All Free Biology MCQs with Answers

721. Haemophilia became known as the royal disease because it

• A. was cured by royal physicians
• B. is common in every royal family
• C. was traced through the descendants of Queen Victoria
• D. was first described by a king

Explanation: Victoria carried the allele and passed it into the royal houses of Russia and Spain, producing affected princes across Europe. The pedigree became the classic textbook example of X linked recessive inheritance.

722. A trait determined by a gene on the Y chromosome is transmitted

• A. from mother to sons
• B. from father to all his sons
• C. equally to sons and daughters
• D. to daughters only

Explanation: Only males carry a Y chromosome, and a father passes it to every son and no daughter, so Y linked traits run strictly down the male line. Nothing on the Y can ever appear in a female.

723. Which of the following human conditions is inherited as an X linked recessive trait?

• A. Red green colour blindness
• B. Sickle cell anaemia
• C. Down syndrome
• D. Albinism

Explanation: The genes for red and green pigments lie on the X chromosome, so colour blindness follows the X linked pattern. Sickle cell anaemia and albinism are autosomal recessive, and Down syndrome is a chromosome number disorder, not a single gene trait.

724. A carrier of haemophilia is typically

• A. a man suffering from the disease
• B. a heterozygous woman with one normal and one haemophilia allele
• C. a homozygous normal woman
• D. a person with an extra chromosome

Explanation: A carrier holds the recessive allele without symptoms because the normal allele on her other X is enough for clotting. A man with the allele is affected rather than a carrier, since he has no second X.

725. A normal man marries a woman whose father had haemophilia. The probability that their first son will have haemophilia is

• A. zero
• B. one quarter
• C. one half
• D. certain

Explanation: The woman inherited her haemophiliac father's X, making her a carrier. She passes that X to half her sons, who will be affected, and the father's normal X contribution is irrelevant to sons, who receive his Y.

726. In the cells of a female mammal, one of the two X chromosomes condenses into a dense body called the

• A. centromere
• B. nucleolus
• C. chiasma
• D. Barr body

Explanation: The inactivated X, or Barr body, equalises the gene dose between XX females and XY males. Males, with a single active X, show no Barr body, which is why the test was once used to check chromosomal sex.

727. The female gonads that produce ova and secrete the hormones oestrogen and progesterone are the

• A. ovaries
• B. uterus
• C. oviducts
• D. vagina

Explanation: The ovaries are both the source of egg cells and an endocrine gland, releasing the hormones that control the menstrual cycle and pregnancy. The uterus receives the embryo and the oviduct is the site of fertilisation, but neither produces gametes.

728. The inner lining of the uterus, which thickens each cycle and is shed during menstruation, is the

• A. perimetrium
• B. endometrium
• C. myometrium
• D. cervix

Explanation: The endometrium is the hormonally responsive layer where the embryo implants. The myometrium is the muscular wall that contracts in labour and the perimetrium the outer covering, so only the endometrium is shed in menstruation.

729. After their production, spermatozoa mature and are temporarily stored in the

• A. seminal vesicles
• B. prostate gland
• C. epididymis
• D. urethra

Explanation: Sperm leaving the seminiferous tubules are not yet motile; they gain the ability to swim while passing through the coiled epididymis where they are stored. The seminal vesicles and prostate only add fluid at the moment of ejaculation.

730. The secretion of the seminal vesicles is rich in a sugar that serves as fuel for sperm. This sugar is

• A. glucose
• B. sucrose
• C. lactose
• D. fructose

Explanation: Fructose provides the energy that powers the tail of the sperm during its journey. The prostate contributes a milky alkaline fluid instead, protecting sperm from the acidity of the vagina.