Mendel’s Legacy Genetics is everywhere these days – and it will continue as a dominant force in...
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Transcript of Mendel’s Legacy Genetics is everywhere these days – and it will continue as a dominant force in...
Mendel’s Legacy
Genetics is everywhere these days – and it will continue as a dominant force in biology and society for decades to come.
Wouldn’t it be nice if people understood it better?
The Fundamental Question
What is the relationship between genes (genotype) and observable characteristics (phenotype)?
The answer?
Phenotype = Genotype + Environment.
Dangerously Ahead of the Game - A Eugenics Exhibit at the 1920 Kansas State Fair
Will History be Repeated?
A Mendelian Genetic Primer
Genes come in pairs that separate in the formation of gametes.
The members of the pair may be identical (homozygous) or non-identical (heterozygous).
Each form of a particular gene is an allele.
A Mendelian Genetic Primer
One allele is dominant over another (or so Mendel believed).
Only two alleles of a given gene are possible in an individual although many alleles of a gene are possible within a population.
The Explanation – there are two alleles for every trait, one dominant over the other. The alleles separate at meiosis so that half the gametes contain one type of allele, and the other half contain the other type. (Principle of Segregation)
Principle of Segregation
The principle of segregation is explained by the behavior of homologous chromosomes at meiosis.
Segregation
What Works for Peas Also Works for Humans
An albino
In the cross Aa x Aa, where A is a dominant allele for wild type (standard) pigmentation and a is a recessive allele for no pigmentation (albinism), ¾ of offspring will be wild type and ¼ will be albino.
Are Two Different Characters Like Color and Shape Inherited Together or Independently?
Mendel performed dihybrid crosses to find out.
A Dihybrid Cross Illustrated Though a Punnett Square
The question’s answer?
Different characters are inherited independently (The Principle of Independent Assortment)
Principle of Independent Assortment
The principle of independent assortment is explained by the behavior of homologous chromosomes at meiosis.
The alignment of one pair of homologs is independent of any other.
A cross between two carriers for deafness and albinism.
This is the same 9:3:3:1 ratio seen for the Mendelian cross involving pea color and shape.
What Works for Peas Also Works for Humans
Some Alleles Are Related Through Partial Dominance
Dominance relationships may differ, but the Principle of Segregation remains the same.
One Allele Can Influence Many Traits
This is known as pleiotropy
Anemia, infections, weakness, impaired growth, liver and spleen failure, death.
Traits (phenotypes) associated with the sickle cell allele.