BackGenetics Fundamentals: Key Concepts and Applications
Study Guide - Smart Notes
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Genetics Basics
DNA Structure and Function
DNA is the fundamental unit of genetics, responsible for storing and transmitting genetic information in living organisms.
DNA Composition: DNA is made up of four bases (nucleotides): Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).
Chargaff's Rules: State that A & T (2 H-bonds) pair together and G & C (3 H-bonds) pair together.
The two strands of DNA are complementary and form a double helix.
Genes: 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.
Example: Alleles vs. Genes
Each chromosome contains genes, and each gene can have different alleles (variants).
In diploid organisms, each gene is present in two copies (one from each parent).
Chromosome | Gene | Allele Variant |
|---|---|---|
Chromosome 1 | Gene A | Allele A.1 |
Chromosome 1 | Gene B | Allele B.1 |
Chromosome 1 | Gene C | Allele C.1 |
Chromosome 2 | Gene A | Allele A.2 |
Chromosome 2 | Gene B | Allele B.2 |
Chromosome 2 | Gene C | Allele C.2 |
From DNA to Protein: Transcription and Translation
Genetic information is used to produce proteins through two main steps:
Transcription: The process of turning DNA into messenger RNA (mRNA).
Transcription also creates 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
Chromosome Structure and Types
Chromosomes are structures that contain many genes and are essential for inheritance.
Homologous chromosomes: Chromosomes that exist in pairs in diploid organisms.
Diploid (2n): Organisms have homologous chromosomes (a chromosome pair).
Haploid (n): Organisms have only one chromosome copy.
Chromosomal theory of inheritance: Describes that inherited traits come from genes on chromosomes, passed through gametes (sex cells).
Cell Division: Meiosis and Mitosis
Meiosis: The process of creating gametes. In diploid individuals, it takes a (2n) cell and produces four (n) cells.
Mitosis: The process of creating somatic cells (all cells but gametes). Turns (2n) cells into two (2n) cells.
Example: Meiosis and Chromosomes
During meiosis, homologous chromosomes separate, resulting in gametes with half the chromosome number.
Genotype and Phenotype
Definitions and Differences
The genetics of an individual can be described in two main ways:
Genotype: The set of alleles for a given trait by an organism.
Phenotype: The observable features or traits of an organism.
Types of Genetic 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.
Example: Pea Plant Color
Phenotype | Genotype |
|---|---|
Yellow | AA or Aa |
Green | aa |
A = dominant allele
a = recessive allele
Divisions of Genetics
Major Fields
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.).
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. A nucleotide variant.
b. Different variants of a gene.
c. Proteins.
d. Codon.
