Autosomal Recessive Inheritance

1
Autosomal Recessive Inheritance

• Characteristics of autosomal recessive
  inheritance
• no difference in expression between males and
  females
• matings between affected individuals produce
  100 affected offspring
• Affected genotype (filled in shape) must be dd
• Unaffected genotypes (empty shapes) can be either
  DD or Dd

2
Autosomal Recessive Inheritance

• Characteristics of autosomal recessive
  inheritance
• no difference in expression between males and
  females
• matings between affected individuals produce
  100 affected offspring
• Affected genotype (filled in shape) must be dd
• Unaffected genotypes (empty shapes) can be either
  DD or Dd

Must be Dd
Must be dd
For the rest of the people you cannot be sure if
they are DD or Dd.
3
Autosomal Dominant Inheritance

• Characteristics of autosomal dominant
  inheritance
• no difference in expression between males and
  females
• no unaffected heterozygous individuals
• does not skip generations
• Affected genotypes (filled in shapes) can be
  either Dd or DD
• Unaffected genotype (empty shape) must be dd

4
Autosomal Dominant Inheritance

• Characteristics of autosomal dominant
  inheritance
• no difference in expression between males and
  females
• no unaffected heterozygous individuals
• does not skip generations
• Affected genotypes (filled in shapes) can be
  either Dd or DD
• Unaffected genotype (empty shape) must be dd

All empty shapes must be dd
Must be Dd
Must be Dd
5
Sex-linked (X-linked) recessive inheritance

• Characteristics of sex-linked (X-linked)
  recessive inheritance
• most affected individuals will be male
• affected females must have an affected father and
  either a heterozygous or affected mother
• affected females will have 100 affected sons
• tends to skip generations
• Affected genotypes (filled in shapes) must be
  XdXd or XdY
• Unaffected genotypes (empty shapes) can be XDXD
  , XDXd , or XDY

6
Sex-linked (X-linked) recessive inheritance

• Characteristics of sex-linked (X-linked)
  recessive inheritance
• most affected individuals will be male
• affected females must have an affected father and
  either a heterozygous or affected mother
• affected females will have 100 affected sons
• tends to skip generations
• Affected genotypes (filled in shapes) must be
  XdXd or XdY
• Unaffected genotypes (empty shapes) can be XDXD
  , XDXd , or XDY

XDY
XDXd
XdY
XDY
XD_
XD_
XdY
XDXd
XD_
7
Sex-linked (X-linked) Dominant Inheritance

• Characteristics of sex-linked (X-linked) dominant
  inheritance
• affected males must have affected mothers
• affected females must have one affected parent
• affected males will have 100 affected daughters
• affected females are expected to produce half
  normal, half affected offspring
• Affected genotypes (filled in shapes) can be
  XDXD , XDXd , or XDY
• Unaffected genotypes (empty shapes) must be XdXd
  or XdY

8
Sex-linked (X-linked) Dominant Inheritance

• Characteristics of sex-linked (X-linked) dominant
  inheritance
• affected males must have affected mothers
• affected females must have one affected parent
• affected males will have 100 affected daughters
• affected females are expected to produce half
  normal, half affected offspring
• Affected genotypes (filled in shapes) can be
  XDXD , XDXd , or XDY
• Unaffected genotypes (empty shapes) must be XdXd
  or XdY

XdXd
XDY
XdY
XDXd
XDXd
XdXd
XDY
XDXd
9
Genetic testing Ethical considerations

• Genetic information often identifies risks of
  medical conditions that do not yet affect the
  patient
• Cancer
• Huntingtons disease (age related
  neuro-degenerative disorder)
• If you carry a mutation associated with disease
• Burden of knowing you have the predisposition,
  particularly if no treatment is available
• Possible overestimation of likelihood of actually
  becoming afflicted (other genes and environmental
  factors also involved)
• If you do not carry a mutation associated with
  disease
• survivor guilt
• Possible underestimation of likelihood of
  actually becoming afflicted (other genes and
  environmental factors also involved)
• Genetic information is about families as well as
  individuals
• Is there an obligation to warn family members who
  are at risk?
• Should employers be warned if a person possesses
  a genetic mutant that may someday pose a threat
  (such as a bus driver at high genetic risk for
  heart failure)?

10
What careers in genetics are available?

• Genetic counselor (requires Masters degree)
• Interact with families and patients
• Clinical geneticist (requires M.D.)
• Study families with genetic diseases- collect DNA
  samples and send to research scientist
• Research scientist (requires Ph.D.)
• Study DNA from families with genetic diseases to
  try to find gene(s) and mutation(s) responsible
  for disease
• Once disease genes are known, perform experiments
  to understand how mutations in the gene affect
  protein function and cellular processes to cause
  disease phenotype