Mendelian Genetics discusses Gregor Mendel's principles of heredity and genetics. It defines key terms like phenotype, genotype, dominant and recessive alleles. It explains Mendel's two laws: 1) The Law of Segregation, which states that alleles segregate and only one allele is passed on from each parent during gamete formation. 2) The Law of Independent Assortment, which demonstrates that inheritance of different traits occurs independently through random assortment and separation of alleles during meiosis. Mendel tested these laws through pea plant experiments to predict inheritance patterns of traits.

1. Mendelian Genetics
Mohd Aminudin Bin Mustapha
Centre for Pre-University Studies
Universiti Malaysia Sarawak
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2. Learning Objectives
• Define the basic principles of heredity
• Explain law of segregations and law of independent
assortments

3. Heredity
 Heredity, the transmission of genetic information from
parent to offspring, generally follows predictable pattern
in organisms.
 One possible explanation of heredity is a “blending”
hypothesis.
 An alternative to the blending model is the “particulate”
hypothesis of inheritance: the gene idea

4. Heredity
 Allele is alternative form of a genetic locus: a single
allele for each locus is inherited separately from each
parent.
 Locus is the specific location of a particular gene on a
chromosome.
 Gene is the fundamental physical and functional unit of
heredity.

5. Heredity
 Phenotype – Observable trait or traits of an individual
 Genotype – The genetic constitution of an organism.
 Heterozygous - Two alleles for a trait are different (Aa)
 Homozygous - Two alleles for a trait are the same (AA
or aa)

6. Heredity
 Dominant allele- a gene is said to be dominant if it
expresses its phenotype even in the presence of a
recessive gene.
 Recessive allele –In heterozygous, an allele whose
expression is fully or partially masked by expression of
its partner; fully expressed only in the homozygous
recessive condition.

7. Law of Segregation
 Different variations of genes accounts for variations in
inherited characters.
 An organism inherits two alleles for every characters
from each parents
 If the two alleles differ, the dominant allele will be fully
expressed in its phenotype, while the recessive does
not.
 The two alleles of each character segregate during
gamete production

8. Law of Segregation
 To test the hypothesis, Mendel predicted the outcome of
a breeding experiment.
 He crossed heterozygous round peas (Rr) with
homozygous wrinkled peas (rr) (test cross), then
predicted the result would be 1 round : 1 wrinkled.
 Mendel crossed pea plants that differed in six other
qualitative traits and the results supported his
hypothesis.

12. Law of Independent Assortment
 During meiosis, members of a pair of genes on
homologous chromosomes get distributed into gametes
independently of other gene pairs.
 The genes for different traits are inherited independently
of each other.
 Many gene pairs tend to sort into gametes independently
of one another.

13.  Mendel realized that the results could only be explained
if the genes for seed shape and color were inherited
independently.
 The second law states that the alleles for one trait may
be distributed to the gametes independently of the
alleles for another traits.
 When paired chromosomes line up during metaphase I,
the orientation of the homologous chromosome of one
pair does not influence the orientation of other pairs.
Law of Independent Assortment