Answer The Following Question.
1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Ana: AnsIn asexual reproduction, the offspring are produced by copying the parent’s DNA through a process that involves chemical reactions. This copying is not always perfect, leading to mutations or variations in the DNA.
However, asexual reproduction typically produces offspring that are genetically very similar to the parent, and variations are relatively limited.
Trait B, present in 60% of the population, indicates a higher frequency, which suggests it has had more time to spread through the population.
Trait A, present in only 10% of the population, is less frequent, suggesting it has arisen more recently or is still in the process of spreading through the population.
Thus, Trait B is more likely to have arisen earlier than Trait A, as it has had more time to establish itself in the population.
2. How does the creation of variations in a species promote survival?
Ans: Variations provide different traits among individuals in a species.
Some traits may offer advantages, such as better resistance to diseases or improved adaptability to environmental changes.
Individuals with beneficial traits are more likely to survive and reproduce, passing these traits on to future generations.
Over time, these advantageous traits become more common, helping the species adapt to changing conditions.
Overall, variations increase the species’ chances of survival through natural selection.
3. How do Mendel’s experiments show that traits may be dominant or recessive?
Ans: Mendel’s experiments demonstrated the concept of dominant and recessive traits through his monohybrid cross. In a cross between a tall and a dwarf pea plant:
F1 generation: All progeny were tall, indicating that the tall trait (T) is dominant over the dwarf trait (t).
F2 generation: The ratio was 3:1, with 75% tall plants and 25% dwarf plants, showing that the dwarf trait (t) is recessive and only appears when the organism has two recessive alleles (tt).
This pattern of inheritance demonstrates that some traits are dominant and others are recessive
4. How do Mendel’s experiments show that traits are inherited independently?
Ans: Mendel’s dihybrid cross experiment with pea plants showed that traits are inherited independently. When a pea plant with round green seeds (RRyy) was crossed with a pea plant with wrinkled yellow seeds (rrYY), the F1 generation all had round yellow seeds (RrYy).
In the F2 generation, however, he observed four different combinations of traits:
Round yellow
Round green
Wrinkled yellow
Wrinkled green
The appearance of these new trait combinations (round yellow and wrinkled green) showed that the traits for seed shape and color are inherited independently of each other. This is known as the law of independent assortment.
5. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits-blood group A or O- is dominant? Why or why not?
Ans: No, this information is not enough to determine which blood group trait is dominant. Blood group is determined by two alleles, one inherited from each parent. In this case, the father with blood group A could have either the genotype AA or AO, and the mother with blood group O must have the genotype OO. For the daughter to have blood group O, she must inherit the O allele from both parents. Therefore, the father must carry the O allele (genotype AO), meaning the O allele is recessive to the A allele. This shows that the A allele is dominant over the O allele, but the information provided alone isn’t sufficient to confirm the dominance without knowing the father’s genotype.
Or
Blood group is determined by two alleles, one from each parent.
The father with blood group A could be genotype AA or AO.
The mother with blood group O has genotype OO.
For the daughter to have blood group O, she must inherit an O allele from both parents.
Therefore, the father must carry the O allele (genotype AO), showing that O is recessive to A.
This information alone is not enough to confirm dominance because we don’t know the father’s exact genotype.
6. How is the sex of the child determined in human beings?
Ans: The sex of the child is determined by the sex chromosomes inherited from the parents:
A child inherits an X chromosome from the mother (since females have two X chromosomes).
If the child inherits an X chromosome from the father, the child will be a girl (XX).
If the child inherits a Y chromosome from the father, the child will be a boy (XY).
Thus, it is the father’s contribution of either an X or a Y chromosome that determines the sex of the child.
7. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
Ans : (c) TtWW
8. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Ans: No, we cannot conclude whether the light eye colour trait is dominant or recessive based solely on this observation. This is because eye colour is determined by two alleles, one inherited from each parent.
To determine whether a trait is dominant or recessive, we need to know the specific alleles that the parents carry (e.g., whether the parents have heterozygous or homozygous alleles).
Recessive traits appear when both parents contribute the recessive allele. However, without knowing the alleles of both parents, we cannot definitively determine if the light eye colour trait is dominant or recessive. From the given information, we can only assume that both parents may be contributing a recessive allele.
9. Outline a project which aims to find the dominant coat colour in dogs.
Ans : Dogs have a variety of genes that govern coat colour. There are at least eleven identified gene series (A, B, C, D, E, F, G, M, P, S, T) that influence coat colour in dog.
A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown.
Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb)
In this case, all the offsprings will be heterozygous (Bb).
Since black (B) is dominant, all the offsprings will be black. However, they will have both B and b alleles.
If such heterozygous pups are crossed, they will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) offsprings.
10. How is the equal genetic contribution of male and female parents ensured in the progeny?
Ans: The equal genetic contribution of male and female parents is ensured during sexual reproduction. Here’s how it works:
Each trait in the progeny is determined by a pair of alleles (one from each parent).
The male and female parents each contribute one allele for each trait through their respective gametes (sperm and egg).
During fertilization, the sperm and egg combine, bringing together their respective alleles to form a pair.
This ensures that the progeny receives an equal genetic contribution (one allele from each parent) for each trait.