Understanding Pedigree Analysis and Inheritance Patterns

• Pedigree analysis helps determine individual genotypes and predict how single gene traits are transmitted in humans.
• In a pedigree:
  • Squares represent males
  • Circles depict females
  • Shaded shapes signify affected individuals
  • Generations are labeled with Roman numerals

Pedigree Analysis

• Pedigree analysis helps determine individual genotypes and predict how single gene traits are transmitted in humans.
• Analyzing mating results, collecting trait history, assembling family tree information, and predicting future offspring traits are all part of pedigree analysis.

Human Genetic Problem Solutions

• Human generation span is approximately 20-30 years.
• Parents produce only a few offspring.
• Breeding experiments are considered unacceptable.

Inheritance Patterns

• Patterns include:
  • Autosomal dominant
  • Autosomal recessive
  • X-linked dominant
  • X-linked recessive
  • Y-linked
  • Maternal inheritance (mitochondrial inheritance)

Chromosomes

• Humans possess 23 chromosome pairs.
• 22 pairs are autosomal
• 1 pair is sex chromosomes.

Autosomal Dominant Inheritance

• The cause is a dominant gene on an autosome.
• Males and females are equally affected.
• Every affected individual has at least one affected parent.
• Affected individuals mating with unaffected ones have a 50% chance of transmitting the trait to their kids.
• Two affected individuals may have unaffected kids.
• Phenotype usually shows up in every generation.
• Examples of autosomal dominant conditions include:
  • Achondroplasia
  • Huntington's disease
  • Widow's peak
  • Dimples
  • Free lobes
  • Tongue-rolling
  • Brachydactyly
  • Hypercholesterolemia
• Neurofibromatosis is a genetic disorder where nerve tissue tumors can cause severe damage by compressing nerves and other tissues.

Autosomal Recessive Inheritance

• A recessive gene on an autosome is the cause.
• Males and females are equally impacted.
• Affected person may have unaffected parents.
• All children of two affected individuals are affected.
• The phenotype may skip a generation.
• Examples of autosomal recessive conditions include:
  • Cystic fibrosis
  • Phenylketonuria
  • Galactosemia
  • Albinism
  • Hemophilia
  • Sickle-cell anemia
  • Tay-Sachs disease

X-linked Dominant Inheritance

• The cause is a dominant allele on the X chromosome.
• Trait is never passed from an affected father to his sons.
• All daughters of an affected father and a normal mother are affected.
• All sons of an affected father and normal mother are normal.
• Females more likely to be affected.
• Examples of X-linked dominant conditions include:
  • Hypophosphatemia
  • Aicardi syndrome
  • Fragile X syndrome

Fragile X Syndrome (FXS)

• It’s an inherited genetic condition causing intellectual and developmental disabilities, also known as Martin-Bell syndrome.
• FXS results from a defect in the FMR1 gene on the X chromosome.
• A mutation on the FMR1 gene prevents the production of a protein called fragile X mental retardation 1 protein, which affects nervous system function.

X-Linked Dominant Disorders

• Some are lethal for males.
• An example of X-linked dominant disorder is Incontinentia pigmenti (IP)
• Lethal in hemizygous males before birth.
• Exclusive in females.
• Affected females produce affected daughters, normal daughters, and normal sons in equal proportions (1:1:1).

X-linked Recessive Inheritance

• It's due to a recessive allele on the X chromosome.
• The trait is never passed from father to son.
• Males are more likely to be affected.
• Trait typically passes from an affected grandfather, through carrier daughters, to half of his grandsons.
• Examples include red and green colorblindness, hemophilia, Duchenne muscular dystrophy, and Hunter syndrome.

Y-linked Inheritance

• Due to an allele on the Y chromosome.
• When a male is affected, all of his male children are also affected.
• Male infertility and hypertrichosis pinnae are examples.

Maternal (Mitochondrial) Inheritance

• This involves the transmission of genes in mitochondria, not in the cell nucleus.
• An affected mother will have all offspring affected.
• If the father is affected, none of the offspring will be affected.
• This is a group of conditions affects the mitochondria.
• Affected females transmit the disease to all their children
• Affected males have normal children.
• Males cannot transmit the disease as the cytoplasm is inherited only from the mother; mitochondria are in the cytoplasm.
• Effects energy metabolism and impacts tissues that require constant energy, like muscles.
• Affected mothers transmit equally to all their children, while affected fathers do not transmit the disease.
• An example is Lebers hereditary optic neuropathy (LHON). It involves rapid optic nerve death, leading to blindness in young adults.

Summary of Inheritance Patterns

• Autosomal Dominant: Affected individuals always have at least one affected parent.
• Autosomal Recessive: Affected individuals often have unaffected parents; can skip generations.
• Y-linked Inheritance: Only affects males, passed from affected father to only sons.
• Maternal Inheritance: If the mother is affected, all offspring are affected; if the father is affected, none are affected.
• X-linked Dominance: Affected father will pass the trait to all daughters; may not skip generations.
• X-linked Recessive: Typically affects males; Criss cross inheritance where trait passes from grandfather through carrier daughter to grandson.