Transcript Sex-linked Traits Traits

More Patterns of Inheritance
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Autosomal inheritance – genes are located on
the autosomes, same for both male and female
Sex-linked inheritance – genes located on the
sex chromosomes, different for male and female
Sex-influenced traits – sex hormones create
different phenotypes in males and females (Ex.
Baldness)
Multiple alleles – has more than 2 alleles for the
same gene (Ex. blood types)
Polygenic inheritance – coded for by many genes
(skin color, hair color, height)
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Sex-linked Traits
Traits (genes) located on the sex
chromosomes
Sex chromosomes are X and Y
XX genotype for females
XY genotype for males
Many sex-linked traits carried on
X chromosome
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Sex-linked Traits
Example: Eye color in fruit flies
Sex Chromosomes
fruit fly
eye color
XX chromosome - female
Xy chromosome - male
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Sex-linked Trait Problem
Example: Eye color in fruit flies
(red-eyed male) x (white-eyed female)
XRY
x
XrXr
Remember: the Y chromosome in males
does not carry traits.
Xr
Xr
RR = red eyed
Rr = red eyed
R
X
rr = white eyed
XY = male
Y
XX = female
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Sex-linked Trait Solution:
Xr
XR
XR
Xr
Y
Xr Y
Xr
XR
Xr
Xr Y
50% red eyed
female
50% white eyed
male
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Sex-linked Inheritance
Color Blindness – recessive, on X chromosome
Normal Vision is dominant
Genotypes:
XCXC – normal female, non carrier
XCXc’ – normal female, carrier (may pass
recessive allele on to sons and/or
daughters)
Xc’Xc’ – colorblind female (will pass recessive
allele to all children
XCY – normal male
Xc’Y – colorblind male (will pass recessive
allele to daughters only)
~Hemophilia – bleeder’s disease, recessive,
linked to the X chromosome
Protein Factor VIII or IX is missing but is
necessary to clot blood
Genotypes:
XHXH – normal female, non carrier
XHXh – normal female, carrier
XhXh – hemophiliac female
XHY – normal male
XhY – hemophiliac male
Genetic Rarities & Abnormalities
• What can happen when meiosis goes awry…
I.
Twins
a)
b)
Identical – develop from the same fertilized egg
(zygote), genetically identical, always same sex
Fraternal – 2 sperm fertilize 2 different eggs, genetically
different
Conjoined
Twins
Fusion OR
fission in utero
Nondisjunction (Chromosomal mutation) –
chromosomes do not separate during meiosis
a)
Sex Chromosomes
i.
ii.
b)
Turner’s Syndrome – XO – 45 chromosomes,
female, sterile
Kleinfelter’s syndrome – XXY – 47, XXXY – 48,
or XXXXY – 49 chromosomes, male, sterile
Autosomes
i.
ii.
Down’s syndrome (Trisomy 21) extra 21st
chromosome
Trisomy 8 and 13 – result in miscarriages
Karyotypes
Down’s Syndrome
•Trisomy 21
•1 in 700 births
•Mental
retardation
•Males are sterile
but females are
not
Klinefelter’s Syndrome
•XXY
•1 in 1,000
•Usually sterile because of
low sperm count
•Tall, sparse body hair
•Suffer from gynecomastiamale breast tissue
•Testosterone treatments
Turner’s Syndrome
•XO genotype—Monosomy X
•1 in 2,500 births
•Short, sterile
•75% result in non-disjunction
from the father
Other Diseases
a) Sickle Cell Anemia – codominant, causes
sickle cell shaped red cells in hemoglobin,
common in people with African descent
b) Tay-Sachs – metabolic disorder,
deteriorates brain, death by age 4,
recessive is lethal
c) Cystic Fibrosis – thick mucus clogs, lungs,
pancreas, liver. Death by age 20 without
proper diet/medication
Sickle cell
Making a Pedigree
• A family tree traces a family name and various
family members through successive generations.
• Through a family tree, you can identify the
relationships among your cousins, aunts, uncles,
grandparents, and great-grandparents.
Female Carriers
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Pedigrees Illustrate Inheritance
• A pedigree is a graphic representation of genetic
inheritance.
• It is a diagram made up of a set of symbols that
identify males and females, individuals affected by
the trait being studied, and family relationships.
Pedigrees Illustrate Inheritance
Male
Parents
Female
Siblings
Affected
male
Affected
female
Mating
Known heterozygotes for
recessive allele
Death
Human Heredity
Pedigrees Illustrate Inheritance
I
Female
1
Male
• In a pedigree, a circle
represents a female; a
square represents a
male.
2
II
2
1
3
4
5
III
?
1
2
4
3
IV
1
2
3
4
5
• Highlighted circles and
squares represent
individuals showing
the trait being studied.
• Circles and squares
that are not
highlighted designate
individuals that do not
show the trait.
Human Heredity
Pedigrees Illustrate Inheritance
• A half-shaded circle or
square represents a
carrier, a heterozygous
individual.
Human Heredity
Pedigrees Illustrate Inheritance
II
• A horizontal line connecting a
circle and a square indicates that
the individuals are parents, and a
vertical line connects parents with
their offspring.
III
• Each horizontal row of circles and
squares in a pedigree designates a
generation, with the most recent
generation shown at the bottom.
I
1
2
1
?
1
2
3
2
4
5
4
3
IV
1
2
3
4
5
• The generations are identified in
sequence by Roman numerals, and
each individual is given an Arabic
number.
Dd
Dd
DD
Dd
Dd
dd
dd
Dd
dd
dd
dd
Dd
DD
DD DD
DD
DD
Dd
Dd
Dd
dd
DD
Dd
Dd
Dd
Dd
Dd
dd
Dd
dd
DD
Dd
Dd
dd
dd
Dd
dd
dd
dd
dd
dd
Hemophilia pedigree beginning with
Queen Victoria
How to know…
• Family history (mostly probabilities)
• Genetic testing (ex: spit test)
• Karyotyping
• Amniocentesis