BIO207H5 Lecture Notes - Lecture 11: Null Allele, Mendelian Inheritance, Mitosis
Notes;
● Mendel
○ He articulated in the 1800s the Law of segregation and law of independent
assortment
● Meiosis I
○ Karyokinesis
○ Cytokinesis
■ These processes follow a pattern that is specific to the Law of
Segregation and Independent assortment
● Mendel’s success in 1st and 2nd law
○ 1 gene
○ 2 alleles for gene
○ We have looked at only Fully dominant / recessive
■ Heterozygous phenotype = Homozygous dominant phenotype
● From now on focus on
○ Dominance may not be complete
○ More than 2 alleles for a given locus
■ Allelic series
○ Lethal genotypes
■ Some are preferred over other
○ Sex-limited traits
○ Gene x Environment interaction
■ Role of environment in phenotype
● Behavior, aggression, mental/focus abilities
○ Incomplete penetrance & Variable expressivity
○ Pleiotropic genes
■ A specific gene has more than one function
○ More than 2 genes for a single trait
○ Gene x gene interaction
● Function effect of mutation and alleles
● The molecular basis of dominance relationship
● For a homozygous individual for wild type Allele
○ Each allele will be transcribed to produce a specific product
● Functional effects of mutations
○ Loss of function
■ Null mutation, or amorphic mutation
■ No functional gene product
● If homozygous for mutant allele → no functional product
● If heterozygous for mutant allele
○ One wild type allele → produces a product
○ One null allele → no functional product
■ Often homozygous lethal
○ Loss-of-function
■ Leaky mutations or hypomorphic mutations
■ Partial loss of function
■ Severity depends mutation activity level
● This change could be due to a mutation or a change in the
nucleotide base sequence in the gene
● If homozygous mutation
○ Both copies are less uncational
● If heterozygous mutation
○ Wild-type copy intact
○ The mutated copy is less function
○ Loss-of function
■ Dominant negative mutations
■ Affects multimeric proteins
● Function protein is more than or equal to 2 polypeptides
● Each polypeptide encoded by 1 gene
■ Amino acid change in one subunit
■ Spoiler effect on the protein as a whole
■ Dominant due to loss of function of the multimeric protein
● If homozygous
○ Both transcribed products of the two copies will spoil the
gene product of the second gene and result in an anbrnal
interaction and produce abnormal multimeric products
● If heterozygous
○ One affected copy will affect the gene product of second
gene resulting in an abnormal multimeric product
○ One wild-type allele transcribed protein will have a normal
interaction and produce a normal protein
○ Gain-of function mutations
■ Hypermorphic mutations
● Produce more gene activity than normal
○ Could be due to high expression of the gene
● Homozygous mutation v/s heterozygous
○ More products will be produced for homozygous
■ Neomorphic mutations
● Acquire novel gene activities
● Not found in the wild type
Document Summary
He articulated in the 1800s the law of segregation and law of independent assortment. These processes follow a pattern that is specific to the law of. Mendel"s success in 1st and 2nd law. We have looked at only fully dominant / recessive. More than 2 alleles for a given locus. A specific gene has more than one function. More than 2 genes for a single trait. For a homozygous individual for wild type allele. Each allele will be transcribed to produce a specific product. If homozygous for mutant allele no functional product. One wild type allele produces a product. One null allele no functional product. This change could be due to a mutation or a change in the nucleotide base sequence in the gene. Function protein is more than or equal to 2 polypeptides. Spoiler effect on the protein as a whole. Dominant due to loss of function of the multimeric protein.
