Chromosomes and Meiosis 6.1
Autosomes
-Chromosome pairs 1 through 22 -Chromosomes that contain genes for characteristics not directly related to the sex of an organism.
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-Each body cell contains a set of 46 chromosomes, which come in 23 pairs. -Cells identical to each other unless mutations have occurred.
Key Concept
-Gametes have half the number of chromosomes that body cells have. -You have body cells and gametes.
Sex chromosomes
-Make up your 23rd pair of chromosomes. -NOT homologous.
Meiosis
A form of nuclear division that divides a diploid cell into haploid cells. -Process essential for sexual reproduction.
Somatic Cells
Also called body cells, makes up all of the body tissues and organs, except gametes. DNA in your body cells is not passed on to your children.(Diploid)
XY system
By which the organism's sex is determined
Haploid
Cells have only one copy of each chromosome. (Gametes)
Diploid
Cells have two copies of each chromosome: one copy from the mother and one from the father. (Body cells) -Can be represented as 2n - in humans, diploid chromosome number is 46.
Why do cells within an organism differ from one another?
Cells within an organism differ from one another because different genes are expressed, not because they have different genes.
Y chromosome
Contains genes that direct the development of the testes and other male traits, smallest chromosome. carries the fewest genes.
Sex chromosomes
Directly control the development of sexual characteristics.
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Each human egg or sperm cell has 22 autosomes and 1 sex chromosome. In the egg - sex chromosome - always an X chromosome. In the sperm cell - sex chromosome - can be an X chromosome or a Y chromosome.
body cells
Example of diploid cells.
gametes
Example of haploid cells.
X and Y
Humans: two different sex chromosomes
Sexual reproduction
Involves the fusion of two gametes, resulting in offspring that genetic mixture of both parents.
X chromosome
Larger sex chromosome, contains numerous genes (including many that are unrelated to sexual characteristics.)
Male
Organism with one X and one Y chromosome.
Female
Organism with two X chromosomes.
Gametes
Sex cells, haploid reproductive cell that unites with another haploid reproductive cell to form a zygote. DNA in your gametes can be passed on to your children.(Haploid)
Specialized cells in your body
Somatic cells and gametes.
Fertilization
The actual fusion of an egg and a sperm cell.
Total number of chromosomes in body cells
Total: 46 chromosomes -Two sets: 23 from your mother and 23 from your father --both sets used to function properly
Homologous chromosomes
Two chromosomes - one inherited from the mother, one from the mother - have the same length and general appearance. -Have copies of the same genes, although the two copies may differ.
What happens when fertilization occurs?
When fertilization occurs, the nuclei of the egg and sperm cell fuse to form one nucleus. -New nucleus - must have correct number of chromosomes for a health organism to develop. -Egg and sperm cell need only half the usual number of chromosomes - one chromosome from each homologous pair.
