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Genetic material found in the nucleus of
eukaryotic cells; in the cytoplasm of
prokaryotes (no nucleus)
A library of genetic information (genes)
located in the nucleus of eukaryotic cells
Made up of one long DNA molecule
wrapped around chunks of protein

Organisms have 2 different types of cells
 Body
(somatic) cells: skin, liver, brain
These cells each have a Complete Set
of chromosomes (46, or 23 pairs)
 Sex cells (gametes): sperm and egg

Because sperm and egg need to meet and
combine their chromosomes to form a new
individual, they have ½ the number of
chromosomes as body cells (23)
Normal Human
Karyotype:
 46 chromosomes


44 autosomes


23 pairs
22 pairs
2 sex chromosomes

1 pair
 XX = female
 XY = male
“TRISOMY 21”
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
A Double helix ladder of connected nucleotides
forming a sugar-phosphate “backbone” and
nitrogen base “steps”
Each nucleotide of DNA consists of:



A sugar “deoxyribose”
A phosphate
A nitrogenous base:
 Adenine
 Cytosine
Thymine
Guanine
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

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Double-helix/spiral ladder
Sugar-phosphate “backbone”
Bases are rungs of ladder
Long sequences of bases make up genes


Bacteria make a copy of their DNA strand
Then splits in two, creating two bacteria.
Mitosis: Division of a cell into BODY cells.
(Body cells = Somatic = liver, brain, skin, etc)
First, DNA is copied, then the nucleus of
eukaryotic cells divide, each new nucleus has a
complete set of chromosomes.
(Really, mitosis = nuclear division)
 Cytokinesis: Cell Division.
The eukaryotic cell divides into two cells, each
with its own nucleus
***These two parts of the cell cycle are often
combined and called ‘mitosis’


Mitosis + Cytokinesis = 2 new cells with the
same genetic information as the original cell
KEY TERMS:
Haploid Cells: The number of
chromosomes in a sex cell
n = 23 in humans
(Sex cells = Gametes = sperm, egg)


Diploid Cells: The number of
chromosomes in a somatic cell
2n = 46 in humans
 The
division of a cell into sex
cells. The number of
chromosomes in the nucleus
is halved. (46 to 23)
n=23
human
sex cell
n=23
sperm
n=23
2n=46
haploid (n)
diploid (2n)
Crossing-over
occurs at this
stage
n=23
n=23
n=23
4 genetically different
gametes are produced
homologous pairs
Tetrad, homol. pairs together
Tetrad
This causes genetic
variation


Nondisjunction is when the chromosomes
don’t split evenly in meiosis, resulting in too
many or too few chromosomes in the sperm or
egg.
Examples of diseases/conditions caused by
non-disjuction:
Down’s Syndrome = 47
 Turner’s Syndrome = 45
 Klinefelter’s Syndrome = 47
http://www.biostudio.com/d_%20Meiotic%20Nondisju
nction%20Meiosis%20I.htm

Protein Synthesis: How DNA
turns the base sequence into
proteins
DNA  RNA  Protein
 1.The
Double Helix ‘unzips’
 2. A matching(complementary)
strand is made of each side,
making two molecules of DNA
Copying
DNA
before the
nucleus
divides
and before
cell
division



As the ‘original copy’ of ALL the cells genetic
information, DNA cannot leave the nucleus
DNA has ALL the genetic material, and cells
only need to use specific information
So a ‘working copy’ is made that can leave the
nucleus and make the needed proteins for the
cells to function.
DNA holds the instructions for the
manufacturing of protein.
This is done through protein synthesis -the
making of proteins from the instructions coded
by the sequence of bases in the DNA
1. Transcription: In the nucleus, the genetic
info is ‘copied’ from DNA to RNA in code.
2. Translation: The RNA leaves the nucleus
and the code is translated on ribosomes to
make specific proteins for gene expression
http://www.biostudio.com/demo_freeman_protein_synthesis.htm
1865 Paper Published by Gregor Mendel based
on his research with garden peas
1. Principle of Dominance and Recessiveness:
There are alternate forms of genes called alleles.
One factor in a pair of genes may mask the effect of
another.
Dominant allele: When only ONE of the alleles affects
the trait. (Use a CAPITAL letter)
Recessive allele: the allele that is NOT expressed if
there is a dominant allele present. (Use a small letter).
1865 Paper Published by Gregor Menel based on
his research with garden peas
 Homozygous – an individual who has the same
alleles for a trait. Ex. 2 genes for cystic fibrosis
(BB = homozygous dominant or bb = homozygous recessive)
 Heterozygous – an individual who has different
alleles for a trait. Ex. One gene for cystic fibrosis,
one for normal (Bb)
Genetics Terminology
Genotype – the genetic makeup of an
organism “Genes”
The many different alleles that an organism
can possess: BB or Bb or bb


Phenotype – the external appearance of
an organism. An organisms physical
appearance, determined by it’s alleles
“Photo”
Generations
 Parent generation = P
 Offspring of P generation = F1
 Offspring of F1 generation = F2
Cross a homozygous dominant purple flower
with a homozygous recessive white flower. Give
the F1 genotype and phenotype percents.
Purple = PP, white = pp
Sex-linked inheritance
 Males and females inherit some diseases with
different frequency.
 This is because the Y-chromosomes have
fewer genes, and with only one X for males,
there are no heterozygotes.
 Examples: hemophilia and color-blindness
 Punnett squares that separate the chances of
males and females getting diseases
How males and females inherit:
XN Y or Xn Y
XN XN or XNXn or XnXn
Pedigree Charts
 Pedigree charts follow a genetic mutation/disease
through several generations of a family.
 You can determine what chance offspring has of
having a disease based on family history and
Punnett Square.
 The main diseases that are tracked this way are:





Tay-sachs
Huntingtons
Colorblindness
Hemophilia
Cystic fibrosis
Basic Symbols
How to read a pedigree
PHENOTYPES
Clear = unaffected
Shaded = affected
GENOTYPES
Not usually
indicated, but
often can be
determined by the
phenotypes
Pedigree:
recessive
genetic
disorder
1. An
individual
who is
affected may
have parents
who are
unaffected.
2. ALL
children of 2
affected
parents are
affected
Pedigree:
Dominant
Inheritance
1.Every affected
individual has
at least one
affected parent
2. Affected who
mate with an
unaffected have
a 50% chance to
pass the trait.
3. Two affected
MAY have
unaffected
children
Sex-Linked Recessive
 males get their X from their





mother
fathers pass their X to
daughters only
females express it only if they
get a copy from both parents.
expressed in males if present
recessive in females
Outsider rule for recessives
(only affects females in sexlinked situations): normal
outsiders are assumed to be
homozygous.
#1 – sickle-cell
Autosomal Recessive (nn)
#4 - colorblindness
X-linked Recessive (Xn)
DiHybrid Cross:
The factors for
different traits are
sorted into the
gametes
independent of
each other.
S = Smooth pea
Y = Yellow Color
Independent Assortment
1. Determine all possible
combinations of alleles in the
gametes for each parent.
DiHybrid Crosses
2. List the
gametes
for Parent
1 along one
edge of the
punnett
square,
and the
gametes
for Parent
2 along the
other edge
DiHybrid Cross
3. Fill out the
squares with
the alleles
from Parent 2
The result is
the prediction
of all possible
combinations
of genotypes
for the
offspring of
the dihybrid
cross,
SsYy x SsYy.
A phenotypic ratio of 9:3:3:1 is predicted for the offspring of
a SsYy x SsYy dihybrid cross.
9 spherical yellow : 3 spherical green
:
3 wrinkled yellow : 1 wrinkled, green