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Transcript of Chaper 4.3
Big Question: how do new organisms form?
4.3 The Cell and Inheritance
photo (cc) Malte Sörensen @ flickr
Mendel's work showed that genes exist, but scientists still did not know what structures inside cells contained genes.
In 1903 Walter Sutton (an American geneticist) was studying the cells of grasshoppers. He wanted to understand how sex cells (gametes) form.
(W) He hypothesized that chromosomes were the key to understanding how offspring have traits similar to those of their parents.
Mendel and Sutton
Sutton found evidence to support his hypothesis in grasshopper's cells.
(W) The body cells of grasshoppers have 24 chromosomes.
(W) Surprisingly, Sutton found that grasshoppers sex cells have only 12 chromosomes.
So, grasshopper's sex cells have exactly half the number of chromosomes found in its body cells
Chromosomes and Inheritance
(W) Sutton observed that when the sperm and the egg cell joined during fertilization, the fertilized egg had 24 formed chromosomes.
As a result, the grasshopper offspring had exactly the same number of chromosomes in its cells as each of its parents.
(W) One chromosome in each pair came from the male parent, and the other from the female parent.
Remember, Mendel discovered that alleles are different forms of a gene and that each offspring receives one allele from each parent.
(W) Sutton knew that alleles exist in pairs and then realized that paired alleles were carried on paired chromosomes.
Sutton's idea became known as:
(W) Chromosome theory of inheritance : genes are carried from parents to their offspring on chromosomes.
In your notes, answer this question:
How did Walter Sutton develop the chromosome theory of inheritance?
(W) How do sex cells end up with half the number of chromosomes as body cells?
(W) Meiosis is the process by which the number of chromosomes is reduced by half to form sex cell (gametes).
(W) How are alleles, genes and chromosomes related?
(W) Alleles are the various types of options that is chosen by the gene.
The gene is the segment of DNA that codes for the protein.
Genes are found on chromosomes.
Chromosomes contain multiple genes.
Remember, sex cells have half the number of chromosomes as body cells. So, at the end of Meiosis, we are going to get sex cells with half the number of chromosomes as the parent cell.
(Every chromosome is copied, so the cell has four copies of each DNA strand)
**Remember: chromosomes are condensed DNA and each rod is an exact copy of the other.
End of Meiosis
Humans have 23 pairs of chromosomes, for a total of 46 chromosomes.
Punnett Squared and Meiosis
Remember, the human body has 23 chromosome pairs.
Chromosomes are made up of many genes joined together like beads on a string.
Even though we only have 23 chromosomes, our body cells have over 35,000 genes.
One chromosome is from the male parent, the other from the female parent.
(W) Each chromosome has the same genes, but the alleles may be different.
(W) This is how some traits become homozygous and others heterozygous.
Write a summary in your notes...
As we watch this video:
record bullet-ed information
copy down the diagrams of both mitosis and meiosis.