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The Zenkey is a hybrid animal produced from a cross between a species of zebra with a diploid number of 44 and a donkey with a diploid number of 62 - VCE - SSCE Biology - Question 1 - 2005 - Paper 1
Question 1
The Zenkey is a hybrid animal produced from a cross between a species of zebra with a diploid number of 44 and a donkey with a diploid number of 62. a. What is the ... show full transcript
Worked Solution & Example Answer:The Zenkey is a hybrid animal produced from a cross between a species of zebra with a diploid number of 44 and a donkey with a diploid number of 62 - VCE - SSCE Biology - Question 1 - 2005 - Paper 1
Step 1
What is the diploid number of the Zenkey?
Answer
To find the diploid number of the Zenkey, we must consider the diploid numbers of the parents—the zebra with 44 chromosomes and the donkey with 62 chromosomes. The diploid number of a hybrid is calculated by taking an average of the parental diploid numbers. In this case, the Zenkey is likely to have a diploid number of 53, which is computed as follows:
ext{Zenkey Diploid Number} = rac{44 + 62}{2} = 53
Step 2
Step 3
Starting with the cell shown below with a pair of homologous chromosomes, draw what happens to the cell and its chromosomes during the process by which gametes are produced.
Answer
In meiosis, the cell undergoes several stages:
- Prophase I: Homologous chromosomes pair up and exchange segments, a process called crossing over.
- Metaphase I: Pairs of homologous chromosomes align at the cell's equatorial plane.
- Anaphase I: The homologous chromosomes are pulled apart to opposite ends of the cell.
- Telophase I & Cytokinesis: The cell divides into two cells, each with half the number of chromosomes.
- Meiosis II: Each of these two cells undergoes another division (similar to mitosis) to form a total of four haploid gametes.
The result from this process involves the production of four gametes each carrying a unique combination of chromosomes.
Step 4
Zenkes are unable to produce offspring. Using your knowledge of gamete formation, suggest why the Zenkey is sterile.
Answer
The sterility of the Zenkey can be attributed to the difference in the number of chromosomes inherited from its zebra and donkey parents. During meiosis, pairing of homologous chromosomes is essential for proper gamete formation. Since the Zenkey has an uneven number of chromosomes (53), it can result in improper pairing and segregation of chromosomes, leading to aneuploid gametes. These nonviable gametes prevent the Zenkey from producing fertile offspring.