Download x2-2 genetics F12

How are our traits related to
genes?
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Ch 9: Genes and Inheritance
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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Genes are sections
of DNA
Babies Inherit Half of Chromosomes
from Mom & Half from Dad
What is heredity?
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Typically bears
>1000 genes
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 Widow’s peaks will
have kids with Widow’s peaks
parents with short fingers will
have kids with short fingers
From Mom
22 chromosomes
X chromosome
44 Chromosomes
XX = Girl
XY = Boy
From Dad
22 chromosomes
X or Y chromosome
Genetics 101: Where do your genes come from? (4:14)
http://www.youtube.com/watch?v=lJzZ7p-47P8&NR=1
Chromosomes are distributed
randomly to sperm (or egg)
Why are we different?
Your Dad’s Chromosomes
Your Mom’s Chromosomes
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Kids get ½
from mom
and ½ from
dad
Circled chromosomes
into sperm
You
Your Sister
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Circled
chromosomes
into egg
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 trillion (extremely
unlikely)
Sperm
Cell
Crossing over creates even more
variation
How do we inherit specific traits?
sister chromatids
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Crossing-over
Synapsis
of homologues
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Chromatids
after
exchange
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Recombinant
daughter
chromosomes
We have 2 copies of
each chromosome
Each chromosome
contains genes
Genes code for
proteins
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The chromosome pairs exchange DNA
This produces hybrid chromosomes and
Increases genetic variability
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The 46 chromosomes of a male
Body structures,
enzymes, etc
Our traits
© CNRI/SPL/Photo Researchers
Ways we inherit traits:
simple dominant-recessive inheritance
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Some traits are controlled
by a single gene
Two versions of the gene
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What is her genotype?
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The gene for freckles has 2
versions (alleles)
A dominant version = F
A recessive version = f
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W = Widow’s peak
w = straight hairline
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Chromosomes are found in pairs
Possible genotypes:
The widow’s peak version
of gene is dominant
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WW → Widow’s peak
Ww → Widow’s peak
ww → straight hairline
F
F
F
f
Because gene F is dominant
Diseases controlled by a
single gene
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Cystic fibrosis
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Interferes
with
breathing
And digestion
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Most common lethal
genetic disease in US
Caused by a recessive
gene
Symptoms: excessive
secretion of a very thick
mucus
Symptoms usually
appear shortly after
birth.
Dominant Disorders
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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
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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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
Ways we inherit traits:
Co-dominance
Pleiotropy
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Normal Blood Cells
Sickle Cells
When a single gene
affects more than 1
trait
Due to a mutation in
hemoglobin gene
Versions of Gene are “Co-dominant” (both are expressed)
If your genes are …
SS → Normal Hemoglobin
Ss → Some Normal AND Some Sickle Hemoglobin
ss → Sickle Cell Anemia
Ways we inherit traits:
Red-green colorblindness
Sex-linked disorders
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Involves genes located
on X or Y
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?
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X-linked disorder
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due to a recessive gene 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
Sex-Linked Disorders
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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Chromosome abnormalities
passed from mother to son
Happen when errors occur
during meiosis
Because the gene is
recessive, a female needs
two X chromosomes with the
defect to show typical male
pattern baldness
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Accidents During Meiosis
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Gametes with extra or
missing chromosomes
In nondisjunction,
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The members of a
chromosome pair fail to
separate
Produces gametes with
an incorrect number of
chromosomes.
trisomy
Chromosome abnormalities
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Down Syndrome:
An Extra Chromosome 21
Large segments of
chromosomes can
be missing,
duplicated or
exchanged
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Down Syndrome is also called trisomy 21.
Beyond simple inheritance
Most traits involve multiple genes
Skin color is determined by several genes
Most traits involve multiple
genes
Most traits involve 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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Courtesy University of Connecticut/Peter Morenus, photographer;
“Environmental” factors also
influence skin color
Many traits are multifactorial
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Sun Exposure
Muscular
development is
controlled by the
interaction of many
genes
Influenced by the
environment
Changes in
Blood Flow
Diet
Some general conclusions
about our traits:
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Most traits are determined by a combination of
genes & the environment
Even sex can be altered by environment!
(ex. exposure to certain hormones/chemicals)
Alters Melanin Production
Red when Vessels Dilated
Carotene
Factors that influence our traits:
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Genes/DNA  instructions for proteins
Environmental Factors  Nutrition, Exercise,
Sunlight, Chemicals, Injuries, etc.
BPA is a chemical used in making some
plastics. Mimics estrogen and might
alter reproductive anatomy and
function in early development.
Not Inherited
But does not change genetic sex!
(XY/XX)
Identical twins (identical DNA) can
have different characteristics
Another factor influences our
traits:
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Genes/DNA
Environment
Epigenetics  involves
chemical signals that switch
genes off and on at strategic
times
Epigenetics
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Traits can be influenced
by:
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the DNA sequence (As,
Cs, Ts and Gs)
the physical form of
chromosomes
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condensed or not
chemical tags on the DNA
http://learn.genetics.utah.edu/content/epigenetics/intro/
Supercoiling of DNA silences
genes
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Epigenetics:
activating and silencing genes
DNA wraps around
proteins called histones
The DNA is packed into
an elaborate, multilevel
system of coiling
Highly condensed DNA
is inactive
What shapes our traits?
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Genes
Environment
Epigenetics
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changes in the physical form of
chromosomes
DNA modified by chemical “tags”
Types of genetic disorders
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Single gene mutations
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Chromosome abnormalities
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Dominant, recessive, X-linked
Abnormal number of chromosomes
Missing or duplicated segments of chromosomes
Multifactorial disorders
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Changes in several genes, environmental factors