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

Basic Terms

Figure 14.0 Painting of Mendel

Figure 14.0x Mendel

Figure 14.x1 Sweet pea flowers

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

Figure 14.1 A genetic cross

Figure 14.2 Mendel tracked heritable characters for three generations

Table 14.1 The Results of Mendel’s F 1 Crosses for Seven Characters in Pea Plants

Figure 14.x2 Round and wrinkled peas

Figure 14.4 Mendel’s law of segregation (Layer 1)

Figure 14.4 Mendel’s law of segregation (Layer 2)

Figure 14.5 Genotype versus phenotype

Figure 14.6 A testcross

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.

Figure 14.3 Alleles, alternative versions of a gene

Figure 14.7 Testing two hypotheses for segregation in a dihybrid cross

Figure 14.8 Segregation of alleles and fertilization as chance events

Complexities of Gene Expression Incomplete Dominance Co-dominance Epistasis Polygenic characters Pleiotropy Environmental effect Developmental effect

Figure 14.9 Incomplete dominance in snapdragon color

Figure 14.9x Incomplete dominance in carnations

Figure Multiple alleles for the ABO blood groups

Figure 14.10x ABO blood types

Figure An example of epistasis

Figure A simplified model for polygenic inheritance of skin color

Figure The effect of environment of phenotype

Figure Pleiotropic effects of the sickle-cell allele in a homozygote

Mendelian Inheritance in Humans Recessive Traits Albinism, Cystic Fibrosis, Tay Sachs, Sickle Cell, PKU, Galactosemia Dominant Traits Achondroplasia Alzheimer’s, Huntington, Hypercholesterolemia

Polygenic Traits Heart Disease Cancer Diabetes Alcoholism Schizophrenia Manic Depression

Figure Pedigree analysis Dominant Traits Widow’s Peak, Freckles and Free Ear Lobe

Figure Large families provide excellent case studies of human genetics

Early Detection of Human Genetic Disorders Amniocentesis Chorianic Villus Sampling (CVS) Ultrasound Fetoscopy Screening of embryos

Figure Testing a fetus for genetic disorders

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