2. INTRODUCTION
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3. Mendel and the Gene Idea
What is genetic principles account for the passing of traits from parents to
offspring?
The “blending” hypothesis is the idea that genetic material from the parents
blends together (like blue and yellow paint blend to make green)
The “particulate” hypothesis is the idea that parents pass on discrete heritable
units (genes)
This hypothesis can explain the reappearance of traits after several
generations
Mendel documented a particular mechanism through his experiments with
garden peas
4. Mendel used the scientific approach to identify two
laws of inheritance
Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments
Mendel’s Experimental, Quantitative Approach
Advantage of pea plants of genetic study
-there are many varieties with distinct heritable features , or characters (such as flower color)
character variants (such as purple or white flower) are called traits
-mating can be controlled
-each flower has sperm-producing organs (stamens) and an egg-producing organ (carpel)
-Cross-pollination (fertilization between different plants)involves dusting one plant with pollen from
another
Mendel chose to track only those characters that occurred in two distinct alternative forms
He also used varieties that were true-breeding (plants that produce offspring of the same variety when they self-
pollinate)
5. Mendel used the scientific approach to identify
two laws of inheritance
In a typical experiment , Mendel mated two contrasting , true-breeding varieties, a process called
hybridization
True-breeding parents are the P generation
The hybrid offspring of the P generation are called F generation
When F1 individuals self-pollinate or cross-pollinate with other
8. ALLELE
Is one member of a pair or series of different forms of a gene.
Homozygous an organism in which 2 copies of genes are identical i.e have same
alleles
Heterozygous an organism which has different alleles of the gene
CHROMOSOMES
Chromatin-DNA,RNA & protein that make up chromosomes.
Chromatids - one of the two identical parts of the chromosome.
Centromere – the point were two chromatids are.
46 chromosomes. 22 pair autosomes and 1 pair sex chromosomes.
9. NUCLEOTIDE: group of molecules that when linked together, form the building
blocks of DNA and RNA;composed of phosphate group, the bases:
adenosine,cytosine,guanine and thymine and a pentose sugar. In case of RNA,
thymine base is replaced by uracil.
CODON: series of three adjacent bases in one polynucleotide chain of a DNA of
RNA molecule which codes for a specific amino acid.
GENETIC CODE: the sequence of nucleotides in a DNA or RNA molecule that
determines the amino acid sequence in the synthesis pf proteins.
Congenital disease.
Disease which are present at brain
Hereditary / Familial disease.
Disease which are derived from one’s parents and transmitted in the
gametes through generations.
Not all congenital disease are genetic (congenital Syphilis) and not all genetic disease are congenital
(huntington disease)
10. Mutations.
Permanent changes in the DNA. Those that affect germ cell are transmitted to
the progeny. Mutations in the somatic cells are not transferred to the progeny
but important in the causation of cancer and some congenital disease.
CAUSES OF MUTATIONS
Chemicals
-nirrous acid
-alkalating agents
-5-bromouracil
-antiviral drug iododeoxy uridine
-benzpyrene in tobacco smoke
-x-rays & ultraviolet light
Certain viruses such as bacterial virus
11. TYPES OF MUTATIONS.
Point Mutation: substitution of a single nucleotide base by a different base
Frameshift Mutations: insertion or deletion of one or two pairs alters the reading frame of
the DNA strand.
Trinucleotide Repeat Mutations: set of genetic disorder caused by trinucleotide repeat in
certain genes exceeding normal, stable threshold e.g. Fragile X Syndrome
Classification of Genetic Diseases:
Single Gene Defeat/Mendelian Disorders.
Disorders with Multifactorial or Polygenic inheritance.
Cytogenetic Disorders.
Disorder showing atypical patterns of inheritance.