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Mendel and the Gene Idea
Marie Černá
1865 – Gregor Mendel
Mating in peas
Carpel – ovules => female gametes
Stamens – anthers (pollen grains) => male gametes
Mendel’s terms
•
•
character – a heritable feature (flower color)
trait – each variant for a character
(purple or white for flower color)
•
hybrid - the result of breeding (hybridization)
two different variants of a character
monohybrid cross - only one character is studied
dihybrid cross - two characters are studied simultaneously
Mendel’s experiments
• P generation (parental) – self-pollinating
their hybrid offspring:
• F1 generation (first filial)
• F2 generation (second filial)
Dominant / recessive alleles
Mendel’s experiment results
• the law of hybrid uniformity
in the F1 generation
• phenotypic ratio of the F2 generation 3:1
• genotypic ratio of the F2 generation 1:2:1
The two fundamental
principles of heredity:
• The law of segregation
• The law of independent assortment
The law of segregation
the two alleles for a character are
packaged into separate gametes
the two alleles for each character
segregate during gamete production
The law of
independent assortment
each pair of alleles segregates
into gametes independently
in polyhybrid cross, where pairs of alleles
are on separate chromosomes
Genetics
Science about heredity and
variability of organisms
Heredity and variability allow evolution of
organisms on the Earth
Heredity
The ability of parent organisms to pass
their characters in form of talents (genes)
on their descendants.
It is manifested by reproduction.
It allow to conserve characters of organisms.
It allow continuing biological species.
Variability
The ability of organisms to change
their characters.
It allow adaptation of organisms to
certain environment.
It allow evolution of biological species.
Gene (character)
information for formation of
certain organism’s biochemical character
DNA region that codes
information for formation of certain protein
Gene expression
- realization of genetic information
- production of certain protein
Allele (trait)
particular form (alternative version) of a gene
is defined by nucleotide alignment in DNA
is characterized by its own function activity
For each gene, an organism inherits two alleles,
one from each parent
in the phenotype of a heterozygote:
• dominant allele – is fully expressed
• recessive allele – is completely masked
Organism’s status
• Homozygous
– having two identical alleles for a gene
• Heterozygous
– having two different alleles for a gene
Genetic terms
• Genome – the complete set of genes
in a species
• Gene pool – the complete set of genes
in a population
• Genotype – the complete set of genes
in an organism (defined by alleles)
Phenotype – appearance of genotype
Literature
Biology, eighth edition,
Campbell, Reece
Unit three: Genetics
Chapter 14: Mendel and the Gene Idea
Pages 262 – 271