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Meiosis, Genetics, and DNA
Study Guide
Meiosis
-Meiosis is the form of cell division that creates the reproductive sex cells. Meiosis in males creates
sperm cells and meiosis in females creates egg cells.
-Four daughter cells form as a result of meiosis.
-The cells that form as a result of meiosis are neither identical to each other nor identical to the original
parent cell.
-The reproductive cells formed through meiosis are said to be haploid, because they contain half the
number of chromosomes as the normal body cells of the organism. Body cells are said to be diploid.
For example, a human skin cell contains 46 chromosomes and a human reproductive cell contains 23
chromosomes.
-For the test, you need to be able to compare meiosis to mitosis.
-Which of the two processes creates haploid cells? Which creates diploid cells? Which creates cells for
growth and repair? Which has only one division of the nucleus? Which has two divisions of the
nucleus?
Genetics
-Who was Gregor Mendel?
-Why did he choose pea plants?
-What results did Mendel get with his pea plants? Did one trait show up more than another? If so, did
he see any particular pattern?
-Mendel thought that one factor blocked another factor. What did he call the factor that was being
blocked? What did he call the factor that was doing the blocking?
-How many factors did Mendel conclude control each inherited trait?
-Remember a Punnett square is a tool used to determine possible traits in offspring. When using a
Punnett square, the alleles for the male go across the top, and the female’s go across the side.
-Three possible genotypes exist: Homozygous dominant AA, Homozygous recessive aa, Heterozygous
Aa
-From the Punnett square we can determine possible genotypes and if we know what the alleles
represent, we can determine the phenotypes (what is looks like).
DNA
-The DNA molecule is the blueprint for life, meaning that it holds all the instructions for making a living
thing.
-DNA holds the instructions for making proteins.
-DNA is made of repeating segments called nucleotides. Each nucleotide has three parts a sugar, a
phosphate and a base. Four types of bases exist in DNA. The four bases are Thymine (T), Adenine (A),
Guanine (G), and Cytosine (C).
-Certain bases always pair with other bases. These are known as complimentary base pairs. A and T are
complimentary and C and G are complimentary.
-DNA needs to make a copy of itself to ensure that new cells that form through mitosis have an exact
copy of the DNA that was in the parent cell. The process of DNA copying itself is known as replication.
Prior to replication, the DNA molecule splits down the middle, and opens up like a zipper unzipping as
the bases pull apart from each other.
-As stated above, the goal of DNA is to make proteins. Proteins are assembled through a combination of
two processes, transcription and translation. These two processes allow for the instructions on DNA to
get out to the cytoplasm to build proteins.
-In transcription, the DNA message copies itself in the form of mRNA. Unlike DNA, mRNA is able to leave
the nucleus. The copy of mRNA takes the code for building a protein from the nucleus out to the
cytoplasm.
-In Translation, the mRNA is read by the ribosome 3 bases at a time. Each three base code on the mRNA
codes for a specific piece of tRNA. Each tRNA has a specific amino acid attached. The tRNA carries the
amino acid to the ribosome where the amino acid is dropped off and added to the prior amino acid.
When enough amino acids are strung together, you end up with a protein.
-RNA is very similar to DNA, but RNA is single stranded and has the base uracil in place of thymine.
-Sometimes when DNA replicates a mistake is made. These mistakes are known as mutations.
Mutations can be harmful, beneficial, or have no effect on the organism. Three types of mutations can
occur during replication. Deletion, substitution, and insertion. A deletion results when bases are left
out of the new DNA strand. In a substitution, a certain base has been replaced with a different base. An
insertion occurs when an additional base is added to the DNA sequence.
Terms to know:
Mitosis, fertilization, zygote, eggs, meiosis, sperm, genetics, homozygous, heredity, dominant factor,
recessive factor, alleles, pedigree, heterozygous, incomplete dominance, phenotype, multiple alleles,
DNA, nucleotide, replication, transcription, translation, RNA, mutation, base