Q.Who had proposed the chromosomal theory of the inheritance?
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Morgan's Fruit Fly Experiments: A First Look
Imagine you're trying to understand how traits pass from parents to children. You could study humans, but that takes decades — one generation every 25 years. What if you could watch a hundred generations in a single year? That's exactly what Thomas Hunt Morgan realised when he picked the fruit fly, Drosophila melanogaster, for his experiments around 1910.
Why Fruit Flies?
Morgan needed an organism that was cheap, fast-breeding, and easy to handle. Fruit flies fit perfectly. They breed every 10–14 days, produce hundreds of offspring, and have just four pairs of chromosomes — simple enough to track. More importantly, they show clear, visible traits: eye colour (red or white), wing shape (normal or vestigial), body colour (grey or black). These traits became Morgan's window into how genes work.
The Breakthrough: The White-Eyed Male
Morgan started by breeding normal red-eyed flies. Then, by chance, he found a single male with white eyes — a mutant. He crossed this white-eyed male with a red-eyed female. All the offspring (the F1 generation) had red eyes. That told him red eye colour was dominant over white.
Then came the crucial step. He bred those F1 red-eyed flies with each other. In the F2 generation, he got a surprise: all the females had red eyes, but half the males had white eyes. The white-eye trait appeared only in males.
This was the first clear experimental evidence that a specific gene is located on a specific chromosome — in this case, the X chromosome. The white-eye gene is on the X chromosome, and males have only one X, so they express whatever is on it. Females have two X's, so a recessive white-eye gene can be hidden by a dominant red-eye gene on the other X.
What Morgan Proved
Before Morgan, scientists knew chromosomes existed, but no one had proven that a particular gene lived on a particular chromosome. Morgan's fruit fly experiments did exactly that. He showed that:
- Genes are physical units located on chromosomes
- The inheritance of a trait (white eyes) follows the inheritance pattern of a specific chromosome (the X)
- Sex-linked traits — those carried on the X chromosome — behave differently in males and females
This was the birth of the chromosomal theory of inheritance. It connected Mendel's abstract "factors" (genes) to real, visible structures inside cells.
Why It Matters for a Commerce/Humanities Student
You might think this is pure biology, but the principle here is about evidence linking a cause to an effect. Morgan didn't just guess that genes were on chromosomes — he designed an experiment where the pattern of inheritance forced that conclusion. This is the same logic used in economics (linking policy changes to market outcomes) or law (linking evidence to a verdict). The method matters as much as the result. …
The chromosomal theory of inheritance was proposed by Walter Sutton and Theodor Boveri independently in 1902. They observed that the behaviour of chromosomes during meiosis closely paralleled the behaviour of Mendelian factors (genes) during inheritance. Sutton worked on grasshoppers while Boveri studied sea urchins, and both noticed that chromosomes paired during meiosis and segregated into gametes, just as Mendel's factors did.
Their key insight was recognizing that chromosomes remain distinct structures throughout the cell cycle and that they occur in pairs in diploid cells — one from each parent. This physical basis explained why traits are inherited in pairs and why they segregate during gamete formation. …
Walter Sutton and Theodor Boveri independently proposed the chromosomal theory of inheritance in 1902, suggesting that chromosomes are the physical carriers of Mendel's hereditary factors.
The chromosomal theory of inheritance emerged at a fascinating moment in biology — just after the rediscovery of Mendel's work in 1900, when scientists were racing to understand where these mysterious "factors" actually resided in the cell. Two researchers working independently on opposite sides of the Atlantic arrived at the same revolutionary insight.
Walter Sutton, an American graduate student studying grasshopper chromosomes at Columbia University, and Theodor Boveri, a German biologist working with sea urchin eggs, both noticed striking parallels between the behaviour of chromosomes during cell division and the inheritance patterns Mendel had described. In 1902, they each published observations that led to what we now call the Sutton-Boveri chromosome theory.
What made their proposal so compelling was the correspondence they observed:
- Chromosomes, like Mendel's factors, occur in pairs in diploid cells
- During gamete formation (meiosis), chromosomes separate so that each gamete receives only one from each pair — exactly as Mendel's factors segregated
- Chromosomes from different pairs assort independently during meiosis, mirroring Mendel's law of independent assortment
- Fertilization restores the paired condition for both chromosomes and hereditary factors …
Sutton and Boveri's argument can be remembered as a simple matching exercise rather than a list of facts: for every behaviour Mendel had already described for his 'factors' (occurring in pairs, segregating into different gametes, assorting independently, pairing up again at fertilisation), find the matching behaviour of chromosomes und …
Showing the 12 most recent of 14 on this concept.
- AP EAPCET 2026Set ap-2026-05-19-FN1 markMCQQ.Identify the wrong match (A) Law of dominance – Mendel (B) Chromosomal theory of inheritance – Sutton and Boveri (C) Experimental proof for chromosomal theory of inheritance – Morgan (D) Genetic maps – Punnett
›Reveal solutionSolution
Genetic/linkage maps are Sturtevant's contribution, not Punnett's (who devised the Punnett square) — making (D) the wrong match.
Concept and Intuition
The history of classical genetics has several well-attributed milestones: Mendel formulated the laws of inheritance including dominance; Sutton and Boveri independently proposed that chromosomes are the physical carriers of Mendelian factors (the chromosomal theory of inheritance); Thomas Hunt Morgan, working with Drosophila, provided the first strong experimental proof of this theory by correlating a specific gene (white eye colour) with a specific chromosome (X). Building on Morgan's linkage studies, his student Alfred Sturtevant developed the first genetic map, using recombination frequencies to order genes on a chromosome. Reginald Punnett, separately, is remembered for the Punnett square, a diagrammatic tool for predicting cross outcomes — not for genetic maps.
Step-by-Step Solution
- Verify (A): law of dominance – Mendel — correct. …
- AP EAPCET 2026Set ap-2026-05-20-FN1 markMCQQ.Choose the correct statements among the following A) Some genes are very tightly linked on the same chromosome, which shows higher recombination. B) Sutton proposed the chromosome theory of inheritance. C) Behaviour of the chromosome was parallel to the behaviour of genes. D) Mendels selection of one of the contrastic traits is seed shape as inflated and wrinkled. (A) A, B (B) C, D (C) A, C (D) B, C
›Reveal solutionSolution
Correct facts: Sutton (chromosomal theory) and the chromosome-gene behaviour parallel are true; linkage lowers recombination (not raises it) and "inflated/wrinkled" mixes up Mendel's pod-shape and seed-shape traits. Answer: B, C.
Concept and Intuition
Walter Sutton (along with Theodor Boveri) founded the chromosomal theory of inheritance by observing that the behaviour of chromosomes during meiosis — their pairing and separation — precisely parallels the behaviour Mendel had inferred for "factors" (genes): segregation and independent assortment. Separately, genetic linkage is the tendency of genes on the same chromosome to be inherited together; the tighter the linkage (the closer two genes are), the lower, not higher, their recombination frequency, since crossing over is less likely to occur between them.
Step-by-Step Solution
- A: tightly linked genes show lower recombination frequency, not higher — false.
- B: Sutton (with Boveri) proposed the chromosomal theory of inheritance — true. …
- AP EAPCET 2025Set ap-2025-05-19-FN1 markMCQQ.Match the following List-I A) Hugo de vries B) Sturtevant C) Morgan D) Sutton and Boveri List-II I) Chromosomal theory II) Linkage III) Mutations IV) Gene Mapping (A) A-III, B-IV, C-II, D-I (B) A-III, B-I, C-IV, D-II (C) A-IV, B-III, C-I, D-II (D) A-II, B-III, C-I, D-IV
›Reveal solutionSolution
De Vries to mutation theory; Sturtevant to gene mapping; Morgan to linkage; Sutton and Boveri to chromosomal theory of inheritance. Mapping: A-III, B-IV, C-II, D-I — option (A).
Concept and Intuition
Several scientists made foundational, distinct contributions to genetics history that are frequently tested together:
- Hugo de Vries studied inheritance in the evening primrose (Oenothera lamarckiana) and proposed the mutation theory, suggesting evolution proceeds via sudden, discrete heritable changes (mutations) rather than only gradual variation.
- A.H. Sturtevant, a student in T.H. Morgan's lab, used recombination-frequency data between linked genes on the same chromosome to construct the very first genetic (linkage) map of a chromosome — establishing "gene mapping" as a technique.
- T.H. Morgan used Drosophila melanogaster to experimentally demonstrate linkage (genes on the same chromosome tending to be inherited together) and crossing over, providing strong experimental support for the chromosomal basis of inheritance.
- Walter Sutton and Theodor Boveri, working independently, proposed the Chromosomal Theory of Inheritance, recognizing the parallel behaviour of chromosomes and Mendelian factors during meiosis and fertilization.
Step-by-Step Solution
- Hugo de Vries to Mutation theory (III). …
- AP EAPCET 2025Set ap-2025-05-20-AN1 markMCQQ.Assertion (A): Genetic maps are exensively used as a starting point in the Human genome sequencing project. Reason (R): Frequency of recombination between gene pairs on the same chromosome as the measure of distance between genes and mapped their position is called gene mapping. Identify the correct option from the following (A) (A) and (R) are true. (R) is correct explanation for (A) (B) (A) and (R) are true. But (R) is not correct explanation for (A) (C) (A) is true, but (R) is false (D) (A) is false, but (R) is true
›Reveal solutionSolution
Genetic (linkage) maps, built from recombination frequencies, were exactly the tool used to lay out gene order before the Human Genome Project's physical mapping.
Concept and Intuition
The Human Genome Project used genetic maps as an early scaffold: recombination frequency between gene pairs on the same chromosome measures their relative distance, letting researchers order genes along a chromosome before doing detailed physical/sequence mapping. So the reason directly explains why genetic maps were the logical starting point.
Step-by-Step Solution
- Assertion: genetic maps were used as the starting point of the HGP — historically accurate.
- Reason: recombination-frequency-based gene mapping is exactly what a 'genetic map' is. …
- AP EAPCET 2025Set ap-2025-05-20-FN1 markMCQQ.Study the following statements and pick up the incorrect statements. I. Haemophilia is an X-linked disorder due to dominant genes. II. Inheritance of colour blindness follows the cris-cross pattern. III. Haemophilia A and Haemophilia C are X-linked disorders. IV. Y-linked genes are called holandric genes. (A) I, II (B) III, IV (C) II, IV (D) I, III
›Reveal solutionSolution
Statement I is wrong (haemophilia is recessive, not dominant) and statement III is wrong (Haemophilia C is autosomal, not X-linked); II and IV are correct. Answer: (D).
Concept and Intuition
Sex-linked inheritance in humans concerns genes carried specifically on the X or Y chromosome, and the mode of inheritance (dominant/recessive, X-linked/Y-linked/autosomal) determines the pattern seen across generations. Several human bleeding disorders are historically grouped as "haemophilias," but they are not all genetically identical — some are X-linked (A, B) while at least one (C) is autosomal, a fact that is frequently tested precisely because it breaks the "all haemophilias are X-linked" assumption.
Step-by-Step Solution
- Statement I: "Haemophilia is an X-linked disorder due to dominant genes." Haemophilia (A and B) is X-linked, but it is caused by a recessive allele, not a dominant one — an affected male has only one X, so one recessive allele is enough to show the disease, while a female carrier (heterozygous) is typically unaffected. So Statement I is incorrect because of the word "dominant."
- Statement II: "Inheritance of colour blindness follows the criss-cross pattern." Colour blindness is a classic X-linked recessive trait: an affected father passes his X (with the recessive allele) to all his daughters, who become carriers (unaffected), and those daughters can pass it to their sons, who then show the trait — the trait effectively "crisses" from father to grandson through a carrier daughter. This is correctly described, so Statement II is correct. …
- AP EAPCET 2024Set ap-2024-05-17-AN1 markMCQQ.In Morgan's linkage experiments on Drosophila recombinants percentage for white eye and yellow body is (A) 37.2 % (B) 1.3 % (C) 62.8 % (D) 98.7 %
›Reveal solutionSolution
White eye and yellow body are tightly linked X-linked genes in Drosophila; Morgan's experiments recorded a recombination frequency of about 1.3%, one of the classic low-recombination examples of linkage. Correct option: (B).
Concept and Intuition
Recombination frequency between two genes reflects how far apart they are on the same chromosome — genes lying very close together are rarely separated by crossing over, giving a low recombination (%) value, while genes far apart (or on different chromosomes) recombine close to 50% of the time (independent assortment). Morgan's Drosophila linkage studies used several X-linked gene pairs as examples of varying linkage strength; the white–yellow gene pair, being extremely close together, is the textbook example of very strong linkage with a very low, single-digit recombination percentage.
Step-by-Step Solution
- Recall that white and yellow are both X-linked Drosophila genes used in Morgan's classic linkage studies. …
- AP EAPCET 2023Set ap-2023-05-23-FN1 markMCQQ.Experimental verification of chromosomal theory of inheritance was done by (A) Sutton – Boveri (B) Gregor Mendel (C) Thomas Hunt Morgan (D) Correns
›Reveal solutionSolution
Sutton–Boveri proposed the chromosomal theory; Thomas Hunt Morgan experimentally verified it using Drosophila. Answer: (C).
Concept and Intuition
A scientific theory proposed on the basis of parallel observations still needs experimental proof. Sutton and Boveri noticed that chromosomes behave exactly as Mendel's factors do (they occur in pairs, segregate during meiosis, and one member of each pair comes from each parent), and proposed that chromosomes carry the hereditary factors. This was a hypothesis until it was tested experimentally.
Step-by-Step Solution
- Sutton and Boveri (early 1900s) independently noted the parallel behaviour of chromosomes and Mendelian factors and proposed the chromosomal theory of inheritance.
- Thomas Hunt Morgan chose Drosophila melanogaster as a model organism — short life cycle, many chromosomes, easily visible mutant phenotypes (like white eye colour) — to test the theory.
- Morgan's cross of a white-eyed male with red-eyed females showed that the eye-colour gene was inherited along with the X chromosome, giving direct experimental proof that genes are located on chromosomes. …
- AP EAPCET 2022Set ap-2022-07-11-AN1 markMCQQ.Repulsion and coupling are two faces of _________________ (A) Mutation (B) Linkage (C) Crossing over (D) Chiasmata
›Reveal solutionSolution
Coupling and repulsion are the two arrangements in which linked genes can occur on homologous chromosomes — this is the phenomenon of linkage.
Concept and Intuition
When two genes lie close together on the same chromosome, they tend not to assort independently (violating Mendel's law of independent assortment) — this is linkage. T.H. Morgan, working with Drosophila, described two configurations in which linked genes can be arranged on a pair of homologous chromosomes: coupling, where the dominant alleles of both genes are on one chromosome and the recessive alleles are on the homologous chromosome; and repulsion, where each chromosome carries one dominant and one recessive allele (a mixed arrangement).
Step-by-Step Solution
- Recall that linked genes (genes on the same chromosome, especially close together) tend to be inherited together rather than independently.
- Morgan classified how linked alleles can be arranged: coupling phase (AB/ab) — dominant alleles together, recessive alleles together.
- Repulsion phase (Ab/aB) — one dominant and one recessive allele on each homolog. …
- AP EAPCET 2022Set ap-2022-07-11-FN1 markMCQQ.The term Linkage was proposed by ________ (A) Punnet (B) Morgan (C) Mendel (D) Boveri
›Reveal solutionSolution
This tests who coined the term "linkage"; the answer is Morgan.
Concept and Intuition
Mendel's law of independent assortment holds only for genes on different chromosomes (or far apart on the same one). When Morgan crossed Drosophila for two genes located on the same chromosome, the F2 ratio deviated sharply from the expected 9:3:3:1, because the genes tended to be inherited together. Morgan interpreted this physical association and named the phenomenon "linkage."
Step-by-Step Solution
- Bateson and Punnett (1906) first observed unusual, non-Mendelian ratios in sweet pea (they called it "coupling"), but did not explain the mechanism.
- Morgan, working with Drosophila, connected this deviation to the physical location of genes on the same chromosome.
- He and his group coined the specific term "linkage" for genes travelling together due to their proximity on a chromosome. …
- AP EAPCET 2022Set ap-2022-07-11-FN1 markMCQQ.What is the ratio of vestigial winged, gray body flies in F2 generation of T.H Morgan's experiment? (A) 9/6 (B) 3/16 (C) 1/16 (D) 9/9
›Reveal solutionSolution
This tests the F2 dihybrid ratio for a specific phenotype combination in Morgan's Drosophila cross; the answer is 3/16.
Concept and Intuition
T.H. Morgan's Drosophila crosses examined two independently scoreable traits together: body colour (gray dominant, G; black recessive, g) and wing type (normal/long wing dominant, V; vestigial wing recessive, v). Crossing heterozygous F1 flies (GgVv × GgVv) to get F2 gives the classic dihybrid 9:3:3:1 ratio across the four possible phenotype combinations, exactly as Mendel's law of independent assortment predicts for two genes.
Step-by-Step Solution
- F1 heterozygote GgVv self-crossed (or intercrossed) produces F2 in the ratio 9 (Gray, Normal wing) : 3 (Gray, Vestigial wing) : 3 (Black, Normal wing) : 1 (Black, Vestigial wing), out of 16 total.
- The phenotype asked for — "vestigial winged, gray body" — corresponds to the class where the dominant body-colour trait (gray) appears together with the recessive wing trait (vestigial). …
- AP EAPCET 2021Set ap-2021-09-03-FN1 markMCQQ.Assertion (A): The proportion of parental gene combinations was much lighter than non-parental type. Reason (R): Gene combination is due to linkage of the two genes (A) A is correct but R is wrong (B) A is wrong but R is correct (C) Both A and R are correct and R is not correct explanation for A (D) Both A and R are correct and R is the correct explanation for A
›Reveal solutionSolution
Linked genes are inherited together more often than not, so parental-type combinations vastly outnumber non-parental (recombinant) combinations — this is precisely what "linkage" means, so the Reason correctly explains the Assertion.
Concept and Intuition
When two genes lie close together on the same chromosome, they are said to be linked: during meiosis, they tend to travel together into the same gamete because crossing over between them is a comparatively rare event. Morgan's classic dihybrid crosses in Drosophila showed that instead of the expected 1:1:1:1 ratio of independent assortment, most offspring showed the parental combinations of traits, with only a smaller proportion showing new (recombinant/non-parental) combinations, produced by crossing over between the linked loci.
Step-by-Step Solution
- Assertion: parental gene combinations occur in much higher proportion than non-parental (recombinant) combinations — this matches the observed data from linkage studies.
- Reason: this pattern (more parental types) is due to the linkage of the two genes — i.e., because the genes are physically close on the same chromosome, they resist separation by crossing over and are usually transmitted together.
- Since linkage is precisely the physical basis for why parental combinations dominate over recombinants, the Reason directly and correctly explains the Assertion. …
- AP EAPCET 2021Set ap-2021-09-03-FN1 markMCQQ.Match the following? List I: a) Duchenne muscular dystrophy DMD, b) Hypertrichosis, c) Incontinentia Pigmenti, d) Secretion of milk. List II: i) X - linked dominant, ii) Sex limited, iii) X - linked recessive, iv) Holandric. List III: p) Mosaic appearance of skin, q) Expression is limited to only one sex, r) Progressive weakening of muscles, s) Excessive growth of hair on the pinna. (A) (a - iii - r), (b - iv - s), (c - i - p), (d - ii - q) (B) (a - i - r), (b - ii - s), (c - iii - p), (d - iv - q) (C) (a - i - r), (b - iv - s), (c - iii - p), (d - ii - q) (D) (a - i - p), (b - ii - q), (c - iii - r), (d - iv - s)
›Reveal solutionSolution
This is a three-way match of four inherited human conditions/traits to their mode of inheritance and their defining phenotypic feature.
Concept and Intuition
Human genetic traits linked to sex chromosomes fall into distinct classes: X-linked recessive (e.g. DMD, haemophilia, colour blindness — mostly affect males, since one recessive X allele is enough in a male's single X), X-linked dominant (rare, e.g. Incontinentia Pigmenti — often lethal in males who have only one X, so it manifests as a mosaic pattern in surviving heterozygous females due to random X-inactivation), Y-linked/holandric (transmitted only father → son, e.g. hypertrichosis pinnae), and sex-limited traits (the gene is present in both sexes but hormonally/anatomically expressed in only one, e.g. lactation).
Step-by-Step Solution
- (a) Duchenne Muscular Dystrophy (DMD) — a well-known X-linked recessive disorder (iii) causing progressive weakening of muscles (r), since dystrophin (needed for muscle fibre integrity) is coded on the X chromosome.
- (b) Hypertrichosis (excessive hair on the pinna of the ear) is a classic holandric/Y-linked trait (iv), transmitted only from father to all sons, producing (s) excessive growth of hair on the pinna.
- (c) Incontinentia Pigmenti is X-linked dominant (i) and typically lethal in hemizygous males; surviving heterozygous females show a mosaic appearance of the skin (p) due to random X-chromosome inactivation (Lyonization), where cells expressing the mutant vs normal X form patches. …
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