Transcript Ch 5 beyond mendel - Arlington High School

Beyond Mendel’s Laws
of Inheritance
AP Biology
2006-2007
Journal Assignment
 For some of the porphyrias,
attacks are precipitated by an
environmental trigger. Using
OMIM, describe factors that
can trigger an attack of two
of the following:
Historical
reference?
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
acute intermittent porphyria

porphyria cutanea tarda

Coproporphyria

porphyria variegate

erythropoietic protoporphyria
Extending Mendelian genetics
 Mendel worked with a simple system
peas are genetically simple
 most traits are controlled by a single gene
 each gene has only 2 alleles, 1 of which
is completely dominant to the other

 The relationship between
genotype & phenotype
is rarely that simple
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Lethal Allele Combinations
 Homozygous recessive lethal alleles
can eliminate a progeny class
 Do they always have to be homozygous
recessive?
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Multiple Alleles
 A gene can have more than two alleles,
but a diploid individual only has one or
two of them.
 Different allele combinations can
produce different phenotypes and
different severities of symptoms.
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Incomplete dominance
 Heterozygote shows an intermediate,
blended phenotype

example:
 RR = red flowers
 rr = white flowers
 Rr = pink flowers
 make 50% less color
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RR
Rr
rr
Incomplete dominance
P
X
true-breeding
red flowers
true-breeding
white flowers
100% pink flowers
F1
100%
generation
(hybrids)
self-pollinate
25%
red
F2
generation
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50%
pink
25%
white
It’s like
flipping 2
pennies!
1:2:1
Incomplete dominance in beta fish.
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Co-dominance
 2 alleles affect the phenotype equally &
separately
not blended phenotype
 example: ABO blood groups
 3 alleles

 IA, IB, i
 IA & IB alleles are co-dominant to each other
 both antigens are produced
 both IA & IB are dominant to i allele

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produces glycoprotein
antigen markers on the
surface of red blood cells
Blood compatibility
1901 | 1930
 Matching compatible blood groups
critical for blood transfusions
A person produces antibodies against
antigens in foreign blood
 wrong blood type


 donor’s blood has A or B antigen that is
foreign to recipient
 antibodies in recipient’s blood bind to
foreign molecules
 cause donated blood cells to clump together
 can kill the recipient
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Karl Landsteiner
(1868-1943)
Blood donation
clotting clotting
clotting
clotting
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clotting
clotting
clotting
The Blood Typing Game
http://www.nobelprize.org/educational/medicine/bloodtypi
nggame/game/index.html
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Pleiotropy
 Most genes are pleiotropic

one gene affects more than one
phenotypic character
 wide-ranging effects due to a single gene
 dwarfism (achondroplasia)
 gigantism (acromegaly)
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Acromegaly: André the Giant
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Epistasis
 One gene completely masks another gene

coat color in mice = 2 separate genes
 C,c:
pigment (C) or
no pigment (c)
 B,b:
more pigment (black=B)
or less (brown=b)
 cc = albino,
no matter B allele
 9:3:3:1 becomes 9:3:4
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How would you know that
difference wasn’t random chance?
Chi-square test!
Epistasis in Labrador retrievers
 2 genes: (E,e) & (B,b)


pigment (E) or no pigment (e)
pigment concentration: black (B) to brown (b)
eebb
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eeB–
E–bb
E–B–
Epistasis in
grain color
X
White
(AAbb)
White
(aaBB)
F1 generation
A = enzyme 1
+
B = enzyme 2

purple color
(anthocyanin)
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All purple
(AaBb)
Eggs
AB
Ab
aB
ab
AB AABB AABb AaBB AaBb
Ab AABb AAbb AaBb Aabb
Sperm
9:3:3:1
aB AaBB AaBb aaBB aaBb
9:7
ab AaBb Aabb aaBb aabb
F2 generation
9/16 purple
7/16 white
Penetrance and Expressivity
 Genotypes vary in penetrance (percent of
individuals with an allele who are
affected, all or none) and expressivity
(severity of symptoms or expression).
Examples: Huntington”s – nearly
completely penetrant
 Polydactyly – incompletely penetrant

 Penetrance and variable expression are
not well understood biochemically and are
probably due to the complex biochemical
environment all genes function in.
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Polygenic inheritance
 Some phenotypes determined by
additive effects of 2 or more genes on a
single character
phenotypes on a continuum
 human traits

 skin color
 height
 weight
 eye color
 intelligence
 behaviors
AP Biology
Eye color is polygenic but follows Mendelian patterns
of inheritance, how?
AP Biology
Skin color: Albinism
Johnny & Edgar Winter
 However albinism can be
inherited as a single gene trait
albino
Africans
melanin = universal brown color
enzyme
tyrosine
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melanin
albinism
OCA1 albino
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Bianca Knowlton
Sex linked traits
1910 | 1933
 Genes are on sex chromosomes



as opposed to autosomal chromosomes
first discovered by T.H. Morgan at Columbia U.
Drosophila breeding
 good genetic subject
 prolific
 2 week generations
 4 pairs of chromosomes
 XX=female, XY=male
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Classes of chromosomes
autosomal
chromosomes
sex
chromosomes
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Discovery of sex linkage
P
F1
true-breeding
red-eye female
X
true-breeding
white-eye male
100%
red eye offspring
Huh!
Sex matters?!
generation
(hybrids)
F2
generation
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100%
red-eye female
50% red-eye male
50% white eye male
What’s up with Morgan’s flies?
x
RR
r
R
Rr
x
rr
Rr
r
Rr
Rr
R
R
r
RR
Rr
Rr
rr
Doesn’t work
this way!
R
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Rr
Rr
100% red eyes
r
3 red : 1 white
What’s up with Morgan’s flies?
x
_____
____
____
____
x
_____
____
_____ _____
_____ _____
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_____
100% red eyes
____
____
____
_____
____
_____ _____
_____ _____
100% red females
50% red males; 50% white males
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Genes on sex chromosomes
 Y chromosome

few genes other than SRY
 sex-determining region
 master regulator for maleness
 turns on genes for production of male hormones
 many effects = pleiotropy!
 X chromosome

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other traits beyond sex determination
 mutations:
 hemophilia
 Duchenne muscular dystrophy
 color-blindness
Human X chromosome
 Sex-linked
Duchenne muscular dystrophy
Becker muscular dystrophy
usually
means
“X-linked”
 more than
60 diseases
traced to
genes on X
chromosome

Chronic granulomatous disease
Retinitis pigmentosa-3
Norrie disease
Retinitis pigmentosa-2
Hypophosphatemia
Aicardi syndrome
Hypomagnesemia, X-linked
Ocular albinism
Retinoschisis
Adrenal hypoplasia
Glycerol kinase deficiency
Ornithine transcarbamylase
deficiency
Incontinentia pigmenti
Wiskott-Aldrich syndrome
Menkes syndrome
Androgen insensitivity
Sideroblastic anemia
Aarskog-Scott syndrome
PGK deficiency hemolytic anemia
Anhidrotic ectodermal dysplasia
Agammaglobulinemia
Kennedy disease
Pelizaeus-Merzbacher disease
Alport syndrome
Fabry disease
Immunodeficiency, X-linked,
with hyper IgM
Lymphoproliferative syndrome
Albinism-deafness syndrome
Fragile-X syndrome
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Ichthyosis, X-linked
Placental steroid sulfatase deficiency
Kallmann syndrome
Chondrodysplasia punctata,
X-linked recessive
Charcot-Marie-Tooth neuropathy
Choroideremia
Cleft palate, X-linked
Spastic paraplegia, X-linked,
uncomplicated
Deafness with stapes fixation
PRPS-related gout
Lowe syndrome
Lesch-Nyhan syndrome
HPRT-related gout
Hunter syndrome
Hemophilia B
Hemophilia A
G6PD deficiency: favism
Drug-sensitive anemia
Chronic hemolytic anemia
Manic-depressive illness, X-linked
Colorblindness, (several forms)
Dyskeratosis congenita
TKCR syndrome
Adrenoleukodystrophy
Adrenomyeloneuropathy
Emery-Dreifuss muscular dystrophy
Diabetes insipidus, renal
Myotubular myopathy, X-linked
Map of Human Y chromosome?
< 30 genes on
Y chromosome
Sex-determining Region Y (SRY)
Channel Flipping (FLP)
Catching & Throwing (BLZ-1)
Self confidence (BLZ-2)
Devotion to sports (BUD-E)
Addiction to death &
destruction movies (SAW-2)
note: not linked to ability gene
Air guitar (RIF)
Scratching (ITCH-E)
Spitting (P2E)
Inability to express
affection over phone (ME-2)
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linked
Selective hearing loss (HUH)
Total lack of recall for dates (OOPS)
Sex-linked traits summary
 X-linked
follow the X chromosomes
 males get their X from their mother
 trait is never passed from father to son

 Y-linked
very few genes / traits
 trait is only passed from father to son
 females cannot inherit trait

AP Biology
X-inactivation - Epigenetics
 Female mammals inherit 2 X chromosomes

one X becomes inactivated during
embryonic development
 condenses into compact object = Barr body
 which X becomes Barr body is random
 patchwork trait = “mosaic”
XH 
XH X h
Xh
AP Biology
X-inactivation & tortoise shell cat
 2 different cell lines in cat
AP Biology
What is epigenome?
 The epigenome is a set of chemical

switches and markers that influence
gene expression.
Specifically factors from your
environment such as diet, physical
activity, and stress influence the
epigenome.
AP Biology
Mitochondrion







Organelle providing cellular energy
Contains small circular DNA
No crossing over or DNA repair
High exposure to free radicals
Mutation rate is greater than nuclear DNA
37 genes without noncoding sequences
Mitochondrial genes are transmitted from
mother to all of her offspring
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Mitochondrial Inheritance
Figure 5.8
Figure 5.7
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Mitochondrial Disorders
 Mitochondrial myopathies – weak
muscles
 Leber optic atrophy – impairs vision
 Ooplasmic transfer technique can enable
woman to avoid transmitting a
mitochondrial disorder
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Linkage
 Linkage is the transmission of two
genes on the same chromosome
 Two genes on the same chromosome
will not assort randomly in meiosis
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Expected Results in a Dihybrid Cross
Figure 5.10
AP Biology
Parents
P
p
L
l
Genotype PpLl
Genes not linked
Self-cross
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P
L
p
l
Genotype PpLl
Genes linked
Self-cross
Parents
P
p
L
l
Genotype PpLl
Genes not linked
Self-cross
P
L
p
l
Genotype PpLl
Genes linked
Self-cross
F1
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Parents
P
p
L
P
L
l
Genotype PpLl
Genes not linked
Self-cross
F1
Male
gametes
Genotype PpLl
Genes linked
Self-cross
Female gametes
PL
pl
Female gametes
PL
Pl
pL
pl
PL
Pl
pL
pl
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p
l
Male
gametes
PL
pl
Parents
P
p
L
l
Genotype PpLl
Genes not linked
Self-cross
F1
Female gametes
PL
Pl
pL
pl
PL
Male Pl
PPLL PPLl PpLL PpLl
PPLl PPll PpLl Ppll
gametes
PpLL PpLl ppLL ppLl
pL
pl
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P
L
PpLl Ppll ppLl ppll
p
l
Genotype PpLl
Genes linked
Self-cross
Female gametes
PL
pl
MalePL PPLL PpLl
gametes
pl PpLl ppll
Parents
P
p
L
l
Genotype PpLl
Genes not linked
Self-cross
F1
Female gametes
PL
Pl
pL
pl
PL
Male Pl
PPLL PPLl PpLL PpLl
PPLl PPll
PpLl Ppll
gametes
PpLL PpLl ppLL ppLl
pL
pl
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PpLl Ppll ppLl ppll
Phenotypic ratio 9:3
P
L
p
l
Genotype PpLl
Genes linked
Self-cross
Female gametes
PL
pl
MalePL PPLL PpLl
gametes
pl PpLl ppll
Phenotypic ratio 3:
Parents
P
p
L
l
Genotype PpLl
Genes not linked
Self-cross
PL
Male Pl
PPLL PPLl PpLL PpLl
PPLl PPll
PpLl Ppll
gametes
PpLL PpLl ppLL ppLl
pL
pl
AP Biology
p
l
Genotype PpLl
Genes linked
Self-cross
Female gametes
PL
Pl
pL
pl
F1
P
L
PpLl Ppll ppLl ppll
Phenotypic ratio 9:
Female gametes
PL
pl
MalePL PPLL PpLl
gametes
pl PpLl ppll
Phenotypic ratio 3:
Parents
P
p
L
l
Genotype PpLl
Genes not linked
Self-cross
F1
Female gametes
PL
Pl
pL
pl
PL
Male Pl
PPLL PPLl PpLL PpLl
PPLl PPll
PpLl Ppll
gametes
PpLL PpLl ppLL ppLl
pL
pl
AP Biology
PpLl Ppll ppLl ppll
Phenotypic ratio 9:3:3
P
L
p
l
Genotype PpLl
Genes linked
Self-cross
Female gametes
PL
pl
MalePL PPLL PpLl
gametes
pl PpLl ppll
Phenotypic ratio 3:
Parents
P
p
L
l
Genotype PpLl
Genes not linked
Self-cross
F1
Female gametes
PL
Pl
pL
pl
PL PPLL PPLl PpLL PpLl
Male Pl
PPLl PPll
PpLl Ppll
gametes
pL PpLL PpLl ppLL ppLl
pl
AP Biology
PpLl Ppll ppLl ppll
Phenotypic ratio 9:3:3:1
P
L
p
l
Genotype PpLl
Genes linked
Self-cross
Female gametes
PL
pl
MalePL PPLL PpLl
gametes
pl PpLl ppll
Phenotypic ratio 3:1
Recombination
 During crossing over in prophase I



chromosomes recombine
New combinations of alleles are created
Parental chromosomes have the original
configuration
Recombinant chromosomes have new
combinations of alleles
AP Biology
Crossing over Disrupts Linkage
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Recombination
 Frequency of recombination is based on
percentage of meiotic divisions that result in
breakage of linkage between parental alleles
 The frequency of recombination between two
genes is proportional to the distance between
the genes
AP Biology