Conceptos básicos en genética

Introduction to Genetics

Overview of Genetics

• Elizabeth introduces the topic of genetics, emphasizing its importance and the variety of terms associated with it.

• Defines genetics as the branch of science studying how characteristics in living organisms are generated, expressed, and transmitted across generations.

Fields of Genetics

• Discusses three main fields within genetics:

• Transmission Genetics: Focuses on inheritance principles and trait transmission from one generation to another.

• Molecular Genetics: Studies molecules containing genetic information and biochemical processes related to gene regulation.

• Population Genetics: Examines genetic composition changes in populations over time, focusing on evolution and genetic equilibrium.

Key Concepts in Genetics

Fundamental Terms

• Introduces DNA (deoxyribonucleic acid) as the biomolecule storing genetic information, structured as a double helix made up of nucleotides.

• Explains RNA (ribonucleic acid), highlighting its differences from DNA and its roles in protein synthesis.

Types of RNA

• Describes various types of RNA:

• mRNA (messenger RNA): Acts as an intermediary between DNA and protein synthesis.

• rRNA (ribosomal RNA): Part of ribosomes that synthesize proteins.

• tRNA (transfer RNA): Transfers amino acids during translation.

Genetic Material and Genes

Genome Composition

• Defines genome as the complete set of genetic material in an organism, consisting of nuclear genomes (linear chromosomes) and mitochondrial genomes (circular chromosomes).

Understanding Genes

• Describes genes as functional units of heredity; they encode for proteins or functional products like RNAs.

• Clarifies that not all genomic elements code for proteins; some have regulatory functions or contribute to gene expression.

Chromosomes Structure

• Explains that genetic material is organized into discrete units called chromosomes, which become visible during cell division processes such as mitosis.

Genetics and Chromosomes

Structure of Chromosomes

• Each chromosome consists of a double-stranded DNA molecule associated with basic proteins called histones, forming a complex structure known as chromatin.

• Humans have 23 pairs of chromosomes, half inherited from the mother and half from the father; the first 22 pairs are autosomal, while the last pair determines sex.

Genes and Alleles

• Different forms of a gene are called alleles, which determine specific traits; a pair of alleles controls characteristics in diploid organisms.

• For example, fur color is determined by two alleles: one for black (dominant) and one for brown (recessive); homozygous individuals express only one trait.

Dominance and Expression

• Alleles can be classified as dominant or recessive; dominant alleles manifest whenever present, while recessive alleles only express in homozygous conditions.

• An example includes eye color where blue (recessive) does not appear if brown (dominant) is present.

Genetic Variation

• Multiple alleles can exist for a single gene; however, an individual can possess only two alleles—one on each homologous chromosome.

• In females with two X chromosomes, different allele expressions can occur. Males have one X and one Y chromosome leading to unique inheritance patterns.

Heredity Concepts

• Heredity encompasses biological processes through which traits are passed from parents to offspring; it involves both constancy within species and variation among individuals.

• The consistency across generations is due to specific genes that define species traits while variations arise from different allele combinations among individuals.

Genotype vs. Phenotype

• The genotype refers to an individual's genetic makeup inherited from parents, encompassing all possible allele combinations.

• The phenotype results from interactions between genotype and environment, representing observable traits such as blood type or height influenced by genetics and external factors.

Environmental Influence on Traits

• An individual's growth may be affected by environmental conditions despite having a genotype for tall stature; nutritional deficiencies could hinder expression of this trait.

Genetic Variability and Its Implications

Understanding Genetic Variability

• Genetic variability refers to the presence of different characteristics within a population of organisms of the same species, resulting from random changes in DNA. This means that not all genetic material shared among individuals is identical.

• In human populations, individuals may possess genotypes that either increase susceptibility or provide protection against diseases. Some may exhibit drug resistance while others metabolize drugs slowly.

Distinguishing Polymorphisms from Mutations

• A polymorphism is defined as a common variation in DNA sequence within a population, whereas a mutation is any abnormal change in the DNA sequence. For an allele to be classified as polymorphic, its less common variant must have a frequency of at least 1% in the population; otherwise, it is considered a mutation.

• If an uncommon gene variant has a frequency below 1%, it is regarded simply as a mutation; if above this threshold, it qualifies as a polymorphism. Gene polymorphisms can occur anywhere in the genome and are mostly silent, meaning they do not alter gene function.

Impact of Polymorphisms on Health

• When a polymorphic variant leads to abnormal gene expression or produces an atypical protein form, it may be associated with disease sensitivity. An example includes the cytochrome P450 4A11 gene variant linked to altered enzymatic activity during drug metabolism.

• Studies indicate that humans carrying this specific variant (a thymine-cytosine change at nucleotide position 8,590) show higher incidences of hypertension, ischemic stroke, and related diseases due to reduced enzymatic activity affecting blood pressure-regulating medications.