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What is Mendel's Law of Segregation?
Grade Level:
Class 12
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Definition
What is it?
Mendel's Law of Segregation states that during the formation of reproductive cells (gametes), the two alleles for each gene separate from each other. This means each gamete receives only one allele for a trait, ensuring genetic diversity in offspring.
Simple Example
Quick Example
Imagine you have a box of laddoos, some are yellow (representing one allele) and some are orange (representing another allele) for sweetness. When you pick laddoos for two different plates, each plate gets only one type of laddoo, not both mixed together. Similarly, for a specific trait, each sperm or egg cell gets only one allele.
Worked Example
Step-by-Step
Let's consider a pea plant's flower colour, where 'P' is the allele for purple flowers and 'p' is for white flowers.
Step 1: A parent pea plant has two alleles for flower colour, say 'Pp' (meaning it has one allele for purple and one for white, but appears purple).
---Step 2: When this parent plant produces gametes (like pollen or egg cells), these two alleles 'P' and 'p' separate from each other.
---Step 3: Each gamete will receive only one allele. So, half of the gametes will carry the 'P' allele, and the other half will carry the 'p' allele.
---Step 4: No gamete will receive both 'P' and 'p' alleles, nor will any gamete receive no allele for flower colour.
Answer: The gametes produced by the 'Pp' plant will be 50% 'P' and 50% 'p', each carrying only one allele.
Why It Matters
Understanding segregation is key to predicting how traits are passed down, which is crucial in fields like Biotechnology for developing new crop varieties or in Medicine for understanding genetic diseases. Genetic counsellors use this knowledge to help families understand inherited conditions, impacting health and well-being.
Common Mistakes
MISTAKE: Students often think that both alleles for a trait stay together in a gamete. | CORRECTION: Remember, the Law of Segregation clearly states that the two alleles *separate* so each gamete gets only one.
MISTAKE: Confusing segregation with independent assortment. | CORRECTION: Segregation is about alleles for *one* gene separating. Independent assortment is about *different* genes separating independently.
MISTAKE: Assuming segregation only happens in dominant/recessive traits. | CORRECTION: Segregation applies to all genes, regardless of whether their alleles show dominance, recessiveness, or co-dominance.
Practice Questions
Try It Yourself
QUESTION: A plant has alleles 'Tt' for height. What alleles will its gametes carry? | ANSWER: Half of its gametes will carry 'T' and half will carry 't'.
QUESTION: If a human has two different alleles for eye colour (say, one for brown and one for blue), how many of these alleles will be present in each of their sperm or egg cells? | ANSWER: Each sperm or egg cell will carry only one allele for eye colour.
QUESTION: A farmer wants to breed cows that produce more milk. If the gene for high milk production has two alleles, 'M' (high) and 'm' (low), and a cow is 'Mm', what proportion of its egg cells will carry the 'M' allele? | ANSWER: 50% of its egg cells will carry the 'M' allele.
MCQ
Quick Quiz
During gamete formation, what happens to the two alleles for a single trait?
They stay together in the gamete.
They separate, so each gamete receives only one allele.
They combine to form a new allele.
Only dominant alleles are passed on to gametes.
The Correct Answer Is:
B
Mendel's Law of Segregation states that the two alleles for each gene separate during gamete formation, ensuring each gamete receives only one allele. Options A, C, and D contradict this fundamental principle.
Real World Connection
In the Real World
This law helps animal breeders in India predict the traits of offspring. For example, a dairy farmer might want to breed cows that give more milk or are resistant to certain diseases. By knowing how alleles for these traits segregate, they can select breeding pairs more effectively, leading to healthier and more productive livestock.
Key Vocabulary
Key Terms
ALLELE: A different form of a gene, like 'P' or 'p' for flower colour | GAMETE: A reproductive cell (sperm or egg) | GENE: A unit of heredity that determines a trait | TRAIT: A specific characteristic, like flower colour or plant height
What's Next
What to Learn Next
Next, you should explore Mendel's Law of Independent Assortment. It builds on segregation by explaining how alleles for *different* traits separate independently, adding another layer to understanding how genetic variation occurs.
