1. Outline 10A: Chromosomes
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Outline 10A: Chromosomes
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2. I. Cell Division A. Production of new cells
B. Also called cell reproduction
C. Used for:
1. Growth & development
2. Repairing wounds
3. Reproduction
a. Asexual - makes copies of cells
b. Sexual - makes gametes, the reproductive cells
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3. D. Bacterial Cell Division
1. Bacteria have a single DNA strand
a. It is circular & attached to cell membrane
2. They divide by a type of cell division called binary fission
a. DNA is copied
b. Bacterium divides in two  Grows new membrane & cell wall in between two DNA molecules
c. End up with 2 identical bacteria (form of asexual reproduction)
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4. II. Eukaryotic Chromosomes
A. Gene
1. Segment of DNA that codes for a protein or RNA molecule
B. When DNA is being used it is stretched out long and thin, called chromatin
C. As a eukaryotic cell prepares to divide, however, the DNA & its associated proteins, called histones, coil up into a structure called a chromosome
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5. D. Structure of a Chromosome
1. Chromosomes have 2 identical copies of DNA attached together. These are called chromatids
a. This is because the DNA copies itself before cell division
2. The chromatids are attached at a point called the centromere
3. The chromatids will become separated from each other during cell division
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6. Centromere
Sister chromatids

7. E. Drawing of a Chromosome
Chromatid
Chromatid
Centromere
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8. F. Chromosome Numbers
1. Each human body cell has pairs of chromosomes, for a total number of 46. This type of cell is called a somatic cell.
2. The 23 chromosomes differ in size, shape, and types of genes they carry.
3. Each chromosome contains thousands of genes for many different functions
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9. 4. Sets of Chromosomes
a. Each pair of chromosomes consists of two homologous chromosomes
 These are chromosomes that are similar in size, shape, and genetic content
 Each homologue comes from one of the two parents:
23 chromosomes from mother
23 chromosomes from father
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10. 5. Chromosome Terminology
a. If a cell contains two complete sets of chromosomes it is said to be diploid
 Most cells in the human body are diploid
b. If a cell contains only one set of chromosomes it is said to be haploid
 This is only found in gametes (eggs or sperm in humans)
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11. 6. Chromosome Symbology
a. The symbol N is used to represent the number of chromosomes in one set of chromosomes.
 This means the haploid number In humans, N= 23
b. 2N is used to represent the number of chromosomes in two complete sets of chromosomes  This means the diploid number
In humans, 2N = 46
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12. c. Fertilization  When 2 haploid gametes fuse
(Sperm fertilizes the egg)
 The resultant fertilized egg now has two sets of chromosomes and is diploid (2N)
 This cell is now called a zygote
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13. 7. Chromosome Diversity
a. Each organism has a characteristic number of chromosomes
b. Table of Chromosome Numbers
Organism Diploid # Haploid #
Housefly ?
Frog ? 13
Mosquito ?
Dog ? 39
Orangutan ?
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14. G. Chromosomes & Sex
1. 22 of the 23 pairs of human chromosomes are called autosomes
a. These are chromosomes that are NOT directly involved in determining gender (sex)
2. 1 of the pairs IS directly involved & will determine sex of individual
a. These are called the sex chromosomes
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15. 3. In humans, the chromosomes are referred to as X and Y
a. Genes on the Y chromosome cause a zygote to become male
 Males = XY
Females = XX
4. Since a female can only give her offspring an X chromosome, the sex of offspring is determined by the male
5. Other species have different sex chromosomes situations
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