Mendelian Genetics K. Sathasivan

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Mendelian GeneticsK. Sathasivan

• Basic genetic terms.
• Mendel's laws of inheritance.
• Complexities of genetic expression.
• Mendelian genetics in Humans

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Basic Terms
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Figure 14.0 Painting of Mendel
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Figure 14.0x Mendel
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Figure 14.x1 Sweet pea flowers
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Law of Segregation

• Allele pairs segregate (separate) during gamete
  formation and the paired condition is restored by
  the random fusion of gametes at fertilization.

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Figure 14.1 A genetic cross
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Figure 14.2 Mendel tracked heritable characters
for three generations
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Table 14.1 The Results of Mendels F1 Crosses
for Seven Characters in Pea Plants
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Figure 14.x2 Round and wrinkled peas
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Figure 14.4 Mendels law of segregation (Layer 1)
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Figure 14.4 Mendels law of segregation (Layer 2)
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Figure 14.5 Genotype versus phenotype
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Figure 14.6 A testcross
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Law of Independent Assortment

• Law The segregation of each allele pair is
  independent of other allele pairs. The individual
  allele pairs need to be located on separate loci,
  far from each other to allow independent
  assortment during gamete formation.

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Figure 14.3 Alleles, alternative versions of a
gene
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Figure 14.7 Testing two hypotheses for
segregation in a dihybrid cross
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Figure 14.8 Segregation of alleles and
fertilization as chance events
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Complexities of Gene Expression

• Incomplete Dominance
• Co-dominance
• Epistasis
• Polygenic characters
• Pleiotropy
• Environmental effect
• Developmental effect

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Figure 14.9 Incomplete dominance in snapdragon
color
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Figure 14.9x Incomplete dominance in carnations
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Figure 14.10 Multiple alleles for the ABO blood
groups
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Figure 14.10x ABO blood types
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Figure 14.11 An example of epistasis
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Figure 14.12 A simplified model for polygenic
inheritance of skin color
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Figure 14.13 The effect of environment of
phenotype
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Figure 14.15 Pleiotropic effects of the
sickle-cell allele in a homozygote
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Mendelian Inheritance in Humans

• Recessive Traits
• Albinism, Cystic Fibrosis, Tay Sachs,
• Sickle Cell, PKU, Galactosemia
• Dominant Traits
• Achondroplasia
• Alzheimers, Huntington, Hypercholesterolemia

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Polygenic Traits

• Heart Disease
• Cancer
• Diabetes
• Alcoholism
• Schizophrenia
• Manic Depression

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Figure 14.14 Pedigree analysis
Dominant Traits Widows Peak, Freckles and Free
Ear Lobe
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Figure 14.16 Large families provide excellent
case studies of human genetics
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Early Detection of Human Genetic Disorders

• Amniocentesis
• Chorianic Villus Sampling (CVS)
• Ultrasound
• Fetoscopy
• Screening of embryos

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Figure 14.17 Testing a fetus for genetic
disorders
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Summary

• Basic genetic terms.
• Genotype, phenotype, gene, allele, dominant,
  recessive, homozygous and heterozygous etc.
• Mendel's laws of inheritance.
• Law of segregation and law of independent
  assortment.
• Complexities of genetic expression.
• Incomplete dominance, codominance, epistasis,
  pleiotropy etc.
• Mendelian genetics in Humans
• Dominant and recessive disorders and early
  detection techniques