Exam 3 Biology HW and practice test questions

The cell cycle must be regulated in a multicellular organism in order to ...

-maintain the proper cell number in tissues. -activate cell division when repair of a tissue is needed. -halt cell division when repair of a tissue is complete. -prevent cancer.

Which of the following happens commonly in BOTH mitosis and meiosis? -paternal vs. maternal chromosomes assort independently into gametes -non-sister chromatids exchange segments during "crossing over" -chromosome number stays the same from start to finish -homologous chromosomes are separated -sister chromatids are separated

-sister chromatids are separated

Recall Mendel's pea plants: the allele for purple flowers, P, is dominant to the allele for white flowers, p. A very large number of offspring from a cross of two plants are observed. If ALL of those offspring have purple flowers, what are the possible genotypes of the parents in the cross? -PP × PP only -PP × PP, PP × Pp, or PP × pp -PP × PP, PP × Pp, PP × pp, or Pp × Pp -pp × pp only -Not enough information is given

PP × PP, PP × Pp, or PP × pp

The number of DNA molecules in a cell changes during which phase(s) of the cell cycle?

S and M -Chromosomes are duplicated during S phase, doubling the number of chromatids in the cell. Copies are separated during M phase, cutting the number of DNA molecules in half.

The copying of chromosomes occurs during which of the following phases of the cell cycle?

S phase -Chromosomes must undergo replication before mitosis can occur; this copying occurs during the S phase.

Which of the following is TRUE for BOTH mitosis and meiosis? -The parent and daughter cells have the same ploidy. -The daughter cells are genetically identical to each other. -Homologous chromosomes are separated during a division. -Crossing over occurs. -Sister chromatids are eventually separated.

Sister chromatids are eventually separated.

Why do neurons and some other specialized cells divide infrequently?

They have been shunted into G0.

What is true of all cancers?

They have escaped normal cell cycle controls.

Cell division is an essential process during the development of a cat. T or F

True

Mitosis is essential for healthy functioning of adult organisms. T or F

True

Mitosis is essential for the growth of a baby. T or F

True

True or false? The same phenotype can be produced by more than one genotype.

True Since there exist dominant and recessive versions of many genes, a phenotype that is based upon the dominant version will be expressed in both homozygous (AA) and heterozygous (Aa) genotypes.

Which of the following is NOT a universal feature of the life cycles of sexually reproducing organisms?

Which of the following is NOT a universal feature of the life cycles of sexually reproducing organisms?

Part complete Suppose that a certain gene functions to enforce a checkpoint on the cell cycle. A mutation causing the loss of this gene's function would cause a person to ...

be more likely to have cancer at some point in his/her life.

True or false? The M phase is characterized by the replication and division of a cell's chromosomes.

false -Cells replicate their chromosomes during the S phase and divide partition their chromosomes during the M phase.

Human gametes are produced by _____.

meiosis

The original (ultimate) source of all genetic variation is

mutation

Consider two imaginary genes, a "finger number gene" and a "hand size gene", in an imaginary population of aliens. Since we're imagining things, let's also imagine that the aliens have diploid genomes and life cycles just like human beings. Each gene has two possible alleles. For the finger number gene, "N" is the dominant allele for having 4 fingers on each hand, and "n" is the recessive allele for having 5 fingers on each hand. For the hand size gene, "H" is the dominant allele for having small hands, and "h" is the recessive allele for having large hands. Neither gene is on a sex chromosome. Suppose an alien with the genotype nnHH mates with an alien having the genotype NNhh. Under the hypothesis of strict dependent assortment, what are the genotypes of gametes that their offspring could produce? nH and NH only nH and Nh only NH and nh only Nh and NH only NH, Nh, nH, and nh

nH and Nh only

A cell is in the process of meiosis, and pairs of homologous chromosomes are present in the cell. Which of the following is most likely TRUE about this cell? -It is at the end of meiosis II -It is in the middle of meiosis II -It could be at the beginning of meiosis I or beginning of meiosis II -It could be at the beginning of meiosis I -It could be in the middle of meiosis I or the middle of meiosis II

-It could be at the beginning of meiosis I

Suppose you are examining a cell under a very powerful microscope. The cell has multiple chromosomes. You can see the chromosomes and you notice that the chromosomes are lined up two-by-two in a line across the middle of the cell. Which of the following is most likely FALSE about this cell? -It is in the process of mitosis -It is in the process of meiosis -DNA has been replicated, but copies have not yet been separated -It is diploid -This cell is going to divide very soon

-It is in the process of mitosis

Which of the following processes most clearly provides the biological mechanism for Mendel's "law of segregation"? -Mitosis -Mutation -Meiosis -DNA replication -Fertilization

-Meiosis

For this question, assume that the species is diploid (and that the gene in question is NOT on a sex chromosome). In a hypothetical species of flower, suppose there is a gene that can cause a flower to be yellow or red. This gene has two alleles, denoted "Y" and "y" (note lower- and upper-case). Suppose there is an additional gene that can cause the flower to have 4 petals or 5 petals. This gene also has two alleles, denoted "P" and "p". A true breeding yellow four-petaled flower is crossed with a true-breeding red five-petaled flower. The F1 offspring of this cross have the genotype YyPp and are yellow with 4 petals. When two F1 individuals are crossed the following F2 offspring are produced: 153 individuals are yellow with 4 petals 51 individuals are yellow with 5 petals 51 individuals are red with 4 petals 17 individuals are red with 5 petals Given the ratios of the offspring in the F2 generation, what can you infer about the genes for flower color and petal number? -The genes are likely to be on different chromosomes -There is not enough information to answer this question -No allele is dominant for either flower color or petal number -This species of flower does not undergo sexual reproduction -The genes are on the same chromosome

-The genes are likely to be on different chromosomes

Which of the following events happens FIRST during meiosis I? -chromosomes line up one-by-one across the middle of the cell -homologous chromosomes are separated -chromosomes line up two-by-two across the middle of the cell -crossing over -sister chromatids are separated

-crossing over

True or false? In diploid organisms, a dominant phenotype will only be expressed if the individual is homozygous dominant for that trait.

False A dominant phenotype is indeed expressed if the individual is homozygous dominant for that trait, but the dominant phenotype is also expressed if the individual is heterozygous for the trait. In fact, heterozygous expression is the definition of dominant.

When, precisely, in the life cycle of a sexually reproducing organism does the transition from haploid to diploid occur?

Fertilization

Most of the cells in your body right now are in which phase of the cell cycle?

G0

How are sister chromatids and homologous chromosomes different from each other?

Homologous chromosomes contain the same gene loci but may have different alleles of a particular gene. Sister chromatids are identical copies of each other produced during DNA replication. -explanation: One homologous chromosome comes from the father, and the other comes from the mother. Sister chromatids are identical copies of each other.

Mendel's law of segregation

states that allele pairs segregate equally into gametes during meiosis. This means that a gamete will have only one allele of any given gene, and that the probability of a gamete having one allele or the other is equal (and therefore ½, or 50%, for either allele).

Which of the following descriptions correctly defines a genome? -representation of a complete set of a cell's polypeptides -a karyotype -the complete set of an organism's polypeptides -the complete set of an organism's genes

the complete set of an organism's genes

What is crossing over?

the exchange of homologous portions of non-sister chromatids explanation: The result of the exchange of homologous portions of non-sister chromatids is new combinations of genetic material (genetic recombination).

The most likely reason that the characters of "seed color" and "seed shape" showed independent assortment in Mendel's experiments is that -the genes for these two characters were very close together on the same chromosome -these two characters were the product of the same gene -the genes for these two characters were on different chromosomes -the genes for both characters were sex-linked

the genes for these two characters were on different chromosomes

Mitosis and meiosis are different in

the number of cells produced

Part complete A tall, purple-flowered pea plant (TtPp) is allowed to self-pollinate. (The recessive alleles code for short plants and white flowers.) The phenotypic ratio of the resulting offspring is 9:3:3:1. What is the genotype of the plant whose phenotype appeared once out of every 16 offspring (the "1" in the 9:3:3:1 ratio)?

ttpp The smallest phenotypic group consists of the homozygous recessive plants, which in this case are short and white flowered.

One replicated chromosome (consisting of two sister chromatids) contains a total of ...

two double-stranded DNA molecules.

Mitosis yields _________ daughter cells that are genetically ____________ and that have ____ ____ number of chromosomes compared to the parent cell.

two, identical, the same

What name is given to the most common phenotype in a natural population?

wild type. The most common phenotype is the wild type.

Your dog has puppies. A pair of homologous chromosomes inside a puppy's cell

will have the same genes at the same locations

Suppose a cell in G2-phase has 12 chromatids. How many double-stranded DNA molecules does it have?

12

A diploid organism whose somatic (non sex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes.

16

Normal human gametes carry _____ chromosomes.

23

Fill in the blanks. Suppose a cell at the end of S-phase has 48 chromatids. At the end of mitosis, each cell produced would have ______ chromosomes and ______ chromatids.

24,24

Part complete Two mice are heterozygous for albinism (Aa) . The dominant allele (A) codes for normal pigmentation, and the recessive allele (a) codes for no pigmentation. What percentage of their offspring would have an albino phenotype?

25 The offspring would be in a 3:1 ratio of normally pigmented mice to albino mice.

If an organism normally has 34 chromosomes, how many molecules of DNA should there be in the G1 phase of the cell cycle?

34 -There is one DNA molecule per chromosome.

Suppose a diploid cell has 4 chromosomes. Due to independent assortment, how many distinct combinations of chromosomes are possible in gametes that might be formed from this cell? (Hint: remember the 2-to-the-nth-power rule.)

4

Great white sharks reproduce sexually and have 82 chromosomes per diploid cell. How many of a great white shark's chromosomes were inherited from one of its parents?

41

Human skin cells typically have 46 chromosomes. A human skin cell in G2 phase has ___________ chromosomes, ____________ chromatids, and ______________ DNA molecules.

46,92,92

Fill in the blanks. Suppose a cell at the beginning of meiosis has 30 chromosomes. This cell has ________ chromatids. At the end of meiosis, each of its "daughter cells" will have _________ chromosomes.

60,15

Fill in the blanks. Suppose a cell at the beginning of meiosis has 36 chromosomes. This cell has ________ chromatids. At the end of meiosis, each of its "daughter cells" will have _________ chromosomes.

72,18

For this question, assume that the species is diploid (and that the gene in question is NOT on a sex chromosome). In a hypothetical species of fox, suppose there is a gene that can cause a fox to have a stripe of gray fur down its side. This gene has two alleles, denoted "s" and "S" (note lower- and upper-case). Foxes with one or two "S" alleles have the stripe, and the stripe looks the same whether an individual's genotype is "SS" or "Ss"; foxes with only "s" alleles have no stripe. If a male and female fox that both have the genotype "Ss" have offspring, what percentage of the offspring are predicted to have a stripe?

75%

If an organism has a diploid number of 6 chromosomes, how many different combinations of maternal and paternal chromosomes are possible in its gametes?

8

Fill in the blanks. Suppose a cell in G1 of the cell cycle has 48 chromosomes. At the end of G2, this cell would have ______ chromatids and ______ chromosomes.

96,48

Which of the following is TRUE about dominant alleles? -Dominant alleles are more likely to be inherited than recessive alleles -Dominant alleles are always more adaptive than recessive alleles. -The dominant allele is always more common than the recessive allele in a population. -A dominant allele affects the phenotype of the organism, whether or not a recessive allele is present. -Every gene has two alleles, with one completely dominant to the other.

A dominant allele affects the phenotype of the organism, whether or not a recessive allele is present.

What is the difference between heterozygous and homozygous individuals?

All of the gametes from a homozygote carry the same version of the gene while those of a heterozygote will differ. Since homozygotes carry two identical copies of a gene, all of the gametes will carry the same version. Heterozygotes have two different versions, so there will be two different types of gametes.

Which of the following contribute(s) to the variation in offspring produced by sexual reproduction? -Crossing over -Mutation -Independent assortment -Random fertilization -All of these

All of these

Which of the following is consistent with the hypothesis of blending inheritance? -Crossing a purple-flowered pea plant with a white-flowered pea plant produces only purple-flowered offspring -Great variability in traits is found within any biological population. -Crossing two pea plants with yellow seeds produces some offspring with green seeds -A phenotype from the "P" generation of a heredity experiment disappears in the "F1" generation then reappears in the "F2" generation -Crossing a red flower with a white flower yields a pink flower

Crossing a red flower with a white flower yields a pink flower

Which of the following lists the processes involved in Meiosis in the correct order?

DNA replication → Separation of homologous chromosomes → Cell division → Separation of sister chromatids → Cell division

When one allele is dominant to another, what is the most common biological mechanism for this dominance?

Dominant alleles often encode functional products, whereas recessive alleles often do not encode functional products

Which statement provides the best description of the interphase portion of the cell cycle?

During interphase, a cell is metabolically active. -Interphase accounts for about 90% of the cell cycle and includes many key events critical to the cell cycle. It is not a resting stage; the cell is metabolically active during this phase.

Which of the following is true of a species that has a chromosome number of 2n = 16?

Each cell has eight homologous pairs.

Two brown-haired parents have a child with bright red hair. Which of the following is the best explanation for this observation? -Each parent has two alleles for brown hair, but red hair is dominant -Each parent has two alleles for red hair, but brown hair is dominant -The mother has one allele for red hair and one allele for brown hair, the father had two alleles for brown hair, and the red allele is dominant -Each parent has one allele for brown hair and one allele for red hair, and the red allele is dominant -Each parent has one allele for brown hair and one allele for red hair, and the brown allele is dominant

Each parent has one allele for brown hair and one allele for red hair, and the brown allele is dominant

In an adult human, mitosis would ONLY occur in tumors. T or F.

False

Suppose you accidentally cut your finger. Healing a wound like this does NOT require mitosis. T or F

False

In which of the following situations would you expect to find the strongest support for the "law of independent assortment"? -If I were studying two characters that were both influenced by the same gene -If I were studying two characters influenced by one gene each, and the two genes involved were located on different (non-homologous) chromosomes -If I were studying three characters influenced by one gene each, and the three genes involved were located on close together on the same chromosome -If I were studying one character influenced by one gene -If I were studying two characters influenced by one gene each, and the two genes involved were located close together on the same chromosome

If I were studying two characters influenced by one gene each, and the two genes involved were located on different (non-homologous) chromosomes

Even in the absence of any mutations or crossing over, what process would still ensure genetic variability in the gametes produced by a single individual?

Independent assortment

For a chemotherapeutic drug to be useful for treating cancer cells, which of the following is most desirable?

It targets only rapidly dividing cells.

When, precisely, in the life cycle of a sexually reproducing organism does the transition from diploid to haploid occur

Meiosis 1

Which of the following processes most clearly provides the biological mechanism for Mendel's "law of independent assortment"? Mitosis Meiosis II Mutation Fertilization Meiosis I

Meiosis I

Horses have 64 chromosomes per diploid cell. When horse parents have horse babies (foals) via sexual reproduction, those babies also have 64 chromosomes per diploid cell. How is this possible?

Meiosis makes horse gametes with 32 chromosomes each, and then fertilization makes a horse zygote with 64 chromosomes

For this question, assume that the species is diploid. In a hypothetical species of antelope, suppose there is a gene that can cause an antelope to have white or brown fur. This gene has two alleles, denoted "f" and "F" (note upper- and lower-case). Antelopes with one or two "F" alleles have brown fur; antelopes with only "f" alleles have white fur. Is the "F" allele dominant or recessive, and why?

The "F" allele is dominant because genotype "Ff " has brown fur

For the first several divisions of early frog embryos, cells proceed directly from the M phase to the S phase and back to M without gaps. Which of the following is likely to be true about dividing cells in early frog embryos?

The cells get smaller with each generation. -Without gap phases, the cells have no opportunity to grow.

Researchers began a study of a cultured cell line. Their preliminary observations showed them that the cell line did not exhibit either density-dependent inhibition or anchorage dependence. What could they conclude right away?

The cells show characteristics of tumors.

"Independent assortment" refers to which of the following?

The orientation of each homologous pair of chromosomes during meiosis I is independent of other pairs.

In human bodies, mitosis is directly involved in all of the following EXCEPT: The growth of fingernails Healing broken bones Replacing hair that falls out every day Healing cuts in your skin The production of sperm and eggs

The production of sperm and eggs

Which of the following is a function of the S phase in the cell cycle?

The synthesis of sister chromatids. -DNA replication occurs during S phase and results in two sister chromatids for each original chromosome.

What is an allele?

an alternative version of a gene. A diploid organism carries two alleles for each autosomal gene. The two alleles are found at comparable locations (loci) on homologous chromosomes. The alleles may be identical or slightly different, but they affect the same genetic character.

In general terms, normally a cell in your body crosses a checkpoint in the cell cycle when ...

concentrations of proteins in the cytoplasm reach the appropriate level.

One difference between cancer cells and normal cells is that cancer cells ________.

continue to divide even when they are tightly packed together

When constructing a Punnett square, the symbols on the outside of the boxes represent _______, while those inside the boxes represent _______.

gametes, progeny The Punnett square is representing all of the possible combinations of the gametes from each parent, with the progeny represented in the interior of each box.

If a diploid organism possesses one dominant allele and one recessive allele for a particular gene, then ________ of its gametes will possess the dominant allele and ________ of its gametes will possess the recessive allele.

half,half

For this question, assume that the species is diploid (and that the gene in question is NOT on a sex chromosome). In a hypothetical species of rabbit, suppose there is a gene that can cause a rabbit to have floppy ears. This gene has two alleles, denoted "E" and "e" (note upper- and lower-case). Rabbits with one or two "E" alleles have ears that stand up straight; rabbits with only "e" alleles have floppy ears. Suppose that a male rabbit with ears that stand up straight and a female rabbit with floppy ears have one offspring, and that offspring has ears that stand up straight. What is the genotype of the male (the father of the offspring)?

his genotype could be "Ee" or "EE"

In general, the frequency with which crossing over occurs between two linked genes depends on __________.

how far apart they are on the chromosome. The farther apart two genes are on a chromosome, the greater the probability that a crossover will occur between them, and therefore the greater the recombination frequency.

If an organism with the genotype AaBb produces gametes, what proportion of the gametes would be Bb?

none Alleles of the same gene must separate during gamete formation; thus, the two B alleles would be distributed to different gametes.

Consider cells in a tissue that is growing by mitosis. The number of chromosomes in these cells changes in which of the following parts of the cell cycle?

none of the phases (chromosome number does not change) -During the cell cycle and mitosis, the number of chromosomes per cell remains constant, though the numbers of chromatids and DNA molecules change in a cyclic manner.