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DNA is shaped like a double helix or a twisted ladder.
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In a DNA strand, the rungs
(the part you step on)
of the “ladder” are made of nucleotide bases.
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In a DNA strand, the sides of the “ladder” are made of alternating sugar and phosphate molecules.
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When DNA copies itself it splits down the middle where the two bases meet. The bases on each side of the molecule can be used as a pattern for a new complementary side.
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In DNA there are four different bases: Adenine, Thymine, Cytosine, and Guanine.
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In DNA, Adenine pairs with Thymine, and Cytosine pairs with Guanine.
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A change in the order of bases in DNA is called a mutation.
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There are three types of mutations: insertion, deletion, and substitution.
 Insertion is when an extra base is added into the sequence.
 Deletion is when a base is deleted from the sequence.
 Substitution is when one base is substituted for another.
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Not all mutations are harmful. Some mutations are beneficial, and others have no effect at all.
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A mutation in DNA could also result in death or a genetic disorder.
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We have certain enzymes that repair most DNA mutations.
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Ultraviolet radiation from the sun is known to cause mutations in skin cells that can lead to cancer, which is why you should wear sunscreen in the summertime.
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A disease that occurs when a child inherits a mutated gene from parents who do not have the disease is a recessive disorder.

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Rosalind Franklin was able to create images of DNA molecules and discover that DNA was spiral shaped.
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Watson and Crick made models to determine DNA structure.
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According to Chargaff’s rules A always pairs with T and C always pairs with G.
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Punnett developed a square that is used to visualize all the possible combinations of alleles in offspring resulting from a genetic cross.
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Mendel used pea plants to study the way traits are passed from one generation to the next.
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Gregor Mendel is considered the father (first to discover) of genetics.
- In a pedigree, a solid black square or circle indicates that the person has a certain trait.
- In a pedigree, squares represent males.
- In a pedigree, circles represent females.
- In a pedigree, a half-filled square or circle indicates that the person is a carrier of a certain trait.

● Two forms of a single gene are known as alleles.
● The set of instructions for each characteristic donated by the parent to the offspring are called genes.
● Most genetic disorders, such as Cystic Fibrosis, are due to a recessive gene.
● Sickle cell anemia could be caused by a change in the order of the bases in a person’s DNA.
● A normal human cell has 46 chromosomes; whereas a human sex cell has only 23 chromosomes.
● Genes are found on chromosomes.
● The trait that seems to recede (hide) in the background in the first-generation offspring is the recessive trait.
● Dolly, the sheep, is the first successfully cloned mammal because of genetic engineering.
● Alleles may be dominant or recessive.
● Probability is the mathematical chance that an event will occur.
● The passing of traits from parents to offspring is heredity.
● A red snapdragon flower crossing with a white snapdragon flower and producing a pink snapdragon flower is an example of incomplete dominance.
● In incomplete dominance, each allele for a trait has its own degree of influence.
● The molecule shown above is a nucleotide.
● A nucleotide in a DNA molecule is made up of a sugar, a phosphate, and a base.

● Traits that are inherited are traits such as eye color and hair color. Your taste in music and what movies you like to watch are NOT inherited.
● The picture above is the basic structure of DNA.
● The picture above consists of nucleotides.
● Phenotype: an organism’s inherited physical appearance (blue eyes, tall)
● Genotype: the inherited combination of alleles (BB, Tt)
Know how to read and draw a Punnett Square.
Understand what a complementary strand of DNA is.