AI-generated explanation. Check against your textbook.
Explanation:
Pleiotropism means one gene affecting many phenotypic traits. So option 4 is correct. A single gene influences multiple features such as color, height, and metabolism in some organisms as described in NCERT discussions of gene action.
🧠 Did You Know?
In pleiotropy, a single mutant gene can cause multiple symptoms or disorders, illustrating how genes can have widespread effects beyond one trait.
💡 NCERT Memory Line:
A single gene may influence more than one character (pleiotropy).
Frequency of recombination between gene pairs on same chromosome as a measure of the distance between genes to map their position on chromosome, was used for the first time by:
AI-generated explanation. Check against your textbook.
Explanation:
The first use of recombination frequency to map gene positions on a chromosome was by Alfred Sturtevant. He proposed that the frequency of crossing over between two genes reflects their distance apart on the chromosome, enabling gene mapping. This idea came from Thomas Hunt Morgan's discovery of linkage and crossing over, but it was Sturtevant who used recombination data to create the first gene map.
🧠 Did You Know?
Sturtevant’s work laid the foundation for genetic mapping, showing that genes are arranged linearly on chromosomes and that recombination frequency correlates with distance.
💡 NCERT Memory Line:
Recombination frequency between two genes is a measure of the distance between them on a chromosome (gene mapping).
Which of the following statements are correct about
Klinefelter's Syndrome?
A. This disorder was first described by Langdon Down (1866).
B. Such an individual has overall masculine development. However, the feminine development is also expressed.
C. The affected individual is short stature.
D. Physical, psychomotor and mental development is retarded.
E. Such individuals are sterile.
Choose the correct answer from the options given below:
AI-generated explanation. Check against your textbook.
Explanation:
Explanation per NCERT: A is incorrect (Klinefelter's described by Klinefelter, not Langdon Down). B is considered correct: individuals are male but may show some feminine features due to hypogonadism. C is incorrect: affected individuals are typically tall, not short. D is not a general NCERT statement; mental development may be affected mildly but is not described as broadly retarded. E is correct: such individuals are sterile due to impaired spermatogenesis.
🧠 Did You Know?
Klinefelter's syndrome results from a 47,XXY karyotype in males, leading to hypogonadism and characteristic features.
💡 NCERT Memory Line:
Klinefelter's syndrome: male with extra X chromosome; often tall, with underdeveloped secondary sexual traits; sterility is common.
Which one of the following symbols represents mating between relatives in human pedigree analysis?
AI-generated explanation. Check against your textbook.
Explanation:
In NCERT biology, a double horizontal line between two individuals in a pedigree denotes mating between relatives (consanguineous mating). Since the stored correct answer is option 3, symbol C represents this double-line mating symbol. Other options typically show a single line for a normal marriage or other non-mating connections, but the double line specifically indicates relatives mating.
🧠 Did You Know?
NCERT uses simple symbols: circle = female, square = male, horizontal line = marriage, and a double line = mating between related individuals.
💡 NCERT Memory Line:
Double line between partners = consanguineous mating (relation-based). Single line = general marriage.
Broad palm with single palm crease is visible in a person suffering from:
AI-generated explanation. Check against your textbook.
Explanation:
A broad palm with a single transverse palmar crease (simian crease) is characteristic of Down's syndrome. In NCERT, Down syndrome is described as having a single palmar crease among other features. This crease results from fusion of first and second palmar creases during fetal development. Therefore, the correct option is 2: Down's syndrome. The other conditions do not classically show this crease: Thalassemia affects blood and does not cause a simian crease; Turner's syndrome features short stature and webbed neck; Klinefelter's syndrome involves an extra X chromosome with tall stature and other signs.
🧠 Did You Know?
The simian crease can appear in healthy individuals too, but it is more commonly associated with Down's syndrome in exams and textbooks.
💡 NCERT Memory Line:
Down's syndrome often shows a single transverse palmar crease (simian crease) on the palm.
Given below are two statements: Statement I: Mendel studied seven pairs of contrasting traits in pea plants and proposed the Laws of Inheritance. Statement II: Seven characters examined by Mendel in his experiment on pea plants were seed shape and colour, flower colour, pod shape and colour, flower position and stem height.
In the light of the above statements, choose the correct answer from the options given below:
AI-generated explanation. Check against your textbook.
Explanation:
Statement I is correct: Mendel studied seven pairs of contrasting traits in pea plants and proposed the Laws of Inheritance. Statement II is also correct: the seven characters examined were seed shape and seed colour, flower colour, pod shape and pod colour, flower position, and stem (plant) height. These together constitute seven distinct traits described by NCERT. Hence, option 1 is the right choice.
🧠 Did You Know?
NCERT mentions seven contrasting characteristics studied by Mendel, which laid the foundation for the Laws of Inheritance (dominant/recessive, segregation, and independent assortment).
💡 NCERT Memory Line:
Mendel studied seven pairs of contrasting characters in peas and formulated the basic laws of inheritance.
AI-generated explanation. Check against your textbook.
Explanation:
XO type sex determination means males have one X chromosome (X0) and no second sex chromosome, while females have two X chromosomes (XX). This system is seen in grasshoppers and some other insects, where the male is the heterogametic sex with a single X. Therefore, option 3 (Grasshoppers) is correct. In Drosophila, birds, and monkeys, different systems operate: Drosophila uses an XY system, birds use a ZW system for females, and monkeys (humans) use an XY system as well. The NCERT description of XO is specifically linked to grasshoppers.
🧠 Did You Know?
In XO species, the sex chromosomes are not a pair in males; the presence of only one X determines maleness, while females have two X chromosomes.
Which of the following occurs due to the presence of autosome linked dominant trait?
AI-generated explanation. Check against your textbook.
Explanation:
Myotonic dystrophy is caused by an autosomal dominant trait, so affected individuals usually have one copy of the mutant allele and the condition appears in successive generations. This is why option 2 is correct. In autosomal dominant traits, both males and females are affected equally, and a child can inherit the trait from an affected parent.
🧠 Did You Know?
Autosomal dominant disorders do not skip generations as often as recessive ones; an affected person has a 50% chance of passing the trait to offspring.
💡 NCERT Memory Line:
Dominant traits may appear in every generation and do not skip generations; recessive traits may skip generations.
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Mendel’s law of Independent assortment does not hold good for the genes that are located closely on the same chromosome. Reason (R): Closely located genes assort independently.
In the light of the above statements, choose the correct answer from the options given below:
If a colour blind female marries a man whose
mother was also colour blind, what are the chances
of her progeny having colour blindness?
AI-generated explanation. Check against your textbook.
Explanation:
Color blindness is an X-linked recessive trait. A color-blind female has genotype XbXb. If she marries a color-blind man (mother color-blind makes him XbY), their children will inherit Xb from the father and Xb from the mother for daughters (XbXb) and Xb from the mother with Y from the father for sons (XbY). Thus all offspring will be color blind. Therefore the chances are 100% (option 3).
🧠 Did You Know?
NCERT states that color blindness is an X-linked recessive trait, so it is passed through X chromosomes and often affects males more commonly.
💡 NCERT Memory Line:
Color blindness is an X-linked recessive trait; a color-blind female (XbXb) crossed with a color-blind male (XbY) yields color-blind offspring of all sexes.
