1. Principle of Genetics
Mendel's laws, monohybrid and dihybrid crosses.
Nucleus
chromosome
Protein
Genotype
The genetic composition
of an organism
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Any change to the
genotype
Mutation
May be inherited by
future generations
made up of many
Genes
Portions of DNA
If more than
two alleles for
each gene.
made up of different
forms called
Alleles
Usually two for each gene
AIf both alleles
express
themselves
equally
Co-dominance
R- dominant
alel
r- recessive
alele
R and rare
allelic pair
of a certain
gene
If alleles express themselves differently
Dominant allele
Expresses itself when
present with the recessive
allele of the same gene
Recessive allele
Does not express itself
when present with the
dominant allele of the
same gene
I
Locus 1
Locus 2
Locus 3l
H and h are
another allelic
pair, but for
another gene
Gene 2
Gene 3
A pair of
homologous
chromosomes
Gametes possess only one allele. Random fusion of gametes means that any allele from one parent can combine
with any allele from the other parent
Dominant
Dominant
Homozygous
dominant
Note:
Gene is a segment of DNA . One
gene carries an information for the
synthesis of one specific protein.
Dominant Recessive
Recessive Dominant
Heterozygous
Environmental effects
Recessive
Recessive
Homozygous
recessive
Allele from
first parent
Allele from
second parent
Phenotype
Actual appearance
of an organism
Any change to the
Modification
Is not inherited by
future generations
Phenotype
Actual appearance
of an organism
phenotype
Modification
Is not inherited by
future generations
Mendel's First Law / Law of Segregation
Explanation of Monohybrid Cross in Pea plants ( Diagram below)
• Monohybrid cross considers the inheritance of only one characteristic eg. the tallness of the plant
• The characteristic eg. tallness of plant consists of two contrasting traits- tall (dominant) and dwarf
(recessive traits) and
• T - dominant allele for tall and t, the recessive allele for dwarf
• Genotype : TT - phenotype is tall ( homozygous dominant)
Tt - phenotype is tall ( heterozygous)
tt - phenotype is dwarf ( homozygous recessive)