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Questions and Answers
Which chromosomes determine the sex of a child in humans?
Which chromosomes determine the sex of a child in humans?
Environmental factors can influence the sex of offspring in some reptiles.
Environmental factors can influence the sex of offspring in some reptiles.
True
What type of traits did Mendel find to be inherited independently in his experiments?
What type of traits did Mendel find to be inherited independently in his experiments?
Seed shape and color
There are a total of __________ chromosomes in humans.
There are a total of __________ chromosomes in humans.
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Match the following traits with their inheritance type:
Match the following traits with their inheritance type:
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If a fertilizing sperm contains a Y chromosome, what will be the sex of the baby?
If a fertilizing sperm contains a Y chromosome, what will be the sex of the baby?
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All offspring inherit the same combination of traits from their parents.
All offspring inherit the same combination of traits from their parents.
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The sex of the baby is determined during __________.
The sex of the baby is determined during __________.
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What chromosome type do women produce in terms of ovum?
What chromosome type do women produce in terms of ovum?
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Intelligence can be passed on to the next generation.
Intelligence can be passed on to the next generation.
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What is an example of an inherited trait?
What is an example of an inherited trait?
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Chromosomes are made up of ______ found in the nucleus.
Chromosomes are made up of ______ found in the nucleus.
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Match the trait types with their definitions:
Match the trait types with their definitions:
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Which of the following is an example of a dominant trait in pea plants?
Which of the following is an example of a dominant trait in pea plants?
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How is the number of chromosomes in offspring established during sexual reproduction?
How is the number of chromosomes in offspring established during sexual reproduction?
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Acquired traits can be passed on from one generation to the next.
Acquired traits can be passed on from one generation to the next.
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What ratio is typically observed in a monohybrid cross?
What ratio is typically observed in a monohybrid cross?
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A recessive allele can express itself in a heterozygous condition.
A recessive allele can express itself in a heterozygous condition.
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What do we call an organism with two different alleles for a trait?
What do we call an organism with two different alleles for a trait?
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The trait that is expressed in the first generation is known as the ______ trait.
The trait that is expressed in the first generation is known as the ______ trait.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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In Mendel's pea plant experiments, what trait was hidden in the first generation after crossing tall and short plants?
In Mendel's pea plant experiments, what trait was hidden in the first generation after crossing tall and short plants?
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A dihybrid cross produces a phenotypic ratio of 9:3:3:1.
A dihybrid cross produces a phenotypic ratio of 9:3:3:1.
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What was the phenotypic ratio in the second generation of Mendel's experiments with the tall and short plants?
What was the phenotypic ratio in the second generation of Mendel's experiments with the tall and short plants?
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Study Notes
Recessive Allele
- An allele that only expresses its trait when two copies are present (e.g., "a" in aa).
Homozygous
- An organism with two identical alleles for a trait (e.g., AA or aa).
Heterozygous
- An organism with two different alleles for a trait (e.g., Aa).
Chromosomes
- Thread-like structures located in the cell nucleus.
- Carry genetic information (DNA).
Monohybrid Cross
- Focuses on one pair of contrasting traits.
- Results in a 3:1 ratio, known as the monohybrid ratio.
Dihybrid Cross
- Involves two pairs of contrasting traits.
- Yields a 9:3:3:1 ratio, known as the dihybrid ratio.
Dominant Trait
- Expresses itself in the first generation.
Recessive Trait
- Does not express itself in the F1 generation but reappears in the F2 generation.
Dominant Gene
- Expressed in both homozygous and heterozygous conditions.
Recessive Gene
- Expressed only in the homozygous condition.
Mendel’s Experiment
- Traits can be either dominant or recessive.
- First generation offspring from a tall pea plant crossed with a short one were all tall.
- After self-pollination in the first generation, the second generation had both tall and short plants in a 3:1 ratio.
- This demonstrated that the short trait was hidden in the first generation, being recessive.
Mendel’s Experiment
- Pea plants with round yellow seeds were crossed with those with green wrinkled seeds.
- All first generation offspring had round yellow seeds.
- Self-pollinating the first generation resulted in a second generation with new trait combinations.
- This indicated that seed shape and color are independently inherited.
Chromosomes
- Chromosome pairs represent the two sets found in most human cells.
- Each set has 23 individual chromosomes, one from the mother and the other from the father.
- Pairs include sex chromosomes (X and Y in humans) and autosomes.
Sex Determination - Environmental Factors
- In reptiles like turtles and crocodiles, sex is determined by egg incubation temperature.
- Higher temperatures produce females, while lower temperatures produce males.
Sex Determination - Genetic Factors
- The type of male gamete fusing with the female gamete determines sex.
- A fertilizing sperm with an X chromosome produces a female, while one with a Y chromosome produces a male.
Sex Determination in Humans
- Humans have 23 pairs of chromosomes, totaling 46.
- 22 pairs are autosomes, and one pair is sex chromosomes.
- Males have XY sex chromosomes, while females have XX.
- The sex of a child is determined during fertilization.
- An X-carrying sperm fertilizes the egg, resulting in a female (XX).
- A Y-carrying sperm fertilizes the egg, resulting in a male (XY).
Important Questions
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It is a matter of chance whether a couple will have a male or a female child.
- Women produce only one type of ovum (carrying the X chromosome).
- Males produce two types of sperm (carrying either X or Y chromosome) in equal proportions.
- The sex of the child depends on which sperm fertilizes the ovum, making it a matter of chance.
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Why traits like intelligence and knowledge aren’t passed down to the next generation?
- Intelligence and knowledge are not heritable traits.
- They do not cause changes in the DNA of germ cells and, therefore, cannot be passed on.
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Distinguish between inherited traits and acquired traits.
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Inherited Trait:
- Genetically inherited.
- Passed from one generation to the next.
- Example: Eye color or height.
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Acquired Trait:
- Result of an individual's experiences during their lifetime.
- Not passed from one generation to the next.
- Example: Power to lift weights or reading French.
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Inherited Trait:
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What is a dominant trait with respect to height in pea plants? Give two examples.
- Characters/Traits like ‘T’ are dominant (they express themselves).
- ‘t’ are recessive traits (they are suppressed).
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What are chromosomes? Explain how sexually reproducing organisms maintain the number of chromosomes in their offspring.
- Chromosomes are thread-like structures composed of DNA found within the nucleus.
- The original number of chromosomes reduces by half during gamete formation.
- When gametes combine, the original number of chromosomes is restored in the offspring.
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Rekha has a dark complexion and seeks beauty products to lighten her skin. Her friend Lila tells her that skin color is determined by birth and advises her against excessive use of such products.
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a. What might have caused Rekha’s color to be dark?
- Rekha’s dark complexion is likely due to her inherited genes.
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b. Briefly explain why Lila’s advice is valid.
- Skin color is primarily determined by genetics and cannot be permanently altered by external products. Excessive use could have harmful side effects.
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a. What might have caused Rekha’s color to be dark?
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Description
Test your knowledge on the fundamentals of genetics with this quiz focusing on Mendel's Principles. Explore concepts such as dominant and recessive alleles, homozygous and heterozygous traits, and the outcomes of monohybrid and dihybrid crosses. It's a great way to prepare for biology exams!
