BIOB11H3 Lecture 1: Lecture 1
Lecture 1
Prokaryote and Eukaryote Cells Have Different Internal Structures
An Overview of Several Important Discoveries on The Nature of Gene
Gene as A Unit of Inheritance
Gregor Mendel experimented by cross breeding pea plants over a number of generations and
observed/followed different plant characteristics
Any given characteristic of the plant is governed by distinct units of inheritance. These distinct units are
called genes.
Each individual has two copies of a gene, one from each parent (inheritance). These alternate forms of
gene are called alleles. The alleles can be dominant or recessive.
oHomozygous: same copy
oHeterozygous: different copy
Each reproductive cell (called gamete) contained only one copy of the gene (allele) for a particular
trait. Therefore, the progeny will have two copies of the gene (2 alleles) for that trait – one from each
parent
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Dominant and Recessive Alleles
The alleles can be identical (homozygous) or non-identical (heterozygous)
Dominant Allele: The allele that determines the phenotype (observable trait) of an individual
If an individual is a heterozygote with one dominant and one recessive allele, the dominant allele will
mask the existence of the recessive allele.
Example:
o‘A’ is the dominant allele for tall height
o‘a’ is the recessive allele for short height
Mendel’s Laws of Inheritance
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A pair of alleles that govern a particular trait remain together
throughout an individual’s life but can be separated
(segregated) during reproduction (formation of gametes /
meiosis)
Law of Segregation: An organism’s two alleles
segregate from one another during gamete formation.
One gamete carries one allele for each trait.
oExample:
‘R’ is dominant allele for ‘round’ seeds
‘r’ is recessive allele for ‘wrinkled’ seeds
oTherefore, ‘Rr’ parent can produce gametes
with either ‘R’ or ‘r’
Segregation of a pair of alleles for one particular trait (e.g. seed colour) has no affect on the segregation of
other alleles (e.g. seed shape). Therefore, the offspring can have the maternal allele for seed shape and
paternal allele for seed colour.
Law of Independent Assortment: Segregation of a pair of alleles for one trait has no effect on the
segregation of alleles for another trait.
oi.e. alleles do not influence each other when it comes to sorting into gametes.
oLeads to a number of possible genetic arrangements.
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Document Summary
Prokaryote and eukaryote cells have different internal structures. An overview of several important discoveries on the nature of gene. Gregor mendel experimented by cross breeding pea plants over a number of generations and observed/followed different plant characteristics. Any given characteristic of the plant is governed by distinct units of inheritance. Each individual has two copies of a gene, one from each parent (inheritance). These alternate forms of gene are called alleles. The alleles can be dominant or recessive: homozygous: same copy, heterozygous: different copy. Each reproductive cell (called gamete) contained only one copy of the gene (allele) for a particular trait. Therefore, the progeny will have two copies of the gene (2 alleles) for that trait one from each parent. The alleles can be identical (homozygous) or non-identical (heterozygous) Dominant allele: the allele that determines the phenotype (observable trait) of an individual.
