Integrated Principles of Zoology Study Set 3

Biology

Quiz 5 :

Genetics: a Review

Quiz 5 :

Genetics: a Review

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What are four ways that genes can be regulated in eukaryotes
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Several metabolic stages in eukaryotes may serve as control points for gene expression. The four ways by which genes are regulated in eukaryotes are as follows:
• Transcriptional control:
This is the most important mechanism for regulating gene expression. Transcription factors have either positive or negative effect on transcription. In some cases these transcription factors act locally in the cells producing them or are transported to different parts of the body for action.
• Silencing of genes:
Silencing of genes by methylation of cytosine bases is another control mechanism. A methyl group binds to the carbon at 5 th position in the cytosine ring. It happens when cytosine is present next to a guanine; thus the bases in the complementary DNA strand would also be a cytosine and guanine. When the DNA is replicated, the enzyme recognizes the CG sequence and quickly methylates the daughter strand, thus keeping the gene inactive.
• Translational control:
Genes can be transcribed and the mRNA sequestered. This delays the translation. When needed, activation of mRNA occurs to give the gene products.
• Gene rearrangement:
Vertebrates contain lymphocytes that bear genes encoding proteins called antibodies. Each type of antibody binds specifically to the antigen. As there are a number of antigens, the number of antibodies should also be high. One source of this diversity is the rearrangement of DNA sequences coding for antibodies during development of lymphocytes.

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Name the purines and pyrimidines in DNA and tell which pairs occur in the double helix. What are the purines and pyrimidines in RNA and to what are they complementary in DNA
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DNA:
The purines present in DNA are adenine and guanine. The pyrimidines in DNA are thymine and cytosine. Adenine pairs with thymine while guanine pairs with cytosine.
RNA:
The purines present in RNA are adenine and guanine. The pyrimidines in DNA are uracil and cytosine. Adenine pairs with uracil while guanine pairs with cytosine.
RNA is similar to DNA in structure except that it consists of a single polynucleotide chain and has ribose instead of deoxyribose, and has uracil instead of thymine.

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Explain how DNA is replicated.
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img During replication, the two strands of the double helix unwind. The direction of one strand is
img while the direction of the complementary strand is
img . Each separated strand serves as a template for the synthesis of a complementary strand.
The enzyme DNA polymerase catalyzes the assembly of a new strand of polynucleotides based on the template. It attaches a thymine group opposite the adenine group in the template strand, a guanine group opposite the cytosine group and vice versa.
DNA polymerase synthesizes new strands only in the
img direction.
Therefore, only the
img strand acts as a template. The
img strand cannot act as a template. Therefore, the synthesis of DNA complementary to
img strand is continuous while the synthesis of DNA complementary to
img strand is discontinuous in the form of fragments.

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Assume right-handedness ( R ) is genetically dominant over left-handedness ( r ) in humans, and that brown eyes ( B ) are genetically dominant over blue ( b ). A right-handed, blue-eyed man marries a right-handed, brown-eyed woman. Their two children are (1) right handed, blue eyed and (2) left handed, brown eyed. The man marries again, and this time the woman is right handed and brown eyed. They have 10 children, all right handed and brown eyed. What are the probable genotypes of the man and his two wives
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Rough coat ( R ) is dominant over smooth coat ( r ) in guinea pigs, and black coat ( B ) is dominant over white ( b ). If a homozygous rough black is mated with a homozygous smooth white, give the appearance of each of the following: F 1 ; F 2 ; offspring of F 1 mated with smooth, white parent; offspring of F 1 mated with rough, black parent.
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Recall that red color ( R ) in four-o'clock flowers is incompletely dominant over white ( R ). In the following crosses, give the genotypes of the gametes produced by each parent and the flower color of the offspring: R/R × R/R ; R /R × R/R ; R/R × R/R ; R/R × R /R .
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Assume that color blindness is a recessive character on the X chromosome. A man and woman with normal vision have the following offspring: daughter with normal vision who has one color-blind son and one normal son; daughter with normal vision who has six normal sons; and a color-blind son who has a daughter with normal vision. What are the probable genotypes of all individuals
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Describe or diagram the sequence of events in meiosis (both divisions).
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Explain the role of mRNA, tRNA, and rRNA in polypeptide synthesis.
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Concisely state Mendel's law of segregation and his law of independent assortment.
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How do the chromosomal mechanisms determining sex differ in the three taxa in question 3
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Diagram by Punnett square a cross between individuals with the following genotypes: A/a × A/a; A/a B/b × A/a B/b.
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What is the relationship between homologous chromosomes, copies of a gene, and alleles
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What are the designations of the sex chromosomes in males of bugs, humans, and butterflies
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Why could a codon not consist of only two bases
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A brown male mouse is mated with two female black mice. In several litters of young, the first female has had 48 black and the second female has had 14 black and 11 brown young. Can you deduce the pattern of inheritance of coat color and the genotypes of the parents
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Explain the transcription and processing of mRNA in the nucleus.
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Distinguish the following: euploidy, aneuploidy, and polyploidy; monosomy and trisomy.
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Assuming brown eyes ( B ) are dominant over blue eyes ( b ), determine the genotypes of all the following individuals. The blue-eyed son of two brown-eyed parents marries a brown-eyed woman whose mother was brown eyed and whose father was blue eyed. Their child is blue eyed.
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In Drosophila melanogaster, red eyes are dominant to white and the variation for this characteristic is on the X chromosome. Vestigial wings ( v ) are recessive to normal ( V ) for an autosomal gene. What will be the appearance of offspring of the following crosses: X W /X w V/v × X w /Y v/v, X w /X w V/v × X W /Y V/v.
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