Thursday, February 3, 2011

Independent Assortment of Chromosomes

Synapsis
Crossing-over
Chiasmata
Bivalents
THREE Sources of Variation
Crossing Over at Prophase I
Crossing Over at Prophase I
Independent Assortment at Metaphase I
Independent Assortment at Metaphase I
Possible combinations = 2n, n = haploid number.
Humans: n = 23.
Possible combinations = 223 = 8.4 million!
Independent Assortment is also known as Mendel’s Second Law
Random Fertilization
Each Gamete
 One out of about 8.4 million (223) possible chromosome combinations due to independent assortment.
2 gametes fuse
 Zygote with any of about 70 trillion (223 X 223) diploid combinations!!
Mendel’s First Law
Law of Segregation

A somatic cell carries two alleles at any one locus.
Alleles of a gene pair segregate during anaphase I of meiosis
Half of the gametes carry one allele of a gene pair; the other half carry the other allele.
Summary of meiosis and mitosis
Assignment
Explain the need for the production of genetically identical cells & fine control of replication

Since the functions of mitosis are to produce new cells for growth, repair of body tissues, and asexual reproduction,
essential that the cells are identical so that the daughter cells would continue to code for essential proteins that can function properly

How to Get Seedless Watermelon?

Double the diploid number (2n) in a normal watermelon plant by the use of the chemical colchicine to tetraploid (4n).
Colchicine’s function?
Tetraploid’s gamete = 2n
Normal watermelon’s gamete = n
Fuse the tetraploid’s gamete (2n) with normal water melon’s gamete (n)

Why is triploid watermelon sterile?
During meiosis the normal pairing of chromosomes cannot properly take place since one set will have no homologous set to pair with

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