Download Chapters 11 and 12 - Helena High School

Genetics and Mendel
Chapters 11 and 12
AP Biology
2006-2007
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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Gregor Johann Mendel
 Austrian Monk, born in what is now Czech
Republic in 1822
 Son of peasant farmer, studied
Theology and was ordained
priest Order St. Augustine.
 Went to the university of Vienna, where he
studied botany and learned the Scientific
Method
 Worked with pure lines of peas for eight years
 Prior to Mendel, heredity was regarded as a
"blending” process and the offspring were
essentially a "dilution"of the different parental
APcharacteristics.
Biology
Genetics terms you need to know:
 Gene – a unit of heredity;

a section of DNA sequence
encoding a single protein
Genome – the entire set
of genes in an organism
 Alleles – two genes that occupy the same

position on homologous chromosomes and
that cover the same trait (like ‘flavors’ of a
trait).
Locus – a fixed location on a strand of DNA
where a gene or one of its alleles is located.
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 Homozygous – having identical genes (one



from each parent) for a particular
characteristic.
Heterozygous – having two different genes
for a particular characteristic.
Dominant – the allele of a gene that masks
or suppresses the expression of an
alternate allele; the trait appears in the
heterozygous condition.
Recessive – an allele that is masked by a
dominant allele; does not appear in the
heterozygous condition, only in
homozygous.
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 Genotype – the genetic makeup of an





organism
Phenotype – the physical appearance
of an organism (Genotype + environment)
Monohybrid cross: a genetic cross involving
a single pair of genes (one trait); parents
differ by a single trait.
P = Parental generation
F1 = First filial generation; offspring from a
genetic cross.
F2 = Second filial generation of a genetic
cross
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Another example: Flower color
For example, flower color:
P = purple (dominant)
p = white (recessive)
If you cross a homozygous Purple (PP) with a
homozygous white (pp):
PP

Pp
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pp
ALL PURPLE (Pp)
Cross the F1 generation:

Pp
P
p
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Pp
P
p
PP
Pp
Pp
pp
Genotypes:
1 PP
2 Pp
1 pp
Phenotypes:
3 Purple
1 White
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
1:2:1
Incomplete dominance
CRCW x C RCW
%
genotype
female / eggs
male / sperm
CR
CW
CR
CW
_____
_____
CRCR
CRCW
____ ____
____ ____
CRCW
_____
_____
C WC W
____ ____
1:2:1
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%
phenotype
1:2:1
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
Genetics of Blood type
phenogenotype
type
A
B
AB
O
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antigen
on RBC
antibodies
in blood
donation
status
IA IA or IA i
type A antigens
on surface
of RBC
anti-B antibodies
__
IB IB or IB i
type B antigens
on surface
of RBC
anti-A antibodies
__
IA IB
both type A &
type B antigens
on surface
of RBC
no antibodies
universal
recipient
ii
no antigens
on surface
of RBC
anti-A & anti-B
antibodies
universal
donor
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
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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Inheritance pattern of Achondroplasia
Aa
x aa
a
a
A
____
____
a
____
50% dwarf:50%
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Aa
x Aa
A
a
A
____
____
____
a
____
____
normal or 1:1
67% dwarf:33% normal or 2:1
Epistasis
 One gene completely 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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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–
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
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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
AP Biology
Classes of chromosomes
autosomal
chromosomes
sex
chromosomes
AP Biology
Discovery of sex linkage
P
F1
true-breeding
red-eye female
X
true-breeding
white-eye male
100%
red eye offspring
generation
(hybrids)
F2
generation
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100%
red-eye female
50% red-eye male
50% white eye male
Genetics of Sex
 In humans & other mammals, there are 2 sex
chromosomes: X & Y

2 X chromosomes
 develop as a female: XX
 gene redundancy,
like autosomal chromosomes

an X & Y chromosome
 develop as a male: XY
 no redundancy
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50% female : 50% male
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
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

AP Biology
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
AP Biology
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
AP Biology
Sex-determining Region Y (SRY)
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

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sex-linked recessive
Hemophilia
Hh x HH
female / eggs
male / sperm
___
___
carrier
disease
___
___
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X-inactivation
 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
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X-inactivation & tortoise shell cat
 2 different cell lines in cat
AP Biology
Male pattern baldness
 Sex influenced trait

autosomal trait influenced by sex hormones
 age effect as well = onset after 30 years old

dominant in males & recessive in females
 B_ = bald in males; bb = bald in females
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Nature vs. nurture
 Phenotype is controlled by
both
environment & genes
Human skin color is influenced
by both genetics &
environmental conditions
Coat color in arctic
fox influenced by
heat sensitive alleles
Color of Hydrangea flowers
APinfluenced
Biology
is
by soil pH
Any Questions?
AP Biology