Sex%20Linked%20Genes

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Sex Linked Genes

• The Xs and Ys of Genetics

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Sex Linked Genes

• There are 23 pairs of chromosomes and one of
  those pairs are the sex chromosomes.
• There are either X chromosomes or Y chromosomes.

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Sex Linked Genes

• These chromosomes not only carry the genes that
  determine male and female traits, but also those
  for some other characteristics as well.

• Genes that are carried by either sex chromosome
  (X or Y) are said to be SEX LINKED

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Males

• Men normally have an X and a Y combination of sex
  chromosomes.
• Since only men inherit the Y chromosome, they are
  the only ones that inherit Y-linked traits.

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Females

• Women have 2 X chromosomes

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X Linked Traits

• Men and Women can get the X-linked traits since
  both inherit X chromosomes.

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Sex inheritance patterns for male and female
children
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X Chromosome Traits

• Men only have one X chromosome
• Therefore genes on that chromosome are expressed
  in the male phenotype, even if it is a recessive
  gene.

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X-linked traits

• In women, a recessive allele on one x chromosome
  is often masked on their phenotype

• May have a dominant normal allele on the other
  carriers of X-linked traits but more rarely have
  them expressed in their own phenotypes

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X-linked traits

• In humans, at least 120 genes are known to be
  X-linked.
• Genes for hemophilia, red-green color blindness,
  congenital night blindness, and Duchene muscular
  dystrophy

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Hemophilia

• An X-linked genetically inherited recessive
  disease
• Can not clot their blood
• Severe bleeding from minor cuts
• Mostly in males

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Red-Green Color Blindness

• X-linked
• Cannot perceive red and green in the same
• Most often afflicts males

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Muscular Dystrophy (MD)

• Characterized by a gradual irreversible wasting
  away of skeletal muscle.
• An X-linked trait most often passed on to sons
  from their mothers.
• Begins to weaken the legs of boys by age 3 and
  gets worse every year.
• No cure and inflicted usually die by age 30.

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Y-linked Traits

• The Y chromosome is small and therefore does not
  contain many genes
• Y linked diseases are very rare
• Only passed from father to son.
• Example Male infertility

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Hypertrichosis Pinnae.

• Hairy ears
• Can happen later in life.
• Y-linked