Mendelian Genetics Quiz

Study Notes

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

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

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 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

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

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

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

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