UNIT IV
Genetics
I. Genetics
A. Mendel – father of genetics
• Inheritance – traits carried on
chromosomes
• Genes – code for certain traits
• Alleles – same gene, different
trait
B. Principle of dominance –
dominant trait will express
itself
1.Dominant traits –
expresses , shows up
2.Recessive traits – will
only show up if both
recessive alleles are
present
C. Genotype – gene, “code”
R = red & r = white
1. Homozygous dominant – 2 dominant
alleles (RR = purebred)
2. Homozygous recessive – 2 recessive
alleles (rr = purebred)
3. Heterozygous – one dominant and
one recessive allele (Rr = hybrid)
D. Phenotype – how genotype
expresses itself , “looks like
C.Punnett square – prediction of pairing
• R = red, r = white
• Genotypes all Rr
R
R
• Phenotypes all red
RR x rr
Rr
r Rr
Heterozygous(hybrid)
cross
r
•R = red, r = white
•Genotypes 1 RR, 2 Rr, 1 rr
•Phenotypes 3 red, 1 white
•Rr x Rr
Rr
Rr
R
r
R
RR
Rr
r
Rr
rr
D. Incomplete dominance – heterozygous
“blending” of dominant and recessive trait
• Genotypes all Rr phenotypes all pink
RR x rr
R
r Rr Rr
r Rr Rr
• 1RR = red, 2Rr = pink, 1 rr = white
R
r
R
RR Rr
r
Rr rr
• 2 pink and 2 white
R
r Rr rr
r Rr rr
r
R
E. Codominance – if heterozygous, both traits
are expressed
Blood types : antigens A, B, AB, O
AB blood - both A and B antigens are present
Positive blood is a separate gene Rh d antigen
F.Multiple alleles – traits expressed on more
than two alleles
1. 3 or more alleles – combinations of alleles
 genotype AABBCCDD whats the
phenotype
2. Human examples
• Hair color – 3 alleles (9)
• Eye color – 3 alleles (9)
• Skin color – 8 alleles (64)
G.Polygenic system – interaction of multiple genes,
determines phenotype
1. Continuous variation – full range of phenotypes –
2. Discontinuous variation – phenotype fall into a few
well separated categories
H. Environmental Influence on gene
expression
1. sun exposure, cold
example: siamese cat and himalayan darker
color on ears, face and paws
I. Principle of segregation
1. Gametes – separation of alleles – occurs
during meiosis
2. Parental – purebreds homozygous,
dominant or recessive (RR x RR or rr x rr) P
generation = RR x rr
3. First filial – F1 generation, offspring of P
generation, hybrids – heterozygous Rr
4. Second filial – F2 offspring of hybrid cross,
phenotype ratio 3:1
J. Independent assortment
•
•
•
•
•
•
Dihybrid cross –TtGg x TtGg
predicted phenotypes 9:3:3:1
T = tall
t = dwarf
fill this in
G = green
g = albino
Being black, sire and dam must both be B-E-; having produced yellow and chocolate
pups, each must also have the b and e alleles, so in each case the genotype is BbEe. A
BbEe parent can contribute the four combinations of alleles BE, bE, Be, and be to
various pups.
Punnett Square for BbEe sire bred to BbEe dam
Dam can contribute
*
Sire
can
contribute
BE
bE
Be
be
BE
BBEE
BbEE
BBEe
BbEe
bE
BbEE
bbEE
BbEe
bbEe
Be
BBEe
BbEe
BBee
Bbee
be
BbEe
bbEe
Bbee
bbee
BBEE (1 pup in sixteen or 6.25%) black
BbEE (2/16 or 12.5%) black
BBEe (2/16 or 12.5%) black
BbEe (4/16 or 25%) black
bbEE (1/16 or 6.25%) chocolate
bbEe (2/16 or 12.5%) chocolate
BBee (1/16 or 6.25%) yellow
Bbee (2/16 or 12.5%) yellow
bbee (1/16 or 6.25%) yellow with brown nose and light eyes
II. Human genetics
A. Karyotyping – human chromosomes
1. Autosomal – 22 pairs of somatic
2. Sex chromosomes – 1 pair XX or XY
B. Pedigree – genetic
relationship in families
http://www.zerobio.com/drag_gr11/pedigree/pe
digree1.htm
C. Abnormalities –
different
from the norm
D. Disease –
serious disorders
or abnormalities
caused by genes
III. Human genes
A. Autosomal recessive inheritance – must
have both recessive alleles
1. Albinism – aa , can’t make melanin
2. Tay-sachs disease – at 6 months
develops spot on retina  blindness,
death
3. Cystic fibrosis – most common 1/2500
children
4. Lactose intolerance – don’t have lactase
5. Sickle cell anemia – red blood cells,
sickle shaped – so can’t carry O2 well
and get stuck in capillaries
B. Autosomal dominant inheritance – two
dominant alleles or heterozygous
1. Darwin tubercle – thickened rim of cartilage
in ear
2. Achondroplasia – dwarfism
3. Huntington’s disease – manifests in 30’s or
40’s, loss of muscle control, loss of brain
tissue
4. Polydactyly – 6 fingers or toes
IV. Sex-linked human inheritance – traits carried on
the x chromosome
A. Sex – linked disorders
XX normal female,
X-X female carrier,
X-X- afflicted female,
X-Y afflicted male,
XY normal male
1. Hemophilia – bleeding disorder X-Y
or X-X2. Colorblindness – red- green –blue ,
X-Y or X-X-
V. Incorrect chromosome number – any number
but 46 in humans (Down syndrome- 47)
trisomy on the 21st chromosome
A. Disjunction abnormalities – extra or too
few, occurs in meiosis, can also result in
some degree of mental retardation and
increased risk of diseases and defects
1. Turners syndrome: XO
2. Klinefelter syndrome: XXY
3. Meta or super female: XXX
4. Jacob syndrome: XYY
VI. Gene Regulation in Eukaryotes
• Female cat cells inactivate one of two X
chromosomes in every cell (producing a Barr
body)
– Different patches of skin cells in a cat inactivate
different X chromosomes
– Patches of fur growing from skin cells may differ in
color if fur genes on X chromosomes differ
VII. Structural abberrations
A. Deletions – part of chromosome is missing,
cri-du-chat syndrome #5, leukemia #21
B. Inversions –part of chromosome is reversed
C. Translocation – part of one chromosome
breaks off and attaches to another
chromosome
D. Duplications – chromosome replicates genetic
material it already has
VIII.Genetic screening
• Ethical issues
• insurance
I.
Chemical nature of genes
A. Coding capacity – genes carry codes produces traits
in the organism
B. Transformation – A T G C
Adenine Thymine Guanine Cytosine
nucleotide code for all traits
II.
DNA – deoxyribonucleic acid
A. Base composition
•
Chargaff’s rule –
•
A – T, T – A, G – C, C - G
B. Double helix model – 1953 by Watson and Crick –
nucleotides form rungs of ladder, phosphate and
ribose (sides)
1.
2.
3.
Purines – 2 carbon ring, adenine and guanine
Pyrimidines – single carbon ring, thymine and cytosine
Base pairing – A  T, G  C
III. DNA replication
A. Template – bases need to form a complimentary strand
B. DNA polymerase – enzyme which separates the base pairs –
separates the DNA molecules
IV. Mutations
•
Alteration of the bases
I.
RNA – ribonucleic acid – one strand
A. Composition – CG, AU , cytosine, guanine, adenine,
uracil
B. Function – carry DNA instructions to various cell parts
C. Protein synthesis – code for amino acid sequences
D. Messenger RNA – mRNA, carries DNA
instructions “codons”
E. Transfer RNA – tRNA, translate the code
“anticodons”
F. Ribosomal RNA – rRNA, from code puts
amino acids together to form proteins
G. RNAi- interference RNA- destroys
“suspect” codes such as viruses
RNA Intermediaries
• There are three types of RNA involved in
protein synthesis
– Messenger RNA (mRNA) carries DNA gene
information to the ribosome
– Transfer RNA (tRNA) brings amino acids to the
ribosome
– Ribosomal RNA (rRNA) is part of the structure of
ribosomes
II.
Transcription – mRNA carries the code
DNA
C–G
T–A
G–C
A–T
C–G
G–C
mRNA
tRNA amino acid
C
G
U
A
aspartic acid
G
C
A
U
C
G
cysteine
G
C
(transcription) (translation)
(codons)
anticodons
III. Translation – tRNA translates the code
IV. Protein synthesis – rRNA makes the protein
rRNA
assemble
amino
acids
make
the
protein
I.
Genetic engineering
A. Recombination in nature
1. Mutations
2. Crossing over
3. Selective breeding
B. Plasmids – DNA bearing units (rings) that lie
outside of bacterial chromosomes used to
incorporate DNA sequences – then clone
B.Restrictive Fragments
1.Restriction enzymes – cut
DNA at specific places –
looks for recognition
sequence
2.Gel electrophoresis –
sizing DNA fragments
D. DNA sequencing – PCR
polymerase chain reaction –
make millions of copies of DNA
sequence
II. Gene manipulation – patented mice, genes
inserted into eggs of organisms
A. Gene insertion – edit the code, frost resistance,
drought resistance, BT corn
B. Genetic engineering of bacteria – insert human
DNA into bacteria, human insulin, HGH
C. Cloning – make an exact genetic copy,
reproductive cloning = Dolly
1. Recombination DNA – Polly, human
DNA for factor IX inserted into sheep
donor cell
2. Xenotransplantation – transplanting of
organs from one species to another
From bacteria (E. coli) and fungus, fruits and vegetables to animals, genetic
manipulation is becoming more and more common in our society. In the US
market now, 60-70% of the processed foods are genetically modified. In 2006,
United States GMO crops reached just shy of 135 million acres, with the total
global area exceeding 250 million acres!¹
This is a short list of the genetically modified food crops that are grown in the
US today:
Corn
Soy bean
Sugar cane
Tomatoes
Potatoes
Sweet peppers
Bananas
Strawberries
Zucchini
Pineapples
Cocoa beans
Yellow squash
III. New human genetics – human genome project,
20,000genes –30,000 genes, 3 billion base pairs
A. Genetic disease – 1,112 disease related genes,
400 base pairs identified
B. Genetic testing: ethical issues –
C. cloning vs. variety,
D. diagnostics vs. treatment
IV. Genetically modified foods
• Golden rice, bacteria + daffodil genes, makes beta
carotene  Vitamin A
• Bt corn & cotton bacteria produces insecticide
• Herbicide resistant soybeans
Concerns: allergies, hybridize
V. Stem Cells