Transcript Genetics

HEREDITY
“The Code of Life”
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What is Genetics?
(Chapter 1)
• Genetics is the study of heredity
• Genetics is the study of how traits are
passed from an organism to its offspring
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Genetics
Genetics helps to explain why living
organisms:
• Resemble their parents
• Each have unique characteristics from any
other living organism
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History of Genetics
Began with Gregor Mendel
• in mid-1800’s
• working with pea plants
– looking for a pattern in the way
certain characteristics (or traits)
are handed down from one
generation to the next.
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Pea Plants
Why were pea plants chosen?
1. Grow and reproduce quickly
2. Have a variety of characteristics (or
traits)
3. Many traits (list) could be studied in one
experiment
4. Can be crossed, or bred, easily
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Reproductive Structures of
Flowers
• Stamen = Male Sex
Structure (pollen)
• Pistil = Female Sex
Structure (seeds)
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Self-Pollination
Pollen from the stamen
(male) of one flower lands
on the pistil (female) of the
same flower, or a different
flower on the same plant.
Since only one plant has
been involved , it has
pollinated itself.
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Cross-Pollination
Pollen from the stamen
(male) of one flower
lands on the pistil
(female) of the flower of
a different plant.
The pollen has crossed
between two plants,
hence cross-pollination.
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Self-Pollination
(Pure Tall x Pure Tall)
Parents
F1 Generation
X
Tall
(TT)
Purebred
=
Tall
(TT)
Tall
(TT)
Tall
(TT)
Tall
(TT)
Tall
(TT)
Purebred
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Self-Pollination
(Pure Short x Pure Short)
Parents
X
Short
tt
Purebred
F1 Generation
=
Short
tt
Short
tt
Short Short
tt
tt
Short
tt
Purebred
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Cross-Pollination
(Pure Tall x Pure Short)
F1 Generation
Parents
X
Tall
TT
Purebred
=
Short
tt
Tall
Tt
Tall
Tt
Tall
Tt
Tall
Tt
Hybrids
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Cross-Pollination
(Hybrid Tall x Hybrid Tall)
F2 Generation
F1 Generation
X
Tall
Tt
Hybrids
=
Tall
Tt
Tall
TT
Purebred
Tall
Tt
Tall
Tt
Hybrids
Short
tt
Purebred
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“Father of Genetics”
• Gregor Mendel became known as the
“Father of Genetics”.
• He identified these traits as “characters”
which we now call genes.
• Genes are the units of heredity.
• Genetics is the study of heredity, or the
passing of traits from an organism to its
offspring.
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Dominant and Recessive
• Dominant means “STRONG”
• Recessive means “weak”
• Mendel found that some traits were
stronger (dominant) while others were
weaker (recessive).
• Generally, letters are used to represent the
gene
– Capital letter is used for the Dominant gene
– Small letter is used for the Recessive gene
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Purebred vs. Hybrid
• Purebred: If genes are alike for a
particular trait
– Example: YY or yy
• Hybrid: If genes are different for a trait
– Example: Yy
– NOTE: Hybrids are produced by crossing two
purebred organisms with opposite traits
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Mendel’s Hypothesis
• Mendel made a hypothesis (suggested
explanation) for the way traits were passed
to the next generation
– Each trait must have a pair of factors, or
genes, for each trait
– Each plant in next generation also had a pair
of genes for each trait, so must have received
one from each parent.
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The Law of Segregation
• During the creation of the sex cells (sperm
for the male, eggs for the female), the
parent’s gene pairs must segregate (or
separate). This is the Law of Segregation.
• Sex cells carry half the gene pair for the
new generation. So that after fertilization
(union of sperm and egg), the new
individual has the completed pair of genes.
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Law of Segregation
Yy
Y
Parent
y
Sex cell
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Law of Independent Assortment
• This law states the each gene pair for a trait
is inherited independently of the gene pairs
for all other traits.
Yy
Y
Tt
y
T
Rr
t
R
Ss
r
S
s
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Incomplete Dominance
• Sometimes, in the gene pairs, neither gene
is dominant nor recessive. Neither gene
has the ability to mask (hide) the other. As
a result, the traits carried by the two genes
appear to be blended. This is Incomplete
Dominance.
X
RR (red)
=
WW (white)
RW (pink)
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Six Genetic Principles
1. Traits, or characteristics, are passed on
from one generation of organisms to the
next generation.
2. The traits of an organism are controlled
by genes.
3. Organisms inherit genes in pairs, one
gene from each parent.
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Six Genetic Principles
(continued)
4. Some genes are dominant, whereas other
genes are recessive.
5. Dominant genes hide recessive genes
when both are inherited by an organism.
6. Some genes are neither dominant nor
recessive. These genes show incomplete
dominance.
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Genetics and Probability
• Probability is the possibility, or likelihood,
that a particular event will occur.
• Probability won’t tell us what WILL
happen, BUT…
• Probability can be used to predict the
results of genetic crosses.
• A probability is usually written as a
fraction or a percentage.
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Punnett Squares
• In addition to probability, a special chart
called a Punnett square is used to show the
possible gene combinations in a cross
between two organisms.
• The chart was developed by Reginald C.
Punnett, an English geneticist.
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Phenotype and Genotype
• The Phenotype refers to the physical
appearance of an organism.
• The Genotype is the actual gene makeup of
the organism.
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Phenotype and Genotypes
Parents
Black
White
X
BB (Purebred)
F1 Generation
Black
Black
Bb
Hybrid
Bb
Hybrid
bb (Purebred)
Black
Black
Bb
Hybrid
Bb
Hybrid
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Phenotype and Genotypes
(continued)
F1 Generation
Black
Black
X
Bb (Hybrid)
F2 Generation
Black
Black
BB
Purebred
Bb
Hybrid
Bb
Black
Bb
Hybrid
(Hybrid)
White
bb
Purebred
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Pea Plant
Characteristics
(or Traits)
•
•
•
•
•
•
•
Tall vs. Short (T and t)
Round Seeds vs. Wrinkled Seeds (R and r)
Yellow Seeds vs. Green Seeds (Y and y)
Colored Seed Coat vs. White Seed Coat (C and c)
Full Pod vs. Pinched Pod (F and f)
Green Pod vs. Yellow Pod (G and g)
Side Flowers vs. End Flowers (S and s)
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•(return)
Human Traits
1. Earlobes
2. Hairline Shape
3. Hair
4. Chin
5. Tongue Rolling
6. Dimples
7. Hand Clasping
8. Handedness
9. Freckles
10. PTC Tasting
11. Colorblindness
Free
Widow’s peak
Curly
Cleft
Can
Present
L over R
Right
Present
Taste
Normal
Attached
Straight
Straight
Smooth
Can not
Absent
R over L
Left
Absent
None
Colorblind
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Sample Punnett Square
Problems:
1. Determine the genotype and phenotype of each
offspring. Find the probability in percent (%).
a. Heterozygous large beaks (B-large beak; b-small beak)
a. AA x Bi
( Blood Type A, B , O (i))
a. XY x XX (Female-XX; Male-XY)
a. Female carrier of colorblindness x male normal
vision (c- colorblindness)
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Quick Lab
1. Go to Pearson: Biology
eTextbook.
2. Do the quick lab: How are
dimples inherited? on page
315.
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Pedigree Symbols
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Pedigree
• A table or chart recording a line of
ancestors, either of persons or of animals.
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Mutations
• Heritable changes in genetic mutations
• Gene mutation = involve changes in one or
a few nucleotides (point mutations)
– a. substitution= one base is changed to a
different base. Affect no more than a single
amino acid and sometimes no effect at all.
– b. insertion= one base is inserted
– c. deletion= one base is removed
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Chromosomal Mutations=involve
changes in the number or structure of
chromosomes
–
–
–
–
a. Deletion
b. Duplication
c. Inversion
d. Translocation
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Environmental Factors
• Radiation
• Mutagens/carcinogens
• Harmful chemicals
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Genetic Mutations
1. Heterochromia
1. Distichiasis
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3. Red Hair
4. Blue Eyes
5. Freckles
6. Cleft Chin
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1. Sickle Cell Anemia
Detection:
Blood Screening
Amniocentesis
1. CCR 532
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Genetic Disease and Disorders
• Phenylketonuria (PKU)
*absence of enzyme to metabolize amino acid
*leads to mental retardation
• Detection : Urine Analysis
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Tay-sach’s Disease
*lack of enzyme to break down lipid in the brain
•Detection: Blood screening and amniocentesis
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Hemophilia
*rare bleeding disorder that prevents the blood
from clotting
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Cystic Fibrosis
• A genetic disorder characterized by the buildup
of thick and sticky mucus that can damage many
of the major body organs.
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Down Syndrome
• Addition of chromosome in the 21st pair of
chromosomes
• Detection:Karyotyping = a test to examine
chromosomes in a sample of cells.
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Additional Links
• http://www.brooklyn.cuny.edu/bc/ahp/MGInv/MGI.Intro.html
• http://anthro.palomar.edu/mendel/mendel_1.htm
• http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/GP/Definition.html
•
•
http://nces.ed.gov/nceskids/probability/
http://nces.ed.gov/nceskids/Games.asp
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