ANSWERS

Process of Science(14.5)

How Do New Species Arise By Genetic Isolation?

Lab Notebook

Plant / Number of Chromosomes for Diploid Cell / Number of Homologous Pairs of Chromosomes for Meiosis / Number of Chromosomes for Gamete (pollen or egg) / Chromosome Number for Zygote Resulting from Self-Fertilization
Plant W / 4 / 2 / 2 / 4
Plant X / 6 / 3 / 3 / 6
WX
Hybrid / 5 / 0
Mitotic Error WX Hybrid / 10 / 5 / 5 / 10
Plant Q / 10 / 5 / 5 / 10
QW
Hybrid / 7 / 2
QX
Hybrid / 8 / 3

Questions

1. Humans have 46 chromosomes in the diploid cell. How many chromosomes would be found in each gamete and in a zygote resulting from normal fertilization?

Each gamete, the sperm or egg, would have 23 chromosomes. The zygote will have 46 chromosomes resulting from fusion of the sperm and egg.

2. Predict the outcomes of a plant with 6 diploid chromosomes that fertilized a similar plant in which the egg failed to undergo meiosis. Assume that the plant producing the sperm undergoes meiosis normally.

The resulting zygote from this fertilization would have 9 chromosomes.

3. Why are the tetraploid plants considered a new species by biologists?

Because they have a new chromosomal arrangement that may give unique traits. In addition, the new chromosomal number prohibits breeding with the diploid plants.

4. Think of a commercial use for triploid plants incapable of producing viable gametes and zygotes.

Triploids are already used to produce seedless bananas, oranges and watermelons. The fruits develop after pollination, however, the resulting seeds never form as a result of the abnormal chromosome number.

5. Is plant Q capable of producing viable gametes? If so, what is the chromosome number of the gametes?

Yes, plant Q is able to pair in meiosis, creating gametes with 5 chromosomes.

6. What is the evidence that this allopolyploid is self–fertile and a new species?

It can produce viable gametes capable of producing offspring with a chromosome arrangement that can undergo meiosis. This allopolyploid is a fertile hybrid, reproductively isolated from the two parent species. It is a new plant species–a product of sympatric speciation by allopolyploidy.

7. Would hybridizing plant Q with plants W or X produce fertile offspring?

No. It is not possible to produce fertile offspring from either cross.

______

Campbell/Reece/Taylor/Simon:Biology: Concepts & Connections, Sixth Edition, © Pearson Education, Inc., publishing as Benjamin Cummings