin is a complex of proteins that hold two sister chromatids together near the kinetochore. Cleavage of cohesion irreversibly separates the two chromosomes. Because replication of chromosomes and segregation of chromosomes occurs at different times, cohesion is very important. Without it, there would be no guarantee that each daughter cell would end up with all the chromosomes and just one copy of each chromosome.

4. How are chromosomes organized in eukaryotic cells? How are they compacted to fit into cells, and how are they compacted further to allow them to be separated during cell division? What is the structure of the nucleosome? What is its role in the structure of chromosomes?

Chromosomes are highly compacted in cells; as they can be literally mm long, they must be compacted to fit into µm long cells. This compaction is hierarchical and can be thought of as occurring in stages. The degree of compaction changes with the cell cycle as they must be maximally compacted for segregation during cell division. At all times, chromosomes are organized into structures we call nucleosomes. These consist of a protein core called the histone octamer. About 200 bp of DNA is wrapped 1.5 times around this histone octamer like string around a ball leaving a short "linker" stretch between adjacent nucleosomes. This can be then coiled into a still higher order structure often called a solenoid where the string of nucleosomes form a higher order coil. This structure, composed of nucleosomes packed together in a coil, is about 30 nm in diameter and is called, rather originally, the "30 nm fiber" (also sometimes called the solenoid for its shape). This is the state of interphase chromatin. To achieve accurate segregation of chromosomes during cell division it is necessary to compact them even further. The details of this are not clear, but it does involve the creation of looped domains of the 30 nm fiber that are then arranged on a scaffold of protein, by looping radially around the scaffold. The protein scaffold has the basic shape of a metaphase chromosome as can be seen when metaphase chromosomes are depleted of DNA.

6. What are cyclins and what is their role in the cell cycle? What are Cdk enzymes and what is their function during the cell cycle?

Cyclins are proteins that are produced and destroyed in concert with the cell cycle. They were first recognized based on their periodic synthesis and destruction, which correlates with the progression of the cell cycle. Mitotic cyclins are made at increasing levels as the cell progresses through interphase and then are rapidly degraded during mitosis. The role of cyclins in the cell cycle is to form a complex with enzymes that are protein kinases: thus Cyclin Dependent Kinases or Cdk's. The Cdk enzymes are not active alone, but require binding to cyclin for activity.The Cdk enzymes control the progress through the cell cycle by phosphorylating a variety of cellular proteins needed for division. This includes the proteins that turn on the expression of genes encoding new protein needed during the cycle, as well as activating existing protein. The cell cycle is sensitive to both the internal state of the cell and to the environment. This control is mediated by a small number of activating enzymes: the Cdks. Thus activation of Cdks sets in motion the diverse events necessary for cell division.The Cdk's are also controlled by phosphorylation of the kinase itself and by the presence/absence of cyclins. These two forms of control of Cdk's act at checkpoints: a Cdk must be activated to enter S phase for example. Internal and external signals all funnel through the Cdks.The case of regulation of the cell cycle during anaphase is a little more subtle and relates to a key difference between prokaryotes and eukaryotes. The signal to proceed through anaphase goes through the anaphase promoting complex (APC). Once the APC is activated, that molecule in turn activates separase, an enzyme that hydrolyses the cohesion proteins holding the two chromatids together. The relationship between the replication of chromosomes and their segregation is thus: during the eukaryotic cell cycle the replication and segregation of chromosomes are not consecutive events the way they are in prokaryotes. This means that after chromosomes are replicated, they must remain attached until the segregation event for maximal accuracy. Thus the two chromatids of a newly replicated chromosomes remain attached at their centromere until anaphase. In fact, the centromere appears to be a single centromere holding together the two chromatids in microscope images. This is an oversimplification but not a bad way to think about it. This is in sharp contrast to the case of binary fission where the two processes of replication and segregation are concerted. This delay between replication and segregation is probably necessary for the construction of the elaborate multiple chromosome genomes that are found in eukaryotes and may be anancient innovation that distinguishes the entire lineage.

Which of the following is/are true concerning the events of a cell cycle?

Cytokinesis is the process of dividing the cytoplasm.

Okazaki fragments are

DNA and require multiple primers for their synthesis.

During the elongation phase of DNA replication, which of the following enzymes is necessary?

DNA polymerase because it assists in the production of phosphodiester bonds.

Which of the following is true about nucleosomes

DNA wraps around 8 histone proteins to form one, and they are a component of chromatin.

A human zygote would be correctly described as

Diploid. 2n = 46, because it has two of each type of chromosome, for a total of 46 chromosomes in the cell.

8. Is dominance absolute? How can dominance be altered? How does this affect your view of the concepts of genotype and phenotype?

Dominance is not absolute, there are many variations on strict dominance. In incomplete dominance, the phenotype of the heterozygote appears intermediate between the phenotypes of the two homozygotes. In codominance, the phenotype of the heterozygote shows the phenotypes due to both alleles. In either case the heterozygote has a phenotype that is distinct from both homozygotes.This all indicates that dominance can be a continuum, or not exist at all. This means that the simple view from Mendel does not always hold. In these cases of altered dominance, the nature of the relationship between genotype and phenotype is even more clear: genotype leads to phenotype. It also leads to a situation in which we can predict the genotype from the phenotype as both incomplete dominance and codominance have the heterozygote has a unique phenotype.

9. What is the difference between a homolog and a sister chromatid? Do all chromosomes have sister chromatids?

In a diploid cell, for each chromosome there are two homologues: a paternal and maternal homolog. After S phase each homolog is composed of two sister chromatids held together at the centromere as we have just seen in mitosis. Thus only cells in G2 through metaphase have sister chromatids. Notice that we call an unreplicated chromosome and a replicated chromosome the same thing (one chromosome) even though they look different and have different amounts of DNA.

If you are looking at a cell under the microscope that produces the protein FtsZ, which of the following would be true about that cell?

It divides by binary fission.

Which of the following correctly describes synapsis?

It occurs during prophase I of meiosis. It produces a tetrad.

10. What is the significance of meiosis I and how does this differ from mitosis? How does meiosis II differ from mitosis?

Meiosis I is the defining division of meiosis, often called the reductive division because at the end, the resulting cells will have half the number of chromosomes. To understand this, you must understand that we count chromosomes by counting centromeres not chromatids (see 10 above). Meiosis I is characterized by the homologues of each chromosome finding their "partner" and pairing along the entire length of the chromosome. This involves the construction of an elaborate structure, the synaptonemal complex, between them. While they are complexed with one another, crossing over can occur. This event recombines parts of one chromosome with its homologue. The result is that the chromosomes an individual inherits are not exact copies of the ones their parents had. Instead, each chromosome is a mosaic of parts of that chromosome from each parent. This dramatically increases the possible genetic diversity that arises through sexual reproduction. Homologues will remain associated through metaphase with homologues becoming attached to microtubules from opposite poles. This leads eventually to homologues moving to opposite poles during anaphase instead of sister chromatids as in mitosis. We say that during meiosis I homologues disjoin and segregate and during mitosis sister chromatids disjoin and segregate.Meiosis II is much like a mitotic division except that it is not preceded by DNA replication and the cells will have half the DNA of the original cell after the division. The behavior of the chromosome during metaphase and anaphase is the same as in mitosis and distinct from the pairing seen in meiosis I.

Cells containing homologous pairs of chromosomes would be produced by which of the following processes?

Mitosis

11. Compare and contrast meiosis and mitosis.

Mitosis results in cells that are essentially identical, or at least with identical genetic material while meiosis produces cells that have half the genetic material (half the number of chromosomes) and are not genetically identical. Mitosis produces two cells while meiosis generally produces 4 cells. Mitosis involves a single round of replication and a single nuclear division while meiosis involves a single round of replication but two rounds of nuclear division. Homologues pair during meiosis I and remain associated until anaphase when they segregate. During this pairing process chromosomes will also exchange material by crossing over (a cytologically visible process), which correlates with genetic recombination as we will see later. Homologues behave independently during mitosis and sister chromatids segregate during anaphase. Different chromosomes behave independently in each kind of division. Cytokinesis is also similar in both kinds of division except that there are two rounds of it during meiosis

2. How is the genetic material of prokaryotic cells organized and how do the cells divide?

Most prokaryotes have a single circular chromosome.Prokaryotic cells divide by binary fission. This process is much simpler than the elaborate process seen in eukaryotes. It does not require a complex cell cycle, and the segregation of chromosomes is much simpler. Contrary to what was thought for many years, the process of chromosome segregation is an active process that requires the participation of a number of proteins. This is not accomplished by the simple growth of the plasma membrane with passive segregation of the attached chromosome.However, replication and segregation of the chromosome are concerted processes during binary fission. That is they occur together with the newly replicated chromosome being segregated to opposite poles by a mechanism that yet unknown. This requirement for replication immediately followed by segregation may limit how complex a chromosomal organization this type of cell can have. A delay between replication and segregation may have been necessary for the evolution of more complex genomes.

Crossing over

Occurs during prophase I of meiosis and results in the reciprocal exchange of genetic material between non-sister chromatids.

3. When we cross round by wrinkled we get only round progeny. Why is this? What do we call the round and wrinkled phenotypes?

Only the round progeny appear in an F1 generation because the round is dominant to wrinkled. The physical basis of this dominance will be something that we approach from different views of the gene. The round phenotype, specified by the round allele, would be the dominant phenotype or allele andthe wrinkled phenotype, specified by the wrinkled allele, would be the recessive phenotype or allele.

10. What is pleiotropy? What do we mean when we talk about "gene interactions"? Give an example from class of such a genetic interaction. How does this affect your view of genotype and phenotype?

Pleiotropy is when a single gene product influences multiple traits. This occurs because of branching biochemical pathways and multifunctional proteins. In many cases, the protein product of a pleiotropic allele may be dominant when acting in one capacity, and recessive when acting in another function. Gene interactions are not contrary to independent assortment although it may appear to be on the surface. The usual ratio expected of independent assortment will be altered but it is still there, much like with incomplete dominance and codominance. The interaction is at the level of the function of the genes: one gene obscures the action of another gene. The example we used in class was coat color in Labrador retrievers. In this case when an individual is homozygous recessive for one gene, the phenotype for another gene is not seen. This is called recessive epistasis. This is a common phenomenon in coat colors in mammals. The gene with the epistatic effect determines the presence or absence of color, the gene whose phenotype is obscured determines the nature of the color. If there is no color at all, how can black or brown be significant?In terms of genotype and phenotype, it leads to even greater complexity as now we must consider the effects of multiple genes together when we think about phenotype. The effect of one gene will only be seen in the presence of certain alleles for another gene, or to use genetic terminology in a particular genetic background. We cannot just think about the effects of different genes individually then sum these effects. Considering the overall complexity of metabolism, it was naïve to think that we could only consider one gene at a time.

Which of the following correctly describes prokaryotes and eukaryotes?

Prokaryotes do not have a cell cycle.

1. Why and when during the cell cycle does DNA replication occur?

Replication occurs during the S (synthesis) phase of the cell cycle. It occurs because the restriction checkpoint has been successfully passed, allowing the cell to make the irreversible commitment to replication.

Cell division in prokaryotes and eukaryotes both require

Replication of Genetic Material & chromosomal compaction

11. What is sex-linkage and how can you recognize it? What is the physical basis for sex-linkage?

Sex-linkage is the alteration in patterns of inheritance based on the sex of the parents. This is seen for loci that are on the so-called sex chromosomes. These are chromosomes that differ between the sexes and these chromosomal differences lead to altered patterns of inheritance. The heterogametic sex (the one with different sex chromosomes) will always show recessive traits.In Drosophila, if we cross white-eyed males with red-eyed females all progeny are red eyed. If we do the reciprocal cross with red-eyed males and white-eyed females, we would normally expect no difference. What we actually observe is red-eyed females and white-eyed males. This difference in reciprocal crosses is the hallmark of sex-linkage. In humans, it leads to males showing sex-linked traits more often (they are the heterogametic sex), and to inheriting these traits from their maternal grandfathers through their mothers.

During which of the following phases of the cell cycle would the amount of DNA per cell be double relative to when the cell was produced by cytokinesis?

Telophase & G2

3. What does it mean for DNA to be replicated semi-conservatively?

The basic mechanism of DNA replication is semi-conservative. The parent molecule is unwound and each strand is copied to produce two new molecules. Each new DNA molecule is composed of one newly synthesized strand and one "old" strand. As each new molecule conserves one of the two parental strands, we call this semi-conservative.

5. What are the phases of the cell cycle and what occurs during each phase? What does it mean to say that cell division is an oscillation between interphase and mitosis?

The cell cycle can be divided, somewhat arbitrarily, into 5 phases: G1 (gap 1), S (synthesis), G2 (gap 2), mitosis and cytokinesis. The two gap phases, G1 and G2, plus the DNA synthesis phase, S phase, are together called interphase. Interphase takes up the majority of the cell cycle and the cycle itself can be seen as oscillating between interphase, or preparing to divide, and mitosis, or actively dividing.The G1 phase is important because it is when the cell decides to actually divide at all. It is also important to prepare the cell for S phase. During S phase the cell replicates all of its DNA, and the centrosomes replicate as well. The cell must accomplish the accurate replication of all of its DNA to be able to proceed to mitosis. During G2 the cell prepares to divide by mitosis. Mitosis involves the actual segregation of genetic material. Cytokinesis is the division of the cytoplasm. Mitosis and cytokinesis are often considered part of the same process and the distinction between the end of mitosis and the beginning of cytokinesis is arbitrary.

Below is the karyotype of a dog (Canis familiaris):

The dog cell is 2n = 78. The cell came from the heterogametic sex

1. Mendel's pea plants exist in both tall and short varieties. You cross a true breeding tall strain to a true breeding short strain and observe all tall offspring. What does this tell you about tall and short? If you intercross the F1, what do you expect? If you cross the F1 back to the short parent, what do you expect?

The first cross tells you that tall is dominant to short (also meaning that short is recessive). For the following crosses, we will use D to symbolize the dominant tall allele and d to symbolize the recessive short allele (the letter d to indicate the dwarf phenotype of the variant). For each line the phenotype is directly indicated with the genotype in parenthesis.P0 Tall (DD) x Short (dd) Gametes D d F1 All Tall (Dd) F1 x F1 Tall (Dd) x Tall (Dd) Gametes D, d D, d F2 1 Tall (DD) 2 Tall (Dd) 1 Short (dd) Phenotypic ratio: 3 Tall:1 Short (3/4 Dominant and 1/4 Recessive) F1 x short Tall (Dd) x Short (dd) Gametes D, d d 1 Tall (Dd) 1 Short (dd) Phenotypic ratio: 1 Tall:1 Short (1/2 Dominant and 1/2 Recessive)

During DNA replication

The leading strand is made continuously using a template strand running 3' 5'

8. What are the phases of mitosis and what is happening during each phase? Why is anaphase so important? What would happen if you had mitosis without cytokinesis?

The phases of mitosis are Prophase, Prometaphase, Metaphase, Anaphase, and Telophase.Briefly, during prophase, the chromosomes condense and become visible. The centrioles move to opposite ends of the cell. The spindle apparatus appears and the nuclear envelope dissolves.Prometaphase is characterized by the attachment of the chromosomes to the spindle apparatus. The attachment occurs at the kinetochore, and the microtubules that make up the spindle apparatus start to move the chromosomes toward the center of the cell.Metaphase is characterized by the arrangement of all chromosomes at the equator, or metaphase plate, of the cell with polar microtubule fibers from opposite poles attached to the centromere of each chromatid. This involves some pulling of chromosomes towards one pole, then the other until they are all arranged in the middle, and are also under tension with sister chromatids of each chromosome oriented towards opposite poles.During anaphase, chromosomes separate their connection at the centromere and move towards opposite poles. This movement is usually called anaphase A and is accompanied or followed by movement of the two poles away from each other, called anaphase B. The actual mechanics of anaphase A appear to involve the degradation of proteins holding the chromosomes together, controlled by the anaphase promoting complex (APC). These proteins that hold chromosomes together are called cohesins. Thus the cohesins are the glue that holds chromatids together after replication, and the APC triggers the removal of this glue at the appropriate time.During telophase, the spindle apparatus disassembles, the chromomosomes start to uncoil, and the nuclear envelope is reassembled. Mitosis without cytokinesis will produce a cell with twice the amount of DNA as its precursor cell. This assumes that the two nuclei that would exist after telophase would fuse, or that the nuclear membrane would reform about both genomes. Anyway you look at it, you would have too much DNA (2X to be exact).

9. How do alterations of dominance affect the results from simple crosses?

The phenotypic ratio is reduced to the genotypic ratio as now all of the genotypes have unique phenotypes. Thus we see a 1:2:1 ratio instead of the 3:1 monohybrid ratio. The usual monohybrid ratio is really a condensed form of the genotypic ratio.

6. What is the principle of independent assortment? What is the physical basis for this principle? How does the process of meiosis allow us to predict the Mendelian ratio seen for a dihybrid cross?

The principle of independent assortment says that different genes will behave independently in the production of gametes and thus in genetic crosses. To put it in more modern terms, alleles of different genes segregate independent of each other. So although alleles happen to be found together in one individual, they do not have to stay together if they are on different chromosomes—they assort and segregate independently of one another. The physical basis for this is that different chromosomes behave independently during the process of meiosis; the chromosomes from one parent don't have to stay together during segregation. That is, when homologues pair and move to the metaphase plate during meiosis I, the homologues of different chromosomes will align on the metaphase plate independently. In a single gamete, the chromosomes are a mix of some paternal and some maternal chromosomes. This behavior of chromosomes means that if we assign symbols to represent alleles of genes, we can manipulate these symbols using rules of probability and they will behave the same as chromosomes. Thus we can predict the gametes made by any individual and then combine these gametes randomly to simulate a cross.

5. What is the relationship between genotype and phenotype for homozygotes and heterozygotes?

The relationship between genotype and phenotype for a homozygote is simple as there are two copies of the same allele. In Mendelian genetics, a heterozygote takes the phenotype of the dominant allele. This means that when you see the dominant phenotype, you do not know the genotype (either homozygous dominant or heterozygous), but if you see the recessive phenotype you do know the genotype (homozygous recessive). In either case, genotype leads to phenotype, keeping in mind rules of dominance. If you know the genotype you can always predict the phenotype, but the converse is not always true.

Which of the following occurs during anaphase of mitosis?

The two chromatids of a chromosome are pulled away from each other.

1. What was the view of genetics prior to Mendel? How did he change this?

The view of inheritance before Mendel was that traits from each parent mix in the offspring: or "blending inheritance." This was not a quantitative concept so one of the biggest differences in methodology between Mendel and the majority of his predecessors was his quantitative approach. His quantitative approach simple by today's standards, but was way ahead of its time and led to the use of probability to predict the outcome of crosses. One of the most important conceptual difference was the idea of particulate inheritance. This is the idea that traits are carried by discrete physical units that do not blend. We now call these genes

7. Are any steps in the cell cycle irreversible? What are the implication of this for the control of the cell cycle and the mechanics of the cell cycle?

There are two steps that may be thought of as irreversible: the decision to divide at all, called START, and the decision to segregate chromosomes during anaphase of mitosis. The irreversible nature of START is obvious: once you have committed to replicating chromosomes, you had better divide the cell as well or you will double the number of chromosomes!

Which of the following correctly describe nucleosomes?

They are a component of chromatin.

Which of the following are true about the events of replication?

They occur after the 'start' cell cycle checkpoint has been passed & A DNA polymerase removes primers.

6. Can two yellow labs ever give rise to black lab pups? You cross a true breeding yellow lab with a true-breeding chocolate lab and get all black pups. What were the genotypes of the parents and what would you expect if you intercross the pups?

To answer this, you must think about what gives rise to the yellow phenotype. To be yellow, an animal must be homozygous recessive for the E locus. This genotype also masks the effects of the brown locus so you cannot have either black or chocolate in this yellow genetic background. This is a good example of the action of the genetic interaction we call epistasis.The true-breeding yellow could be either BB ee or bb ee while the true breeding chocolate must be bb EE. Since the pups are black, the yellow parent is therefore BB ee. The F1 is heterozygous for both loci, so this is the same as our usual Mendelian dihybrid cross. The crosses including the intercrossed F1are shown below:Phenotypic ratio: 9 Black:3 Chocolate:4 YellowNote: This is the normal dihybrid ratio except because Yellow is epistatic to brown this compresses the ratio to 9:3:4 or 9:3:3+1.

The principle of independent assortment is illustrated by which of the following data?

When F2's are produced from offspring of true-breeding dominant and recessive parents in a dihybrid cross, the F2's exhibit four phenotypes.

7. What do we mean by the term: "progeny testing"? How does this relate to the concepts of genotype and phenotype?

When we look at an individual who displays the dominant phenotype, we cannot tell their genotype, that is if they are a homozygous for the dominant allele or heterozygous. We can determine this experimentally if we do a test cross--cross this individual to the homozygous recessive genotype and observe the progeny. If the recessive allele segregates then the original parent was a heterozygote.

Which of the following is a correct statement about mitosis and meiosis II?

Which of the following is a correct statement about mitosis and meiosis II?

For cells undergoing meiosis in the human testes:

a cell is 2 n = 46 at telophase II because sister chromatids have separated. C. a cell is 1n = 23 after interkinesis.

. (Bonus) As temperatures rise due to climate change, you expect crocodiles to produce

a higher proportion of females due to temperature-dependent sex determination.

Compared to when a cell began G1, at which of the following stages would the cell have DOUBLE the amount of DNA?

at the end of G2 at the end of S

Vinblastine is a medicine derived from the plant Vinca rosea. Vinblastine treatment of cells blocks microtubules from properly binding to chromosomes and helping the chromosomes move to opposite poles. From this information you know that vinblastine

blocks microtubule attachment to kinetochores and inhibits microtubule depolymerization.

Which of the following are composed of DNA?

centromeres telomeres alleles

Mitosis and meiosis differ because

chromosomes independently assort in meiosis but do not independently assort in mitosis.

In DNA, hydrogen bonds occur between

complementary bases such as A and T on the interior of the helix, and may be prevented from reforming by single-stranded binding proteins.

A pea plant has the genotype AABbCC. The three genes assort independently. How many different gametes can this plant make?

equal numbers of 2 kinds of gametes

Maturation promoting factor (MPF)

has a cyclin component & is produced at the restriction checkpoint.

4. What is the principle of segregation? What is the physical basis behind this principle?

he principle of segregation says that during the process of gamete formation, different forms of a gene (alleles) are segregated into gametes. This means that they are physically separated into different gametes. During fertilization, individual (single copy) alleles from different parents are united, restoring diploidy so that each embryo has two copies of each gene. A more modern statement would be that different alleles of a gene segregate during meiosis. Note that this is only visible in a heterozygote as homozygotes make only one type of gamete because all copies of a gene are the same allele.The physical basis for segregation is the behavior of chromosomes during meiosis. Each pair of homologues disjoin during Meiosis I (more to opposite poles) leading to cells that ultimately contain only one of each homologous chromosome. The principle of segregation says that during the process of gamete formation, different forms of a gene (alleles) are segregated into gametes. This means that they are physically separated into different gametes. During fertilization, individual (single copy) alleles from different parents are united, restoring diploidy so that each embryo has two copies of each gene. A more modern statement would be that different alleles of a gene segregate during meiosis. Note that this is only visible in a heterozygote as homozygotes make only one type of gamete because all copies of a gene are the same allele.The physical basis for segregation is the behavior of chromosomes during meiosis. Each pair of homologues disjoin during Meiosis I (more to opposite poles) leading to cells that ultimately contain only one of each homologous chromosome.

Incomplete dominance and codominance differ because

in incomplete dominance, the heterozygote's phenotype is intermediate between the two homozygotes and in codominance the heterozygote may shows features of both homozygotes.

Heterogametic means that

individuals have two types of sex chromosomes.

12. Anueploidy

is a condition in which gametes lack or have duplicate copies of a particular chromosome. Fertilization of such a gamete by a normal gamete can result in zygotes that have abnormal numbers of chromosomes. For example, Down syndrome is most frequently caused by the presence of three copies of chromosome 21 (trisomy 21). Given your knowledge of gamete formation, hypothesize a mechanism by which aneuploidy can occur. Be explicit about the stages of meiosis that are relevant. Anueploidy may occur if homologous chromosomes fail to separate during anaphase I, or if sister chromatids fail to separate in anaphase II.

During which of the following phases of the cell cycle would a chromosome be made up of two chromatids?

mitotic metaphase & G2

Compared to G1 of interphase, which of the following phases has the same number of chromosomes per cell?

telophase

. Enamel hypoplasia is a sex-linked genetic condition in which tooth enamel is normally developed but extremely thin, making teeth particularly prone to wear and decay. The teeth of afffected individuals may also have a striped appearance. A female with normal tooth enamel is married to a man with enamel hypoplasia. All five of their daughters have enamel hypoplasia, but none of their five sons have the condition. Based on this information you can conclude that

the disease is caused by a dominant allele and the female has a homozygous genotype.

For traits that are determined by genes on different chromosomes, independent assortment of these traits is due to

the random alignment of chromosomes during metaphase I.

In a dividing cell, a septum

would be composed of FtsZ proteins and would be found in prokaryotes.

When true-breeding red four o'clock flowers are crossed with true-breeding white four o'clocks, the offspring produced are pink. When a pink offspring is crossed with a white-flowered plant, what fraction of the offspring are expected to be pink?

½