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Patterns of Inheritance (Classical Genetics (Crosses (Dihybrid Cross (two…
Patterns of Inheritance
Mendel's Laws
Law of Segregation
Law of Independent Assortment
Classical Genetics
Crosses
Dihybrid Cross
(two characters)
Testcross
(cross with homozygous recessive to determine unknown genotype)
Monohybrid
(one character)
Diagrams
Punnett Square
Pedigree
Generations
F1 (offspring of parental cross)
F2 (offspring of F1 cross)
P (parental)
Analysis
Determine expected ratio of genotypes/phenotypes of offspring based on parents
Deduce probable genotypes/phenotypes of parents based on offspring
Genes
Genotype
Heterozygous
"hybrid" / "carrier"
Homozygous
"pure-bred"
Alleles / Traits
Recessive
Dominant
Phenotype
Wild-Type
(most common in nature)
Mutant
Variations on Mendel's Laws
Pleiotropy
(one gene influences many characters)
Polygenic inheritance
(one character affected by many genes,
leading to a continuum of phenotypes)
Co-dominance
(both traits are expressed at the same time)
Incomplete dominance
(dominant trait expressed less strongly,
leading to intermediate phenotype)
Chromosomal Basis of Inheritance
genes on different chromosomes assort independently during meiosis
genes far apart on the same chromosome
assort independently because of crossing over
alleles on homologous chromosomes segregate during meiosis
Gene Linkage
Autosomal Linkage:
genes close together on the same chromosome are linked and tend to be inherited together
Sex-Linkage:
genes on sex chromosomes
can be inherited disproportionately between men and women
Role of Environment
Epigenetic Inheritance
(transmission of traits by mechanisms beyond DNA sequence)