Sex Linkage and Sex detrmination

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Sex Linkage and Sex detrmination
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Test Cross

• A mating between to determine genotype of an
  individual of unknown genotype and a homozygous
  recessive individual
• Example C__ x cc
• CC curly hair
• Cc curly hair
• cc straight hair

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Test Cross

• Possible results

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Sex Determination
Sex Chromosomes
XX chromosome - female
Xy chromosome - male
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Sex Determination
X X
X y
X X
X y
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Other Sex Determination

• The Y chromosome sometimes does not dictate its
  maleness
• Absence of a second X
• XY fruit fly is male
• XXY fruit fly is female

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Environmental Sex Determination

• Sex may be determined after fertilization
• Determined by temperature during early embryonic
  development
• Turtles produce more females at a higher
  temperature
• Alligators and many lizards produce more males at
  a higher temperature

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Sex-linked Traits

• Traits (genes) located on the sex chromosomes
• Hemophiliacs (X-linked)
• Male Pattern Baldness (X-linked)
• Color-blindness (X-linked)
• Male Ear Hair (y-linked)

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Sex-linked Traits
Sex Chromosomes
fruit fly eye color
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XN XN
XN y
XN Xn
Xn y
N normal n Hemophilia
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Male Pattern Baldness
XN XN
XN y
XN Xn
Xn y
N normal n Bald
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Colorblindness
XN XN
XN y
XN Xn
Xn y
N normal n Colorblind
http//www.toledo-bend.com/colorblind/Ishihara.htm
l
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Y-linked Ear-Hair
X X
X y
X X
X y
y Ear Hair
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Barr 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 XP active
• some have the XM active

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Barr Bodies

• Fur coloration of calico cats is governed by two
  alleles (black and orange - multiple alleles )
• Both attached to the same loci on a homologous
  pair of X chromosomes
• In black fur cells orange allele is inactive
• In orange fur cells black allele is inactive
• Explained in more detail at Barr Bodies and
  Gender Verification 

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XN XN
XN y
XN Xn
Xn y
N normal n Hemophilia
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Single gene traits studied using a pedigree
Why do we need to study pedigrees to understand
Mendelian inheritance in humans?
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.
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Conventional Symbols for Human Pedigrees
Mating
Normal male
Normal female
Normal, sex irrelevant or unknown
Between relatives
Affected male
Affected female
I
Affected, sex irrelevant or unknown
II
Last born
Sibling birth order from left to right
siblings
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Pedigree Analysis
Widows peak dominant
Attached ear lobe recessive
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Autosomal Recessive Pedigree
Many people in these pedigrees were probably
carriers - heterozygotes
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Autosomal Dominant Pedigree
No carriers
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Karyotype

• A method of organizing the chromosomes of a cell
  in relation to number, size, and type.

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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

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Karyotyping
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Karyotyping
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FREQUENCY OF ABNORMALITY ()
http//www.carolguze.com/text/442-4-chromosome_abn
ormalities.shtml
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Reciprocal Translocation Philadelphia Chromosome
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Reciprocal Translocation Philadelphia 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
  Leukemia (CML) patients
• the cells that produce blood cells for the body
  (the hematopoietic cells) grow uncontrollably,
  leading to cancer