Genetics Sex Determination Quiz Chatgpt

1. What is the function of the SRY gene?
A. Inactivate extra X chromosomes
B. Determine female phenotype
C. Trigger testis development
D. Regulate X-linked inheritance

C. Trigger testis development

Explanation:
The SRY gene (Sex-determining Region Y) triggers the development of testes in embryos by producing the testis-determining factor (TDF). It doesn’t inactivate X chromosomes — that’s related to dosage compensation.

2. In the XX/XO system found in some insects, what determines maleness?
A. Presence of Y chromosome
B. Absence of one X chromosome
C. Autosomal mutations
D. Random fusion of gametes

B. Absence of one X chromosome

Explanation:
In the XX/XO system (e.g., Protenor insects), sex is determined by the number of X chromosomes. XO = male, XX = female. There's no Y chromosome involved.

3. What determines sex in Drosophila?
A. Y chromosome
B. Number of X chromosomes
C. Ratio of X chromosomes to autosome sets
D. Hormone signals from mother

C. Ratio of X chromosomes to autosome sets

Explanation:
Drosophila sex determination is based on the X:A ratio.

• XX:2A → female (1.0)

• XY:2A → male (0.5)
  The Y chromosome is not required for maleness — just for male fertility.

4. In mammals, how is dosage compensation for X-linked genes achieved?
A. Y chromosome inactivation
B. Upregulation of Y genes in males
C. X chromosome inactivation in females
D. Equal expression of all alleles regardless of sex

C. X chromosome inactivation in females

Explanation:
Females (XX) inactivate one of their X chromosomes in somatic cells to match gene expression with XY males. This is known as X-inactivation, forming Barr bodies.

5. Which syndrome is caused by a 45,XO karyotype?
A. Klinefelter syndrome
B. Turner syndrome
C. Triplo-X
D. Supermale syndrome

B. Turner syndrome

Explanation:
Turner syndrome results from a 45,XO karyotype. Individuals are phenotypic females with underdeveloped ovaries and may have short stature and learning issues.
Supermale syndrome refers to 47,XYY.

6. The Lyon Hypothesis addresses:
A. Environmental sex determination
B. X-inactivation in mammals
C. Mutations in the SRY gene
D. Mosaicism in male embryos

B. X-inactivation in mammals

Explanation:
The Lyon Hypothesis states that one X chromosome in each female cell is randomly inactivated during early embryonic development. This explains dosage compensation.

7. In the ZW system of sex determination, what is true?
A. Males are ZW
B. Males are homogametic
C. Females are ZZ
D. Both sexes have one Z and one W

B. Males are homogametic

Explanation:
In the ZW system (used by birds, reptiles, some fish), males are ZZ (homogametic), and females are ZW (heterogametic). This is the opposite of the mammalian XY system.

8. In C. elegans, what is the most common result of self-fertilization?
A. Male offspring
B. Female offspring
C. Hermaphrodite offspring
D. Sterile offspring

C. Hermaphrodite offspring

Explanation:
In C. elegans, hermaphrodites (XX) self-fertilize to produce mostly hermaphrodite offspring. Males (XO) occur at low frequency, usually <1%.

9. Which karyotype corresponds to a phenotypic male with some female characteristics, tall stature, and infertility?
A. 47,XYY
B. 45,XO
C. 47,XXY
D. 47,XXX

C. 47,XXY

Explanation:
This describes Klinefelter syndrome. Males with an extra X chromosome (XXY) are often tall, have small testes, reduced fertility, and mild learning difficulties.

10. What enzyme is associated with temperature-dependent sex determination in reptiles?
A. Kinase
B. Telomerase
C. Aromatase
D. Helicase

C. Aromatase

Explanation:
Aromatase converts androgens to estrogens. It’s temperature-sensitive in species with TSD (temperature-dependent sex determination), influencing whether gonads develop into ovaries or testes.

11. What is a Barr body?
A. A gene on the Y chromosome
B. An extra Y chromosome
C. A condensed, inactivated X chromosome
D. An autosomal structure found in females

C. A condensed, inactivated X chromosome

Explanation:
A Barr body is the inactivated X chromosome seen in females (XX) to balance gene expression between sexes. It appears as a dark spot in interphase nuclei.

12. Why do individuals with abnormal numbers of sex chromosomes still often show symptoms, despite X-inactivation?
A. X-inactivation never occurs in humans
B. The Y chromosome is highly toxic
C. Some genes on the inactivated X are still expressed
D. Dosage compensation causes chromosome instability

C. Some genes on the inactivated X are still expressed

Explanation:
Not all genes on the inactivated X are turned off — some escape inactivation. This partial expression contributes to phenotypes seen in conditions like Klinefelter or Turner syndrome.

1. Which of the following best explains why individuals with a 47,XXX karyotype can appear phenotypically normal?
A. The presence of a functional Y chromosome compensates for the extra X
B. All three X chromosomes are inactivated
C. Only one X chromosome remains active; the rest are inactivated via the Lyon mechanism
D. The extra X is eliminated during embryogenesis

C. Only one X chromosome remains active; the rest are inactivated via the Lyon mechanism

Explanation:
Only one X chromosome is active in each somatic cell due to X-inactivation (Lyon Hypothesis). The others become Barr bodies. This compensates for dosage imbalance, which is why some 47,XXX females show no obvious phenotype.

2. In mammals, which region of the Y chromosome is critical for pairing with the X chromosome during meiosis?
A. MSY (male-specific region of Y)
B. PAR (pseudoautosomal region)
C. TDF (testis-determining factor)
D. SRY (sex-determining region Y)

B. PAR (pseudoautosomal region)

Explanation:
The pseudoautosomal regions (PARs) on both ends of the Y chromosome are homologous to regions on the X and allow proper pairing and recombination during male meiosis.

3. What mechanism most directly explains why calico cats are almost always female?
A. Environmental sex determination
B. Hormonal suppression of coat pigment
C. X-linked gene mosaicism resulting from random X-inactivation
D. Female-specific activation of the SRY gene

C. X-linked gene mosaicism resulting from random X-inactivation

Explanation:
Calico coloring is caused by X-linked coat color genes. Random X-inactivation in different cells leads to mosaicism (patches of different color). Since only females have two Xs, only they can express both coat color alleles in a mosaic pattern.

4. In humans, what is the direct functional outcome of the SRY gene's activation during early embryogenesis?
A. Initiation of X-inactivation
B. Development of ovaries
C. Differentiation of bipotential gonads into testes
D. Suppression of autosomal gene expression

C. Differentiation of bipotential gonads into testes

Explanation:
The SRY gene triggers expression of the testis-determining factor (TDF), which initiates the differentiation of the bipotential gonads into testes. This is the starting point for male sexual development.

5. In organisms that utilize temperature-dependent sex determination (TSD), such as some reptiles, what molecular factor is primarily involved in the determination process?
A. SRY transcriptional repression
B. Telomerase activation in somatic cells
C. Temperature-sensitive activation of aromatase
D. DNA methylation of the Z chromosome

C. Temperature-sensitive activation of aromatase

Explanation:
The enzyme aromatase converts androgens to estrogens, and its expression can be temperature-sensitive. This plays a central role in sex determination in many reptiles with TSD.

6. Which of the following statements best describes the Genic Balance Theory in Drosophila?
A. Presence of the Y chromosome determines sex
B. Equal numbers of autosomes and X chromosomes result in male development
C. A specific X:A ratio determines sex, independent of the Y chromosome
D. Sex is determined by differential methylation of autosomal genes

C. A specific X:A ratio determines sex, independent of the Y chromosome

Explanation:
In Drosophila, sex is determined by the X:A ratio, not by the presence of a Y chromosome.

• 1.0 = Female (XX:2A)

• 0.5 = Male (X:2A)

7. A male human with an SRY gene translocated onto one of his X chromosomes and no Y chromosome would most likely be:
A. Phenotypically female with Turner syndrome
B. Phenotypically male despite having two X chromosomes
C. Sterile but otherwise female
D. Genetically female but hormonally male

B. Phenotypically male despite having two X chromosomes

Explanation:
If an SRY gene is present, even without a Y chromosome, the individual typically develops as a phenotypic male. This is an example of how SRY alone is sufficient to initiate male development.

8. Which of the following is a true statement about dosage compensation in mammals?
A. All X chromosomes are inactivated in female somatic cells
B. The X chromosome in males is partially inactivated to balance expression
C. Only one X chromosome remains active in each somatic cell of a female
D. The Barr body is a heterochromatinized Y chromosome

C. Only one X chromosome remains active in each somatic cell of a female

Explanation:
In female mammals, only one X remains active in each somatic cell. The other becomes a Barr body. This ensures dosage compensation between XX females and XY males.

9. Which of the following best defines the bipotential gonad?
A. A gamete precursor present only in males
B. A structure that differentiates into testes or ovaries depending on genetic and hormonal cues
C. A primitive duct that leads to reproductive organs
D. A sex chromosome that has both X and Y features

B. A structure that differentiates into testes or ovaries depending on genetic and hormonal cues

Explanation:
During early embryogenesis, the gonadal ridge is bipotential — it can become testes or ovaries depending on genetic signals (e.g., SRY presence or absence).

10. In the ZW sex-determination system, which of the following gamete combinations results in a female offspring?
A. Z egg + Z sperm
B. Z egg + W sperm
C. W egg + Z sperm
D. W egg + W sperm

C. W egg + Z sperm

Explanation:

• ZW system (used by birds, reptiles, etc.):

  • Females are ZW

  • Males are ZZ

• Females produce two types of eggs (Z or W)

• Males produce only Z sperm

Therefore:

• Z egg + Z sperm = ZZ = male

• W egg + Z sperm = ZW = female

1. Which of the following best describes the difference between primary and secondary sexual differentiation?
A. Primary refers to external traits; secondary refers to gonads
B. Primary involves the gonads; secondary includes body features like mammary glands
C. Primary refers to sexual behavior; secondary refers to genetic mutations
D. Primary occurs after birth; secondary begins during puberty

B. Primary involves the gonads; secondary includes body features like mammary glands

Explanation:

• Primary differentiation: development of the gonads (testes/ovaries)

• Secondary differentiation: development of traits like mammary glands, body hair, external genitalia, etc.
  So your answer is spot-on.

2. Which organism's sex is determined by the ratio of X chromosomes to sets of autosomes, not the presence of a Y chromosome?
A. Humans
B. Chickens
C. Drosophila
D. C. elegans

C. Drosophila

Explanation:
In Drosophila, sex is determined by the ratio of X chromosomes to autosomes (X:A).

• 1.0 = female (XX:2A)

• 0.5 = male (X:2A)
  The Y chromosome does not determine sex (but is needed for male fertility).

3. Which genotype would you expect to result in a phenotypic female with underdeveloped ovaries and short stature?
A. 47,XXY
B. 45,XO
C. 46,XY with SRY
D. 47,XXX

B. 45,XO

Explanation:
This describes Turner syndrome (45,XO) — phenotypic females with short stature, rudimentary ovaries, and sometimes learning disabilities. Nice job!

4. What is the biological significance of the pseudoautosomal regions (PARs) on the sex chromosomes?
A. They code for secondary sex traits
B. They allow recombination and pairing of X and Y during meiosis
C. They are the location of the SRY gene
D. They trigger X-inactivation

B. They allow recombination and pairing of X and Y during meiosis

Explanation:
PARs are the homologous regions on the X and Y chromosomes that allow them to pair and recombine during meiosis. They are not sex-determining but crucial for proper segregation.

5. Which of the following statements about the MSY (male-specific region of the Y) is correct?
A. It is found in both males and females
B. It contains the gene for Barr body formation
C. It includes regions that do not recombine with the X chromosome
D. It is responsible for inactivating the X chromosome in males

C. It includes regions that do not recombine with the X chromosome

Explanation:
The MSY (male-specific region of the Y) contains genes that do not recombine with the X. It includes the SRY gene and other male-specific factors. Some parts are euchromatic (active) and others are heterochromatic (inactive).

6. What would be the number of Barr bodies in a somatic cell of a person with a 48,XXXX karyotype?
A. 0
B. 1
C. 2
D. 3

D. 3

Explanation:
According to the N-1 rule, the number of Barr bodies = number of X chromosomes - 1.
So: 4 X chromosomes → 4 - 1 = 3 Barr bodies.

7. In reptiles with TSD Case I, what sex is produced at lower incubation temperatures?
A. Males
B. Females
C. Both equally
D. It varies by species

B. Females

Explanation:
In Case I of temperature-dependent sex determination (TSD):

• Low temperatures → females

• High temperatures → males
  (Seen in many turtles.)

8. Which of the following most accurately describes how hermaphrodites in C. elegans reproduce?
A. By cloning
B. Through fertilization with male sperm only
C. By self-fertilization using both eggs and stored sperm
D. Through binary fission

C. By self-fertilization using both eggs and stored sperm

Explanation:
C. elegans hermaphrodites produce both eggs and sperm. They self-fertilize, using stored sperm.

• Offspring are mostly hermaphrodites

• Less than 1% are males (which arise from X chromosome loss)

9. In the N-1 rule of X-inactivation, what does "N" represent?
A. Number of chromosomes in a cell
B. Number of autosomes
C. Number of total sex chromosomes
D. Number of X chromosomes in a cell

D. Number of X chromosomes in a cell

Explanation:
N = number of X chromosomes in a somatic cell.
The rule says all but one X chromosome are inactivated.

10. What explains why Turner syndrome (XO) individuals still show developmental abnormalities despite dosage compensation?
A. Their Y chromosome is partially active
B. The X chromosome is entirely inactivated
C. Not all genes on the single X are expressed
D. Some X-linked genes escape inactivation early in gonadal development

D. Some X-linked genes escape inactivation early in gonadal development

Explanation:
Even though X-inactivation balances gene expression, some X-linked genes escape inactivation, especially early in gonadal development — this can lead to Turner syndrome symptoms despite having only one X.

1. Which of the following best explains why XX males can exist in humans?
A. Loss of Barr bodies during embryonic development
B. Translocation of the SRY gene to an X chromosome
C. Homozygosity for TDF alleles
D. Activation of the XIST gene on both X chromosomes

B. Translocation of the SRY gene to an X chromosome

Explanation:
XX males result from the SRY gene being translocated to an X chromosome. This gene triggers testis development even in the absence of a Y chromosome.

2. Which structural feature of the Y chromosome is essential for male meiosis and segregation of sex chromosomes?
A. MSY
B. TDF region
C. PAR regions
D. Centromere

C. PAR regions

Explanation:
The PAR regions (pseudoautosomal regions) on the Y chromosome pair and recombine with homologous regions on the X chromosome during meiosis — essential for proper segregation.

3. A fruit fly with a genotype of XX:3A will develop as:
A. Female
B. Male
C. Metamale
D. Intersex

C. Metamale

Explanation:
In Drosophila, sex is determined by the X:A ratio:

• 1.0 = female (XX:2A)

• 0.5 = male (XY or X:2A)

• <0.5 = metamale (XX:3A) → a weak, sterile male

4. What is a defining difference between sex determination in humans and Drosophila?
A. Both rely solely on the Y chromosome
B. Humans require the X:A ratio, Drosophila do not
C. Drosophila rely on the X:A ratio; humans rely on presence of SRY
D. Both require TDF activation for maleness

C. Drosophila rely on the X:A ratio; humans rely on presence of SRY

Explanation:
Drosophila use the X:A ratio to determine sex.
Humans rely on the presence or absence of the SRY gene on the Y chromosome. The Y is essential in humans, but not in Drosophila.

5. Which of the following would result in no Barr bodies in a somatic cell?
A. 46,XX
B. 47,XXY
C. 45,XO
D. 47,XXX

C. 45,XO

Explanation:
45,XO (Turner syndrome) has only one X chromosome, so nothing to inactivate.
→ No Barr bodies

6. The TDF protein is classified as which of the following?
A. DNA helicase
B. Transcription factor
C. Hormone receptor
D. DNA methyltransferase

B. Transcription factor

Explanation:
Testis-Determining Factor (TDF) is a transcription factor encoded by SRY, activating genes needed for testis development.

7. Why might females with 47,XXX or 48,XXXX karyotypes still show symptoms despite X-inactivation?
A. The extra X chromosomes become Y-like
B. The PAR regions are not silenced
C. X-inactivation is incomplete; some genes escape silencing
D. They lack aromatase expression

C. X-inactivation is incomplete; some genes escape silencing

Explanation:
Some genes on the X chromosome escape inactivation, particularly in pseudoautosomal regions, leading to dosage imbalance even when extra Xs are present.

8. Which sex-determining system involves females as the heterogametic sex?
A. XY (mammals)
B. XO (insects)
C. ZW (birds, reptiles)
D. X:A ratio (Drosophila)

C. ZW (birds, reptiles)

Explanation:
In the ZW system (e.g., birds, reptiles):

• Females = ZW (heterogametic)

• Males = ZZ

9. Which of the following best defines a genetic mosaic in the context of sex determination?
A. A cell with three sets of chromosomes
B. A tissue with only paternal X chromosome expression
C. An organism composed of cells with different patterns of X-inactivation
D. A result of recombination between autosomes

C. An organism composed of cells with different patterns of X-inactivation

Explanation:
Females with random X-inactivation have cells expressing different X-linked alleles. This patchwork makes them genetic mosaics.

10. In mammals, X-inactivation occurs during:
A. Gametogenesis
B. The blastocyst stage of embryogenesis
C. Meiosis I in oocytes
D. Fertilization

B. The blastocyst stage of embryogenesis

Explanation:
X-inactivation begins in early embryogenesis — during the late blastocyst stage, not during gametogenesis.

11. The Barr body forms from:
A. The Y chromosome
B. The active X chromosome
C. A pseudoautosomal region
D. A randomly inactivated X chromosome

D. A randomly inactivated X chromosome

Explanation:
The Barr body is the condensed, inactivated X chromosome, and it arises randomly from either the maternal or paternal X.

12. Which of the following best supports the Lyon Hypothesis?
A. Male cats are often calico
B. Turner syndrome individuals have two Barr bodies
C. Heterozygous females for X-linked traits show patchy phenotypes
D. Males with 47,XYY develop as intersex

C. Heterozygous females for X-linked traits show patchy phenotypes

Explanation:
Heterozygous females for X-linked traits (like fur color or sweat glands) show patchy expression, proving random X-inactivation.

13. What is the effect of aromatase on sex differentiation in reptiles with TSD?
A. Converts testosterone to estrogen, promoting female development
B. Enhances androgen receptor signaling
C. Inhibits egg incubation
D. Blocks SRY transcription

A. Converts testosterone to estrogen, promoting female development

Explanation:
Aromatase converts testosterone to estrogen, pushing gonads toward ovary formation at certain temperatures — key in TSD (temperature-dependent sex determination).

14. Which of the following is true regarding sex reversal mutants in maize?
A. Tassel seed (ts) mutants produce only male flowers
B. Silkless (sk) mutants block ovary development
C. Mutations in ts and ba result in complete sterility
D. ts and sk mutations are dominant

B. Silkless (sk) mutants block ovary development

Explanation:

• Tassel seed (ts) mutants actually interfere with tassel (male) production and promote female structures.

• Silkless (sk) mutants prevent pistil (female organ) development → only male flowers.
  So B is correct.

15. Why does the X chromosome in Drosophila males undergo transcriptional upregulation?
A. To prevent SRY expression
B. To match gene expression of XX females
C. To enable Barr body formation
D. To ensure recombination with the Y

B. To match gene expression of XX females

Explanation:
To match gene expression levels of XX females, the single X chromosome in males is transcriptionally upregulated — a unique dosage compensation mechanism in Drosophila.