Modern Genetics and Chromosomal Conditions Quiz

In Drosophila, eye color is determined by a gene located on the X chromosome. Since males only have one X chromosome, a recessive mutation on that X chromosome will manifest in male offspring because they lack a second X chromosome to mask the trait.

Sturtevant's genetic evidence showed that Drosophila genes are grouped into four distinct sets of linked genes on different chromosomes, indicating the presence of four pairs of chromosomes in Drosophila.

Klinefelter syndrome is associated with low levels of testosterone and increased levels of estrogen, leading to decreased fertility and small testes. The correct answer, increased testosterone, is not expected in individuals with this syndrome.

The presence of 3 X chromosomes in a female individual is a genetic condition known as Triple X syndrome, also called Trisomy X. However, individuals with Triple X syndrome typically lead normal lives and do not show significant physical or cognitive differences compared to females with two X chromosomes. Thus, the expected phenotype for a woman with 47 chromosomes including 3 X chromosomes would be a normal female.

Sex-linked traits are carried on the X chromosome. Males have only one X chromosome, making them more susceptible to sex-linked traits compared to females who have two X chromosomes.

In mammals, the typical chromosomal system for determining sex is X-Y, where males have one X and one Y chromosome, and females have two X chromosomes.

Birds use the Z-W chromosomal system for sex determination where males have two Z chromosomes (ZZ) and females have one Z and one W chromosome (ZW), in contrast to mammals (X-Y system).

The Sex-determining Region Y (SRY) gene is a gene region located on the Y chromosome that plays a crucial role in initiating male development. Therefore, the correct answer is the one that mentions its association with the Y chromosome and male development.

In this scenario, the black female will pass on the black allele to her male offspring, resulting in black males. The orange male will pass on the orange allele to his female offspring, resulting in tortoiseshell females due to the mixing of black and orange alleles in the heterozygous state. Therefore, the expected offspring from this cross would be tortoiseshell females and black males.

In this case, the son is color-blind which means he inherited the color-blindness allele from his mother. Since red-green color blindness is a sex-linked recessive trait, it is carried on the X chromosome. Therefore, the mother must be a carrier of the color-blindness allele (XCXc). The father has a Y chromosome, so he can't be a carrier. The father must have a normal X chromosome (XCY).

In a sex-linked recessive characteristic like cinnabar eyes, if a female with cinnabar eyes is crossed with a wild-type male, all F1 males will inherit the cinnabar eye trait as they receive the recessive gene from the female.

Calico cats are almost always female due to the genetic traits associated with their coloration, primarily related to the X chromosome inheritance.

In this scenario, the male is heterozygous (Zz) for the lethal allele on the Z chromosome. Since males are ZZ, one of the Z chromosomes carries the lethal allele. When this male is crossed with a normal female (ZW), the offspring will have a 2:1 male to female sex ratio. The male offspring can inherit the normal Z chromosome from the female, resulting in ZZ (males), or the Z chromosome with the lethal allele from the male, resulting in Zz (males).

Since achondroplastic dwarfism is autosomal dominant and red-green color blindness is X-linked recessive, none of the daughters would be expected to be color-blind dwarfs as the daughters would inherit a normal vision gene from the father and a normal height gene from the mother.

Inheritance patterns of color-blindness and height follow different genetic mechanisms. In this case, color-blindness and height are considered independently, so the chance of having a color-blind and normal height son is half.

The daughter is a dwarf with normal color vision, indicating that she must be heterozygous for both genes with a probability of 1.00.

A Barr body is a condensed, inactive X chromosome typically found in somatic cells of females due to X-chromosome inactivation.

In the case of translocation of SRY to an autosome of a 46, XX individual, the presence of the SRY gene on an autosome can lead to the development of male phenotype despite the typical female chromosome composition. This abnormality can alter the usual sex determination process by allowing male characteristics to develop.

The correct answer is A) The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them because the physical distance between genes influences the likelihood of genetic recombination during crossover events.

During crossing over, segments of DNA are exchanged between homologous chromosomes, leading to new combinations of alleles on a chromosome. This process results in genetic diversity among offspring.

A frequency of recombination of 50% indicates independent assortment of genes, meaning they are likely to be located on different chromosomes.

A 0.1% frequency of recombination suggests that the genes are located very close to one another on the same chromosome. This low frequency indicates that the likelihood of recombination occurring between these genes is minimal due to their proximity.

Linked genes are inherited together because they are physically close to each other on the same chromosome, leading to them being passed on as a unit during cell division and reproduction.

The correct gene order is determined by the recombination frequencies, placing genes in the order with the lowest recombination frequencies first.

In Drosophila, genes are organized linearly on chromosomes creating a genetic map. The genes b and rb are the closest together on this map, hence the correct answer choice E)