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ANSWERS
Process of Science
How Do New Species Arise By Genetic Isolation?
Lab Notebook
Number of
Chromosomes
for Diploid
Cell
Number of
Chromosomes
for Gamete
(pollen or egg)
2
Chromosome
Number for
Zygote
Resulting from
SelfFertilization
4
3
6
Plant W
4
Number of
Homologous
Pairs of
Chromosomes
for Meiosis
2
Plant X
6
3
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
Plant
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?
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Copyright © 2010 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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.
____________________________________________________________________________________
Copyright © 2010 Pearson Education, Inc., publishing as Pearson Benjamin Cummings