Mendel and his peas
The basic laws of inheritance in simple binary traits were first discovered in the 1860s by Austrian monk, Gregor Mendel, through experiments on peas
Mendel’s Experiment
Cross-pollinating purebred “parent” peas with different traits and observing the ratios of that trait in the next generations.
He started by cross-pollinating, then let the peas exist on their own.
Violet flowers ended up being the dominant trait, and white flowers the recessive.
Genes and Alleles
Each individual inherits two alleles, which may be homozygous or heterozygous.
Homozygous
Having two of the same alleles
Heterozygous
Having two different alleles
Genotype
a particular combination of alleles
Phenotype
the observable characteristics of an organism based on their genotype
Mendel’s 3 Laws of Inheritance
The Law of Dominance
The Law of Segregation of Genes
The Law of Independent Assortment
Dominance
Organisms will portray the dominant alleles if they have Bb or BB.
Relates to how genes encode for proteins.
Incomplete Dominance
Occurs when the heterozygote has a phenotype that’s distinct from both homozygotes, and often intermediates
Example: when one parent flower is red, the other is white, and so the child flower is pink
Codominance
Occurs when two alleles in a gene pair can be fully expressed at the same time.
Ex: Blood Type AB
Segregation in Gene Inheritance
Only one copy of each gene is inherited from each parent.
Mendel didn’t know this, but it is now easy to see that the division of chromosomes in meiosis
Independent Assortment
The alleles for different genes segregate independently of each other.
In this case, whether an offspring receives Y or y from the parent is independent of receiving R or r, but this is sometimes not the case
Epistasis
When the effect of one gene depends on another.
Ex: coat colours in Labrador retrievers
How are genes communicated?
Genes are encoded with protein amino acid sequences.
Genes are transcribed into RNA, which is translated into functioning proteins by ribosomes
How can Gene expression by reduced?
Making the gene inaccessible by changing the chromosomal structure.
Preventing expression or binding of transcription factors.
Many other ways.
