Human Genetics

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Human Genetics
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Human Inheritance

• Inheritance patterns of diseases are often used.
• Easy to trace (see), and area of concern for
  humans.

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Pedigree Analysis

• Many traits are Mendelian in their inheritance
  patterns.
• These traits can be followed using a pedigree
  chart.

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Pedigree Chart Symbols
(Female Circle) Affected Male
Normal Female
Normal Male Female Carrier
(Male Square)
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Patterns of Inheritance

• Certain phenotypes follow predictable patterns.
• Many human traits are polygenic and cant be
  followed using a pedigree.

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PolyWHAT?

• Polygenic simply means that a trait is controlled
  by more than one gene.
• This pattern does not follow Mendels rules.

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Difficult Humans

• Humans have over 30,000 genes.
• Difficult to study
• Long life cycle.
• Relatively few offspring.

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Types of Genetic Patterns

• Autosomal Recessive
• Autosomal Dominant
• X-linked
• Multiple Alleles
• Polygenic

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Single Allele Traits

• Controlled by a single allele of a gene.
• Can be dominant or recessive.

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Recessive Single Alleles

• Recessive Alleles show up if homozygous
  recessve.
• Autosomal-recessive pattern.
• Albinism
• Cystic fibrosis
• Phenylketonuria (PKU)
• Sickle cell anemia

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Dominant Single Alleles

• Dominant Alleles Can show up in homozygous or
  heterozygous genotype.
• Autosomal-dominant pattern.
• Huntingtons Disease
• Achondroplasia (dwarfism)
• Polydactyly

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Multiple Allele Traits

• Gene that controls a trait has 3 or more alleles.
  
• Human blood type is controlled by 2 genes.
• ABO gene 1 gene, 3 alleles.
• Rh gene 1 gene, 2 alleles.

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Blood Type Inheritance

• 3 alleles for ABO
• IA codes for type A blood.
• IB codes for type B blood.
• IA and IB are codominant.
• i codes for type O blood.
• i is recessive to IA and IB .

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Production of Antigens

• IA and IB alleles tell the cell to produce A
  and B antigens.
• Antigens are sugars on the surface of red blood
  cells.
• They tell the immune system that the cells are
  its own cells.

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Production of Antigens (Cont.)

• i alleles tell the cell not to produce any
  antigens.
• If a person has the genotype ii, they will have
  no A or B antigens on RBCs.

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What is Your Blood Type?

• The alleles you get from your parents, determine
  your blood type.
• Can your parents have type A or B blood if you
  are type O?

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Blood Types
Phenotype (Blood type)
Antigen on RBC
Safe Transfusions
Genotype
To
From
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Rh Factor

• Dominant single allele , recessive allele -.
• Controls production of a sugar on surface of RBC.
• Follows simple dominance.

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Polygenic Traits

• Most human traits are polygenic.
• Controlled by several genes, not just one.

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Some Polygenic Traits

• Skin color 3 to 6 genes.
• Affect production of melanin.
• Eye color similar to skin color.
• Polygenic traits are highly influenced by
  environment.

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X-Linked Traits

• Also called sex-linked traits.
• Genes located on X or Y chromosome.
• X-linked conditions more common in males.

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X-Linked Disorders

• Colorblindness 8 of males affected.
• Hemophilia primarily males.
• Duchenne muscular dystrophy
• Most X-Linked traits are not disorders.

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Sex-Influenced Traits

• Expression of traits is affected by male and
  female hormones.
• Males and females will have different phenotypes
  with the same genotype.

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Sex-Influenced Examples

• Baldness controlled by an allele (B).
• B is dominant in males, but recessive in females.
• Both homozygous genotypes will eventually lose
  their hair.

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A Cruel Joke?

• Heterozygous bald genotypes (BB) in males will
  become bald.
• Heterozygous women will not be bald.
• Caused by higher testosterone in males.

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Chromosomal Disorders

• Many caused by non-disjunction.
• Monosomy Human with only 45 chromosomes.
• Trisomy Human with 47 chromosomes.

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Effects of Chromosomal Disorders

• Often lethal.
• Trisomy 21 Downs syndrome.
• Non-disjunction of X chromosome
• Turners syndrome (XO) monosomy.
• Klinefelters syndrome (XXY) trisomy.