Mendelian Genetics Quiz

Mendelian Genetics (Transmission Genetics)

• Gregor Mendel, in 1866, conducted significant research on heredity using pea plants (Pisum sativum)
• Mendel's work focused on discrete units of inheritance (genes)
• Seven traits in pea plants were studied (e.g., seed shape, seed color)
• Each trait had two contrasting forms (alleles).
• The pea plant was a good model organism because of its fast development, easy growth, and clear traits
• Mendel discovered that traits passed from generation to generation in a predictable pattern

Definitions

• Allele: One variant of a gene
• Chromosome: A structure made of DNA containing many genes, arranged in a linear strand
• Compound Heterozygote: Possesses two different recessive alleles for the same gene
• DNA: Deoxyribonucleic acid
• Dominant allele: An allele whose trait appears even if only one copy is present. A dominant allele tends to "mask" a recessive allele
• Gene: A unit of inherited information
• Genotype: The combination of alleles for a particular gene in an organism
• Heterozygous: Having two different alleles for a particular gene
• Homozygous: Having two identical alleles for a particular gene
• Mutant Phenotype: A variation in a gene's expression caused by a change (mutation)
• Phenotype: An organism's observable characteristics
• Recessive allele: An allele whose trait doesn't show up unless two copies are inherited, or if the dominant allele is not present
• Traits are discrete units of inheritance
• Genes determine trait expression, and are represented by pairs of discreet units - units which Mendel called “elementen”

Single-Gene Inheritance

• Single-gene diseases differ from others in how easily they can be predicted in families and how the associated genes differ between individuals in a population

Modes of Inheritance

• Inheritance patterns are predictable using Mendel's Laws
• Modes of inheritance depend on the location of the gene (autosomal or sex chromosome), and whether the allele is recessive or dominant

Autosomal Inheritance

• Autosomal dominant conditions appear in each generation because one dominant allele is necessary for the trait
• Autosomal recessive conditions may not appear in every generation because a carrier (heterozygote) can pass the recessive allele without expressing the condition

Monohybrid Cross

• A monohybrid cross examines the inheritance of one trait
• The Punnett square is a useful tool for predicting the outcome of genetic crosses
• Test crosses determine an unknown genotype by mating it with a known homozygous recessive

Dihybrid Cross

• A dihybrid cross examines a genetic cross to look at the inheritance of two traits
• Results follow a 9:3:3:1 phenotypic ratio, showing that traits are independently assorted in gametes
• Independent assortment of homologous chromosomes separates during meiosis so the alleles of different genes are sorted into different gametes at random

Beyond Mendel's Laws

• Some characteristics of traits do not follow the pattern of Mendelian ratios
• Incomplete dominance: Heterozygotes have an intermediate phenotype between two homozygous types
• Codominance: Alleles are both expressed in the heterozygote. The example of the ABO blood type system is cited
• Epistasis: One gene affects the expression of another gene. In the case of albinism, cited here, which results from the interaction of genes that result in color expression
• Pleiotropy: One gene affects multiple traits. Example of Marfan Syndrome cited
• Phenocopies: Environmental factors can produce phenotypes similar to those caused by genes

Other concepts

• Lethal alleles: Cause death before the organism can reproduce
• Mitochondrial inheritance: Traits are passed only from the mother
• Heteroplasmy: Presence of both wild type and mutant mitochondrial alleles in the same cell. 
• Epistasis, pleiotropy, and phenocopies are examples of complex inheritance patterns that deviate from Mendel’s simple ratios

Test your knowledge on Mendelian genetics and the foundational principles established by Gregor Mendel. This quiz covers key concepts such as alleles, traits, and inheritance patterns observed in pea plants. Explore the definitions and significance of terms that define heredity and genetic study.