Genetics:
From Genetic Screening to Plant Breeding
Joseph Geissler
Newark Science Park High School
Mrs. Paulose
Lesson Objectives
• What is genetics?
– The study of heredity in an organism or population
– The study of variation in an organism or population
• How can we investigate genetics?
– Punnett Squares
• Mendelian Patterns of Inheritance
– Complete Dominance
• How will you used these principles to grow tall
hairy plants???
Genotype vs Phenotype
• Genotype- the genetic makeup of an organism
– Hereditary information, the sequence of alleles
• i.e. RR, Rr, rr
• Phenotype- the expression of a genotype in
the appearance or function of an organism
– An physical, observable trait
• i.e. size, shape, color, growth
Genetic Nomenclature
• Allele- represents one copy of a gene; gene expression is
dependent on the strength of the two alleles
• Monohybrid cross- investigation of one trait
• Dihybrid cross- investigation of two traits
• Dominate trait: the presence of only one allele is needed
for gene expression
• Recessive trait: both alleles must be present for gene
expression
• Capital letters represent a dominate trait
• Lower case letters represent a recessive trait
Types of Genotypes
• Homozygous genotype ::
RR or rr
– Both alleles are the same (dominate or recessive)
– True-breeding organisms are homozygous for a particular
trait
• Heterozygous genotype ::
Rr
– Contains mixed alleles
– Observed in F1 plants of true-breeding cross
Punnett Squares of Probability
Monohybrid cross of two
true-breeding organisms
R
Monohybrid cross of two
heterozygous organisms
R
R
r
r
Rr
Rr
R
RR
Rr
r
Rr
Rr
r
Rr
rr
4 Dominate: 0 Recessive
3 Dominate : 1 Recessive
Autosomal Dominant Disorders
For inheritance, only one parents needs to be affected
One dominant allele confirms phenotype
Huntington’s Disease
Hypercholesterolemia
Autosomal Recessive Disorders
For inheritance, both parents must be either affected or a
carrier
Two recessive alleles confirms phenotype
Sickle-cell
Anaemia
Cystic
Fibrosis
Autosomal recessive disorders can be lost and reappear several generations later
X-Linked Recessive Disorders
Disorder is passed to a boy from its mother,
who is a carrier of the disease
Hemophilia
Color blindness
Gregor Mendel’s Investigation of
Pea Plant (1860s)
Determined dominant and recessive traits of pea plants by
performing monohybrid crosses
Self-pollinating and
cross pollinating
techniques used to
investigate individual
traits
Parental Generation
Cross pollination of two true breeding plants
R
Genotype
Phenotype
RR
rr
Round-seeded plants
r
R
Rr
Rr
Rr
Rr
Wrinkled-seeded plants
r
F1
generation
So, what is the phenotype of F1?
F2 Generation
Self-fertilization cross of F1 generation plants
R
r
R
r
RR
Rr
Rr
Genotype
Phenotype
RR
Round-seeded plant
Rr
Round-seeded plants
rr
Wrinkled-seeded plant
rr
Genotypic Ratio
Phenotypic Ratio
1 RR : 2 Rr : 1 rr
3 Round : 1 Wrinkled
Incomplete Dominance
Phenotype is an intermediate between the parents
Genotype
Phenotype
RR
Red Flower
Genotypic
Ratio
Rr
Pink Flower
1rrRR : 2 RrWhite
: 1Flower
rr
Phenotypic Ratio
1 red : 2 pink : 1 white
Blood Type
Multiple alleles
A,B, and i
Phenotype
Genotype
(Blood type)
Carbohydrate on surface
of red blood cells
Antibody Response
Type A
I AI A or I A i
A
Anti-B
Type B
I AI A or I B i
B
Anti-A
Type AB
I AI B
A and B
Neither Anti-A nor Anti-B
Type O
ii
Neither A nor B
Anti-A and Anti-B
Tall and Hairy
• Two advantageous traits a plant can possess it to
be tall and hairy.
• For this experiment, you will apply your
knowledge of botany and genetics to generate
true-breeding plants for these traits.
• Thanks to Mendel, we can accurately predict the
outcomes of our crosses and do not need years
of experiments to do so.
LETS PLANT