Genetics Overview Quiz

Genetics Overview

• Genetics is the study of inheritance and variation of traits in living organisms.
• It encompasses Classical Genetics, Molecular Genetics, and Evolutionary/Population Genetics.

Important Terms

• Gene: A hereditary unit of information, often defined as a segment of DNA that codes for a specific protein or functional RNA.
• Gene Locus: The specific position of a gene on a chromosome.
• Allele: One of two or more alternative forms of a gene, found at the same locus and differing in DNA sequence.
• Genotype: The genetic makeup of an organism, specifically the combination of alleles it carries for a particular gene.
• Phenotype: The observable characteristics of an organism, determined by its genotype and environmental influences.
• Wild type: The most common phenotype in a population occurring naturally.
• Mutant (phenotype): A variant phenotype due to a change in DNA sequence, deviating from the wild type.
• Dominant: A phenotype observed in heterozygotes (organisms with different alleles), where one allele exerts more influence than the other.
• Recessive: A phenotype only observed in individuals homozygous for the recessive allele (carrying two copies of the same recessive allele).

The Molecular Basis of Dominance

• Loss of function: A type of mutation where the mutated allele leads to a significant decrease or complete loss of the functional gene product.
• Gain of function: A type of mutation where the mutated allele leads to a new function or increased expression of the gene product compared to the wild type.
• Incomplete dominance: A situation where heterozygotes display an intermediate phenotype compared to individuals with two copies of either allele.
• Codominance: Both alleles are expressed equally, and their effects are both apparent in the heterozygote.

Blood Type Example

• ABO blood type system involves three alleles: IA, IB, and i.
• IA and IB are codominant, producing distinct antigens, but completely dominant over i, which produces no antigen.
• This results in four blood types: Type O (i/i), Type A (IA/IA or IA/i), Type B (IB/IB or IB/i), and Type AB (IA/IB).

Dominance & Recessiveness Revisited

• Recessiveness: Observed in mutations of genes that are functionally haplosufficient, meaning one copy of the wild-type allele is sufficient for normal function. The mutated allele is the recessive allele.
• Dominance: Observed in genes that are haploinsufficient, where a single wild-type allele cannot provide enough function alone. The mutated allele is the dominant allele.
• Nomenclature:
  • Single letter denotes a mutant phenotype or recessive allele if the mutant is unknown.
  • Uppercase denotes a dominant allele.
  • Lowercase denotes a recessive allele.
  • Slashes indicate alleles for genes on homologous chromosomes.
  • Semicolons indicate genes on non-homologous chromosomes.

Single Gene Inheritance (Chapter 2)

• Many traits are coded for by a single gene.
• Mutations in a gene can lead to observable changes in phenotype.
• Gregor Mendel's work laid the foundation for understanding single gene inheritance.

Gregor Mendel

• Studied seven traits in garden peas (Pisum sativum).
• All traits were discontinuous, meaning they exhibited distinct "either/or" phenotypes.

Mendel’s Law of Equal Segregation

• Pure lines: Plants that produced offspring identical to themselves after self-pollination (homozygous).
• Monohybrid cross: A cross between two pure lines differing in only one trait.
• Parent (P0) generation: The original pure lines.
• First Filial (F1) generation: Offspring from the P0 cross, all exhibiting the dominant phenotype in a monohybrid cross.
• Second Filial (F2) generation: Offspring from selfing F1, exhibiting a 3:1 phenotypic ratio in a monohybrid cross.

Key Concepts from Mendel

• Genes exist in pairs: One allele from each parent.
• Gametes contain only one allele of each gene pair: Half of the gametes carry one allele, half carry the other.
• Equal segregation: Mendel's first law.
• Random fertilization: Gametes combine randomly.
• Phenotype: Observable characteristics.
• Genotype: The combination of alleles.

Cell Division

• Mitosis: Cell division where each daughter cell receives a complete copy of the parental genome.
• Meiosis: Cell division specific to gamete formation, where each gamete receives half of the parental genome.

Chromosomal Theory of Inheritance

• Sutton and Boveri proposed that Mendel's "particles" were associated with chromosomes.
• This was later confirmed by Morgan's experiments.

Sex linkage

• Non-autosomal chromosomes are called sex chromosomes.
• Homogametic: Having a matching pair of sex chromosomes.
• Heterogametic: Having a nonmatching pair of sex chromosomes.

Reciprocal Cross

• A cross where the parental phenotypes are reversed to determine if a trait follows sex-linked inheritance.
• In sex-linked inheritance, reciprocal crosses result in different F1 and F2 phenotypes.

Human Pedigree Analysis

• Used to trace genetic traits through family trees.
• Propositus: The individual who first brings the family to the attention of a geneticist (usually has the disease).
• Ratios may differ from ideal 3:1 and 1:1 due to small family size.

Autosomal Recessive Pedigree

• Often shows up in unaffected parents who are carriers.
• If both parents have the trait, all children will have it.
• Males and females are equally likely to exhibit the trait.

Autosomal Dominant Pedigree

• No skipping of generations: Each affected individual must have at least one affected parent.
• Males and females can transmit the mutant allele to both sons and daughters.

Test your knowledge on the fundamentals of genetics, including key terms and concepts such as genes, alleles, and phenotypes. This quiz will cover aspects of Classical, Molecular, and Evolutionary Genetics. Perfect for students looking to reinforce their understanding of genetic principles.