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Cellular Reproduction
Cell Reproduction
• What is cell reproduction?
• How many cells make up your body?
• How does the chromosome transmit information from one generation to another?
• DNA is a molecule that contains the genetic code of an organism.
• A GENE is a segment of DNA that transmits information from parent to offspring. A single molecule of DNA has thousands of genes lines up end to end.
• Like the strands of a sock…DNA coils tightly before cell division. If it were straight the DNA would be approximately 5 cm long. (2 inches)
Gene
• When the cell is going to divide the DNA coils up into a dense chromosome structure.
Chromosome
• Cellular structure on which genes are located.
• Pg. 212
• Chromosomes are 40% DNA and 60% protein that supports the DNA (histones).
• Scientists have mapped the 100,000 genes that make up the chromosomes of humans.
A set of chromosomes from a female
Chromosome structure
• Chromatids are the two copies of each chromosome.
• Centromeres are protein disks that attach the two chromatids.
• A karyotype is the collection of chromosomes found in an organisms cells. Arranged in order of size and shape.
Karyotype Cont.
• It is a display of chromosomes of a single cell. To obtain it, the cell is stained, then a picture is taken of it through a microscope just before cell division, when the chromosomes are easiest to see.
• Somatic cells contain 23 different chromosomes, but contain two copies of each, a total of 46 chromosomes. All the cells in our body All the cells in our body other than gametesother than gametes
• Homologous chromosomes are the two copies of each chromosome type (for example chromosomes 13 are homologous because they are the same type.
Homologous Chromosomes & Somatic Cells
Homologous Chromosomes
• Chromosomes that are similar in shape, size, and the genes they carry.
They do NOT have the same types of DNA sequence!
Allele
An alternate form of a gene that is located at a specific position on a specific chromosome.
• A homologue is a half set of chromosomes. One chromosome of a pair.
• Diploid cells contain two homologues. The symbol for diploid is 2n. All somatic cells are diploid. It contains exactly two copies of each chromosome.
• Haploid cells contain only one homologue; if it contains exactly half of a species’ typical full set of genetic material . Only sex cells are haploid (n).
• Gametes are sex cells and are haploid. An organism’s reproductive cells, such as An organism’s reproductive cells, such as sperm or egg cellssperm or egg cells
Draw the following table
symbol Cells # of homologues
Diploid 2n Somatic 2 (46 chromosomes)
23 pairs
haploid n gametes 1 (23 chromosomes)
23 individual
chromosomes
A zygote is the fusion of a haploid sperm cell and a haploid egg cell. A fertilized egg cell, A fertilized egg cell, the first cell of a new individual.the first cell of a new individual.
Chromosome numbers of various organisms
Organism Number of Chromosomes
Penicillium 1-4
Saccharomyces (yeast) 18
Mosquito 6
Housefly 12
Garden Pea 14
Corn 20
Adder’s tongue fern 1,262
Frog 26
Human 46
Orangutan 48
Dog 78
Adders Tongue Fern
Each Chromosome is important to the development of a normal organism.
Monosomy is a condition in which a diploid cell is missing a chromosome. Most embryos will not survive if missing a chromosome.
Down Syndrome:
Jared has a condition in which his 21st chromosome number is three instead of two.(trisomy 21 or down syndrome). Pg 335
In Amniocentesis Amniotic fluid is tested for chromosome problems.
The normal frequency of down syndrome is 1 in 1500. For couples who are older than 30 it is 1 in 1000. In couples 35-40 it is 1 in 750. In couples older than 45 the risk is 1 in 16.
Alterations in chromosomes usually lead to mutations. There are four types of alterations.
Mutations: alterations in chromosomes.
PG. 306
• Deletion is a process in which a chromosome is damaged as fragments break off the chromosome and are lost.
• Duplication occurs as fragments attach to the homologous chromosomes.
• Inversion happens when fragments of the original chromosome attach in reverse order.
• Translocation occurs when a fragment may join a non-homologous chromosome.
Of the 23 pairs of chromosomes in human somatic cells, 22 pairs are the same. These chromosomes are called autosomes-not directly involved in determining not directly involved in determining the sex.the sex.
The Sex Chromosomes, X,Y, determine the sex of the organism. These chromosomes are called sex chromosomes.
A combination of XX is a female.
A combination of XY is a male
Because an egg cell carries only the X chromosome and the sperm cell carries either X or Y the sex of an offspring is determined by the male sex cells.
Meiosis• A form of cell division that halves
the number of chromosomes when forming specialized reproductive cells, such as gametes or spores.
• Results in four haploid cells
pg. 273
Lab Partner Questions:
• Can meiosis be asexual?
• What phase is responsible for the law of independent assortment?
• When will crossing over occur?
Crossing Over
• The exchange of reciprocal segments of DNA by chromosomes at the beginning of meiosis
pg. 277
The separation of genes during crossing over occurs more frequently between genes that are far apart on a chromosome than for genes that are close together.
When these chromosomes segregate in meiosis, they form gametes that have completely new combinations of alleles.
Reviewing Information
Binary fission is a type of asexual reproduction that produces identical offspring. (happens in prokaryotic cells such as bacteria)
When Eukaryotic cells split the internal organelle must also divide and the process is much more complex. This process is known as the cell cycle.
Cell Cycle is a diagram of the growth and division of a cell.
