Download Study Guide for LS

Study Guide for LS. 12 Test
Know the following facts:
DNA:
- DNA is shaped like a double helix or a twisted ladder.
- In a DNA strand, the rungs (the part you step on) of the “ladder” are made of nucleotide bases.
- In a DNA strand, the sides of the “ladder” are made of alternating sugar and phosphate
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molecules.
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.
- In DNA there are four different bases: Adenine, Thymine, Cytosine, and Guanine.
- In DNA, Adenine pairs with Thymine, and Cytosine pairs with Guanine.
Mutations:
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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.
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 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.
Not all mutations are harmful. Some mutations are beneficial, and others have no effect at all.
A mutation in DNA could also result in death or a genetic disorder.
We have certain enzymes that repair most DNA mutations.
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.
A disease that occurs when a child inherits a mutated gene from parents who do not have the
disease is a recessive disorder.
Important People:
- Rosalind Franklin was able to create images of DNA molecules and discover that DNA was
spiral shaped.
- Watson and Crick made models to determine DNA structure.
- According to Chargaff’s rules A always pairs with T and C always pairs with G.
- Punnett developed a square that is used to visualize all the possible combinations of alleles in
offspring resulting from a genetic cross.
- Mendel used pea plants to study the way traits are passed from one generation to the next.
- Gregor Mendel is considered the father (first to discover) of genetics.
Pedigree Charts:
- 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.
Other important facts:
● 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)
ALSO:
Know how to read and draw a Punnett Square.
Understand what a complementary strand of DNA is.