Reproduction
Reproduction occurs throughout the summer (June and July). A female black bear is sexually mature at three to six years old and a male bear will be ready at about age four. The female bear will have the baby in January. Bears produce very similarly to humans. After all they are mammals too. They have same sex organs as us, humans. However their ovum does not fertilize for several months. They have something called embryonic delay. When a female is ready to reproduce she will leave a scented trail that the male will follow.Then when the male bear and the female bear come into contact with each other they will nuzzle and get to know each other for a couple of days. Some males lead the female to a private place away from other bears and then they will reproduce. This lasts for a couple of days. The gametes of a male bear is sperm while the gamete for a female black bear is her eggs. In black bears there are 76 chromosomes, which means that a haploid cell must have 38 chromosomes in it. As a male and female are reproducing the male will release sperm into the females vagina. Then the sperm will fight to get into the egg and when it finally enters the egg starts to fertilize and create a cub.
Development
The gestation period of a female black bear takes about 225 days. The maturity of a bear will depend on its sex. If its a female it will most likely be mature at 2-3 years old and a male will be ready at about 4 years old. The life expectancy of an American black bear is 10 years. Bears go through the same stages of development as humans. First there is the zygote (diploid cell, result of fertilization), then the blastocyst (many cells, then the embryo (offspring in the first 9 weeks, organs have not been made yet and finally the fetus (unborn offspring). However bears have a longer time of blastocyst stage which lasts several months. The typical number of offspring is 2 but bears can have up to 6 cubs. The male leaves after sexual intercourse occurs. When the cubs first come out they have their eyes closed for about 4 to 6 weeks. They will leave shelter for the first time at around two months. The mother will care for the bears for 5 more months. The cubs will leave the coming spring.
Mitosis and Meiosis
Mitosis is cell replication/tissue growth. Mitosis helps build the embryo by making the tissue and cell and is usually associated with asexual reproduction. It is the creation of two daughter cells with the same amount of chromosome before and after it replicates. Meiosis is creation of sex cells (gametes). The sperm and the egg. Meiosis takes place in animal, plants, and fungi. It is also the creation of four daughter cells and results in one cell having half the amount of chromosomes, 38, which is called a haploid. Mitosis can occur in bears when they have wounds and need to heal them up. Mitosis will create new tissue for the wound. Mitosis is also shown in development of an embryo when all the tissue is being made. Meiosis occurs in the testicles for males and the ovaries for females. In the testes the sperm is created due to meiosis and ovary eggs have been made by meiosis. Remember that eggs are made before the female is even born. So females have all of their eggs all ready. Meiosis also works with chromosome combinations (crossing over of genetic material).
Genes:
Genes are what make a protein. Genes are made up of DNA and every animal has genes. Mitosis and meiosis are both process that deal with genes. In mitosis the genetic material will stay exactly the same when the cell replicates itself. In Meiosis the genetic information in the chromosomes is split in two. Making a higher chance for variety because each daughter cell contains 23 different chromosomes.
Sources:
-http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20101/Bio%20101%20Laboratory/Mitosis/mitosis.htm
-http://www.nature.com/scitable/topicpage/mitosis-meiosis-and-inheritance-476
Genes:
Genes are what make a protein. Genes are made up of DNA and every animal has genes. Mitosis and meiosis are both process that deal with genes. In mitosis the genetic material will stay exactly the same when the cell replicates itself. In Meiosis the genetic information in the chromosomes is split in two. Making a higher chance for variety because each daughter cell contains 23 different chromosomes.
Sources:
-http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20101/Bio%20101%20Laboratory/Mitosis/mitosis.htm
-http://www.nature.com/scitable/topicpage/mitosis-meiosis-and-inheritance-476
Reproduction and Development:
Sources:
-http://www.esf.edu/aec/adks/mammals/black_bear.htm
-http://animals.about.com/od/bears/p/american-black-bear.htm
Sources:
-http://www.esf.edu/aec/adks/mammals/black_bear.htm
-http://animals.about.com/od/bears/p/american-black-bear.htm