Case 12 Listen to what Mendel had to say
Learning goals
Who is Mendel?
Mendel discovered some fundamental principles of genetics.
o 3 laws (briefly)
1. The principle of segregation: Recessive traits, which are masked in
the F1 from a cross between two true-breeding strains, reappear in a
specific proportion in the F2. In modern terms this means that the two
members of a gene pair (alleles) segregate (separate) from each other
during the formation of gametes in meiosis. Half the gametes carry
one allele, and the other half carry the other allele, they randomly
unite at fertilization.
2. The principle of independent assortment: The factors for different
pairs of traits assort independently of one another. In modern terms,
this means that pairs of alleles for genes on different chromosomes
segregate independently in the formation of gametes. (crossing-over)
3. The principle of dominance: States that in an individual that is
heterozygous for a genetic trait the recessive allele will always be
masked by the dominant allele. Therefore, a cross between a
homozygous and a homozygous recessive will always express the
dominant phenotype, while still having a heterozygous phenotype
Mendelian trait: a Mendelian trait is one that is controlled by a single locus in an inheritance
pattern in such cases, a mutation in a single gene can cause a disease that is inherited
according to Mendel’s law.
Mendelian population: is a group of interbreeding individuals who share a
common set of genes.
What is an allele frequency?
Number of copies of a given allele/ Sum of counts of all alleles in the population. How
common an allele is in a population
Genotype: Set of alleles
Phenotype: Observable features
o What is an allele?
An allele is one or two, or more forms of a given gene.
o Types of alleles
Learning goals
Who is Mendel?
Mendel discovered some fundamental principles of genetics.
o 3 laws (briefly)
1. The principle of segregation: Recessive traits, which are masked in
the F1 from a cross between two true-breeding strains, reappear in a
specific proportion in the F2. In modern terms this means that the two
members of a gene pair (alleles) segregate (separate) from each other
during the formation of gametes in meiosis. Half the gametes carry
one allele, and the other half carry the other allele, they randomly
unite at fertilization.
2. The principle of independent assortment: The factors for different
pairs of traits assort independently of one another. In modern terms,
this means that pairs of alleles for genes on different chromosomes
segregate independently in the formation of gametes. (crossing-over)
3. The principle of dominance: States that in an individual that is
heterozygous for a genetic trait the recessive allele will always be
masked by the dominant allele. Therefore, a cross between a
homozygous and a homozygous recessive will always express the
dominant phenotype, while still having a heterozygous phenotype
Mendelian trait: a Mendelian trait is one that is controlled by a single locus in an inheritance
pattern in such cases, a mutation in a single gene can cause a disease that is inherited
according to Mendel’s law.
Mendelian population: is a group of interbreeding individuals who share a
common set of genes.
What is an allele frequency?
Number of copies of a given allele/ Sum of counts of all alleles in the population. How
common an allele is in a population
Genotype: Set of alleles
Phenotype: Observable features
o What is an allele?
An allele is one or two, or more forms of a given gene.
o Types of alleles
