Download Heredity: Chapter 29

Gene
• A unit of heredity
that controls the
development of one
trait
• Made of DNA
Allele
• Member of a paired gene
– One allele comes from each parent
• Dominant alleles are expressed
• Recessive alleles are not expressed in the presence of a
dominant allele
– Recessive alleles are only expressed if both recessive alleles are
present
Examples of Alleles
Dwarfism = D
Normal height = d
DD = Dwarfism
Dd = Dwarfism
dd = Normal height
Dwarf Band
Genotype
• Genetic make up
• Represented by alleles
• DD & Dd are genotypes for dwarfism
Phenotype
• A trait
• Genotype determines the phenotype
• Dwarfism is a phenotype
Codominant
•
•
•
•
Two different alleles are both dominant
A = allele for type A blood
B = allele for type B blood
AB = results in type AB blood
Karyotype
• Picture of chromosomes from an
individual
Homologous Chromosomes
• Chromosomes of the same pair
• Karyotypes are usually arranged with
homologous chromosomes paired
together
Mutation
• Change in a
gene or
chromosome
• Causes an
abnormal
trait
Mutagen
Agent that causes mutations
•Cigarette smoke
•Pesticides
•X-rays
•Ulatraviolet light
•Nuclear radiation
Sex Chromosomes
• Male have Xy
– Male gametes have either X or y
• Females have XX
– Female gametes have X
Autosomes
Chromosomes 1-22
X-Linked (vs Y- linked)Traits
• Why are
there more
X-linked that
Y- linked
disorders?
• Who suffers
more
frequently
from sexlinked
disorders?
Why?
Which karyotype is which?
A
B
Trisomy 21: Down Syndrome
•
•
•
•
Large tongue
Flat face
Slanted eyes
Single crease
across palm
• Mental retardation
– Some are not
Maternal Age & Down
Syndrome
Trisomy 18: Edward Syndrome
•
•
•
•
•
•
•
Heart defects
Displaced liver
Low-set ears
Abnormal hands
Severe retardation
98% abort
Lifespan < 1 year
Trisomy 13: Patau Syndrome
• Cleft lip and palate
• Extra fingers &
toes
– polydactylism
• Defects
– Heart
– Brain
– Kidneys
• Most abort
• Live span < 1 month
Klinefelter Syndrome
• Breast
development
• Small testes
• Sterile
• Low intelligence
– Not retarded
Klinefelter Website
Turner Syndrome
• Short
• Not go
through
puberty
• Produce little
estrogen
• Sterile
• Extra skin on
neck
Fetal Testing
Complete
Dominanc
e
Incomplete
Dominan
ce
CODominanc
e
Multiple
Alleles
Number of
Alleles
2
2
2
3
Example of
Alleles
A
a
A
A’
A
B
IA
Heterozygote
Phenotyp
e
Dominant parent
Neither parent
Both parents
Dominant OR
both
parents
depends
Number of
genotypes
3
3
3
6
5
Possible
Genotype
s
AA, Aa, aa
AA, AA’, A’A’
AA, BB, AB
IA IA, IB IA, IA I, IB
IB, IBi, ii,
XA XA, XA Xa,
XaXa, XAY,
XaY,
2
Number of
phenotype
s
3
3
4
2
A, B
Possible
phenotype
s
A, A’ , AA’
A, B, AB
A, B, AB, O
A, a
IB
i
Sex-Linked
Traits
XA Xa
Classical
Example
Pea plants
4 o clock
flowers
Roan cows
ABO Blood
group
Hemophilia
Color blindness
Example
Blue eyes X
Blue eyes X
Blue eyes X
various
Males determines
A man & woman are both
carriers (heterozygous) for
albinism. What is the chance
their children will inherit
albinism?
AA = Normal
pigmentation
Aa = Normal
pigmentation
(carrier)
Man = Aa
Woman = Aa
aa = Abino
A
A
a
a
A
a
A
AA
Aa
a
Aa
aa
AA
Aa
Genotypes
1 AA, 2Aa, 1aa
Phenotypes
Aa
aa
3 Normal
1 Albino
Probability
25% for albinism
A man & woman are both
carriers (heterozygous) for
PKU disease. What is the
chance their children will
inherit PKU disease?
PP = Normal
Pp = Normal
(carrier)
P
p
P
PP
Pp
p
Pp
pp
pp = PKU disease
PP
Pp
Genotypes
1 PP, 2Pp, 1pp
Phenotypes
Pp
pp
3 Normal
1 PKU disease
Probability
25% for PKU disease
A man with sickle cell anemia
marries a woman who is a
carrier. What is the chance
their children will inherit
sickle cell anemia?
SS = Normal
Ss = Normal
(carrier)
S
s
s
Ss
ss
s
Ss
ss
ss = Sickle Cell
Ss
ss
Genotypes
2 Ss, 2ss
Phenotypes
Ss
ss
2 Normal (carriers)
2 Sickle cell
Probability
50% for Sickle cell
A man with heterozygous
dwarfism marries a woman
who has normal height. What
is the chance their children
will inherit dwarfism?
Dwarfism is dominant.
DD = Dwarf
Dd = Dwarf
dd = Normal
d
d
D
Dd
Dd
d
dd
dd
Dd
Dd
Genotypes
2 Dd, 2dd
Phenotypes
dd
dd
2 Normal
2 Dwarfs
Probability
50% for Dwarfism
XH XH = Normal Female
XH Xh = Normal Female
(Carrier)
Xh Xh = Hemophilic Female
XHy =
Normal Male
Xhy =
Hemophiliac Male
A man with hemophilia marries
a normal woman who is not a
carrier. What is the chance
their children will inherit
hemophilia? Hemophilia is Xlinked recessive.
Xh XH = Normal Female
XH Xh = Normal Female
(Carrier)
Xh Xh = Hemophilic Female
XHy =
Xhy =
Normal Male
XH
X
Xh
XH Xh
XH Xh
y
XHy
XHy
Hemophiliac Male
H
XH
Xh
XH
Xh
X
H
XH
Genotypes
Xh
2 XH
Xh, 2XHy
Phenotypes
y
XHy
2 Carrier Females
XHy
2 Normal Males
Probability
O% for Hemophilia
A normal man marries a
normal woman who is a carrier
for hemophilia. What is the
chance their children will
inherit hemophilia?
Xh XH = Normal Female
XH Xh = Normal Female
(Carrier)
Xh Xh = Hemophilic Female
XHy =
Xhy =
Normal Male
XH
Xh
XH
XH XH
XH Xh
y
XHy
Hemophiliac Male
X hy
XH
Xh
Genotypes
XH
XH
XH
XH
Xh
XH XH , XH Xh, XHy,
X hy
Phenotypes
2 Normal Females
y
XHy
X hy
1 Normal Males
1 Male Hemophiliac
Probability
50% for Male Hemophilic
0% for Female Hemophilic