Modes of inheritance
patterns in which single-gene traits and disorders occur in families.
autosomal dominant disease
Huntington disease is an example
Affects both sexes and appears in every generation
autosomal recessive
Cystic fibrosis is an example
Affects both sexes and can skip generationsthrough carriers
Monohybrid cross
Follows one trait and the self-crossed plants are hybrids.P Parental generation | Tall × Short↓F1 All tall↓F2 1/4 Short: 3/4 Tall
Mendel’s First “Law”—Segregation
each element (gene) separates in the gametes. This reflects the actions of chromosomes and the genes they carry during meiosis
Homozygous
carry same alleles TT or tt
Heterozygous
carry different alleles Tt
Genotype
Organism’s alleles
Phenotype
= Outward expression of an allele combination
Wild Type
Most common phenotype (Recessive or dominant)
Mutant phenotype
Variant of a gene’s expression that arises when the gene undergoes mutation
Modes of Inheritance
Rules that explain the common patterns of single-gene transmission
Passing of a trait depends on whether:Gene is on an autosome (chromosomes 1-22) or on a sex chromosome (X and Y)Allele is recessive or dominant
Lethal Alleles
A lethal genotype causes death before the individual can reproduce
Removes an expected progeny class following a specific cross. For example, a double dose of adominant allele may be lethal.
Incomplete Dominance
Heterozygous phenotype is intermediate between those of the two homozygotes
Codominance
Heterozygous phenotype results from the expression of both alleles.
ABO gene encodes
a cell surface glycoprotein and there are 3 alleles.
one allele produces A antigen. one allele produces B antigen. one allele does not produce antigens.