Download xCh 20 genetics W11b

Bio11 – Announcements
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TODAY – Genetics
Test 2 AVG = 73 pts
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Ch. 20 Patterns of Inheritance
Test scores posted
Next week’s lab: Case study
presentations
Extra credit due Thur Mar 3
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How traits are passed from
generation to generation
15 pts available, see my website
Human Chromosomes
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DNA packing in chromosomes
46 chromosomes in
pairs
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22 pairs of matching
chromosomes
Plus 1 pair of sex
chromosomes
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XX or XY
Chromosomes contain
DNA and protein
The long strands of
DNA are condensed
The DNA is packed into
an elaborate, multilevel
system of coiling and
folding.
This is a human karyotype
Male or female?
Chromosomes and genes
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Each chromosome
contains one very long
DNA molecule
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Typically bears thousands
of genes
Genes carry our traits
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What is heredity?
Genes are segments of
DNA
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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 black hair will have
kids with black hair
Tall parents will have tall kids
Genetics 101: Where do your genes come from? (4:14)
http://www.youtube.com/watch?v=lJzZ7p-47P8&NR=1
Genotype and phenotype
Genes carry our traits
Genes
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found at specific locations on a chromosome
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Alleles are different versions of a gene
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What is her genotype?
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The gene for freckles has 2 alleles
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The dominant allele F codes for freckles
The recessive allele f does not
She has two copies of each
chromosome
Possible genotypes: FF or Ff
F
F
F
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f
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More about alleles
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They are alternative
versions of the same
gene
The gene for hairline has
2 alleles
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P for Widow’s peak
p for straight hairline
F
Phenotype – what an
individual looks like
These 3 traits are
determined by simple
dominant-recessive
inheritance
Possible genotypes for
someone with
freckles? FF and Ff
Without freckles? ff
More about alleles
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Widow’s peak
For each trait, we inherit two
alleles, one from each
parent.
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Straight hairline
F
Gene “F” codes for freckles
Examples of traits controlled
by a single gene in humans
Genotype and phenotype
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Genotype – an individual’s
genes
The alleles can be the same or
different
If they are different, the
organism is heterozygous – Pp
If they are the same, the
organism is homozygous for
that gene – PP, pp, YY
Widow’s peak
Straight hairline
Inheriting a trait
More about alleles
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Alleles can be dominant
or recessive.
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The dominant allele
determines the
organism’s appearance
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Phenotypes:
Dad
Mom
Use upper case: P
The recessive allele has
no noticeable effect
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If a man with short fingers marries a woman
with long fingers, what genotypes and
phenotypes will their children have?
Genotypes?
PP or Pp
pp
Use lower case: p
Dominant trait
SS or Ss
Forming the gametes
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Forming the gametes
Gametes carry only one allele for each
inherited characteristic.
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Dad
Gametes carry only one allele for each
inherited characteristic.
Mom
S
S
S
meiosis
Genotype = SS
s
s
S
S
s
meiosis
Gametes only carry
one copy of each
chromosome
Genotype = ss
Fertilization
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Recessive trait
ss
Forming the gametes
When sperm and egg unite at fertilization,
each contributes its allele.
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What if dad is Ss?
Dad
S
s
Fertilized egg
S
S
s
meiosis
Genotype = Ss
Genotype = Ss
Phenotype?
S
s
s
S
Then after fertilization …
Dad
Mom
s
S
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s
s
Crosses (one-trait inheritance)
If neither parent has freckles, what will
be the genotype of their offspring?
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents
Gametes:
S or s
All s
no freckles
no freckles
ff
ff
meiosis
Fertilized egg:
genotype?
phenotype?
Ss or ss
gametes
Offspring
f
f
Offspring
ffff
no freckles
Crosses (more complicated)
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If both parents are heterozygous for
freckles, what will be the genotype of
their offspring?
Punnett square analysis
Used to predict the genotypes of the offspring
#1 Decide what gametes would be produced by each parent.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents
no freckles
Freckles
ffFf
Ff
ff
F
Genotype? Gametes?
no
freckles
Freckles
Mom
Ff
F
f
Dad
Ff
F
f
f
F
meiosis
gametes
f
Gametes?
f
Gametes?
Offspring
f
ff
no freckles
Punnett square analysis
What are the genotypes of the offspring of two
heterozygous freckled parents (Ff)?
F
f
F
FF
Ff
f
Ff
Ratio: 1FF, 2 Ff, 1 ff
ff
What are the phenotypes?
Human Disorders Controlled
by a Single Gene
Recessive disorders
Recessive disorders
Most human genetic
disorders are recessive.
Albinism
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Cystic fibrosis
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lack of melanin pigment in
the eyes, skin and hair
affects mammals (including
humans), fish, birds, reptiles
and amphibians
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Most common lethal
genetic disease in US
Symptoms: excessive
secretion of a very thick
mucus which interferes
with breathing
Symptoms usually
appear shortly after birth.
Albino alligator
Dominant Disorders
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Some human genetic
disorders are dominant.
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Achondroplasia is a
common form of
dwarfism.
Cause: abnormal bone
and cartilage formation
Huntington’s disease:
a dominant genetic disorder
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Caused by a dominant
allele–every individual who
carries the allele gets the
disorder
Fatal: causes progressive
deterioration of the brain
Late age of onset: most
people do not know they
are affected until they are
more than 30 years old
Many neurons in
normal brain.
Loss of neurons in
Huntington brain.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Some traits are controlled by
multiple genes
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At least 180 genes
control how tall a
person will grow
Beyond simple inheritance
Incomplete Dominance
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The heterozygotes have an
intermediate phenotype
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Incomplete Dominance:
Hypercholesterolemia
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appearance is between the phenotypes of
the two parents.
Alleles are not fully dominant or fully
recessive
Multiple Alleles:
ABO blood groups
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Three alleles for the
same gene
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Both alleles are
expressed in the
heterozygote.
Genes located on a sex
chromosome, usually
the X chromosome.
Their pattern of
inheritance reflects the
fact that females have
two X chromosomes,
but males have only
one.
Sex-Linked Disorders in
Humans
Inheritance of colorblindness
Sex-linked disorders
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IA = A antigen on RBC
IB = B antigen on RBC
i = neither A or B antigen
Sex-linked genes
The I A and IB alleles
exhibit codominance.
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Characterized by dangerously high levels of
cholesterol in the blood
due to recessive alleles
seen mostly in males
Example
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Red-green color
blindness
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characterized by a
malfunction of lightsensitive cells in the
eyes.
An X-linked, recessive disorder
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XB = normal vision
Xb = color blindness
Write the following genotypes
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Normal man
Color-blind man
Normal woman
Woman carrier
Inheritance of colorblindness
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A man with normal vision and a woman
carrier have children. What is the
chance that the couple will have a colorblind daughter? A color-blind son?
Man’s genotype
Man’s gametes
Woman’s genotype
Woman’s gametes
Sex-linked disorders:
Duchenne muscular dystrophy
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Set up a Punnett square
XB
Mom = XB , X b
Xb
Dad = XB , Y
XB
Possible genotypes and
phenotypes of
Sons?
Daughters?
Y
Sex-linked disorders:
Hemophilia
X-linked recessive disorder
Symptoms: Wasting away of
the muscles
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Inheritance of colorblindness
Eventually confined to
wheelchair
Death by age 20
Hemophilia: an X-linked, recessive trait
Two genes that encode blood-clotting
proteins are on the X chromosome
Due to absence of protein
involved in release of Ca
from ER in muscles
Family pedigrees
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Used to find out if a particular
human trait is inherited
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geneticists can’t control the
mating of their subjects, so they
analyze the results of matings
that have already occurred
Assemble info into a family tree
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represent males,
females
Colored symbols = person has
trait being studied
Any male (XY) who inherits the mutant gene
will develop hemophilia
Rare: occurs in 1/10,000 Caucasian males
Practice problems
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Prepare for the quiz on Thur
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Questions at end of Chapter 20:
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#1, 3, 7, 11, 13, 15, 16, 19, 20, 26, 27
and 30