Chapter 13: Chromosomes, Mapping and The Meiosis Inheritance Connection

In Drosophila, the sex of an individual is influenced by the number of copies of the X chromosome. Drosophila has a system called the X:A ratio, where the presence of one or two X chromosomes determines the sex. Females have two X chromosomes (XX), while males have one X chromosome (XY). The number of X chromosomes determines the sex determination pathway and the development of sexual characteristics. Therefore, the correct answer is X.

Monosomics refers to humans who have lost one copy of an autosome, resulting in a missing chromosome pair. This condition can lead to various genetic disorders and health issues. Tetrasomics, trisomics, bisomics, and nullisomics are not the correct terms for individuals with a missing autosome.

Crossing over is the process in which genetic material is exchanged between two homologous chromosomes during meiosis. It occurs when the chromosomes align and break at corresponding points, allowing for the exchange of genetic material. The distance between genes on a chromosome pair plays a role in determining the likelihood of crossing over. If the distance between genes is greater, there is a higher probability of crossing over occurring. Therefore, crossing over is the correct answer as it explains the genetic exchange between two arms of a chromosome pair when the distance between genes is great.

The correct answer is X because the question states that the white eye mutation in Drosophila is sex-linked, which means it is associated with the sex chromosomes. In Drosophila, the sex chromosomes are denoted as X and Y, with females having two X chromosomes (XX) and males having one X and one Y chromosome (XY). Therefore, the gene responsible for the white eye mutation must be located on the X chromosome.

Nondisjunction is the correct answer because it refers to the failure of chromosomes to separate properly during meiosis, resulting in an abnormal number of chromosomes in the resulting cells. This can lead to conditions such as Down syndrome, Turner syndrome, or Klinefelter syndrome, where individuals have an abnormal number of chromosomes. Epistasis, pleiotropy, and autosomy are unrelated terms that do not describe this specific phenomenon. Disjunction is not the correct term as it does not specifically refer to the failure of chromosome separation during meiosis.

Trisomy refers to the presence of an extra copy of a chromosome in an individual's cells. The most common condition of trisomy is trisomy 21, also known as Down syndrome, where there are three copies of chromosome 21 instead of the usual two. This condition occurs due to an error during cell division, resulting in an extra copy of the chromosome. Trisomy 13, 15, and 18 are also known conditions, but they are less common compared to trisomy 21.

Hemophilia is a recessive condition because it is caused by a mutation in one of the genes responsible for blood clotting. This mutation is carried on the X chromosome, and since males have only one X chromosome, they are more likely to express the condition if they inherit the mutated gene. Females, on the other hand, have two X chromosomes, so they can be carriers of the condition without showing any symptoms. This pattern of inheritance is characteristic of a recessive condition.

Sickle cell anemia is caused by a defect in the oxygen carrying pigment hemoglobin. Hemoglobin is a protein found in red blood cells that carries oxygen from the lungs to the body's tissues. In sickle cell anemia, there is a mutation in the gene that codes for hemoglobin, causing it to form abnormal, sickle-shaped red blood cells. These cells can get stuck in blood vessels, leading to reduced oxygen flow and various complications. Therefore, the defect in hemoglobin is the cause of sickle cell anemia.

Turner syndrome is a genetic condition that affects females who have only one X chromosome instead of the usual two. This condition can cause various developmental and physical abnormalities, including short stature, infertility, and heart defects. It is not related to Alzheimer's disease, hemophilia, Klinefelter syndrome, or Down syndrome, which are caused by different genetic factors.

A Barr body is an inactivated X chromosome that appears as a condensed, dark-staining structure in the nucleus of female cells. In normal human females, one of the two X chromosomes is randomly inactivated in each cell during early development. This process ensures dosage compensation between males and females, as males only have one X chromosome. Therefore, a normal human female will have one Barr body in each of her cells.

Individuals with a genotype of XO do not have a Y chromosome, which is necessary for male development. In humans, the presence of two X chromosomes typically results in female development. Therefore, if a non-disjunction event leads to an individual with a genotype of XO, they would be female.

Individuals with a genotype of XXY have an extra copy of the sex chromosomes, resulting in a condition known as Klinefelter syndrome. This condition typically affects males, as they have one X and one Y chromosome. The presence of the Y chromosome determines male development, so individuals with XXY genotype would develop male characteristics, although they may also experience some physical and reproductive challenges associated with Klinefelter syndrome.

The correct answer is Morgan. Thomas Hunt Morgan, a geneticist, discovered the white eye mutation in Drosophila, commonly known as fruit flies. His research on fruit flies helped establish the concept that genes are carried on chromosomes. Morgan's work was groundbreaking in understanding the role of chromosomes in inheritance and laid the foundation for the field of modern genetics.

A test cross is a breeding experiment used to determine the genotype of an individual with a dominant phenotype. By crossing the individual with a homozygous recessive individual, the presence or absence of the recessive phenotype in the offspring can reveal whether the dominant individual is homozygous or heterozygous for the trait. This method can also gather genotype information from phenotype information by observing the phenotypes of the offspring. However, a test cross cannot directly identify the chromosome on which a gene is located. This requires other techniques such as genetic mapping or cytogenetics.

Amniocentesis is a procedure used for diagnosis of genetic disorders. It involves the extraction of a small amount of amniotic fluid surrounding the fetus, which contains fetal cells. These cells can be analyzed to detect any genetic abnormalities or chromosomal disorders in the fetus, such as Down syndrome or spina bifida. This procedure is typically recommended for pregnant women who are at a higher risk of having a baby with a genetic disorder, based on factors like maternal age or family history.

Mitochondria DNA is solely inherited from the mother and not from the father. Therefore, both sons and daughters will inherit all their mitochondria DNA from their mother and none from their father.

Huntington's disease is a human hereditary disease caused by a dominant allele. However, affected individuals do not show symptoms of the disease until they reach middle age. This delayed onset distinguishes Huntington's disease from other hereditary diseases like cystic fibrosis, sickle cell anemia, Tay-Sachs disease, and hemophilia, where symptoms typically appear earlier in life.

If a female is a carrier for sex-linked color blindness, it means she has one normal copy of the gene and one copy that causes color blindness. Since color blindness is a sex-linked trait, it is passed down from the mother to her children. If she has a male child, there is a 50% chance that she will pass on the color blindness gene to him, making him color blind. Therefore, the percentage of her male children who would be color blind is 50%.

If a human female has two Barr bodies, it is almost certain that she developed from a fertilized egg with 3 X chromosomes. Barr bodies are inactivated X chromosomes, and in females, one of the X chromosomes is randomly inactivated in each cell to achieve dosage compensation. Therefore, if a female has two Barr bodies, it indicates that she has three X chromosomes, with two X chromosomes being inactivated and forming the Barr bodies. This condition is known as Triple X syndrome or Trisomy X.

Calico cats cannot be male. They are almost always female due to the genetic makeup that produces their unique coat color. This is because the gene for coat color is located on the X chromosome, and female cats have two X chromosomes while males have one X and one Y chromosome. The inactivation of one X chromosome in female cats leads to the patches of different colored fur, making them genetic mosaics. The variation in coat color is an example of an epistatic interaction, where the interaction of multiple genes determines the phenotype.

Cystic fibrosis is the most common fatal genetic disorder among Caucasians. It is a hereditary condition that affects the lungs, digestive system, and other organs. The disorder is caused by a mutation in the CFTR gene, which leads to the production of thick and sticky mucus in the body. This mucus clogs the airways and causes respiratory problems, as well as affects the function of the pancreas and other organs. Without proper treatment and management, cystic fibrosis can significantly reduce life expectancy.

The theory of chromosomal inheritance refers to the idea that genes are located on chromosomes and are passed down from parents to offspring. This theory was first proposed by Thomas Hunt Morgan and Alfred Henry Sturtevant in the early 20th century. However, the correct answer to this question is Sutton. Edmund B. Wilson and Nettie Stevens independently discovered the connection between chromosomes and inheritance in the late 19th and early 20th centuries. Walter Sutton, an American geneticist, published the first comprehensive theory of chromosomal inheritance in 1902, providing strong evidence to support the chromosome theory.

Nondisjunction of autosomes refers to the failure of chromosomes to separate properly during cell division, resulting in an abnormal number of chromosomes in the resulting cells. This can lead to aneuploidy, which is the presence of an abnormal number of chromosomes (either too many or too few). Monosomy refers to the presence of only one copy of a particular chromosome, while trisomy refers to the presence of three copies of a particular chromosome. Euploidy, on the other hand, refers to the normal, balanced number of chromosomes in a cell or organism. Therefore, the correct answer is euploidy, as it is not a consequence of nondisjunction.

Polymorphisms refer to the genetic differences between individuals in a population. These variations can occur in the form of different alleles, or alternative versions of a gene, which can result in observable differences in traits or characteristics. Polymorphisms are common in populations and can be used as markers to study genetic diversity, inheritance patterns, and the association between certain genetic variations and diseases. Therefore, polymorphisms are the correct answer in this context.

As genetic distance increases, the recombination frequency first increases in a linear fashion, but then levels off to a frequency of 0.5. This means that initially, as the distance between genes on a chromosome increases, the likelihood of recombination events also increases in a predictable and proportional manner. However, after a certain point, the recombination frequency reaches a maximum value of 0.5, indicating that further increases in genetic distance do not result in a higher probability of recombination. This leveling off suggests that there may be a limit to the distance over which recombination can occur effectively.

In sickle cell anemia, the defective hemoglobin differs from the normal hemoglobin by the size of the molecule. This is because in sickle cell anemia, there is a mutation in the gene that codes for hemoglobin, leading to the production of abnormal hemoglobin molecules. These abnormal molecules cause the red blood cells to become misshapen and rigid, which can block blood flow and cause various health problems. The change in size of the hemoglobin molecule is a key characteristic of sickle cell anemia.

Chromosomes are structures found in the nucleus of eukaryotic cells that carry genetic information in the form of DNA. This genetic material is organized into genes, which are responsible for the inheritance of traits from one generation to the next. During cell division, chromosomes ensure that genetic information is accurately replicated and distributed to daughter cells. Unlike options A, C, and D, chromosomes are not involved in protein transport, energy generation, or protein synthesis, but rather in storing and transmitting genetic information.

The condition described in the question is characterized by the presence of alternative alleles with detrimental effects in significant proportions in populations. This condition is referred to as a genetic imbalance, as it indicates an imbalance in the distribution of different alleles within a population, leading to negative effects on the overall genetic makeup.