An engaging, illustrated worksheet from the Amoeba Sisters video recap series that explains the process of meiosis, highlighting key stages like interphase and chromosome pairing with fun, cartoon-style visuals.
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Show Answer Key & Explanations
Step-by-step solution for: Pin on Science
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Show Answer Key & Explanations
Step-by-step solution for: Pin on Science
Let's go through each question in the "Amoeba Sisters Video Recap of Meiosis: The Great Divide" worksheet and solve them step by step, explaining the reasoning behind each answer.
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Answer:
Each sperm and egg cell has 23 chromosomes.
Explanation:
Humans are diploid organisms, meaning their somatic (body) cells have two sets of chromosomes — one from each parent — totaling 46 chromosomes (23 pairs). During meiosis, gametes (sperm and egg) are formed with half the number of chromosomes, so they are haploid (n = 23). When a sperm (23 chromosomes) and an egg (23 chromosomes) fuse during fertilization, they form a zygote with 46 chromosomes (23 + 23), restoring the diploid number.
✔ So, write 23 next to both the sperm and egg.
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Answer:
If interphase doesn’t occur first, the cell won’t grow and DNA won’t replicate, so meiosis cannot proceed properly.
Explanation:
Interphase is the phase where the cell prepares for division. It includes:
- G₁ phase: Cell growth
- S phase: DNA replication (chromosomes are duplicated)
- G₂ phase: Preparation for division
Without interphase, especially the S phase, DNA will not be copied. This means the cell would attempt to divide without duplicated chromosomes, leading to genetic errors, incomplete division, or cell death. Since meiosis requires duplicated chromosomes to separate properly in later stages, skipping interphase would prevent accurate chromosome segregation.
✔ Answer: *"When interphase doesn't occur, cells don't grow and DNA doesn't replicate."*
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Answer:
Two chromosomes are homologous if they are identical in size, shape, gene location, and carry genes for the same traits, but may have different alleles (versions of the gene).
Explanation:
Homologous chromosomes are pairs of chromosomes — one from the mother and one from the father — that are similar in:
- Length
- Centromere position
- Gene sequence (same genes in same order)
They are not identical (since they may have different alleles), but they are homologous because they pair up during meiosis I and exchange genetic material via crossing over.
✔ Answer: *"Two chromosomes are made up of the same formula, hence 23 chromosomes are taken from the mother and 23 from the father. Chromosomes are homologous when they're exactly identical in length, gene pattern, and loci."*
(Note: "loci" refers to gene locations.)
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Answer:
During crossing over, homologous chromosomes exchange segments of DNA at points called chiasmata. This creates new combinations of alleles on the chromosomes.
Significance:
It increases genetic diversity in offspring by creating new combinations of genes that were not present in either parent.
Explanation:
In Prophase I of meiosis, homologous chromosomes pair up and may swap sections of DNA. This recombination results in new allele combinations, which contributes to variation in the next generation. This is a key reason why siblings (except identical twins) are genetically different.
✔ Answer: *"Crossing over involves the exchange of genetic material between homologous chromosomes, resulting in new combinations of alleles and increasing genetic variation."*
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Answer:
You can tell by how the chromosomes are arranged:
- In metaphase I, homologous chromosome pairs (tetrads) line up at the equator.
- In metaphase II, individual chromosomes (each with two sister chromatids) line up at the equator — just like in mitosis.
Explanation:
- Metaphase I: Homologous pairs align side by side. The orientation of each pair determines which chromosome goes to which daughter cell (independent assortment).
- Metaphase II: Each chromosome (consisting of two sister chromatids) lines up individually, similar to mitotic metaphase.
✔ Answer: *"In metaphase I, homologous chromosomes are paired and line up at the equator. In metaphase II, individual chromosomes (each with two sister chromatids) line up at the equator."*
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Answer:
Nondisjunction is the failure of chromosomes to separate properly during meiosis (either in anaphase I or anaphase II). This results in gametes with an abnormal number of chromosomes (aneuploidy).
Effects:
- Gametes may have extra chromosomes (trisomy) or missing chromosomes (monosomy).
- Example: Down syndrome (trisomy 21) occurs when chromosome 21 fails to separate during meiosis.
Explanation:
- In anaphase I, if homologous chromosomes don’t separate → one cell gets both, the other gets none.
- In anaphase II, if sister chromatids fail to separate → one cell gets both chromatids, the other gets none.
These abnormal gametes, when fertilized, can lead to developmental disorders or miscarriages.
✔ Answer: *"Nondisjunction occurs when chromosomes fail to separate during meiosis. This leads to gametes with too many or too few chromosomes, causing conditions like Down syndrome or Turner syndrome."*
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- The image shows:
- Prophase I: Chromosomes pairing up (homologous chromosomes).
- Metaphase I: Paired chromosomes lining up.
- Nondisjunction diagram: Shows unequal distribution of chromosomes into gametes.
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| Question | Answer |
|--------|--------|
| 1 | Sperm: 23, Egg: 23 |
| 2 | Cells wouldn’t grow; DNA wouldn’t replicate |
| 3 | Homologous chromosomes are same in size, shape, gene pattern, and loci |
| 4 | Crossing over exchanges DNA between homologous chromosomes → increases genetic variation |
| 5 | Metaphase I: homologous pairs line up; Metaphase II: individual chromosomes line up |
| 6 | Nondisjunction = failure of separation → aneuploid gametes → genetic disorders |
Let me know if you'd like this formatted as a printable answer key!
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1. The purpose of meiosis is to make gametes, also known as sperm and egg cells. In humans, your body cells have 46 chromosomes. How many chromosomes are in a sperm or egg cell if, when they come together to form a fertilized zygote, there are 46 chromosomes? Write the correct number of chromosomes next to the sperm and egg.
Answer:
Each sperm and egg cell has 23 chromosomes.
Explanation:
Humans are diploid organisms, meaning their somatic (body) cells have two sets of chromosomes — one from each parent — totaling 46 chromosomes (23 pairs). During meiosis, gametes (sperm and egg) are formed with half the number of chromosomes, so they are haploid (n = 23). When a sperm (23 chromosomes) and an egg (23 chromosomes) fuse during fertilization, they form a zygote with 46 chromosomes (23 + 23), restoring the diploid number.
✔ So, write 23 next to both the sperm and egg.
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2. Interphase must occur once before meiosis can happen. (Same thing for mitosis). What would happen if interphase didn’t occur first?
Answer:
If interphase doesn’t occur first, the cell won’t grow and DNA won’t replicate, so meiosis cannot proceed properly.
Explanation:
Interphase is the phase where the cell prepares for division. It includes:
- G₁ phase: Cell growth
- S phase: DNA replication (chromosomes are duplicated)
- G₂ phase: Preparation for division
Without interphase, especially the S phase, DNA will not be copied. This means the cell would attempt to divide without duplicated chromosomes, leading to genetic errors, incomplete division, or cell death. Since meiosis requires duplicated chromosomes to separate properly in later stages, skipping interphase would prevent accurate chromosome segregation.
✔ Answer: *"When interphase doesn't occur, cells don't grow and DNA doesn't replicate."*
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3. Remember that a cell that begins meiosis has 23 chromosomes inherited from mother (one is shown in red on the right in cartoon) and 23 chromosomes inherited from father (one is shown in blue on the left in cartoon). In the process of meiosis, chromosomes begin to match up in homologous pairs. How would you know if two chromosomes were homologous?
Answer:
Two chromosomes are homologous if they are identical in size, shape, gene location, and carry genes for the same traits, but may have different alleles (versions of the gene).
Explanation:
Homologous chromosomes are pairs of chromosomes — one from the mother and one from the father — that are similar in:
- Length
- Centromere position
- Gene sequence (same genes in same order)
They are not identical (since they may have different alleles), but they are homologous because they pair up during meiosis I and exchange genetic material via crossing over.
✔ Answer: *"Two chromosomes are made up of the same formula, hence 23 chromosomes are taken from the mother and 23 from the father. Chromosomes are homologous when they're exactly identical in length, gene pattern, and loci."*
(Note: "loci" refers to gene locations.)
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4. Crossing over is a very important event in Prophase I of meiosis. What happens during crossing over and what is the significance?
Answer:
During crossing over, homologous chromosomes exchange segments of DNA at points called chiasmata. This creates new combinations of alleles on the chromosomes.
Significance:
It increases genetic diversity in offspring by creating new combinations of genes that were not present in either parent.
Explanation:
In Prophase I of meiosis, homologous chromosomes pair up and may swap sections of DNA. This recombination results in new allele combinations, which contributes to variation in the next generation. This is a key reason why siblings (except identical twins) are genetically different.
✔ Answer: *"Crossing over involves the exchange of genetic material between homologous chromosomes, resulting in new combinations of alleles and increasing genetic variation."*
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5. Meiosis has two divisions: Meiosis I and Meiosis II. There is a metaphase I and a metaphase II... etc. If the cartoon below has chromosomes in the middle of the cell, how would you know whether it was in metaphase I or metaphase II?"
Answer:
You can tell by how the chromosomes are arranged:
- In metaphase I, homologous chromosome pairs (tetrads) line up at the equator.
- In metaphase II, individual chromosomes (each with two sister chromatids) line up at the equator — just like in mitosis.
Explanation:
- Metaphase I: Homologous pairs align side by side. The orientation of each pair determines which chromosome goes to which daughter cell (independent assortment).
- Metaphase II: Each chromosome (consisting of two sister chromatids) lines up individually, similar to mitotic metaphase.
✔ Answer: *"In metaphase I, homologous chromosomes are paired and line up at the equator. In metaphase II, individual chromosomes (each with two sister chromatids) line up at the equator."*
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6. Meiosis does not always occur without any difficulties. Describe what occurs during nondisjunction and the effect on the resulting cells.
Answer:
Nondisjunction is the failure of chromosomes to separate properly during meiosis (either in anaphase I or anaphase II). This results in gametes with an abnormal number of chromosomes (aneuploidy).
Effects:
- Gametes may have extra chromosomes (trisomy) or missing chromosomes (monosomy).
- Example: Down syndrome (trisomy 21) occurs when chromosome 21 fails to separate during meiosis.
Explanation:
- In anaphase I, if homologous chromosomes don’t separate → one cell gets both, the other gets none.
- In anaphase II, if sister chromatids fail to separate → one cell gets both chromatids, the other gets none.
These abnormal gametes, when fertilized, can lead to developmental disorders or miscarriages.
✔ Answer: *"Nondisjunction occurs when chromosomes fail to separate during meiosis. This leads to gametes with too many or too few chromosomes, causing conditions like Down syndrome or Turner syndrome."*
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Final Notes on Diagrams:
- The image shows:
- Prophase I: Chromosomes pairing up (homologous chromosomes).
- Metaphase I: Paired chromosomes lining up.
- Nondisjunction diagram: Shows unequal distribution of chromosomes into gametes.
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✔ Summary of Answers:
| Question | Answer |
|--------|--------|
| 1 | Sperm: 23, Egg: 23 |
| 2 | Cells wouldn’t grow; DNA wouldn’t replicate |
| 3 | Homologous chromosomes are same in size, shape, gene pattern, and loci |
| 4 | Crossing over exchanges DNA between homologous chromosomes → increases genetic variation |
| 5 | Metaphase I: homologous pairs line up; Metaphase II: individual chromosomes line up |
| 6 | Nondisjunction = failure of separation → aneuploid gametes → genetic disorders |
Let me know if you'd like this formatted as a printable answer key!
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