Question

1) toe drom rod-groen color blindness numan population over the To express a poly genetic trait : a. Geres must interact w/ the environment b. Several gones must act together occur in the same tamily Aultiple mutations must d. Renetrance must occur 15) A normal male and a temale carrier from red-green color a mate. Given that red-green color blindress is an X-linked rece troit, what is the likelihood of their children being affected! 0.23% c. Females must atlected, no males aflected b. 50% d. makes most affected, no females attected (6) the gradual increase in height among the human past 100 years is an example of: population a. polygenic trait Co Crossing over b. multifactorial trait di recombination 17) When discussing DNA replication, which enzyme is most important? a. RNA polymerase c. Messenger RNA b. Transfer RNA d. DUA Polymerase 18) When the surse is teaching the staff about x linked recessive disorders, which information should the nurse include? (check all that apply) a. The trait is seen much more often in females than in b. the trait is males never transmitted from father to son C. The gene can be transmited through a series of carrier females do the gone is passed from an affected father to all his daughters. e. He tait never skips generationis 19) sequence the events that occur during protein synthesis. Place the steps in order. - - MRNA is spliced to remove Translation - MRNA leaves the nucleus non-coding sections Transcription RNA polymerase binds to DNA promotor site

Answer 1

14. To express a polygenic trait:

b. Several genes must act together.

Polygenic trait is by definition, a trait, whose phenotypic expression is affected by more than one gene. Thus, to express a polygenic trait, several genes must act together.

The following options are incorrect because:

a. Genes must interact with the environment.

Certain traits are expressed in a certain way under environmental influence. Temperature, drug, chemical imbalance can all affect gene expression. However, expression of polygenic trait is not exclusively dependent on environmental factors, and their expression may occur quite independently.

c. Multiple mutations must occur in the same family.

Multiple mutations occurring in the same family of genes can severely affect a phenotype, and may eventually in the course of evolution may even give rise to a novel phenotype. Such mutations are in no way a precondition to expression of a polygenic trait.

d. Penetrance must occur.

Penetrance is the proportion of individual in a population possessing a particular variation of a gene, who actually exhibit the associated characters. This means the proportion of carriers of genes that actually exhibit the relevant phenotype. This term is mainly associated with the expression of a recessive allele in population. A polygenic trait will be expressed, in varying degrees, regardless of the variant of gene present, as long as all the genes are expressed.

15. The likelihood of the children being color blind if a normal male and a female carrier mates is:

a. 25%

Colorblindness is a X linked recessive trait. Thus the mutant recessive allele responsible for color blindness must be located on X chromosome. For a female to be color blind, she must possess recessive allele on both X chromosomes. On the other hand, since males have only one X chromosome, they will be color blind if they have recessive allele on their singular X chromosome.

In the given case, the male does not have recessive allele on his X chromosome, and hence has normal color vision. The female is carrier for color blindness, which means she has recessive allele in one of her X chromosomes.

Now, all female children will receive a normal X chromosome from their father. They might receive either the affected or the normal X chromosome from their mother. But regardless, they would not be affected with color blindness, since it is a recessive trait, and the female children will definitely have one chromosome with the normal dominant allele. They will be either normal or carriers for color blindness depending on the chromosome they receive from their mother.

All male children would receive Y chromosome from their father. They might receive the affected or the normal X chromosome from their mother. If they receive the chromosome bearing the affected recessive allele from their mother, they would be color blind. The possibility of receiving the affected allele is 1 in 2, or 50%. Thus only 50% of the sons can possibly be color blind.

There is a 50% chance (1 in 2) that a son would receive the affected X chromosome from his mother. Further, there is a 50% (1 in 2) chance that the child would be male in the first place.

Thus the overall possibility of having colorblind children = 1/2 x 1/2 = 1/4, or, 1 in 4, or 25%.

The following options are incorrect because:

b. 50%

As shown above, in this case the probability of having affected children is 25%. It would have been 50% if either all males would have been affected or if 50% each of male and female would have been affected. The first case would be possible in the mother was color blind instead of just a carrier. The second case would have been possible if the father was color blind and the mother was the carrier.

c. Females must be affected, no males affected.

Since color blindness is a X linked recessive trait, for females to be affected they must inherit the affected allele from both their parents. Thus both their father and mother must have been color blind for this to happen, which is not the case. Further, if the mother was color blind, the sons would have inherited the affected allele from her and would have been colorblind too. Thus this scenario is not possible.

d. Males must be affected, no females affected.

For all males to be affected, the mother must have no possibility of passing on a normal allele. Therefore, the mother must be colorblind, and not just a carrier for all males to be affected. The females would not have been affected as they would have received the normal allele from their father. They all would have been carriers of the condition.

16. The gradual increase in height in the human population over the past 100 years is an example of:

b. Multifactorial trait.

Multifactorial traits are those which are controlled by multiple genes and is significantly affected by environmental factors as well. Height in humans is affected by numerous genes and is also by external factors such as nutrition, temperature etc. Infact, the increase in human height over the past century, especially in industrilized nations have been largely attributed to improvement in childhood nutrition.

The following options are wrong because:

a. Polygenic trait.

Polygenic traits are those which are affected by numerous genes but not environmental factors. Height is not such a trait.

c. Crossing over

Crossing over occurs during meiosis I, where homologous chromosomes exchange genetic materials. As stated before, height increase is attributed to environmental factors such as nutrition and not genetic changes.

d. Recombination.

Recombination is the process where segments of DNA is broken down and recombined in a novel fashion to give rise to variation in offspring genotype. Again, as height is a multifactorial trait, it has significant environmental influence and not just genetic ones in its change.

17. The enzyme most important in regards to DNA replication is:

d. DNA polymerase.

DNA polymerase is the key enzyme in DNA replication. It is responsible for synthesis and elongation of nascent DNA strands by polymerizing the nucleotides according to a template DNA. It is therefore the most important enzyme in the process of DNA replication.

The following options are wrong because:

a. RNA polymerase.

It is the key enzyme in the synthesis of RNA during the transcription of DNA to RNA. It uses the DNA as a template to synthesize a RNA molecule. It is responsible for the transcription of DNA and not the replication.

b. Transfer RNA.

tRNA or transfer RNA is reponsible for bringing in amino acids during formation of polypeptide chain from a mRNA molecule. It plays an important role in the translation of mRNA to protein. It is, therefore, not an enzyme and not involved in DNA replication.

c. Messenger RNA.

mRNA or the messenger RNA is produced as a result of transcription of DNA to RNA and further post transcriptional modifications. It acts as a template for synthesis of polypeptide chain during the translation of RNA to protein. It, like tRNA is also not an enzyme involved in DNA replication.

18. The information that the nurse should include about X linked recessive disorders are:

b. The trait is never transmitted from father to son.

As it is a X linked trait it can not be passed from father to son. The son will never inherit the X chromosome from his father, always the Y chromosome. Thus the corresponding trait in the X chromosome will not be passed on to the son from the father.

c. The gene can be transmitted through a series of carrier females.

Females have two X chromosomes. Thus, unlike the males, they can posses the affected allele of the gene in one of their X chromosome, but never express the corresponding trait. As they bear the allele they can pass it on to their children. These individuals are known as carriers as they can pass on the diseased gene without being affected by it themselves. X linked recessive traits can pass through generations without being expressed through these carrier females.

d. The gene is passed from affected father to all his daughters.

If a man is affected by a X linked recessive disorder, he has the affected allele of the gene on his only X chromosome. As daughters inherit X chromosome from their father, they will receive the affected gene from their father. As there is only one X chromosome present in the father, all daughters will receive the same affected gene from their father.

The following options are incorrect because:

a. The trait is seen much more often in females than in males.

Females have XX genotype while males have XY genotype. If a female has the affected allele in one of her chromosomes, she still would not express the trait,as the dominant allele will mask its expression. However, since males have only one X chromosome if they have the affected allele in that X chromosome they will express the trait. Thus in same situation of inheriting the affected gene from one parent and having the affected allele in one chromosome, males will express the trait and females won't. Females would only express the trait if they inherit the gene from both her parents, which is a much rarer situation. Hence the trait is not more common in females.

e. The trait never skips generations.

As stated earlier, the trait can be passed through several generations in form of a carrier female. These women would carry the affected allele but never express the trait. The trait can be passed from an affected father to his daughter, who would be a carrier if she has a normal mother. The trait may again resurface in her son if he receives the affected allele from her. Thus this trait can easily skip generations.

19. The sequence of events during protein synthesis is:

i. RNA polymerase binds to the DNA promoter site.

First before transcription can occur, appropriate enzyme must be present. RNA polymerase, the required enzyme, binds to the DNA promoter site and that marks the beginning of transcription.

ii. Transcription.

Transcription is the synthesis of RNA molecule with DNA strand as a template. Appropriate portions of the DNA strand is transcribed into the mRNA molecule by the RNA polymerase enzyme.

iii. mRNA is spliced to remove non coding sections.

In eukaryotic genome, mRNA contains sections that do not code for protein. This portions are called introns and they are removed by a process called splicing by spliceosomes before translation can occur.

iv. mRNA leaves the nucleus.

Translation of mRNA to protein occurs in the cytoplasm by ribosomes. Thus for translation to occur, mRNA must first leave the nucleus and be transported to cytoplasm.

v. Translation.

Translation is the process of synthesis of polypeptide chain using mRNA as a template. This process is catalyzed by ribosomes and is aided by tRNAs which brings in the appropriate amino acid to be added in the polypeptide chain that is being synthesized.