1. DNA is the inherited material responsible for variation.
Section 3
DNA is the inherited material responsible for variation.

2. 3.1 DNA- Transmitter of Genetic Code
All sexually reproducing species have the best chance of long-term survival if there is a lot of variation within their species.
Without variation, the species would be unable to survive changes in the environment, and would be more vulnerable to extinction.

3. DNA Deoxyribonucleic acid, DNA for short.
Every multi-cellular organism on Earth contain this blueprint for making a copy of itself in each of its body cells.
The inherited material responsible for variation

4. DNA and the Genetic Code
James Watson and Francis Crick began unraveling the DNA structure, and revealed how the same chemical building blocks could carry such a wide range of instruction needed for diversity in the world.
The DNA model can be compare to as a ladder that has been twisted into a spiral.
The “legs” of the ladder are identical but…
The “rungs” vary in their building blocks. There are 4 chemicals, paired the following way:
Cytosine (C) pairs with Guanine (G)
Adenine (A) pairs with Thiamine (T)

6. Chromosomes
                                                                   
If DNA in a human was stretched out, it would be 2 meters long.
To fit so much DNA into cells, they have to be packages into chromosomes.
They are located in the cell nucleus
In the human body there is 46 chromosomes, grouped into 23 pairs.
Different organisms have different #’s of chromosomes.

7. Genes Are responsible for the inheritance of an organism’s features.
Genes are located on chromosomes.
Each chromosome contains many gene locations.
Alleles: genes that exist in an array of possible forms.
Example: straight or curly hair

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9. 3.2 Cell Division
In multicellular organisms, the process that produces two new cells with the same number of chromosomes is called mitosis.
Mitosis: occurs in the body cells of multicellular organisms and is responsible for the growth and repair of cells.

10. Mitosis

11. During sexual reproduction, the sex cells (gametes) join to make a zygote, which make a new individual. The gametes only have half the number of chromosomes and divide through meiosis.
Meiosis: a type of cell division that produces cells with only half the DNA of a normal cell. The female gamete, and male gamete combine to make a full set of DNA.

12. Meiosis

13. Complete the table to compare chromosome numbers in the species below.
Organism
# of chromosomes in a cell at the end of mitosis
# of chromosomes in a body cell
# of chromosomes in a gamete
# of chromosomes in a zygote
# of pairs of chromosomes
Guinea Pig 64
Potato 24

14. 3.3 Patterns of Inheritance
Traits: desirable characteristics in organisms. We will uses animal fur color to focus on patterns of inheritance in this section.
Purebred: organisms whose ancestors have only produced white fur offspring for several generations.
Hybrid: an individual produced by crossing two purebred parents that differ in a trait such as fur color.

15. Dominant Traits
If we cross a purebred white female with a purebred black male, we notice the result is that all offspring have the same black coat. W B BW
F E M A L E
M A L E
Black fur is dominant because all offspring have black coats.

16. Recessive Traits
Has the white coat allele in the hybrid offspring disappeared?
No, to find out, we need to cross the hybrid female offspring with the hybrid male offspring.
The result is that ¾ of the offspring are black, and ¼ is white. B W BB BW WB WW
F E M A L E
M A L E
The white fur kitten is and example of a recessive trait.

17. Incomplete Dominance
Sometimes the dominant-recessive pattern does not always work.
When a purebred black cat and a purebred white cat are crossed its offspring are grey.
Neither of the parents’ alleles are dominant or recessive.