Class 12/Question Bank
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Questions on Pedigree
Unit 2, Chapter 1: Principles of Inheritance and Variation
Total Questions: 50
Instructions: Choose the best answer for each question.
Which of the following is a key feature of an autosomal dominant inheritance pattern?
In an autosomal recessive inheritance pattern, what is the approximate percentage of offspring affected when two carrier parents mate?
What is a characteristic feature of X-linked dominant inheritance?
In X-linked recessive inheritance, who are usually the carriers of the trait?
If a trait appears in every generation and affects both males and females equally, what is the most likely mode of inheritance?
What does "consanguinity" in a pedigree chart suggest?
In X-linked dominant inheritance, if an affected mother passes the trait, what is the probability of her offspring being affected?
What is the term for an individual who is heterozygous for a recessive trait but does not show the phenotype?
Which inheritance pattern shows no male-to-male transmission?
If an unaffected individual has an allele for a dominant trait, what would be the outcome?
In a pedigree, what does a horizontal line connecting a square and a circle represent?
What is the genotype of an individual affected by an autosomal recessive trait?
If an affected male has an X-linked recessive trait, from whom did he inherit the allele?
What is the key feature of Y-linked inheritance?
In mitochondrial inheritance, who transmits the trait?
What does a shaded symbol in a pedigree chart represent?
If a trait skips generations, which of the following is a possible mode of inheritance?
What is the term for the assumption that an individual marrying into a family with a rare trait is not a carrier?
In X-linked recessive inheritance, what is the status of all daughters of an affected father (assuming the mother is not a carrier)?
If an affected individual is heterozygous (Aa) for an autosomal dominant trait, what is the probability of passing the trait to their offspring?
Instructions: State whether the following statements are true or false.
In autosomal dominant inheritance, affected individuals must have at least one affected parent.
X-linked recessive traits affect more females than males.
An unaffected individual can be a carrier of a dominant trait.
A father can transmit an X-linked gene to his son.
In autosomal recessive inheritance, two unaffected parents can have an affected child.
Y-linked traits are passed from a father to all his daughters.
Mitochondrial DNA is inherited from the father.
In X-linked dominant inheritance, affected fathers pass the trait to all their daughters.
A trait that appears in every generation is likely recessive.
Complete penetrance means that an individual with the disease-causing genotype will always express the phenotype.
Instructions: Provide a brief answer to each question.
What are the three simplifying assumptions made in the provided pedigree problems?
What are the five key clues to remember when reasoning about pedigrees?
Explain the difference between autosomal and X-linked inheritance.
What is "criss-cross inheritance"?
Why are males more commonly affected by X-linked recessive traits?
How can you distinguish between autosomal dominant and X-linked dominant inheritance?
What is the genotype of a female carrier for an X-linked recessive trait?
What is the significance of assuming a trait is "rare-in-population"?
What are the key features of mitochondrial inheritance?
What is the genotype of an affected male with an X-linked dominant trait?
Instructions: Analyze the following pedigrees and answer the questions.
[Pedigree chart would be displayed here]
What is the mode of inheritance shown in this pedigree?
What is the genotype of individual I-1?
What is the genotype of individual II-2?
[Pedigree chart would be displayed here]
What is the most likely mode of inheritance in this pedigree?
Can this be an X-linked dominant trait? Why or why not?
What is the genotype of individual III-1?
[Pedigree chart would be displayed here]
What is the mode of inheritance shown in this pedigree?
Why can't this be an autosomal recessive trait?
What is the genotype of individual II-5?
If individual III-2 marries an unaffected man, what is the probability of them having an affected child?
The three simplifying assumptions are:
The five key clues are:
Autosomal inheritance involves genes on the autosomes (non-sex chromosomes), and it affects males and females equally. X-linked inheritance involves genes on the X chromosome, leading to different patterns of inheritance in males and females.
Criss-cross inheritance is a pattern of inheritance where a trait is transmitted from father to daughter to grandson, or from mother to son to granddaughter. It is characteristic of X-linked recessive traits.
Males are more commonly affected by X-linked recessive traits because they are hemizygous (have only one X chromosome). A single recessive allele on the X chromosome will cause the trait to be expressed in males, whereas females need two recessive alleles to be affected.
To distinguish between autosomal dominant and X-linked dominant inheritance, look for the transmission from an affected father. In X-linked dominant inheritance, an affected father will pass the trait to all his daughters and none of his sons. In autosomal dominant inheritance, an affected father can pass the trait to both sons and daughters.
The genotype of a female carrier for an X-linked recessive trait is XAXa.
Assuming a trait is "rare-in-population" simplifies pedigree analysis by allowing us to assume that individuals marrying into the family are homozygous for the normal allele and are not carriers of the trait.
The key features of mitochondrial inheritance are:
The genotype of an affected male with an X-linked dominant trait is XaY.
Case 1: The mode of inheritance is autosomal recessive.
Case 1: The genotype of individual I-1 is Aa (carrier).
Case 1: The genotype of individual II-2 is Aa (carrier).
Case 2: The most likely mode of inheritance is autosomal dominant.
Case 2: This cannot be an X-linked dominant trait because there is male-to-male transmission (e.g., individual I-1 passes the trait to his son II-5).
Case 2: The genotype of individual III-1 is aa (unaffected).
Case 3: The mode of inheritance is X-linked recessive.
Case 3: This cannot be an autosomal recessive trait because if it were, the affected female II-5 (aa) would have to have an affected father (aa), but her father I-1 is unaffected.
Case 3: The genotype of individual II-5 is XaXa (affected female).
Case 3: Individual III-2 is a carrier female (XAXa). If she marries an unaffected man (XAY), the probability of them having an affected child (XaY) is 25% (50% of sons).
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