401. In a standard pedigree, a square usually represents
ⓐ. a male
ⓑ. a female
ⓒ. an affected child
ⓓ. an unknown parent
Correct Answer: a male
Explanation: Pedigree charts use standard symbols so that family relationships can be read quickly and consistently. A square is the conventional symbol for a male. A circle is used for a female. Learning these symbols is essential before interpreting inheritance patterns in a family tree.
402. In a standard pedigree, a circle usually represents
ⓐ. an affected individual
ⓑ. a gamete
ⓒ. a female
ⓓ. a recessive trait
Correct Answer: a female
Explanation: A circle is the usual pedigree symbol for a female. This standardization helps geneticists read family charts clearly across generations. The symbol itself does not indicate whether the person is affected unless additional shading is shown. Symbol meaning and trait status must therefore be read separately.
403. In a pedigree chart, a shaded symbol generally indicates
ⓐ. an affected individual
ⓑ. a dominant allele
ⓒ. a carrier male only
ⓓ. a homozygous recessive genotype in every case
Correct Answer: an affected individual
Explanation: Shading in pedigree charts is commonly used to mark individuals who express the trait being studied. The chart does not automatically reveal the exact genotype in every case, but it does show trait expression. This makes shading very helpful when tracing inheritance through a family. The meaning depends on the particular trait under investigation.
404. Which statement best describes the main use of a pedigree chart?
ⓐ. It predicts the exact DNA sequence of a gene.
ⓑ. It directly shows chromosome pairing during meiosis.
ⓒ. It replaces all other methods of genetic study.
ⓓ. It helps trace the inheritance pattern of a trait through family generations.
Correct Answer: It helps trace the inheritance pattern of a trait through family generations.
Explanation: A pedigree chart organizes family information in a way that makes inheritance patterns easier to follow. By comparing affected and unaffected individuals across generations, one can infer whether a trait is dominant, recessive, or sex-linked. It does not directly reveal DNA sequence or chromosome behavior. Its strength lies in pattern analysis across related individuals.
405. A trait appears in every generation of a family pedigree and affected individuals usually have an affected parent. This pattern most strongly suggests
ⓐ. mitochondrial inheritance only
ⓑ. dominant inheritance
ⓒ. mutation in every generation
ⓓ. absence of heredity
Correct Answer: dominant inheritance
Explanation: Dominant traits often show vertical transmission, meaning they appear generation after generation. In such cases, an affected person usually has at least one affected parent. This contrasts with many recessive traits, which can skip generations. The repeated presence across successive generations is therefore a useful clue for dominance.
406. In a pedigree, two unaffected parents have an affected child. Which pattern is most strongly suggested for an autosomal trait?
ⓐ. autosomal dominant
ⓑ. codominant
ⓒ. incomplete dominant
ⓓ. autosomal recessive
Correct Answer: autosomal recessive
Explanation: If both parents are unaffected but produce an affected child, it suggests that both parents may be carriers of a recessive allele. The child becomes affected when it inherits the recessive allele from both sides. This is a classic clue for autosomal recessive inheritance. Dominant traits usually require an affected parent in such simple pedigree reasoning.
407. A trait is much more common in males than in females, and affected females are rare. Which inheritance pattern is suggested most strongly?
ⓐ. autosomal dominant
ⓑ. X-linked recessive
ⓒ. autosomal recessive
ⓓ. codominant
Correct Answer: X-linked recessive
Explanation: X-linked recessive traits are expressed more often in males because males have only one X chromosome. A single recessive allele on that X can therefore produce the trait. Females usually need two recessive alleles to be affected, so affected females are less common. This unequal sex distribution is one of the strongest clues in pedigree interpretation.
408. Which statement about pedigree analysis is correct?
ⓐ. It is useful only for plant breeding experiments.
ⓑ. It helps study inheritance in humans where direct crossing experiments are not possible.
ⓒ. It can be used only for traits controlled by more than two genes.
ⓓ. It identifies only chromosome number and not inheritance pattern.
Correct Answer: It helps study inheritance in humans where direct crossing experiments are not possible.
Explanation: Pedigree analysis is especially valuable in human genetics because direct mating experiments cannot be performed. By studying how a trait appears among relatives, geneticists can infer inheritance patterns. The method is useful for dominant, recessive, and sex-linked traits. Its value lies in tracing transmission through real families rather than in direct experimental crossing.
409. In a pedigree chart, individuals placed on the same horizontal level usually belong to
ⓐ. the same genotype class
ⓑ. different family branches only
ⓒ. the same generation
ⓓ. the same phenotype only
Correct Answer: the same generation
Explanation: Pedigree charts are organized generation by generation. Individuals in one row usually belong to the same generation, while the next row represents their offspring or later descendants. This arrangement makes inheritance patterns easier to follow across time. Reading generations correctly is important before attempting pattern analysis.
410. In a standard pedigree, a horizontal line connecting a square and a circle usually represents
ⓐ. mating between the two individuals
ⓑ. mutation in one of the parents
ⓒ. a trait skipping one generation
ⓓ. independent assortment of chromosomes
Correct Answer: mating between the two individuals
Explanation: A horizontal line joining a male symbol and a female symbol indicates a mating pair in a pedigree. From this line, vertical lines may extend downward to show their children. The symbol does not itself show whether the individuals are affected or unaffected. It simply marks a parental relationship in the family chart.
411. Which pedigree clue most strongly supports autosomal inheritance rather than X-linked recessive inheritance?
ⓐ. The trait is seen mostly in males.
ⓑ. The trait is passed through unaffected carrier mothers to sons.
ⓒ. Affected females are very rare.
ⓓ. Father-to-son transmission is observed.
Correct Answer: Father-to-son transmission is observed.
Explanation: Father-to-son transmission is not expected for an X-linked trait because a father passes his Y chromosome, not his X chromosome, to his sons. Therefore, when a trait clearly passes from father to son, autosomal inheritance becomes much more likely. This clue is especially helpful when distinguishing autosomal traits from X-linked recessive ones. Pattern interpretation in pedigrees often depends on such transmission details.
412. A pedigree shows that unaffected parents can produce affected sons, while affected females are very uncommon. Which pattern is most strongly suggested?
ⓐ. autosomal dominant
ⓑ. X-linked recessive
ⓒ. codominant
ⓓ. incomplete dominant
Correct Answer: X-linked recessive
Explanation: X-linked recessive traits often appear more frequently in males because they have only one X chromosome. An unaffected mother may carry one recessive allele and pass it to her sons, who then express the trait. Affected females are much less common because they usually need the recessive allele on both X chromosomes. This sex bias is one of the strongest clues in pedigree analysis.
413. Which feature of a pedigree most strongly suggests dominant inheritance?
ⓐ. The trait appears in successive generations without usually skipping one.
ⓑ. The trait is seen only in one sex.
ⓒ. The trait appears only when both parents are unaffected.
ⓓ. The trait is always linked with the Y chromosome.
Correct Answer: The trait appears in successive generations without usually skipping one.
Explanation: Dominant traits often show vertical transmission through a pedigree, meaning they tend to appear generation after generation. An affected individual usually has at least one affected parent. This contrasts with many recessive traits, which may remain hidden in carriers and reappear after skipping generations. Continuous appearance across generations is therefore a useful clue for dominance.
414. In a pedigree, what does a vertical line descending from a mating line usually indicate?
ⓐ. a mutation event
ⓑ. sex determination of the child
ⓒ. chromosome separation in meiosis
ⓓ. descent to offspring
Correct Answer: descent to offspring
Explanation: The vertical line extending downward from a mating line leads to the offspring of that couple. This helps show parent-child relationships within the family. The chart is therefore not just a list of individuals, but a structured map of inheritance across generations. Reading these connecting lines correctly is essential in pedigree interpretation.
415. Which statement about pedigree analysis is most appropriate?
ⓐ. It is useful mainly because it can replace chromosome studies entirely.
ⓑ. It can help distinguish dominant, recessive, and sex-linked patterns in humans.
ⓒ. It reveals the exact DNA sequence responsible for a trait.
ⓓ. It is limited only to traits controlled by a single dominant allele.
Correct Answer: It can help distinguish dominant, recessive, and sex-linked patterns in humans.
Explanation: Pedigree analysis is valuable because it allows inheritance patterns to be inferred from family histories. By examining which individuals are affected across generations and between sexes, one can often identify whether a trait is dominant, recessive, autosomal, or sex-linked. It does not reveal DNA sequence directly. Its strength lies in pattern recognition within families.
416. Which situation in a pedigree most strongly suggests that a trait may be recessive?
ⓐ. Every affected individual has an affected parent.
ⓑ. The trait appears equally in all generations without interruption.
ⓒ. Two unaffected parents produce an affected child.
ⓓ. Only one sex ever appears in the pedigree.
Correct Answer: Two unaffected parents produce an affected child.
Explanation: Recessive traits can remain hidden in carriers, so two unaffected parents may each carry one recessive allele and still have an affected child. This is a classic clue in pedigree analysis. Dominant traits usually do not show this pattern so simply, because affected individuals tend to have an affected parent. The appearance of an affected child from unaffected parents therefore strongly suggests recessive inheritance.
417. Which statement best defines a Mendelian disorder?
ⓐ. It is a disorder caused by alteration in a single gene and inherited according to Mendelian principles.
ⓑ. It is a disorder produced only by changes in chromosome number.
ⓒ. It is a disorder caused entirely by poor nutrition during growth.
ⓓ. It is a disorder that always involves both autosomes and sex chromosomes together.
Correct Answer: It is a disorder caused by alteration in a single gene and inherited according to Mendelian principles.
Explanation: Mendelian disorders arise due to changes in individual genes rather than whole-chromosome abnormalities. Their transmission follows recognizable inheritance patterns such as dominant, recessive, autosomal, or sex-linked. This makes them different from disorders caused by aneuploidy or structural chromosome change. Several important human disorders fall into this category.
418. Which of the following is the most accurate description of Mendelian disorders in humans?
ⓐ. They are always caused by mutation in mitochondrial DNA only.
ⓑ. They may be autosomal or sex-linked and may show dominant or recessive inheritance.
ⓒ. They are all chromosomal disorders caused by nondisjunction.
ⓓ. They can be studied only through controlled breeding experiments.
Correct Answer: They may be autosomal or sex-linked and may show dominant or recessive inheritance.
Explanation: Mendelian disorders are not limited to one mode of inheritance. Some are autosomal, while others are sex-linked; some are dominant, while others are recessive. This variety is why pedigree analysis is important in identifying their transmission pattern in humans. The key point is that they still involve single-gene inheritance.
419. Which of the following is not a single-gene Mendelian disorder?
ⓐ. Haemophilia
ⓑ. Colour blindness
ⓒ. Down’s syndrome
ⓓ. Sickle-cell anaemia
Correct Answer: Down’s syndrome
Explanation: Down’s syndrome is classified as a chromosomal disorder because it results from an abnormal chromosome number. By contrast, haemophilia, colour blindness, and sickle-cell anaemia are Mendelian disorders involving single genes. This distinction matters because gene-level disorders and chromosome-level disorders are not grouped together. Their causes and inheritance logic are different.
420. Which statement correctly distinguishes Mendelian disorders from chromosomal disorders?
ⓐ. Mendelian disorders affect only visible characters, whereas chromosomal disorders do not affect phenotype.
ⓑ. Mendelian disorders occur only in males, whereas chromosomal disorders occur only in females.
ⓒ. Mendelian disorders are always recessive, whereas chromosomal disorders are always dominant.
ⓓ. Mendelian disorders usually involve single genes, whereas chromosomal disorders involve chromosome number or structure.
Correct Answer: Mendelian disorders usually involve single genes, whereas chromosomal disorders involve chromosome number or structure.
Explanation: The main difference lies in the level of genetic change involved. Mendelian disorders arise from mutation or alteration in a single gene, while chromosomal disorders involve abnormalities of whole chromosomes or their structure. Because chromosomes carry many genes, chromosomal disorders often have broader effects. Keeping these two categories separate helps organize inherited disease more clearly.
