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Unit 4
Genetics and Advances in
Genetics
Genetics
• The study of
heredity
GregorMendel
• Father of Genetics
• Lived 1822-1884
• Austrian monk
who worked with
pea plants
Summary of Mendel’s Work
• Genes are located on
chromosomes.
• Variations of genes are called
alleles.
• For each characteristic, an
organism inherits 2 alleles.
– If the alleles are the same,
the individual is
homozygous.
– If the alleles are different,
the individual is
heterozygous.
• The allele expressed in a
heterozygous (Bb) individual is
called dominant.
– A capital letter is used to
represent the name of the
dominant allele (B)
• The masked allele in a
heterozygous (Bb) individual is
called recessive.
– The lowercase version of the
same letter represents the
recessive allele (b)
Genotype- genetic makeup or
allele combination (BB,Bb, bb)
Phenotype- observable trait
(Black or White)
Detached (free) Lobes are
dominant over attached lobes
Tongue Rolling is dominant
over non-rolling
Ear Wiggling is dominant over
non-wiggling
https://www.youtube.com/watch?v
=2y9ihlB9xJI
Dimples are dominant over
non-dimples
Hand clasping left thumb on
right is dominant over right
on left
Cleft chin is dominant over
non-cleft chin
Widow’s Peak is dominant
over straight hairline
Mid-digital hair is dominant
over non-mid-digital hair
Phenylthiocarbamide Tasting
(PTC) is dominant over nontasting
Monohybrid Cross- pairing
in which parents differ in only
one trait (flower color)
Trends to expect in monohybrid crosses….
 The crossing of 2 heterozygotes results in a 1:2:1
genotype ratio and a 3:1 phenotype ratio
 If 1 parent is homozygous dominant, 100% of the
offspring will have the dominant phenotype
 If 1 parent is heterozygous and the other homozygous
recessive, there will be a 50:50 ratio or dominant to
recessive phenotypes
 “Test Crossing” a dominant phenotype individual
with a homozygous recessive individual will
determine if the dominant phenotype expression is
homozygous or heterozygous
Dihybrid Crosses… and tri- and tetra- and penta-…….
• Genetic cross between individuals differing in 2 traits
– A dihybrid cross of 2 heterozygotes results in a 9:3:3:1
phenotype ratio
– Each trait maintains its 3:1 phenotype ratio
• The probability of two traits being inherited together
is the product (x) of their individual probabilities.
Let’s practice…
Problem A: Suppose that black hair (B) is
dominant over blonde hair (b) and brown eyes (E)
are dominant over blue eyes (e). Cross a
completely recessive person with a blonde hair and
heterozygous brown eyed person.
1. What percent of the offspring will be
totally heterozygous?
2. What is the phenotype ratio?
3. What percent of the offspring will have
blonde hair and blue eyes?
Problem B: Yellow fruit and dwarf vines are
recessive traits in tomatoes. Red fruit and tall vines
are dominant. Cross a completely dominant red
and tall plant with a heterozygous red and dwarf
plant.
1. What percent of the offspring will be
totally heterozygous?
2. What is the phenotype ratio?
3. What percent of the offspring will have
yellow fruit and dwarf vines?
Problem C: Using the same traits, cross
heterozygous red and dwarf plant with a yellow
and heterozygous tall plant.
1. What percent of the offspring will be
totally heterozygous?
2. What is the phenotype ratio?
3. What percent of the offspring will have red
fruit and dwarf vines?
Intermediate/ Incomplete Dominance
• Neither allele
is dominant
• Heterozygotes
have a
phenotype
that is the
intermediate
of the two
phenotypes
Codominance
• Both alleles are
expressed in
heterozygotes
Multiple Alleles and Codominance
Type A
Type B
Type AB
Type O
Multiple Alleles
– More than 2 alleles for a given trait
• (ex) A, B, and O alleles
Codominance
– Heterozygotes express both alleles (not blended)
• (ex) Type AB blood
AA or Ao
BB or Bo
AB
oo
Multifactorial Inheritance
• Traits controlled by more
than one factor (genes,
environment, diet, exercise,
medication, etc.)
– Diabetes (chromosome 6)
– Asthma (chromosome 5)
– Obesity (chromosome 7)
Polygenic Inheritance
•
•
•
Traits coded by more
than one gene
– Eye color (11, 12)
– Skin color (1,2
and 4)
– Hair color
(3,4,10 and 18)
Phenotypes are the
combined effect of
more than 1 pair of
alleles
Usually a spectrum
of phenotypes
Linked Traits
• Traits coded by
genes located on the
same chromosome
• The closer they are
on the same
chromosome, the
more likely they’ll be
inherited together.
X-Linked Traits
• Traits coded by
genes on the X
chromosome
– Females have 2
alleles
– Males have 1 only
– Men are more likely
to express recessive
X-linked traits
because only 1
recessive allele is
required for
expression.
http://www.iflscience.c
om/plants-andanimals/why-arewomen-stripy
Homologous
Chromosomes
•
Pairs of chromosomes.
– One inherited from mother.
– One inherited from father.
•
Identical in size, centromere
position, and the traits they code
for
Karyotype
•
•
•
Visual display of an individual’s
chromosome pairs
Pairs 1-22 are autosomes (code
for most body traits)
23rd pair are sex chromosomes
(determines the sex of the
individual)
Chromosomal Errors can
cause disorders
Nondisjunction
homologous chromosomes
or sister chromatids failing
to separate during meiosis
Even if all chromosomes are present
in normal numbers in a cell, changes
in chromosome structure may also
cause disorders
Jeans for Genes Films
http://www.jeansforgenesday.org/disorders/childrensfilms
A pedigree is a family tree that
traces the occurrence of a trait in a
family.
Autosomal Dominant Inheritance
Usually
expressed in
every generation
Equally
expressed
among males
and females
Autosomal Recessive Inheritance
Usually skips generations
Equally expressed by both
males and females
Recessive Sex-Linked Inheritance
Usually skips
generations
Mostly
affects males
What do you think?
Sex-Linked
Recessive
Inheritance
What do you think?
Dominant
Inheritance
http://learn.genetics.utah.edu/units/addiction/genetics/pi.cfm
University of Utah Online Pedigree Activity
Ghost in Your Genes
https://www.youtube.com/watch?v=fMxgkSgZoJs
The role of Bacteria in
Recombinant DNA Biotechnology
• Vectors (vehicles) for gene
delivery.
Many bacteria contain
plasmids.
– Small, circular DNA separate
from the bacterial
chromosome
– Capable of replicating itself
• one copy can pass from one
bacterial cell to another,
resulting in gene "sharing"
among bacteria
Recombinant DNA
Techniques
Restriction Enzymes
• Found in nature in
bacteria
• recognize specific
nucleotide sequences in
DNA
• make staggered cuts
leaving single-stranded
DNA on the ends (called
“sticky ends”).
– complementary sticky
ends join together by
base-pairing
– DNA ligase, "pastes" the
sticky ends together
Cloning Recombinant DNA
Gel Electrophoresis
Used to compare DNA samples
from different sources
Genetic Markers are segments of
DNA that are variable among
individuals (introns)
1.
2.
3.
4.
DNA is collected from the
crime scene and suspect(s).
DNA is copied to make
enough DNA to work with.
Genetic markers (introns)
are removed from each
sample.
DNA samples are digested
by the same restriction
enzyme(s) and run on a gel
for comparison.
DNA Fingerprinting
Crime scene and suspect DNA are treated
with the same restriction enzyme (cuts samples
in unique sequence)
DNA fragments are negatively chargedattracted to positive end (allows them to travel)
Small segments travel faster and further
Bands consist of fragments of equal length
Banding patterns are unique to the
individual (DNA fingerprint)
Paternity Testing
Lane 1 Standard
Lane 2 Mother
Lane 3 Child
Lane 4 Father #1
Lane 5 Father #2
Genetically Modified Organisms
Transgenic
Organisms contain
DNA from different
species
Genetically Modified Products
Pros
– Reduces the need for water
– Reduces the need for
fertilizers/ pesticides
– Greater yields than
conventional crops
– Faster growth
– Cold/heat resistant
– GM Foods can deliver
vaccines
– Nutrient enhanced foods
– Trees that produce new
plastics
BBC Documentary 2013 Genetically
Modified Foods in America
http://www.youtube.com/watch?v=G
GnRNYSvp0M
Cons
– Loss of biodiversity
– Allergic reactions
– Antibiotic resistance
– Pesticide/ herbicide
resistance
– Domination of world
food production by a few
companies
– Increasing dependence
on Industrialized nations
by developing countries
– Objections to consuming
animal genes in plants
– Stress on animal
Cloning
http://www.youtube.com/watch?v=e1VL4XiC9nM