23.Heredity. Mendel’s lows and deviations from predicted ratio. Gene interactions and patterns of inheritance.
Covers Mendel's basic concepts of alleles, genotype and phenotype, then his law of segregation and law of independent assortment, including the 9:3:3:1 dihybrid ratio and the meiotic basis of independence. It goes on to autosomal dominant and recessive patterns of inheritance and finishes with X-linked inheritance in XX and XY individuals. Gene interactions and deviations from predicted ratios are named in the title but not developed in the text.
Topic 23 of 63 in the MU Pleven syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 7 sections, about 417 words (3 min of reading), with 21 flashcards.
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Heredity. Mendel’s laws and deviations from predicted ratio. Gene interactions and patterns of inheritance.
Mendel’s Basic Concepts
Mendel’s Laws
Law of Segregation (First Law)
Law of Independent Assortment (Second Law)
Patterns of Inheritance
Sex-Linked (X-Linked) Inheritance
Heredity. Mendel’s laws and deviations from predicted ratio. Gene interactions and patterns of inheritance.
Heredity is the passing of traits from parents or ancestors to their offspring. Through heredity, offspring acquire characteristics of their parents. Variations produced by heredity accumulate across generations and contribute to evolutionary change.
Mendel’s Basic Concepts
Mendel proposed that each individual carries two factors (alleles) for every trait — one inherited from each parent.
If both alleles are the same → homozygous.
If the alleles differ → heterozygous.
Alternative versions of a gene are called alleles.
Genotype refers to the collection of alleles an individual has.
Phenotype is the physical appearance, influenced by genotype + environment.
An individual passes one allele to each gamete during gamete formation. Even if an allele is present, it may not be expressed — in heterozygotes, the dominant allele masks the recessive one (except in conditions like codominance).
Law of Segregation (First Law)
Every diploid individual has a pair of alleles for each trait. During meiosis, these alleles separate so that each gamete receives only one allele.
At fertilization, gametes combine to restore the pair.
This law explains how paternal and maternal alleles are separated and distributed into different gametes.
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