BackGenetics Fundamentals: DNA, Chromosomes, and Inheritance
Study Guide - Smart Notes
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Genetics Basics
DNA Structure and Function
Deoxyribonucleic acid (DNA) is the fundamental unit of genetics, encoding the information necessary for the development and functioning of living organisms.
DNA is composed of four bases (nucleotides): Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).
Chargaff's Rules state that A pairs with T (via 2 hydrogen bonds) and G pairs with C (via 3 hydrogen bonds).
The two strands of DNA are complementary and form a double helix.
DNA contains genes, which are stretches of DNA that have the information for a protein.
Genes have regulatory elements that control whether or not the gene is expressed.
Genes come in different varieties called alleles.
An allele is a gene variant. In diploid cells, there are two alleles per gene.
Alleles vs. Genes
Each gene can have multiple alleles, which are different versions of the same gene. In diploid organisms, each individual has two alleles for each gene, one from each parent.
Gene: A segment of DNA that codes for a specific protein.
Allele: A variant form of a gene.
Example Table: Alleles vs. Genes
Chromosome | Gene | Allele Variant |
|---|---|---|
1 | Gene A | Allele A.1 / Allele A.2 |
1 | Gene B | Allele B.1 / Allele B.2 |
1 | Gene C | Allele C.1 / Allele C.2 |
From DNA to Protein: Transcription and Translation
The process of gene expression involves two main steps:
Transcription: The process of turning DNA into messenger RNA (mRNA).
Other types of RNA produced include transfer RNA (tRNA) and ribosomal RNA (rRNA).
Translation: The process of turning mRNA into proteins.
DNA does not encode a protein in a 1:1 ratio; multiple codons can code for the same amino acid.
Chromosomal Fundamentals
Chromosomes and Genes
Chromosomes are structures within cells that contain many genes.
Homologous chromosomes: Chromosomes that exist in pairs in diploid (2n) organisms.
Haploid (n) organisms have only one chromosome copy.
Chromosomal theory of inheritance: Traits are inherited through genes located on chromosomes, which are passed through gametes (sex cells).
Cell Division: Meiosis and Mitosis
Meiosis: The process of creating gametes (sex cells). In diploid individuals, it takes a 2n cell and produces four n cells.
Mitosis: The process of creating somatic cells (all cells but gametes). It turns a 2n cell into two 2n cells.
Genotype and Phenotype
Definitions and Examples
The genetics of an individual can be described in two main ways:
Genotype: The set of alleles for a given trait in an organism.
Phenotype: The observable features or traits of an organism.
Example Table: Phenotype vs. Genotype
Phenotype | Genotype |
|---|---|
Yellow | AA or Aa |
Green | aa |
A = dominant allele, a = recessive allele
Types of Traits
Morphological Traits: Affect the appearance of the organism.
Physiological Traits: Affect the ability of an organism to function properly.
Behavioral Traits: Affect the way an organism responds to its environment.
Divisions of Genetics
Transmission genetics: Studies the ability to pass traits onto the next generation.
Molecular genetics: Studies gene activity at a molecular level (DNA replication, transcription, etc.).
Population genetics: Studies genetic variation within populations and how it changes over time.
Practice Questions
True or False: In a diploid cell, the number of alleles is the same as the number of genes.
What is an allele?
A nucleotide variant.
Different variants of a gene.
Proteins.
Codon.
