GENETICS OVERVIEW
REMINDER YOUR UNIT 6 TEST IS TOMORROW!! YOU NEED TO KNOW AND
UNDERSTAND THE FOLLOWING!!
DNA Structure and DNA Replication
o DNA = Deoxyribonucleic acid = the genetic code =
nucleic acid
o DNA made of a sugar (deoxyribose), a phosphate group and a
base (Adenine, Thymine, Guanine or Cytosine)
o DNA is made up of nucleotides 
o A nucleotide is a sugar, a phosphate and a base
o The base pairs are “complimentary”, meaning Adenine always bonds with Thymine and
Cytosine always bonds with Guanine.
o The complimentary strand to TGA-GCC is ACT-CGG
o DNA is double stranded and in the shape of a double helix
o The bases (A,T, C and G) are held together by weak
hydrogen bonds
o The order of the bases (A,T,C and G) helps determine
different characteristics/traits (eye color, fur
thickness, height, etc) by coding for specific proteins
(refer to protein synthesis) =
GENETIC CODE!
o In eukaryotes, DNA is found in the
nucleus. Is prokaryotes, DNA is found
“floating” in the cytoplasm
o Before a cell can divide, the DNA must
replicate.
o Because DNA is ALWAYS in the nucleus,
DNA replication takes place in the
nucleus
o Once there are two identical stands of DNA, the cell can divide into two new cells (each
getting a strand of DNA)
Meiosis
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Makes gametes (sex cells- sperm and egg)
Makes FOUR cells/gametes
These four gametes/cells are not identical to one another
or the parents (this is why you and your siblings aren’t
identical to one another or your mom/dad)
These four gametes/cells are not identical to the parents
Gametes have 23 chromosomes 23 for the sperm, 23 for
the egg
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Meiosis has two divisions of the
nucleus: P1,M1,A1,T1, and then
repeats P2,M2,A2,T2.. cytokinesis
(refer to mitosis)
The gametes produced are
HAPLOID
Sexual reproduction produces
MORE genetic variation than
asexual reproduction
Crossing over provides new
combinations of genes that are
different than the parents.
Happens in prophase 1
Independent assortment is when
homologous chromosomes are distributed randomly during meiosis
PROTEIN SYNTHESIS:
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Protein Synthesis in a nutshell:
o mRNA is made from the DNA found in the nucleus
o making mRNA from DNA is called TRANSCIPTION and takes place in the
nucleus
o G bonds with C, and A bonds with U
o If DNA read ACT-GCA the mRNA made would be UGA-CGU
o Once the mRNA is made, it leaves the nucleus and travels through the cytoplasm
o mRNA attaches to the ribosome (which is floating in the cytoplasm)
o At the ribosome, mRNA provides the codon that “tells” tRNA what amino acid it needs
to bring to the ribosome.
o tRNA is floating in the cytoplasm attached to a specific amino acid
o if mRNA read AUG-CGA the tRNA that would attach to it would be UAC-GCU
o The amino acid that tRNA brings would be:
o The process of tRNA bringing mRNA amino acids at the ribosome is called
TRANSLATION
o Translation takes place at the
ribosome/cytoplasm
o To determine what amino acid
tRNA needs to bring you can use a
codon table chart YOU USE THE
mRNA TO READ THE CHART:
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mRNA read AUG- CGA so the amino acids
that tRNA needs to bring to the
cytoplasm are Methionine/initiation codon
and Arginine.
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A chain of amino acids = 1 protein
If you changed the DNA template/code because of a mutation, it would most likely
change the protein being made.
Chromosomes/Karyotypes
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ChromaTIN is THIN threadlike DNA
When chromatin is coiled up it is called a ChromaTID
Two sister chromatids make up a chromosome
Sister chromatids are held together by a centromere
Chromosomes look like this -
They contain the DNA that make up genes that
make us who we are
A GENE is a segment of a
chromosome (or an allele =
different form of a gene)
genes can be affected by THE
ENVIRONMENT!
Humans have 23 pairs of chromosomes for
a TOTAL of 46.
So, humans have 46 total chromosomes
A karyotype is a picture of
chromosomes arranged from largest
to smallest
Genetics
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Phenotype is what you see- purple,
wrinkles, freckles, etc
Genotype are the letters, and code for
phenotype BB, Bb, bb
Homozygous/Purebred- same sized
letters- BB, bb, TT, tt, PP,pp
Heterozygous/Hybrid- different sized
letters- Rr, Tt, Bb
Gregor Mendel is the father of genetics- he studied pea plants
Dominant Alleles are always seen and can mask recessive alleles!
Monohybrid cross:
A heterozygous blue flower is crossed with a homozygous white flower.
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Dihybrid cross:
A heterozygous tall, green pea plant is crossed with a homozygous short, heterozygous green
pea plant.
Parents:
Gametes:
Dihybrid Probability:
1. In a rabbit, Brown fur (B) is dominant to white (b) and Long fur (L) is dominant to short fur (l). What percent
of the offspring is expected to be heterozygous for both traits when crossing the following parents:
BbLl
x
bbll
2. In a rabbit, Brown fur (B) is dominant to white (b) and Long fur (L) is dominant to short fur (l). What percent
of the offspring is expected to be BBLl when crossing the following parents:
Bbll
x
BBLl
3. What is the expected phenotype when crossing:
BBLl
X
bbll
4. If given the following egg cell, what would its gametes look like?
BbLl
Ll