Download x2-5 genetics Sp12

What are Genes?
Ch.18 and 20
Genes and Inheritance
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Each chromosome
contains one very
long DNA molecule
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How traits are passed from
generation to generation
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Genes carry our
traits
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What is heredity?
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Typically bears
thousands of genes
Genes are sections
of DNA
When is baby’s sex determined?
Heredity – passing traits
from parent to offspring
The genes for certain traits are
passed down in families from
parents to children.
For example,
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parents with curly hair will have
kids with curly hair
parents with short fingers will
have kids with short fingers
22 Chromosomes
& X Chromosome
22 Chromosomes
& X Chromosome
Genetic sex is set from
the moment X or Y
sperm fertilizes egg.
22 Chromosomes
& Y Chromosome
Genetics 101: Where do your genes come from? (4:14)
http://www.youtube.com/watch?v=lJzZ7p-47P8&NR=1
Babies Inherit Half of Chromosomes
from Mom & Half from Dad
Why are we different?
Your Dad’s 23 Chromosome Pairs
Your Mom’s 23 Chromosome Pairs
Kids get ½
from mom
and ½ from
dad
From Mom
22 chromosomes
X chromosome
44 Chromosomes
XX = Girl
XY = Boy
From Dad
22 chromosomes
X or Y chromosome
Circled chromosomes
into sperm
Why not
identical
25% of
Time???
You
Your Sister
Circled
chromosomes
into egg
Chromosomes are distributed
randomly to sperm (or egg)
Crossing over creates even more
variation
sister chromatids
During meiosis, a random
assortment of chromosomes
is placed in the nucleus
 Chances of getting same
combinations of
chromosomes is 0.5^46 = 1
in 70,368,744,177,664
(extremely unlikely)
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Crossing-over
Synapsis
of homologues
Sperm
Cell
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Chromatids
after
exchange
Recombinant
daughter
chromosomes
The chromosome pairs exchange DNA
This produces hybrid chromosomes and
Increases genetic variability
Ways we inherit traits:
How do we inherit specific traits?
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We have 2 copies of
each chromosome
Each chromosome
contains genes
Genes code for
proteins
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The 46 chromosomes of a male
simple dominant-recessive inheritance
Some traits are controlled
by a single gene
Two versions of the gene
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W = Widow’s peak
w = straight hairline
The widow’s peak version
of gene is dominant
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Body structures,
enzymes, etc
Our traits
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WW → Widow’s peak
Ww → Widow’s peak
ww → straight hairline
© CNRI/SPL/Photo Researchers
Some diseases are controlled
by a single gene
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Cystic fibrosis
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Most common lethal genetic
disease in US
Caused by a recessive gene
Symptoms: excessive
secretion of a very thick
mucus which interferes with
breathing
Symptoms usually appear
shortly after birth.
Genetic disorders:
Cystic fibrosis
H2 O
H2 O
Cl-
Cl Cl-
Cl-
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ClH2 O
nebulizer
defective
channel
percussion
vest
CF is due to a faulty
protein that is
supposed to
regulate the flow of
chloride ions into
and out of cells
thick mucus
© Pat Pendarvis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dominant Disorders
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Check your understanding
Achondroplasia is a
common form of
dwarfism.
Caused by a mutation in
the FGFR3 gene on
chromosome 4
→ abnormal bone and
cartilage formation
Just need 1 copy of
mutated gene
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Peter is a 18-year old
man whose parents
have achondroplasia
dwarfism, a dominant
genetic disorder.
What is the probability
that Peter is of normal
height?
Ways we inherit traits:
Ways we inherit traits
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Incomplete Dominance
Very few of our traits
are inherited by simple
dominant/recessive
inheritance.
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Ways we inherit traits:
Co-dominance
Curly hair
Wavy hair
Straight hair
hh
Hh
HH
A single dose of the gene gives an intermediate result
The genes are not fully dominant or fully recessive
Pleiotropy
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Normal Blood Cells
Sickle Cells
Versions of Gene are “Co-dominant”
If your genes are …
SS → Normal Hemoglobin
Ss → Some Normal AND Some Sickle Hemoglobin
ss → Sickle Cell Anemia
Due to a mutation in
hemoglobin gene
When a single gene
affects more than 1
trait
Marfan syndrome–
an example of pleiotropy
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Beyond simple inheritance
A mutation in the FBN1
gene
Most traits involve multiple genes
Connective tissue
defects
Disproportionately long
hands, a weak aorta,
caved in breastbone,
and other symptoms
Skin color is determined by several genes
Ways we inherit traits:
Most traits are controlled by
multiple genes
traits controlled by multiple genes
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At least 180 genes control how tall a
person will grow
Also influenced by environment
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Can’t just track versions of 1 gene –
Need to track numerous chromosomes
Further complicated by
• Random Assortment of chromosomes
• Crossing Over
Simple Punnett squares are not very realistic
when it comes to understanding the
inheritance of most of our traits!
Courtesy University of Connecticut/Peter Morenus, photographer;
Ways we inherit traits:
Many traits are multifactorial
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Muscular
development is
controlled by the
interaction of many
genes
Influenced by the
environment
Sex-linked inheritance
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Involves genes located on
a sex chromosome
Most are on the X chromosome
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X chromosomes contains
nearly 2000 genes
Y chromosomes contains only
80 genes
Whether you’re male or female
affects the pattern of
inheritance
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Why?
Ways we inherit traits:
Red-green colorblindness
Sex-linked disorders
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Disorders caused by sexlinked recessive alleles:
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X-linked disorder
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Red-green colorblindness
Hemophilia
Male-pattern baldness
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due to a recessive allele on
the X chromosome
Red-green color blindness
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The light-sensitive cells in
the eyes don’t function
properly.
Mostly found in males
Prevalence: 5-10% of males
A test for red-green
colorblindness
When is baby’s skin color
determined?
Sex-Linked Disorders
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Our chromosomes hold information about skin color
and various other traits.
Male pattern baldness
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Largely sex-linked, but other
genes are also involved
Gene is on the X
chromosome
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From Mom
22 chromosomes
X chromosome
passed from mother to son
Because the allele is
recessive, a female needs
two X chromosomes with the
defect to show typical male
pattern baldness
44 Chromosomes
XX = Girl
XY = Boy
From Dad
22 chromosomes
X or Y chromosome
These characteristics are determined at moment of fertilization
But what else effects skin color???
Some general conclusions
about skin color and sex:
Non-Genetic “Environmental”
Factors Also Influence Skin Color
Sun Exposure
Alters Melanin Production
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Changes in
Blood Flow
Diet
…and makeup,
rashes, etc…
Red when Vessels Dilated
Carotene
Most traits are determined by a combination of
genes & environment
Even sex can be altered by environment!
(ex. exposure to certain hormones/chemicals)
BPA is a chemical used in making some
plastics. Mimics estrogen and might
alter reproductive anatomy and
function in early development.
But does not change genetic sex!
(XY/XX)
These things are (mostly) not inherited on DNA!
Factors that influence our traits:
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Genes/DNA  Blueprints for Proteins
Nutrition, Exercise, Sunlight, Chemicals,
Injuries, etc.  Environmental Factors
Not Necessarily Inherited
Factors that influence our traits:
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Genes/DNA  Blueprints for Proteins
Epigenetics  involves chemical signals
that switch parts of the genome off and
on at strategic times
Can be passed on to daughter cells after cell division
Identical twins (identical DNA) can
have different characteristics
Cells with the same DNA become
different by turning genes On/Off
Epigenetics
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Heritable traits can
be coded in 2 ways:
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Actin Gene
Turned On
Actin Gene
Turned Off
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By the DNA
sequence (As, Cs,
Ts and Gs)
By the physical form
of chromosomes and
chemical
modification of DNA
http://learn.genetics.utah.edu/content/epigenetics/intro/
Supercoiling of DNA silences
gene expression
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DNA wraps around
proteins called histones
The DNA is packed into
an elaborate, multilevel
system of coiling
Highly condensed DNA
is inactive
Epigenetics:
activating and silencing genes
Changing gene expression
Altering histones (DNA coiling proteins) → tightly
wrapped genes that are unreadable
Changing gene expression
Can add chemical tags (methyl groups) to
→ change the expression of genes
DNA
Chemical
tags added
to histones
Methyl
groups
Tightly wrapped DNA → silenced genes
Epigenetics = changes in
expression of genes (not DNA itself)
Makes genes unreadable or easier to read
Some environmental effects
are obvious…
Sun Exposure
Environmental factors like…
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•
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Cigarette smoking can damage
not only your DNA but also your
epigenome.
Diet
Behavior
Where you live
Your group of friends
…can change the way your
DNA is expressed to form
your traits!
Exercise
…and many more can
change your traits without
altering your DNA.
All change gene
expression.
Hormones & Other Chemicals
Possibly even decrease
influence of genetic
predisposition to diseases!
Examples of environmental
changes to traits
Cancers are a mix of genetic
and epigenetic changes
Some environmental effects are subtle…
Mice licking/grooming
each other
Un-licked mouse
Changes in expression of stress
hormone receptor genes 
difficulty responding appropriately
to stress signals
Social interactions can alter gene expression!
Discover Magazine Article http://discovermagazine.com/2010/jun/15-brain-switches-that-can-turn-mental-illness-on-off
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Cancer cells have
abnormal chemical
tags in addition to
DNA mutations