X-linked Inheritance

X-linked Inheritance MDCAT MCQs with answers

30 past paper MCQs on X-linked Inheritance, from the Inheritance unit of MDCAT Biology. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

Read the notes first Practise the unit as a quiz

1.To study sex linkage in Drosophila, Morgan mated white eyed males with wild type red eyed females. What will be the phenotype of the offspring? (MDCAT 2022)

  1. all red eyed males and females
  2. red eyed females and white eyed males
  3. white eyed females and red eyed males
  4. all white eyed females and males
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Correct answer: (a) all red eyed males and females

Every daughter gets a red allele from her mother and every son gets his single X from her too, so the whole $F_1$ is red eyed.

2.The mode of inheritance in humans can be traced through: (MDCAT 2022)

  1. experimental mating
  2. chi square charts
  3. pedigree analysis
  4. probability analysis
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Correct answer: (c) pedigree analysis

Human families cannot be bred to order, so the record of a trait through the generations is what is studied.

3.Which one of the following is an X-linked dominant disorder? (MDCAT 2023)

  1. haemophilia
  2. colour blindness
  3. hypophosphataemic rickets
  4. hypertrichosis
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Correct answer: (c) hypophosphataemic rickets

Hypophosphataemic rickets is carried on the X chromosome and shows in the heterozygote; haemophilia and colour blindness are X-linked recessive.

4.A baby girl is born with hemophilia, which is an X-linked recessive disorder. What are the most likely genotypes of her parents? (UHS MDCAT 2025)

  1. The mother is a carrier and the father is normal.
  2. The mother is hemophiliac and the father is normal.
  3. The mother is carrier and the father is hemophiliac
  4. Both are normal.
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Correct answer: (c) The mother is carrier and the father is hemophiliac

A girl needs the allele on both X chromosomes, so her father must be affected and her mother at least a carrier.

5.If a normal person marries with colour blind female what will be the possibility of normal male child: (UHS MDCAT 2025)

  1. 0%
  2. 25%
  3. 50%
  4. 75%
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Correct answer: (a) 0%

A son takes his only X from his mother, and both of hers carry the allele, so none can be normal.

6.A carrier female for an X-linked recessive disorder: (KMU MDCAT 2025)

  1. Expresses the disorder fully
  2. Cannot pass the disorder to her sons
  3. Can pass the disorder to her sons
  4. Only pases the disorder to her sons
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Correct answer: (c) Can pass the disorder to her sons

A son takes his single X from his mother, so half the sons of a carrier are affected.

7.Which of the following is an X-linked recessive disorder in humans? (KMU MDCAT 2025)

  1. Cystic fibrosis
  2. Thalassemia
  3. Hemophilia
  4. Sickle cell anemia
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Correct answer: (c) Hemophilia

Haemophilia is carried on the X chromosome; the other three are autosomal.

8.Which of the following CORRECTLY describes the expected outcome of children from a carrier mother for hemophilia (X^h X^h) and a normal father (X^Y)? (KMU MDCAT 2025)

  1. All sons will have hemophilia
  2. All daughters will be carriers
  3. 50% of sons will have hemophilia, and 50% of daughters will be carriers
  4. All offspring will be unaffected
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Correct answer: (c) 50% of sons will have hemophilia, and 50% of daughters will be carriers

Half her sons take the affected X and half her daughters take it and become carriers.

9.If a male with hemophilia marries a non-carrier female, what is the likelihood of their sons inheriting the condition? (SIBA MDCAT 2025)

  1. 50%
  2. 100%
  3. 0%
  4. 25%
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Correct answer: (c) 0%

A son takes his X from his mother, and hers are both normal, so no son can be affected.

10.If the disease is caused due to a defective gene located on the X chromosome, then defectives gene can only be transmitted to male offspring by the: (SIBA MDCAT 2025)

  1. Female gamete
  2. Male gamete
  3. Bacteria
  4. Mutation
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Correct answer: (a) Female gamete

A son takes his X only from his mother, so the defective gene reaches him through the egg.

11.A carrier mother for hemophilia and a normal father can produce: (SZABMU MDCAT 2025)

  1. All hemophilic sons
  2. 25 % Hemophilic among sons
  3. 50 % hemophilic among sons
  4. All normal sons and daughter
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Correct answer: (c) 50 % hemophilic among sons

Half the sons take her affected X, so half of them are haemophilic.

12.Y-linked inheritance refers to which mode of the inheritance? (SZABMU MDCAT 2025)

  1. Crisscross
  2. Straight
  3. Loop
  4. Jumping
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Correct answer: (b) Straight

A Y-linked gene passes from father to son in every generation, so the inheritance is straight.

13.If a colorblind lady marries a normal man, their children will be: (SZABMU MDCAT 2025)

  1. Normal daughters and normal sons
  2. Normal sons and carrier daughters
  3. Colorblind sons and carrier daughters
  4. Colorblind sons and colorblind daughters
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Correct answer: (c) Colorblind sons and carrier daughters

Every son takes her affected X and every daughter takes one affected and one normal X.

14.Which is true for an X linked dominant trait? (KMU MDCAT 2024)

  1. All female offspring of the affected father will be affected
  2. Half of the female offsprings of the affected father will be affected
  3. No male offspring of an affected mother will be affected
  4. No female offspring of the affected father will be affected
Show answer

Correct answer: (a) All female offspring of the affected father will be affected

An affected father passes his only X to every daughter, so all of them show a dominant trait.

15.A carrier female for hemophilia is married to an affected male. What would be the probable percentage for their sons to be affected? (NUMS MDCAT 2024)

  1. 100%
  2. 50%
  3. 25%
  4. 0%
Show answer

Correct answer: (b) 50%

Half her sons take the affected X from her, so half of them are affected.

16.Which is correct for pattern baldness? (NUMS MDCAT 2024)

  1. It is sex linked trait
  2. Occurs due to hormonal differences between sexes
  3. Heterozygous male is normal
  4. Heterozygous female is affected
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Correct answer: (b) Occurs due to hormonal differences between sexes

Baldness is autosomal but sex influenced: the heterozygote is bald in a man and not in a woman.

17.To study sex linkages in Drosophila, Morgan mated white eyed males with wild type red eyed females. What will be the phenotype of offspring? (UHS MDCAT 2023)

  1. All red eyed males and females
  2. Red eyed females and white eyed males
  3. White eyed females and red eyed males
  4. All white eyed females and males
Show answer

Correct answer: (a) All red eyed males and females

Red is dominant and the mother gives every offspring a red-bearing X, so all the F1 are red eyed.

18.Which one of the following is X Linked Dominant disorder? (UHS MDCAT 2023)

  1. Haemophilia
  2. Color blindness
  3. Hypophosphatemic rickets
  4. Hypertrichosis
Show answer

Correct answer: (c) Hypophosphatemic rickets

Hypophosphataemic rickets is carried on the X chromosome and is dominant.

19.Which of the following traits is transmitted directly from an affected father to only his son? (NUMS MDCAT 2023)

  1. Autosomal
  2. X-linked
  3. Y-linked
  4. X-Y linked
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Correct answer: (c) Y-linked

A gene on the Y chromosome goes from father to son and to no daughter.

20.Which of the following is a dominant x-linked trait in human? (PMC MDCAT 2022)

  1. Testicular feminization
  2. Haemophllia
  3. Colorblindness
  4. Hypophosphatemic rickets
Show answer

Correct answer: (d) Hypophosphatemic rickets

Hypophosphataemic rickets is carried on the X chromosome and is dominant.

21.A diseased man marries a normal woman.They have five daughters and three sons.All the daughters were diseased and sons were normal. The gene of this disease is: (PMC MDCAT 2022)

  1. X linked dominant
  2. X-linked recessive
  3. Autosomal recessive
  4. Autosomal dominant
Show answer

Correct answer: (a) X linked dominant

Every daughter takes her father’s X and shows the trait; no son does, so it is X-linked dominant.

22.A man receives his X chromosome from: (PMC MDCAT 2022)

  1. His mother only
  2. Part from his father and part from his mother
  3. His father only
  4. Either his mother or his father, It depends upon luck
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Correct answer: (a) His mother only

A man has one X and one Y; the Y came from his father, so the X came from his mother.

23.Which of the following is the wildtype phenotype of eye color in Drosophila (PMC MDCAT 2022)

  1. Black eyes
  2. White eyes
  3. Light red eyes
  4. Bright red eyes
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Correct answer: (d) Bright red eyes

The wild type Drosophila has bright red eyes; white is the mutant Morgan studied.

24.Which of the following disease has greater incidence in human male than female? (PMC MDCAT 2022)

  1. Haemophilia
  2. Cystic fibrosis
  3. Thalassemia
  4. Cretinism
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Correct answer: (a) Haemophilia

Haemophilia is X-linked recessive, so a man needs only one copy to show it.

25.Which traits are most likely to affect men than women? (PMC MDCAT 2020)

  1. X linked recessive
  2. X linked dominant
  3. Autosomal dominant
  4. Autosomal recessive
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Correct answer: (a) X linked recessive

A man has only one X, so a single recessive allele on it shows at once.

26.Haemophilia occurs because of: (PMC MDCAT 2020)

  1. Mutation in an autosome
  2. Mutation of Y-chromosome
  3. Mutation of X-chromosome
  4. Deficiency of iron
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Correct answer: (c) Mutation of X-chromosome

The gene for the missing clotting factor lies on the X chromosome.

27.If a carrier haemophilic female (XHXh) is married to a haemophilic male (XhY). What will be the ratio of presence of haemophilia in the children. (UHS MDCAT 2019)

  1. 100% all females and males will be haemophilic
  2. Females have 50% chances of getting haemophilia and males will be 100% haemophilic
  3. Carrier female 25%, haemophilic female 25%, normal male 25% and 25% haemophilic male
  4. Females and males both have 50% chances of getting haemophilia
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Correct answer: (c) Carrier female 25%, haemophilic female 25%, normal male 25% and 25% haemophilic male

Half the daughters are carriers and half affected; half the sons are normal and half affected.

28.XO-XX is associated with: (UHS MDCAT 2017)

  1. Fishes
  2. Man
  3. Drosophila
  4. Grasshopper
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Correct answer: (d) Grasshopper

In the grasshopper the female is XX and the male has a single X and no Y.

29.Which one of the following is X-linked trait? (UHS MDCAT 2016)

  1. Male pattern baldness
  2. Diabetes mellitus
  3. Haemophilia
  4. Erythroblastosis fetalis
Show answer

Correct answer: (c) Haemophilia

Haemophilia is carried on the X chromosome.

30.X-linked recessive trait is: (UHS MDCAT 2015)

  1. Hypophosphatemia
  2. Vitamin-D resistant rickets
  3. Haemophilia
  4. Diabetes Mellitus
Show answer

Correct answer: (c) Haemophilia

Haemophilia is carried on the X chromosome and is recessive.

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