Upload
eugenia-jessica-sherman
View
217
Download
0
Embed Size (px)
Citation preview
Sex Linkage and Sex detrmination
Test CrossTest CrossA mating between to determine genotype of an individual of unknown genotypeunknown genotype
and a homozygous recessivehomozygous recessive individual•Example:Example: C__ C__ x cccc
CC = curly hair
Cc = curly hair
cc = straight hair
CC ______
cc
Test CrossTest Cross
Possible results:Possible results:
CC ______
cc Cc Cc
C CC ______
cc Cc ccor
c
Sex DeterminationSex DeterminationSex ChromosomesSex Chromosomes
XX chromosome - female Xy chromosome - male
Sex DeterminationSex Determination
X X
X X
X y
X y
X y
X
X
Other Sex DeterminationSex Determination
• The Y chromosome sometimessometimes does not dictate its maleness –Absence of a second X
• XY fruit fly is male • XXY fruit fly is female
Environmental Sex DeterminationSex Determination
• Sex may be determined after fertilizationafter fertilization
• Determined by temperaturetemperature during early embryonic development – Turtles produce more females at a higher
temperature – Alligators and many lizards produce more
males at a higher temperature
Sex-linked TraitsSex-linked Traits
Traits (genes) located on the sex sex chromosomeschromosomes
• Hemophiliacs (X-linked)
• Male Pattern Baldness (X-linked)
• Color-blindness (X-linked)
• Male Ear Hair (y-linked)
Sex-linked TraitsSex-linked TraitsSex ChromosomesSex Chromosomes
fruit flyeye color
XX chromosome - female Xy chromosome - male
XN XN
XN Xn
XN y
Xn y
XN
XN y
Xn
N = normal
n = Hemophilia
XN XN
XN Xn
XN y
Xn y
XN
XN y
Xn
Male Pattern Male Pattern BaldnessBaldness
N = normal
n = Bald
XN XN
XN Xn
XN y
Xn y
XN
XN y
Xn
CoCololorbrblilindndnenessss
N = normal
n = Colorblind
http://www.toledo-bend.com/colorblind/Ishihara.html
X X
X X
X y
X y
X
X y
X
Y-linked Ear-HairY-linked Ear-Hair
y = Ear Hairy = Ear Hair
Barr BodiesBarr Bodies• Barr discovered the Barr Body• An inactive X chromosome
– a darkly staining body in the nuclei of females
• Mary Lyon, identified the Barr body as an inactive X chromosome– Inactivation is random, with a 50 - 50 chance of
inactivating the maternal or paternal X– The mammalian female is a genetic mosaic
• some cells have the XXPP active • some have the XXMM active
Barr BodiesBarr Bodies• Fur coloration of calico cats is governed
by two alleles (blackblack and orangeorange - multiple alleles )
• Both attached to the same loci on a homologous pair of X chromosomes– In black fur cells – In black fur cells – orange allele is inactiveorange allele is inactive– In orange fur cellsIn orange fur cells –black allele is inactive –black allele is inactive
Explained in more detail at Barr Bodies and Gender Verification
XN XN
XN Xn
XN y
Xn y
XN
XN y
Xn
N = normal
n = Hemophilia
Because: • The human generation time is about 20 years. • Humans produce relatively few offspring compared
to most other species. • Well-planned breeding experiments are impossible.
Why do we need to study pedigrees to understand Mendelian inheritance in humans?
Single gene traits studied using a pedigree:
Conventional Symbols for Human PedigreesConventional Symbols for Human Pedigrees
Normal male
Normal female
Normal, sex irrelevant or unknown
Affected male
Affected female
Affected, sex irrelevant or unknown
Mating
Between relatives
I
IILastborn
siblings
Sibling birth order from left to right
Pedigree AnalysisPedigree Analysis
Widow’s peak: dominant
Attached ear lobe: recessive
Autosomal Recessive PedigreeAutosomal Recessive Pedigree
Many people in these pedigrees were probably “carriers” - heterozygotes
Autosomal Dominant PedigreeAutosomal Dominant Pedigree
No carriers
KaryotypeKaryotypeA method of organizing the A method of organizing the chromosomes chromosomes of a of a
cell in relation to number, size, and type.cell in relation to number, size, and type.
Karyotyping• Chromosomes can tell us
– an unborn baby may have a genetic disorder
– a person will be male or female
• Scientist can analyze – chromosomes in prenatal testing – diagnose specific diseases
KaryotypingKaryotyping
KaryotypingKaryotyping
FREQUENCY OF ABNORMALITY (%)FREQUENCY OF ABNORMALITY (%)
Chromosome abnormality
Spontaneous abortion
Stillbirths Live births Probability of survival to term
All 50 5 0.5 5
Trisomy 16 7.5 - - 0
Trisomy 13,18,21 4.5 2.7 0.14 15
XXX,XXY,XYY 0.3 0.4 0.15 75
All other trisomies 13.8 0.9 - 0
45,X 8.7 0.1 0.01 1
Triploidy 3n 6.4 0.2 - 0
Tetraploidy 4n 2.4 - - 0
Structural Abnormalities 2.0 0.8 0.3 45
http://www.carolguze.com/text/442-4-chromosome_abnormalities.shtml
Reciprocal Translocation: Reciprocal Translocation: Philadelphia ChromosomePhiladelphia Chromosome
Reciprocal Translocation: Reciprocal Translocation: Philadelphia ChromosomePhiladelphia Chromosome
• Abnormal chromosome in karyotype– 46 chromosomes with a translocation between chromosome
9 and chromosome 22 (Philadelphia chromosome)– Most of chromosome 22 has been translocated onto the long
arm of chromosome 9– The small distal portion of the short arm of chromosome 9 is
translocated to chromosome 22
• Translocation found only in Chronic Myelogenous Chronic Myelogenous LeukemiaLeukemia (CML) patients– the cells that produce blood cells for the body (the
hematopoietic cells) grow uncontrollably, leading to cancer