Question

are unsure) The Pizzly Bear ne Pizzly Bear is a great example of an interesting creature, and also an interesting way to really think about meiosis. The Parly Bear (sometimes called the rolar Bearl occurs as a result of a mating between a Grizzly and a Polar Bear. These offspring have c urred in several zoos and in the wild. They are fertile. Do a little research and answer the following a) pts) Complete the table. Bear Number of Number of Chromosomes in Chromosomes in Somatic Cell Sperm or Egg (gamete) Grizzly Bear (also o called Brown Bear) 74 37 Polar Bear Pizzly Bear 74 74 37 37 b) (3 pts) Unlike most hybrid animals, the "Pizzly is fertile. Using your understanding of meiosis what does this tell us with regards to the genomes of the Grizzly and the Polar Bear? Specifically refer to TWO things the NUMBER of chromosomes and the KIND OF DNA SEQUENCES on those chromosomes. Use the word "homolog" or "homologous". This answer shouldn't be long, and it doesn't have to have specific gene names in it, but it might be helpful if you refer to the location of centromeres c) (4 pts) We know the Pizzly bear is fertile (makes working gametes). But we also know the mule (another hybrid animal) is NOT7 Based on your understanding of meiosis, and what homologs are and using some research into both these organism (the Pizzly and the mule), propose an explanation for the fertility of the Pizzly, and the lack of fertility of the mule.

Answer 1

b.

Polar bear lives in the arctic regions and brown bear lives in forests and in mountains. The two evolved from the ancestors not very long ago. Because of this they did not develop many genetic differences. Thei chromosomal number is also same '74'. So the offspring Groalar bear has 37 brown bear chromosomes and 37 polar bear chromosomes. Because the number of chromosomes from both is same and also the genetic differences are not many. When genetic differences are many, DNA sequences will be similar hence, the homologous chromosomes pair during meiosis prophase. Location of the centromere also is same with less genetic differences. This allows the pairing of homologous chromosomes resulting in fertile offspring.

c.

Mule is not fertile because the number of chromosomes in horse is 64 where as that of donkey is 62. So the offspring , mule produced due to hybridization of donkey and horse is not fertile. This is because of the failure of the chromosomes to pair during prophase of meiosis. The two animals evolved from their ancestor, long before and developed number of genetic changes, including difference in the number of chromosomes. Faiure to pair during meiosis will result in failure to produce gametes. So the mule is infertile.

Where as the Groalar bear is fertile as the number of chromosomes is same and the genetic differences in the DNA are also less. If the pairing of homologous chromosomes is possible, gametes can be formed.