Heredity and Evolution

(a) Mendel found that only tall pea plants were produced in the first generation when he crossed pure-bred tall pea plants with pure-bred dwarf pea plants (F1). The tall plants and dwarf plants were produced in the second generation, or (F2), in a ratio of 3:1. He then self-crossed the tall pea plants of the …

How do Mendels experiments show that
(a) traits may be dominant or recessive?
(b) inheritance of two traits is independent of each other? (Delhi 2017) Read More »

Human beings have 23 pairs(46) of chromosomes (22 pairs of autosomes +1 pair(2) of sex chromosomes). A male has one X chromosome and one Y chromosome whereas a female has XX chromosomes. The sex of a child depends on the two conditions which take place during fertilisation. The two conditions are given below: If a …

How is the sex of the child fixed during the fertilisation, step in human beings? Explain. (Foreign 2011) Read More »

(A) The F1 generation of plants will all be tall plants.(b) The F2 generation has a 3:1 ratio of tall to dwarf plants.(c) Dwarf plants first arose in the F2 general ion and were not present in the F1 generation. This is because only the dominant trait (tall) expresses itself in the F1 generation, while …

If we cross pure-breed tall (dominant) pea plants with pure-breed dwarf (recessive) pea plants we will get pea plants of the F1 generation.
If we now self-cross the pea plant of the F1 generation, then we obtain pea plants of the F2 generation.
(a) What do the plants of the F1 generation look like?
(b) State the ratio of tall plants to dwarf plants in the F2 generation.
(c) State the type of plants not found in the F1 generation but appeared in the F2 generation, mentioning the reason for the same. (AI 2012) Read More »

(A) The F1 generation’s flower will be blue in colour.(b) If the F1 generation’s flowers self-pollinate, then 25% of the F2 generation’s flowers must be white.(c) A 1:2 ratio between the genotypes BB and Bb is expected in the progeny of the F2 generation.The cross shown above could represent the results mentioned above:

(a) The possible cross of Mendel’s experiment is: As a result, tallness (T) is dominant and dwarfness (t) is recessive. Only dominant traits show in the F1 generation; recessive traits are suppressed. Both dominant and recessive features, or F2 generation, express themselves. Mendel’s experiment demonstrated that the traits (tall and dwarf) are inherited independently in …

(a) Mendel crossed tall pea plants with dwarf pea plants in his experiment. Write his observations giving reasons for the F1 and F2 generations.
(b) List any two contrasting characters other than the height that Mendel used in his experiments in pea plants. (Delhi 2014) Read More »

(a) The cross in question was produced with two pea plants only used for breeding, one with round, green seeds and the other with wrinkled, yellow seeds.Green seed colour and wrinkled seed shape are dominant to yellow seed colour and spherical seed shape. Recessive features are stifled in the F1 generation, while dominant traits are …

A cross was made between pure breeding pea plants, one with round and green seeds and the other with wrinkled and yellow seeds.
(a) Write the phenotype of F1 progeny. Give reason for your answer.
(b) Write the different types of F2 progeny obtained along with their ratio when F1 progeny was selfed. (Delhi 2014, Delhi 2013C) Read More »

When male and female gametes fuse during fertilisation, sex is formed. Gametes with an X or Y chromosome are produced by males, whereas gametes with an X chromosome are produced by females. When male and female gametes combine to form a zygote during fertilisation, the sex of the baby is determined. The offspring will be …

“It is a matter of chance whether a couple will have a male or a female child.” Justify this statement by drawing a flow chart. (Foreign 2015) Read More »

A pure tall pea plant and a pure dwarf pea plant were crossed by Mendel. Every plant produced from the F1 generation was tall. Mendel obtained both tall and dwarf plants in the ratio of 3:1 in the F2 generation when he selfed plants from the F1 generation.As an example, consider the following: This explains …

Explain Mendel’s experiment with peas on inheritance of characters considering only one visible contrasting character. (Foreign 2016, 2014) Read More »

Differences between dominant traits and recessive trait are given below: Dominant trait Recessive trait (i) It is the trait controlled by the dominant allele. It is a recessive allele-controlled characteristic. (ii)It is the feature that the F1 generation expresses. It is the feature that does not emerge in the F1 generation but does in the …

List two differences in tabular form between dominant trait and recessive traits. What percentage/proportion of the plants in the F2 generation/progeny were round, in Mendel’s cross between round and wrinkled pea plants? (Foreign 2016) Read More »

The example provided can help to clarify how a trait might be inherited but not always expressed. The F1 generation of pea plants was all tall because a tall pea plant and a dwarf pea plant were crossed. Selfed F1 plants generated plants that were both tall and dwarf in the F2 generation. This demonstrates that …

With the help of an example justify the following statement: “A trait may be inherited, but may not be expressed.” (AI 2016) Read More »