Heredity-Exercise
Biology - Exercise
Q1. 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
Answer
The correct answer is:
(d) TtWw
Explanation:
In this Mendelian experiment, two types of traits are studied—plant height (tall or short) and flower color (violet or white). All the progeny display violet flowers, which means violet color is dominant over white.
Almost half of the progeny are short. This shows that the tall parent must be heterozygous for the height gene—having one dominant (T) and one recessive (t) allele. That way, when crossed with a short plant (tt), both tall (Tt) and short (tt) offspring can occur.
Since every progeny plant has violet flowers, it means that all received at least one dominant allele (W) for violet color. This tells us the tall parent must carry at least one dominant W allele, but could also have a recessive w, making the genotype for flower color Ww.
Therefore, the genetic makeup that allows the tall parent to produce both tall and short offspring (Tt), but ensures all progeny have violet flowers (Ww), is TtWw.
Q2. 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?
Answer
No, we cannot conclusively say whether the light eye colour trait is dominant or recessive based only on the observation that children with light-coloured eyes often have parents with light-coloured eyes.
This pattern simply shows that the trait runs in families, indicating that it is inherited. However, both dominant and recessive traits can consistently appear in children when parents express the same trait. If light eye colour were dominant, parents with light eyes could have both light-eyed and dark-eyed children, depending on their genetic makeup and partner’s alleles. If it were recessive, only parents who carry two copies of the light eye colour gene (homozygous recessive) would show the trait and pass it to their children.
In summary, the information from this study tells us that the trait is genetic, but does not provide enough evidence to decide if light eye colour is dominant or recessive. To answer this, we would need details about the inheritance pattern over several generations, the eye colour of other family members, or cross-breeding data showing which traits are masked and which appear in offspring.
Q3. Outline a project which aims to find the dominant coat colour in dogs.
Answer
Project Outline: Finding the Dominant Coat Colour in Dogs
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Select a Dog Population
Choose a group of dogs with known and visible variations in coat colours (for example, black, brown, white, or golden). Ensure that the parentage of each dog is either recorded or can be reasonably traced.
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Collect Family Data
Document the coat colours of parent dogs, their puppies, and grandparents if possible. Obtain information on as many generations as you can to understand how colours are passed down.
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Organize Controlled Breeding
If possible, arrange controlled breeding experiments between dogs of different coat colours. For example, breed a black-coated dog with a brown-coated dog and observe the coat colours of the offspring. Repeat such crosses with other colour combinations.
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Record and Analyze Offspring Results
Write down the coat colours observed in each litter. Pay special attention to cases where all puppies show the same colour as one parent or where different colours appear.
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Identify Patterns
Look for patterns in the inheritance of coat colour. If a particular colour always appears in the first-generation puppies regardless of the breeding partner (for example, all black or all brown), that colour may be dominant. If a colour only appears when both parents show it, it may be recessive.
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Test with Second-Generation Crosses
To confirm, breed two first-generation puppies with each other (F1 generation) and observe the coat colours in their offspring (F2). If the original colour reappears along with other colours, note the frequency.
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Draw Conclusions
Based on these observations, decide which coat colour appears most consistently when its allele is present. The colour that shows up in both mixed and purebred dogs in every generation is likely the dominant trait.
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Present Findings
Prepare a report summarizing your method, observations, patterns, and conclusion regarding the dominant coat colour in the studied dog population.
This project combines real observations with simple genetic principles to identify dominant coat colour in dogs.
Q4. How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer
Equal genetic contribution from both male and female parents in progeny is ensured through the process of sexual reproduction. During this process, both parents produce specialized cells called gametes—sperm from males and eggs from females. Each gamete contains half the usual number of chromosomes, a condition known as haploid.
When fertilization occurs, a sperm and an egg fuse together to form a new cell called a zygote. This zygote contains a complete set of chromosomes: half inherited from the mother and half from the father. As a result, the offspring receives one set of genes from each parent, ensuring that their genetic material is equally represented.
This mechanism guarantees that every child carries an equal share of genetic information from both parents. It is this equal mix of genes that leads to variations in inherited traits, while still maintaining fairness in parental contribution across generations.
