III. Genetics & Genetic Engineering
Presentation # 3
Ch. 11, 13, & 14
• Gregor Mendel - the “Father of
Genetics”
• Was an Austrian monk
• Worked in a monastery garden
• Cross-pollinated plants, studied
traits (characteristics) of offspring
• Looked at true-breeding pea
plants - if pollinated produced
offspring identical to themself
• Looked at hybrids - the offspring
of crosses between parents of
different traits
Some of Mendel’s crosses:
Section 11-1
Seed Coat
Color
Pod
Shape
Pod
Color
Smooth
Green
Seed
Shape
Seed
Color
Round
Yellow
Gray
Wrinkled
Green
White
Constricted
Round
Yellow
Gray
Smooth
Flower
Position
Plant
Height
Axial
Tall
Yellow
Terminal
Short
Green
Axial
Tall
III. Genetics
– A . Terms to Memorize:
• 1. Gene - units of DNA passed from parent to offspring. Each adult has
two copies of each gene - 1 from each parent
• 2. Allele - a specific form or expression of a gene trait
– Example - brown eyes, Curly hair.
• 3. Dominant - an allele that is always expressed or seen
– Dark pigments are usually dominant
• 4. Recessive - an allele that is can be hidden, it will not be
expressed if present with a dominant allele
• 5. Phenotype - actual gene expression - what is physically seen
• 6. Genotype - the actual pair of alleles present
– Homozygous = same 2 alleles in gene pair BB, bb (purebred)
– Heterozygous= = different alleles present in gene pair Bb, Tt (Hybrid)
• 7. Probability - the likelihood that a particular event will occur
- Q:If you flip a coin 4 times in a row, what is the probability that it will land
on tails every time?
- A: 1/2 x 1//2 x 1/2 x 1/2 = 1/16
Each coin flip is an independent event.
- Q: What is the probability of having 3 girls in a row?
- A: 1/2 x 1//2 x 1/2 = 1/8
Each baby is an independent event.
III. Genetics
Probability can help us predict the outcomes of genetic crosses.
– B. Genetic Crosses
• 1. Monohybrid - 1 trait crosses
–
–
–
–
–
–
–
Studies 1 set of alleles from both parents
a) identify the trait and letters to be used - brown hair (B) or blond (b)
b) write the genotypes - i.e. Bb or BB or bb for both parents
c) separate the alleles into possible gametes b , B for each parent
d) draw a Punnett square and write one allele by each row and column
Join gametes together
Determine ratios
of phenotypes and
genotypes
B
B
b
B
III. Genetics
– B. Genetic Crosses
• 2.Dihybrid - 2 trait crosses
– Studies 2 sets of alleles from both parents
– Steps are the same but more complex because of more combinations
– To identify # of possible gametes - look at how many different alleles there are
for each trait then multiply.
– Example - BbFf - 2 different b’s and 2 different f’s 2x2=4
– Use foil to get possible gametes f-firsts, 0-outer, i-inner, l-lasts
– Use punnett square to determine offspring
Dihybrid Cross
BF
Bf
BF
BBFF
BBFf
BbFF
BbFf
Bf
BBFf
BBff
BbFf
Bbff
BbFF
BbFf
bbFF
bbFf
BbFf
Bbff
bF
bf
bF
bbFf
bf
bbff
An example of a
Dihybrid cross
Section 11-3
Another Dihybrid cross:
III. Genetics
– B. Genetic Crosses
• 3. Incomplete Dominance
– Two alleles are neither dominant or recessive
– The two show a blending of their phenotypes
– Example: red carnations crossed with white carnations produce all pink
carnations
– CRCR= red CWCW = white CRCW = pink
• 4. Co dominance
– Two alleles are both dominant or expressed at the same time
– Example: hair color in cattle Red and White hair crossed = Roan
– HRHR = red hair
HWHW = white HRHW = roan (red and white hair)
Incomplete
Dominance:
III. Genetics
– B. Genetic Crosses
• 5. Polygenic traits
–
–
–
–
More than one gene will determine phenotype
Hair color in humans is controlled by more than one gene
Eye color in humans also is polygenic
Epistatic traits - one gene exerts control over another gene expression.
- Ex: More than 12 pairs of alleles interact in various ways to produce coat
color in rabbits.
- Ex: 2 gene pairs interact together to produce 8 types of combs in roosters.
• 6. Multiple Alleles
– More than two alleles are possible for one gene
– Example: Blood type
» Type A = “A” antigen on the blood cell
» Type B = “B” antigen on the blood cell
» Type O = NO antigen on the blood cell
IA = A allele
IB = B allele
i = O allele
Multiple alleles- Blood Typing
Polygene inheritance
III. Genetics
– C. Genetic Disorders/Diseases
• 1. Detection - obtaining fetal cells to do karyotyping and biochemical tests
– A) amniocentesis (see next slide)
– B) Chorionic villus sampling (see next slide)
• 2. Sex-linked traits - genes only found on the X or Y chromosomes
– A) colorblindness
– B) hemophilia
– C) muscular dystrophy
– Do a Punnett Square example:
• Question:
•Can 2 normal parents have
a colorblind child? If so, what is
the sex of that child?
• A: Yes (If mom is a carrier). Male.
XC
Xc
XC
XCXC XCXc
Y
XCY
XcY
III. Genetics
– C. Genetic Disorders/Diseases
• 4. Gene mutations - changes in DNA sequence caused by exposure to radiation or
chemicals, crossing over or genetic errors
– Sickle-celled anemia - blood cells are misshaped due conditions of low oxygen
» Recessive trait, no known cure
– Cystic fibrosis - recessive allele, causes thick mucous build up in the lungs and
intestines, can cause liver disease, diabetes
» Recessive trait, no know cure
– Tay-Sachs - slow degenerative disease of optic and mental function in
young children
» Recessive trait carried on chromosome 15, no known cure
D. How have humans created new breeds?
www.vwgs.com/
• Selective Breeding - allowing
only those animals with desired
characteristics to produce the
next generation.
• Ex: breeds of dogs, horses, cats,
farm animals, crops.
• Hybridization - crossing
dissimilar individuals to bring
together the best of both
organisms. Ex: daisies, crops
• Inbreeding - continued breeding
of individuals with similar
characteristics.
• Ex: Golden retrievers, German
shepherds
• All of the above have been done
for years, without altering the
genetic code.
IV. DNA Technology
– A. Genetic Engineering-making changes in the DNA code
• Restriction Enzymes- proteins that “cut” DNA at specific locations,
looks for a certain nucleotide (base) sequence
• DNA recombination
– Cutting and splicing pieces of DNA into other strands of DNA
» Plasmids - circular DNA molecules found in bacteria, separate
from other bacterial DNA
» Sticky ends - matching or complimentary segments of DNA that are
produced by restriction enzymes
» Human genes can be inserted into bacterial plasmids so the bacteria can
produce human enzymes or proteins = recombinant DNA
How restriction enzymes are used to edit DNA:
• Enzymes cut the DNA molecule at a certain site.
• Different restriction enzymes recognize and cut different sequences of
DNA.
• The cut ends are called sticky ends because they may “stick” to other
complementary bases by means of H bonds.
• Can then take a gene from one organism and attach it to the DNA of
another organism = Recombinant DNA.
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Overview: Making a
Recombinant DNA
molecule.
• Ex: Genetically Engineered
Insulin - Produced by
splicing the human gene for
making insulin into the
plasmid of E.coli host cells.
• The genetically modified
bacteria then produces
insulin; it is collected and
used for diabetics.
• Was 1st recombinant DNA
drug approved for use in
humans.
• Another Ex: Human Growth
Hormone
Example: Steps in producing Human Growth Hormone
Example of Using DNA Technology:
DNA Fingerprinting:
Process of cutting apart DNA from two
sources and comparing the results from gel
electrophoresis.
Utilized in criminal investigations and
paternity/maternity cases. (No individual is
exactly alike.)
Weblink
http://www.pbs.org/wgbh/nova/sheppard/labwave.html
DNA Fingerprinting Procedure:
Gel enzyme.
Electrophoresis
• A small sample of DNAFigure
is cut with13-6
a restriction
(From sperm, blood, hair, or other material.)
Section 13-2
• The DNA fragments are separated by size using gel electrophoresis.
• The shorter fragments move faster toward the + charge.
• Patterns of bands are compared to see if suspect’s band pattern is the same as that of the
crime scene material.
Power
source
DNA plus restriction
enzyme
Longer
fragments
Shorter
fragments
Mixture of DNA
fragments
Gel
Applications of Genetic Engineering:
www.mun.ca/.../Luciferase_ reporter_gene.htm
• Transgenic Organisms - they
contain genes from another
species
• Examples:
• tobacco plant which glows in
the dark (see top photo)
• corn which produces a natural
pesticide
• mice with similar immune
systems as humans - are used
study effects of diseases
• sheep which carry a gene for a
human blood protein. They
secrete it in their milk - helps
patients with cystic fibrosis.
(See GM sheep, bottom photo)
More applications of Genetic Engineering: Cloning.
Steps of cloning:
Section 13-4
A donor cell is taken from
a sheep’s udder.
Donor
Nucleus
These two cells are fused
using an electric shock.
Fused Cell
Egg Cell
The nucleus of the
egg cell is removed.
An egg cell is taken
from an adult
female sheep.
The fused cell
begins dividing
normally.
Embryo
Cloned Lamb
The embryo
develops normally
into a lamb—Dolly
Foster
Mother
The embryo is placed
in the uterus of a foster
mother.
Decision Making - Safety and Ethical Issues of
DNA Technology:
• Can DNA technology create hazardous
new pathogens? Could they escape
from the lab?
• Is genetically modified food safe to eat?
• Can transgenic plants pass their new
genes to other plants in wild areas?
• Who should be allowed to take Human
Growth Hormone?
• Should we try to eliminate genetic
defects in our children?
• Should everyone get a DNA fingerprint
ID?
• Can the Human Genome Project result
in human health discrimination?
Chromosomal Abnormalities and
Nondisjunction
• Nondisjunction in meiosis results in gametes with
abnormal chromosome number
• Most cases produce gametes that are not viable
Down Syndrome – Trisomy 21
• Extra 21st
chromosome
• Causes physical and
mental abnormalities
Trisomy 18
Edward’s
Syndrome
Trisomy 13
Patau’s
Syndrome
Turner’s Syndrome
• Female with only one X
chromosome (XO)
• Sterile
Klinefelter’s Syndrome
• Male XXY, XXXY, or XXXXY
• Sterile
Jacob’s Syndrome (XYY)
• Men are mostly normal
• Increased aggression
and learning
disabilities