Question 1

Which of the following statements is generally true of aneuploidies in newborns?

Accepted Answer

Monosomy X, also known as Turner syndrome, is indeed the only monosomy that is generally viable in humans. Most other monosomies (the loss of one chromosome from a pair) result in prenatal lethality. Trisomies (the addition of an extra chromosome to a pair), such as Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome), and Trisomy 13 (Patau syndrome), can also be viable but are less common than monosomy X in terms of survivable conditions.

Question 2

Some snail species' shells can have right-handed direction of shell coiling or left-handed direction of shell coiling. The direction of coiling depends on a protein deposited by the mother in the egg cytoplasm with DD and Dd mothers depositing a protein that directs right-handed direction of coiling in shells. If Dd egg-producing snail and a dd sperm-producing snail mate what genotype(s) and phenotype(s) of offspring will result?

Accepted Answer

The Dd egg-producing snail will produce 1/2 D eggs and 1/2 d eggs. The dd sperm-producing snail will produce only d sperm. Therefore, the possible genotypes of the offspring are 1/2 Dd and 1/2 dd. Since D is dominant, all offspring will have right-coiling shells.

Question 3

Use the following figure to answer the question. Shaded symbols indicate affected individuals.  The pedigree in the figure shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely ________.

Accepted Answer

The answer of Use the following figure to answer the...

Question 4

A patient has 47 chromosomes, including three X chromosomes. Which of the following statements describes her expected phenotype?

Accepted Answer

A patient with 47 chromosomes, including three X chromosomes, typically presents as a female (due to the presence of more than one X chromosome) and may be of slightly above-average height. This condition is known as Triple X syndrome. It does not typically result in masculinization or sterility.

Question 5

If a pair of homologous chromosomes fails to separate during meiosis I, select the choice that shows the chromosome number of the four resulting gametes with respect to the normal haploid number (n)?

Accepted Answer

This phenomenon is known as nondisjunction, and when it occurs during meiosis I, it results in two gametes having an extra chromosome (n + 1) and two gametes missing a chromosome (n - 1).

Question 6

Which of the following statements correctly describes what happens to a chromosome after a nonreciprocal translocation?

Accepted Answer

In a nonreciprocal translocation, a chromosome transfers a fragment to another chromosome but does not receive any fragment in return, leading to an imbalance in genetic material.

Question 7

German scientist Carl Correns found that the inheritance of variegated color on the leaves of certain plants was determined only by the maternal parent. Which of the following phenomena best explains this pattern of inheritance?

Accepted Answer

The inheritance pattern described by Carl Correns, where the variegated color of leaves in certain plants is determined only by the maternal parent, is best explained by the inheritance of plastid genes. Plastids, including chloroplasts, are cytoplasmic organelles that contain their own DNA and are inherited maternally in most plants. This means that the traits governed by plastid genes are passed from the mother to all her offspring, regardless of the offspring's sex.

Question 8

Genomic imprinting is generally due to the addition of methyl (-CH3) groups to cytosine nucleotides to silence a given allele of a gene. If this process depends on the sex of the parent who transmits the gene, which of the following statements must be true?

Accepted Answer

Methylation involved in genomic imprinting must be reversible in the germ cells (ovarian and testicular cells) to ensure that each generation can establish its own imprinting patterns based on the sex of the parent transmitting the gene. This reversibility allows for the erasure and re-establishment of methylation marks according to whether the allele is being transmitted by the mother or the father.

Question 9

Which of the following statements describes the most likely result of a defect in meiosis that results in the failure of spindle microtubules to bind some kinetochores?

Accepted Answer

The failure of spindle microtubules to bind some kinetochores during meiosis would likely result in incorrect distribution of chromosomes to the daughter cells, leading to aneuploidy, where cells have an abnormal number of chromosomes.

Question 10

A couple has a child with Down syndrome. Which of the following is the most probable cause of the child's condition?

Accepted Answer

Down syndrome is most commonly caused by nondisjunction during meiosis, leading to an extra copy of chromosome 21. This is a random event that can occur in the sperm or egg cells of either parent.

Question 11

Which of the following is an example of monosomy in humans?

Accepted Answer

Turner syndrome is an example of monosomy, where an individual has only one X chromosome instead of the usual two sex chromosomes (either XX or XY).

Question 12

A phenotypically normal couple seeks genetic counseling because the man's karyotype showed that his chromosomes had a reciprocal translocation between chromosomes 4 and 12. Because the translocation is reciprocal there was no genetic information lost and he is healthy; however, he and his wife want to know the probability that his sperm cells will be abnormal. Which fraction of his sperm cells is predicted to carry at least one chromosome with a translocation?

Accepted Answer

In cases of reciprocal translocation, during meiosis, chromosomes align in such a way that three out of the four resulting gametes will have chromosomes involved in the translocation. This results in 3/4 of the sperm carrying at least one chromosome with a translocation, while only 1/4 will have both chromosomes 4 and 12 unaffected.

Question 13

Abnormal chromosomes are frequently found in malignant tumors. Errors such as translocations may place a gene in close proximity to different control regions that could result in which of the following events?

Accepted Answer

Translocations can cause genes to be placed near different regulatory elements, leading to their abnormal expression. In the context of cancer, this often results in the activation of oncogenes or the inactivation of tumor suppressor genes, promoting inappropriate cell division and tumor growth.

Question 14

Which of the following correctly describes a Philadelphia chromosome?

Accepted Answer

The Philadelphia chromosome is characterized by a specific genetic abnormality, which is a translocation between chromosome 9 and chromosome 22. This translocation results in the fusion of the BCR gene on chromosome 22 with the ABL gene on chromosome 9, leading to the formation of a hybrid gene known for its association with chronic myeloid leukemia (CML) and other types of cancer.

Quiz 15: Linkage and Chromosomes