Heredity – Notes, MCQs, Quiz & Worksheet

Mendel crossed plants with two different traits and found new combinations in the next generation.
Traits like seed shape and seed colour got mixed in different ways.
This showed that each trait is inherited independently of the other.

Mendel crossed a tall plant with a short plant. All the plants in the first generation were tall. This means the tall trait hides the short trait.
When these tall plants were crossed again, the short plants came back in the next generation.
This showed that:
Tall trait = dominant (shows itself)
Short trait = recessive (gets hidden but is not lost)
So Mendel proved that some traits hide others, which is why they are called dominant and recessive.

Variations help a species survive because they make some individuals better suited to changes in the environment.
If the climate changes, food becomes less, or a new disease appears, not all individuals will be affected in the same way.
Those with useful variations will survive and reproduce, while others may die.

So, variations increase the chances that at least some members of the species will survive, even when conditions change.

No, we cannot say whether light eye colour is dominant or recessive.
Children often resemble their parents, but this does not tell us which trait is stronger.
To know dominance or recessiveness, we need controlled crosses or more detailed genetic information, not just observation.

In humans, the mother always gives an X chromosome. The father can give either an X or a Y chromosome.
If the father gives X, the child is girl (XX).
If the father gives Y, the child is boy (XY).

So, the sex of the child is determined by the father.

During reproduction, both parents produce gametes (sperm and egg) that contain half the number of chromosomes.
When the sperm and egg fuse during fertilisation, the child gets half the genes from the father and half from the mother.
This ensures equal genetic contribution from both parents in the progeny.

Short parent = ttww (short + white)
All progeny have violet flowers, so the tall parent must give a W to every child → therefore the tall parent must be WW.
Almost half of the progeny are short, which means the tall parent must be Tt (so it can give t to some children).

So the tall parent’s genotype = TtWW
Correct option: (c) TtWW

Trait B must have appeared earlier.
This is because in asexually reproducing organisms, traits spread very slowly. Since Trait B is found in 60% of the population and Trait A only in 10%, the trait that is present in more individuals must have been there for a longer time.

So, Trait B arose earlier than Trait A.

No, this information is not enough to tell which blood group is dominant.
The father could be AA or AO, and the mother is OO, so the child can get O only if the father has an O gene (AO).

So we cannot decide dominance just from this one family — we need more crosses to be sure.

A mutation is a spontaneous, heritable change in the DNA sequence. It is a primary source of new alleles and genetic variation.

Since R (round) is dominant over r (wrinkled), and Y (yellow) is dominant over y (green), the genotype RrYy will express the Round, yellow phenotype.

The F1 generation will all be tall (Tt). When F1 is self-crossed (Tt x Tt), the F2 genotypes are TT, Tt, Tt, tt. The dwarf phenotype (tt) constitutes 25% of the F2 generation.

Heterogametic refers to an individual producing two different types of gametes with respect to sex chromosomes. Human males (XY) produce X-sperm and Y-sperm, thus they are heterogametic.

A homozygous black, short-haired guinea pig has genotype BBSS. A white, long-haired guinea pig has genotype bbss. The cross BBSS x bbss will yield all F1 offspring with genotype BbSs.

By definition, a dominant allele expresses its trait even when only one copy is present, masking the effect of a recessive allele in a heterozygous individual.

Acquired traits are developed during an individual's lifetime due to environmental factors or activities and are not passed on to offspring (e.g., learning to play a musical instrument, developing strong muscles from exercise). Inherited traits are genetically determined and passed down from parents to offspring through genes (e.g., eye color, blood group, height).

This is a case of incomplete dominance. The F1 (pink) has genotype RW. Self-pollinating F1 (RW x RW) results in F2 genotypes RR (red), RW (pink), RW (pink), WW (white). The phenotypic ratio is 1 Red : 2 Pink : 1 White.

Sex-linked diseases like hemophilia are often carried on the X chromosome. Males have only one X chromosome, so if they inherit the recessive allele on that X, they will express the disease. Females have two X chromosomes, so they must inherit two copies of the recessive allele (one on each X) to express the disease, making it less common for them to be affected.

The F1 generation will be Tt. Backcrossing F1 (Tt) with the dwarf parent (tt) results in a cross Tt x tt. The progeny will have genotypes Tt and tt in a 1:1 ratio.

Crossing over is the exchange of genetic material between homologous chromosomes during meiosis, leading to new combinations of alleles on the chromatids and increasing genetic variation.

Since unaffected parents have an affected son, it suggests a recessive inheritance. The fact that only the son is affected, and the daughter is not, points towards X-linked recessive inheritance, where the mother is a carrier.

DNA carries the genetic instructions for the development, functioning, growth, and reproduction of all known organisms. It contains genes, which are specific segments that code for particular proteins. The sequence of nucleotides in DNA dictates the sequence of amino acids in a protein, through the processes of transcription and translation, thus controlling traits and cellular functions.

The Law of Segregation states that during the formation of gametes, the two alleles for a heritable character separate (segregate) from each other so that each gamete carries only one allele.

The cross is TtPp x TtPp. The probability of dwarf (tt) is 1/4. The probability of white flowers (pp) is 1/4. Since these traits assort independently, the probability of dwarf with white flowers is (1/4) * (1/4) = 1/16.

Yes, environmental factors can significantly modify the expression of inherited traits. For example, a person may inherit genes for tallness, but if they suffer from poor nutrition during childhood, their actual height may be less than their genetic potential. Similarly, skin color darkens with exposure to sunlight, even though the base skin pigmentation is inherited.

Human females produce only X-bearing egg cells. Human males produce both X-bearing and Y-bearing sperm cells. Therefore, the sperm cell from the father determines whether the offspring will be XX (female) or XY (male).

A gene is a unit of heredity, a segment of DNA that codes for a specific protein or characteristic. An allele is an alternative form or variant of a gene. For example, the gene for flower color in peas might have alleles for purple (P) and white (p) flowers.

Variation provides a diverse range of traits within a population. In a changing environment, individuals with certain advantageous variations are more likely to survive, reproduce, and pass on those beneficial traits. This allows the species to adapt and prevents its extinction by ensuring some individuals are better suited to new conditions.

To determine if a dominant phenotype is homozygous (PP) or heterozygous (Pp), a test cross is performed. This involves crossing the unknown dominant individual with a homozygous recessive individual (pp). If any white-flowered offspring appear, the unknown parent must be heterozygous (Pp).

Genetic information is encoded in the DNA located on chromosomes within the nucleus of cells. During reproduction, parents pass on half of their genetic material (chromosomes) to their offspring through gametes (sperm and egg). Fertilization combines these haploid gametes, restoring the diploid number of chromosomes and creating a unique combination of genes from both parents in the new individual.