Question 1

In Drosophila,X^wdenotes a white eyed allele and X⁺denotes the red-eyed allele.An X^wX^wY female is crossed with an X⁺Y male.What are the possible progeny genotypes? A) X^wX^wX⁺, X^wY B) C) D) E) None of these

Accepted Answer

The answer of In Drosophila,X^wdenotes a white eyed allele...

Question 2

An individual with two kinds of gametes (i.e.X bearing and Y bearing)is referred to as:
A) Homogametic
B) Heterogametic
C) Heterozygous
D) None of these
E) All of these

Accepted Answer

An individual with two kinds of gametes (i.e. X bearing and Y bearing) is referred to as heterogametic. Homogametic refers to individuals with only one type of gamete (i.e. XX or YY). Heterozygous refers to individuals with two different alleles of a gene on the homologous chromosomes. None of these options fully describe an individual with two types of gametes. Therefore, the best answer is B, heterogametic.

Question 3

In Drosophila the Y chromosome is not required for male sex determination.However,it is required for :
A) Male sterility
B) Male fertility
C) Female sterility
D) Female fertility
E) None of these

Accepted Answer

The Y chromosome in Drosophila is not required for male sex determination because the ratio of X chromosomes to autosomes determines sex in this species. However, the Y chromosome is required for male fertility. This is because the Y chromosome harbors genes necessary for spermatogenesis, the process by which sperm are produced. Without these Y-linked genes, males are sterile.

Question 4

In humans the Y chromosome carries _________ genes than the X chromosome.
A) Fewer
B) More
C) Similar
D) All of these
E) None of these

Accepted Answer

The Y chromosome carries fewer genes than the X chromosome. This is because the Y chromosome is smaller than the X chromosome and has lost genes over time through a process called degeneration.

Question 5

A color blind male mates with woman who has normal vision.The woman has no history of colorblindness in her family.What percentage of their sons are expected to be colorblind?
A) 25%
B) 50%
C) 75%
D) 100%
E) 0%

Accepted Answer

Color blindness is a recessive X-linked trait. The color blind male has an X chromosome with the color blindness allele and a Y chromosome. The woman has two normal X chromosomes. All sons receive the Y chromosome from their father and a normal X chromosome from their mother, so none of the sons will be colorblind.

Question 6

Down Syndrome occurs when there is an extra chromosome #21.Such individuals therefore have 47 chromosomes.Assume that a mating occurs between a female with Down Syndrome and a normal male.Assuming normal disjunction during meiosis,what percentage of offspring would be expected to have Down Syndrome?
A) 25%
B) 50%
C) 75%
D) 100%
E) 0%

Accepted Answer

In this scenario, the female with Down Syndrome has three copies of chromosome 21. During meiosis, her eggs will end up with either one or two copies of chromosome 21. A normal male will produce sperm with one copy of chromosome 21. Therefore, fertilization will result in embryos with either two copies (normal) or three copies (Down Syndrome) of chromosome 21. This means that there is a 50% chance for an offspring to inherit Down Syndrome.

Question 7

The sex-linked disease called testicular feminization,if transferred from mother to son,forms:
A) males (XY) that are phenotypically female and sterile.
B) females (XY) that are sterile.
C) males (XY) that are sterile.
D) females (XY) that are phenotypically male and are sterile.
E) fertile males (XY)

Accepted Answer

Testicular feminization is caused by a mutation in the gene for the androgen receptor, which leads to the inability of cells to respond to testosterone. As a result, XY individuals with this condition have male internal organs but female external genitalia and secondary sex characteristics. They are typically raised as females, but they are sterile because they lack ovaries and have testes that do not produce sperm. If the condition is inherited from a mother who is a carrier, there is a 50% chance that her sons will inherit the mutation and develop testicular feminization. These sons will be phenotypically female but genetically male, and they will be sterile.

Question 8

In humans an individual who is genotyped as XO is a:
A) Male
B) Female
C) Hermaphrodite
D) None of these
E) All of these

Accepted Answer

An individual who is genotyped as XO has only one X chromosome and no second sex chromosome. This condition is called Turner Syndrome and is exclusive to females. Therefore, the correct answer is B.

Question 9

Which of Mendel's principles is based on the separation of homologous chromosomes during the anaphase of the first meiotic division?
A) Dominance/Recessiveness
B) Segregation
C) Independent Assortment
D) All of these
E) None of these

Accepted Answer

Segregation is the principle that states that homologous chromosomes, with their different versions of genes, separate from each other and end up in different cells during meiosis I. This is due to the separation of homologous chromosomes during the anaphase of the first meiotic division. Dominance/recessiveness and independent assortment are not specifically related to this event in meiosis.

Question 10

In a human,what is the best explanation for being XX and phenotypically male?
A) One of the X's is incomplete resembling a chromosome.
B) A small piece of the Y-chromosome, containing the SRY region, is inserted on the X-chromosome.
C) Both the X's have a mutation deleting the "female" forming genes.
D) There is a fragment of the Y-chromosome inserted on an autosomal chromosome.
E) The SRY gene has mutated.

Accepted Answer

The presence of the SRY region on the Y chromosome determines male development. In rare cases, a small piece of the Y-chromosome can be inserted onto the X-chromosome, resulting in a male individual with XX chromosomes. This insertion contains the SRY region, leading to male phenotypic expression.

Question 11

When chromosomes fail to separate during meiosis,thereby producing an egg with two X chromosomes or an egg with no X chromosome at all,this event is referred to as:
A) Nondisjunction
B) Disjunction
C) Polyploidy
D) Polysomy
E) None of these

Accepted Answer

Nondisjunction is the failure of chromosome separation during meiosis, resulting in an egg or sperm cell with an abnormal number of chromosomes. In this case, it can lead to the production of an egg with two X chromosomes (XX) or no X chromosome at all (0X), which can cause genetic disorders like Turner Syndrome or Klinefelter Syndrome, respectively. Disjunction is the normal separation of chromosomes during cell division, and polyploidy and polysomy refer to having extra sets of chromosomes or extra copies of individual chromosomes, respectively, which are not directly related to the failure of separation during meiosis.

Question 12

A(n)________________ gene has a locus on both the X-and Y-chromosome
A) Autosomal
B) Psedoautosomal
C) X-linked
D) Y-linked
E) None of these

Accepted Answer

A gene that has a locus on both the X and Y chromosomes is called a pseudoautosomal gene. This is because the X and Y chromosomes contain very few homologous regions, but the pseudoautosomal region is a small region where the X and Y chromosomes do share homologous sequences. Therefore, genes located in this region can be inherited like autosomal genes, and their expression is not limited by the sex of the individual.

Question 13

Which of Mendel's principles is a statement about the random alignment of different pairs of chromosomes at metaphase during meiosis?
A) Dominance/Recessiveness
B) Segregation
C) Independent Assortment
D) All of these
E) None of these

Accepted Answer

Independent Assortment is the principle that states that during meiosis, different pairs of chromosomes align randomly at metaphase, resulting in a random distribution of maternal and paternal chromosomes into gametes.

Question 14

A Drosophila is determined to have the genotype XO.What can you determine about this individual based upon this information?
A) The individual is mae
B) The individual is sterile
C) The individual is male and sterile
D) The individual is female and sterile

Accepted Answer

The genotype XO in Drosophila indicates that the individual is a female with only one X chromosome. This condition is known as Turner syndrome, and it often results in sterility in females.

Question 15

Which of the following is an X-linked disorder in human beings?
A) Hemophilia
B) Color blindness
C) HIV
D) Hemophiila and Color blindness
E) All of these

Accepted Answer

Hemophilia and color blindness are both X-linked disorders, meaning they are associated with genes found on the X chromosome.

Question 16

The view that all genes are located on chromosomes and that Mendel's principles can be explained by the transmissional properties of chromosomes during reproduction is known as:
A) The Cell Theory
B) The Chromosome Theory of Heredity
C) The Sex-Linked Inheritance Theory
D) All of these
E) None of these

Accepted Answer

The Chromosome Theory of Heredity is the view that all genes are located on chromosomes and that Mendel's principles can be explained by the transmissional properties of chromosomes during reproduction. The Cell Theory is a separate theory that states all living things are composed of cells, while the Sex-Linked Inheritance Theory is a specific application of the Chromosome Theory that explains certain patterns of inheritance of genes located on sex chromosomes. Therefore, the answer is B.

Question 17

Sexual dimorphism can be determined by:
A) The environment
B) Temperature
C) Genetic factors
D) All of these
E) None of these

Accepted Answer

Sexual dimorphism, which refers to the differences in appearance between males and females of the same species, can be influenced by a variety of factors including the environment, temperature, and genetic factors. Environmental conditions can affect the development and expression of physical traits, temperature can influence sex determination and differentiation in some species (such as reptiles), and genetic factors are fundamentally involved in determining the sex and associated characteristics of an organism.

Question 18

A white eyed Drosophila female is crossed with a red-eyed male.Assuming the trait for eye color is sex-linked,what are the possible phenotypes of the progeny?
A) All red eyed individuals
B) Red and white eyed females and males
C) Red eyed females and white eyed males
D) Red and white eyed males and only white eyed females
E) None of these

Accepted Answer

If the trait for eye color is sex-linked, then it is likely that the gene for eye color is on the X chromosome. The white-eyed female must have the genotype XwXw, meaning she has two copies of the white eye gene. The red-eyed male must be XRY, meaning he has one copy of the red eye gene on his X chromosome and no copies on his Y chromosome. 
All of the resulting offspring will inherit one X chromosome from the female and either an X or a Y chromosome from the male. Therefore the possible genotypes and corresponding phenotypes are: 
- XRXR red-eyed female 
- XRXw red-eyed female 
- XwXR white-eyed male 
- XwY white-eyed male 
Since half of the offspring will inherit the X chromosome from the male and be male themselves, and since the white-eyed gene is recessive, it is possible for there to be red-eyed females and white-eyed males. Therefore, the best choice is C.

Question 19

Which of the following is the part of the Y chromosome that is critical for normal male development?
A) SRY
B) Pseudoautosomal region
C) Centromere
D) All of these
E) None of these

Accepted Answer

The SRY (Sex-determining Region Y) is a gene located on the Y chromosome that is critical for normal male development. It encodes for a protein called testis-determining factor (TDF) which triggers the development of testes in an embryo. The pseudoautosomal region and centromere are also important parts of the Y chromosome, but they are not critical for male development in the same way that SRY is.

Question 20

Why is it easier to identify a recessive sex-linked trait in human beings than a recessive autosomal trait?
A) A male needs only to inherit one recessive allele to express an X-linked trait
B) A male needs to inherit two recessive alleles to express an X-linked trait
C) A female only needs to inherit one recessive allele to express an X-linked trait
D) All of these
E) None of these

Accepted Answer

In human beings, males only have one X chromosome and one Y chromosome, while females have two X chromosomes. Since the gene for a recessive sex-linked trait is present on the X chromosome, if a male inherits a single recessive allele on his X chromosome, he will express the trait. On the other hand, autosomal recessive traits require the individual to inherit two recessive alleles, one from each parent, to express the trait. Therefore, identifying a recessive sex-linked trait is easier because it only requires one recessive allele in males.

Quiz 5: The Chromosomal Basis Of Mendelism

In Drosophila,X^wdenotes a white eyed allele and X⁺denotes the red-eyed allele.An X^wX^wY female is crossed with an X⁺Y male.What are the possible progeny genotypes?

An individual with two kinds of gametes (i.e.X bearing and Y bearing) is referred to as:

In Drosophila the Y chromosome is not required for male sex determination.However,it is required for :

In humans the Y chromosome carries _________ genes than the X chromosome.

A color blind male mates with woman who has normal vision.The woman has no history of colorblindness in her family.What percentage of their sons are expected to be colorblind?

Down Syndrome occurs when there is an extra chromosome #21.Such individuals therefore have 47 chromosomes.Assume that a mating occurs between a female with Down Syndrome and a normal male.Assuming normal disjunction during meiosis,what percentage of offspring would be expected to have Down Syndrome?

The sex-linked disease called testicular feminization,if transferred from mother to son,forms:

In humans an individual who is genotyped as XO is a:

Which of Mendel's principles is based on the separation of homologous chromosomes during the anaphase of the first meiotic division?

In a human,what is the best explanation for being XX and phenotypically male?

When chromosomes fail to separate during meiosis,thereby producing an egg with two X chromosomes or an egg with no X chromosome at all,this event is referred to as:

A(n) ________________ gene has a locus on both the X-and Y-chromosome

Which of Mendel's principles is a statement about the random alignment of different pairs of chromosomes at metaphase during meiosis?

A Drosophila is determined to have the genotype XO.What can you determine about this individual based upon this information?

Which of the following is an X-linked disorder in human beings?

The view that all genes are located on chromosomes and that Mendel's principles can be explained by the transmissional properties of chromosomes during reproduction is known as:

Sexual dimorphism can be determined by:

A white eyed Drosophila female is crossed with a red-eyed male.Assuming the trait for eye color is sex-linked,what are the possible phenotypes of the progeny?

Which of the following is the part of the Y chromosome that is critical for normal male development?

Why is it easier to identify a recessive sex-linked trait in human beings than a recessive autosomal trait?