Inheritance Patterns Many inherited disorders in humans are controlled by a single gene. All of our somatic cells possess two copies of each gene, one inherited from your mother and one inherited from your father. 46,XY male karyotype

–Autosomes are the 22 pairs of chromosomes that are not the sex chromosomes –Alleles are all of the alternate forms of a gene (ie. B and b) –Recessive means it takes two abnormal copies to exhibit the full blown phenotype – Examples of autosomal recessive disorders are : cystic fibrosis, sickle-cell disease, PKU –A Punnet Square demonstrating inheritance of an autosomal recessive deafness is found at the right Most inherited disorders are caused by autosomal recessive alleles Figure 9.9A DD dd Normal Dd Normal Dd DD Normal Dd Normal (carrier) Dd Normal (carrier) dd Deaf EggsSperm PARENTS OFFSPRING

Found on Chromosome 12

A few inherited disorders are caused by dominant alleles. Dominant alleles hide recessive alleles, phenotypically. Figure 9.9B –Examples: achondroplasia, Huntington’s disease

Autosomal Dominant Inheritance

Table 9.9

Most sex-linked human disorders are due to recessive alleles These sex linked alleles are forms of genes found on the X chromosome. A male has only one X chromosome –Examples: hemophilia, red-green color blindness –These are mostly seen in males, but can be seen in females. –A male receives a single X-linked allele from his mother, and will have the disorder, while a female has to receive the allele from both parents to be affected Sex-linked disorders affect mostly males Figure 9.23A

–Their inheritance pattern reflects the fact that males have one X chromosome and females have two Figure 9.22B-D –These figures illustrate inheritance patterns for white eye color (r) in the fruit fly, an X-linked recessive trait FemaleMaleFemaleMaleFemaleMale XrYXrYXRXRXRXR XRXrXRXr XRYXRY XRXR XrXr Y XRXrXRXr XRXR XrXr XRXRXRXR XRXR Y XRYXRY XrXRXrXR XRYXRY XrYXrY XRXrXRXr XRXR XrXr XrXr Y XRXrXRXr XrXrXrXr XRYXRY XrYXrY XrYXrY R = red-eye allele r = white-eye allele

X-Linked Recessive Inheritance

X-Linked Dominant Inheritance

When an offspring’s phenotype—such as flower color— is in between the phenotypes of its parents, it exhibits incomplete dominance Incomplete dominance results in intermediate phenotypes P GENERATION F 1 GENERATION F 2 GENERATION Red RR GametesRr White rr Pink Rr Rr RR rr 1/21/2 1/21/2 1/21/2 1/21/2 1/21/2 1/21/2 SpermEggs Pink Rr Pink rR White rr Red RR Figure 9.12A

Incomplete dominance in human hypercholesterolemia (high levels of cholesterol in the blood) Figure 9.12B GENOTYPES: HH Homozygous for ability to make LDL receptors Hh Heterozygous hh Homozygous for inability to make LDL receptors PHENOTYPES: LDL LDL receptor Cell NormalMild diseaseSevere disease

Codominance-The individual expresses both phenotypes and neither is dominant.

Type AB express both antigens

Mitochondrial Gene Inheritance

Mitochondrial Disorders

mtDNA Point mutations Cardiomyopathy Leber's optic neuropathy Leigh's syndrome MELAS MERRF NARP/MILS Single deletion or duplication Ataxia, Leukodystrophy Diabetes: Maternal inheritance Kearns-Sayre Pearson's PEO: Sporadic Multiple deletions Aging Myositis Inclusion body COX- muscle fibers MNGIE PEO Wolfram Cardiomyopathy Leber's optic neuropathy Leigh's syndrome MELAS MERRF NARP/MILS Ataxia, Leukodystrophy Diabetes Kearns-Sayre Pearson's PEO: SporadicInclusion bodyCOX- muscle fibers MNGIE PEO Wolfram Depletion of mtDNA Infantile myopathy Fatal "Later-onset" AZT treatment Several types of mtDNA defect Deafness Diabetes External ophthalmoplegia (PEO) Sporadic Maternal Dominant Recessive Leigh's Myopathy Rhabdomyolysis Sensory neuropathy Systemic disordersFatal"Later-onset" AZT treatment Deafness Diabetes External ophthalmoplegia (PEO)SporadicMaternalDominantRecessive Leigh's Myopathy Rhabdomyolysis Sensory neuropathy Systemic disorders

Mitochondrial Inheritance Mitochondrial disease begins to become apparent once the number of affected mitochondria reaches a certain level; this phenomenon is called 'threshold expression'.threshold expression

In class………………………. What is the mode of inheritance of the disorder you are researching? If you are studying a particular cell type, are there diseases associated with this cell type when it is mutated and how are those diseases inherited?