Fundamentals of Genetics

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Fundamentals of Genetics

• Chapter 11

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Genetics

• The scientific study of heredity.
• Trait a characteristic that can be passed from
  parent to offspring.
• Traits usually come in different forms. (i.e.
  Blue or brown eyes, tall or short, etc.)

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Alleles

• Different forms of a gene.
• For example
• Blue or brown eyes.
• Blue one allele.
• Brown a different allele.

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Genes

• Sections of a chromosome that code for a trait.
• For example
• Brown or blonde hair.
• Fish have fins, dogs have legs.
• Six fingers or five.

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Dominant vs. Recessive Alleles

• When both a dominant and a recessive allele are
  present
• Dominant allele can be seen (expressed).
• Recessive allele cannot be seen but is still
  present and may be seen in later generations.

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Genotype and Phenotype

• Genotype the genetic makeup of an organism.
  (What genes does it have?)
• Phenotype The outward expression of a trait.
  (What you can see.)
• Bb or BB or bb genotype
• Brown Brown Blue phenotype

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Homozygous vs. Heterozygous

• Homozygous Same form of the gene from both
  parents.
• Homozygous recessive bb or rr
• Homozygous dominant BB or RR
• Heterozygous Different forms of the gene from
  each parent.
• For example Bb or Rr

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Mendels Laws of Genetics

1. Law of Segregation Gene pairs separate when
   gametes form.
2. Law of Independent Assortment Genes separation
   is random and independent.
3. Law of Dominance A dominant allele will be seen
   and the recessive allele will be hidden.

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What makes us unique?

• Sexual Reproduction
• Genes from both parents
• Crossing over
• Swapping genes
• Mutations
• Random changes in genetic makeup
• Recombinations

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Crossing-Over
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Meiosis
Meiosis I
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Meiosis II
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter
cells, each with half the number of chromosomes
as the original.
The chromosomes line up in a similar way to the
metaphase stage of mitosis.
The sister chromatids separate and move toward
opposite ends of the cell.
Meiosis II results in four haploid (N) daughter
cells.
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Gregor Mendel (1822-1884)

• 1860s did experiments with pea plants.
• Conducted experiments that established modern
  genetics.

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Gregor Mendel

• Chose peas because they had seven traits that
  were unusual.
• Each trait only had two forms.
• Tall or short
• Purple or white
• Yellow or green

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Purebred

• Mendels peas could self-fertilize.
• Purebred the offspring receives the same trait
  from both parents.
• Hybrid the offspring receives different forms
  of the trait from each parent.

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Principles of Dominance
Section 11-1
P Generation
F1 Generation
F2 Generation
Tall
Short
Tall
Tall
Tall
Tall
Tall
Short
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Mendels Seven F1 Crosses on Pea Plants
Seed Shape
Flower Position
Seed Coat Color
Seed Color
Pod Color
Plant Height
Pod Shape
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Wrinkled
Green
White
Constricted
Yellow
Terminal
Short
Round
Yellow
Gray
Smooth
Green
Axial
Tall
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Chromosomal Theory of Heredity

• States that the material of inheritance is
  carried by genes on the chromosomes.
• Walter S. Sutton proposed the theory in 1903.

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What are the chances?

• Can be expressed as
• Fractions 1/3
• Percentages 33
• Ratios 12

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Punnett Squares

• Show the probabilities are not guaranteed.
• Monohybrid Cross studying one trait at a time.
• Dihybrid Cross studying two traits at a time.
• Test Cross a monohybrid cross in which one of
  the parents is homozygous recessive. This cross
  reveals hidden alleles.

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Monohybrid Cross
Tt
Parent 1
T
t
T
T
T
T
t
Parent 2
TT
T
T
T
T
t
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Probabilities

• P(1) x P(2) x P(3) Total Probability
• Example
• Tt x TT
• Hh x hh
• Ww x Ww
• What the chance of having offspring with the
  following genotype Tthhww

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Dihybrid Cross
TtGg
Parent 1
T
G
T
g
t
G
t
g
t
G
T
t
G
G
TtGg
ttGG
ttGg
Parent 2
TtGg
Ttgg
ttGg
ttgg
ttGg
t
g
G
t
TtGG
TtGg
ttGG
ttGg
t
g
TtGg
Ttgg
ttGg
ttgg
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Test Cross
rr
Parent 1
Homozygous recessive
r
r
Parent 2
RR
R
R
r
R
r
or
Can roll
Can roll
Rr
?
?
r
?
r
Tongue Roller
Can roll
Can roll
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Autosome and Sex-Linked

• Autosomal- Genes or traits found on any
  chromosome except sex chromosome
• Sex-Linked- genes or traits found on the sex
  chromosomes

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Figure 14-13 Colorblindness
Section 14-2
Father (normal vision)
Normal vision
Colorblind
Male Female
Daughter (normal vision)
Son (normal vision)
Mother (carrier)
Daughter (carrier)
Son (colorblind)
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Exceptions to the dominant recessive rule.

• Incomplete Dominance offspring show an
  intermediate form of the trait.
• Codominance offspring show both forms of the
  trait.
• Polygenic Traits traits that are controlled by
  two or more genes.
• Multiple Alleles three or more alleles control
  a trait.
• Pleiotropy one gene affects more than one trait.

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Examples of the exceptions...

• Incomplete Dominance red and white colored
  flowers have offspring with pink flowers.
• Codominance Human blood type (A, B, AB, O).
• Polygenic Traits Human eye color.
• Multiple Alleles Human hair color.
• Pleiotropy Sickle-cell anemia disease.

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Incomplete Dominance in Four OClock Flowers
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Blood Groups
Safe Transfusions
Antigen on Red Blood Cell
Phenotype (Blood Type
Genotype
From
To
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Pedigree

• A chart that shows how a trait is inherited
  within a family.

Carriers
Phenotype
bb
Bb
bb
Bb
Bb
Bb
Bb
Genotype
bb
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Pedigree
Figure 14-3 A Pedigree
Section 14-1
A circle represents a female.
A square represents a male.
A horizontal line connecting a male and female
represents a marriage.
A vertical line and a bracket connect the parents
to their children.
A half-shaded circle or square indicates that a
person is a carrier of the trait.
A circle or square that is not shaded indicates
that a person neither expresses the trait nor is
a carrier of the trait.
A completely shaded circle or square indicates
that a person expresses the trait.
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Identifying types of inheritance by pedigree
charts

• Autosomal-trait appears in both sexes
• X-linked-trait appears in only one sex
• Dominant- no carriers are shown
• Recessive- carriers are present
• Four types
• Autosomal dominant, autosomal recessive, x-linked
  dominant, x-linked recessive

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The Cause of Cystic Fibrosis
Chromosome 7
CFTR gene
The most common allele that causes cystic
fibrosis is missing 3 DNA bases. As a result,
the amino acid phenylalanine is missing from the
CFTR protein.
Normal CFTR is a chloride ion channel in cell
membranes. Abnormal CFTR cannot be transported
to the cell membrane.
The cells in the persons airways are unable to
transport chloride ions. As a result, the airways
become clogged with a thick mucus.
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Genes can react to the environment

• Body temperature causes a rabbit to have black or
  white fur.
• Soil acidity determines blue or pink flowers.
• Japanese goby fish will change from female to
  male and back again.
• Human height.

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Gene Therapy
Bone marrow cell
Nucleus
Normal hemoglobin gene
Chromosomes
Bone marrow
Genetically engineered virus