Genetics

Genetics

Genetics

is the study of genes, heredity, and the variation of inherited traits in living organisms.

DNA (Deoxyribonucleic Acid)

a molecule that contains the genetic information in all living organisms.

Genes

segments of DNA that encode instructions for building and maintaining an organism.

Alleles

a different version of a gene that can result in different variations of a particular trait.

Gregor Mendel

is considered the father of modern genetics, as he conducted groundbreaking experiments with pea plants in the 19th century, leading to the discovery of the basic principles of inheritance.

Dominant alleles

expressed in an organism's phenotype when present.

Recessive alleles

expressed when two copies are present.

Genotype

refers to the genetic makeup of an organism.

Phenotype

refers to the observable characteristics resulting from the interaction of genes and the environment.

DNA (Deoxyribonucleic Acid)

is a double-stranded, helical molecule that carries genetic information in all living organisms.

Each strand of DNA

is composed of nucleotides, which consist of a sugar molecule (deoxyribose), a phosphate group, and one of four nitrogenous bases (adenine, thymine, cytosine, or guanine).

Adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G) through hydrogen bonds, creating complementary base pairs.

Genetic code

set of rules that determines how the nucleotide sequence of DNA and RNA is translated into the amino acid sequence of proteins. A universal code, meaning the same genetic code is used by almost all organisms, from bacteria to plants, animals, and humans.

There are _____ possible codons (triplets of nucleotides) in the genetic code, including three stop codons (UAA, UAG, and UGA) that signal the end of protein synthesis.

64

Genetic mutations

are alterations or changes in the DNA sequence of an organism's genome. It can occur naturally due to errors during DNA replication, exposure to mutagens (radiation, chemicals) or spotaneously through genetic combination.

Point mutations

involve the substitution of a single nucleotide with another.

Three types of point mutations:

Silent Mutation, Missense Mutation and Nonsense Mutation.

Silent Mutation

The mutation does not change the amino acid sequence due to the redundancy of the genetic code.

Missense Mutation

The mutation results in the substitution of one amino acid with another, potentially affecting protein function.

Nonsense Mutation

The mutation creates a premature stop codon, leading to the formation of a truncated, nonfunctional protein.

Frameshift mutations

involve the insertion or deletion of one or more nucleotides, which shifts the reading frame of the genetic code during translation. It can result in significant changes to the amino acid sequence and usually leads to nonfunctional proteins.

Chromosomal mutations

involve changes in the structure or number of chromosomes.

chromosomal

Deletion, duplication, inversion and translocation are type of _____________ mutations.

Deletion

part of a chromosome is lost.

Duplication

a segment of a chromosome is duplicated.

Inversion

a segment of a chromosome is reversed in orientation.

Translocation

a segment of one chromosome is transferred

to another non-homologous chromosome.

Translation

is the process of synthesizing a protein using the information encoded in the mRNA (messenger RNA) molecule transcribed from DNA during transcription. The process of translation occurs on ribosomes, which are complexes of RNA and proteins found in the cytoplasm.

Translation occurs in three main steps: ________, __________, ____________

initiation, elongation, and termination

Mendelian inheritance

refers to the patterns of inheritance of single gene traits as described by Gregor Mendel in his pea plant experiments in the 19th century. Mendel studied seven distinct traits in pea plants, such as flower color, seed shape, and plant height.

Mendel observed that each trait is determined by discrete units, which we now call _______, and that these genes are passed from parents to offspring in predictable patterns.

genes

It refers to different versions or forms of a gene that occupy the same locus (position) on homologous chromosomes.

allele

Spontaneous mutations

occur without exposure to external mutagens and are a natural consequence of cellular processes.

Induced mutations

result from exposure to mutagens, such as radiation, chemicals, or certain environmental factors.

The central dogma of genetics was proposed by ____________ in 1958 and is a foundational concept in molecular biology.

Francis Crick

Central dogma of genetics

outlines the unidirectional flow of genetic information from DNA to RNA to protein.

The central dogma consists of three main processes: __________ , ____________ , ___________

replication, transcription, and translation

DNA replication

is the process of copying DNA to produce identical daughter DNA molecules. It occurs during the S (synthesis) phase of the cell cycle, ensuring each daughter cell receives a complete set of genetic information during cell division.

Single-strand binding proteins (SSBs)

stabilize the separated DNA strands, preventing them from re-annealing.

DNA polymerase

is the key enzyme responsible for synthesizing new DNA strands. DNA polymerase adds nucleotides to the 3' end of the growing strand, using the original DNA strand as a template.

Leading strand

is synthesized continuously in the 5' to 3' directiontoward the replication fork.

Lagging strand

is synthesized discontinuously in short fragments called Okazaki fragments in the 5' to 3' direction away from the replication fork.

DNA ligase

joins the Okazaki fragments on the lagging strand to create a continuous DNA strand.

Transcription

is the process by which a segment of DNA is used as a template to synthesize a complementary RNA molecule.

The enzyme responsible for transcription is _______________, which binds to a specific region of DNA called the promoter to initiate the process.

RNA polymerase

Mendel’s Law of Dominance

implies the existence of dominant and recessive alleles for each gene whereby dominant alleles mask the effect of recessive alleles in heterozygous individuals.

Mendel's Law of Segregation

states that during gamete formation, the two alleles of a gene segregate (separate) from each other and end up in different gametes.

Mendel's Law of Independent Assortment

states that the alleles ofdifferent genes segregate independentlyduring gamete formation, leading to theinheritance of traits independently of one another.

Punnett squares

are used to predict the genotypic and phenotypic ratios of offspring resulting from specific crosses between parents with known genotypes.

Mendelian inheritance

explains the inheritance of simple, single-gene traits • and is applicable to many human genetic disorders and traits like cystic fibrosis,sickle cell anemia, and widow's peak hairline.

Non-Mendelian inheritance patterns

involve more complex genetic • mechanisms and interactions, often influenced by multiple genes or the environment.

Incomplete Dominance

In this pattern, heterozygotes sho an intermediate phenotype between the two homozygotes. For example, in snapdragons, a red-flowered plant crossed with a white-flowered plant produces pink-flowered offspring.

Codominance

In this pattern, both alleles are fully expressed in heterozygotes, resulting in a distinct phenotype for each allele. An example is the ABO blood group system, where individuals with the AB blood type express both A and B antigens.

Multiple Alleles

Instead of just two alleles for a gene, multiple alleles can exist in a population. However, an individual can only carry two alleles at a specific gene locus. An example is the human ABO blood group system, which has three alleles: A, B, and O.

Epistasis

occurs when the alleles of one gene mask or modify the expression of alleles at another gene. This interaction alters the expected phenotypic ratio. An example is coat color in Labrador Retrievers, where one gene controls pigment production, and another gene controls pigment deposition.

Polygenic Inheritance

In this pattern, multiple genes contribute to a single trait, and the trait exhibits a continuous range of variation. Examples include human height and skin color.

Pedigree analysis

is the study of the inheritance of traits and genetic disorders within families across generations.

Pedigrees

are graphical representations of family relationships, showing the transmission of traits from one generation to the next.

Autosomal Recessive Inheritance

In pedigrees, two unaffected carriers (heterozygous) have an affected child. The trait can skip generations and affects males and females equally.

X-Linked Dominant Inheritance

In pedigrees, an affected individual (homozygous dominant or heterozygous) has an affected parent. The trait affects both males and females, and all daughters of an affected male will inherit the trait.

X-Linked Recessive Inheritance

In pedigrees, an affected individual (hemizygous for males or homozygous recessive for females) is usually born to unaffected carrier mothers. The trait is more common in males, and carrier females can pass the trait to their sons.

Y-Linked Inheritance

In pedigrees, the Y chromosome is passed exclusively from father to son. Y-linked traits are only observed in males and affect all sons of an affected male.

Down Syndrome (Trisomy 21)

caused by the presence of an extra copy of chromosome 21. Symptoms include intellectual disability, characteristic facial features, heart defects, and increased susceptibility to certain health conditions.

Cystic Fibrosis

An autosomal recessive disorder caused by mutations in the CFTR gene. Results in the production of thick and sticky mucus, affecting the respiratory and digestive systems. Common symptoms include chronic lung infections, difficulty breathing, and poor nutrient absorption.

Hemophilia

X-linked recessive disorder affecting blood clotting. Caused by mutations in the genes for clotting factors VIII (hemophilia A) or IX (hemophilia B). Results in prolonged bleeding and easy bruising.

Sickle Cell Anemia

Autosomal recessive disorder caused by a mutation in the HBB gene, leading to abnormal hemoglobin (HbS). Red blood cells become sickle-shaped, causing blockages and reduced oxygen delivery. Symptoms include anemia, pain crises, and organ damage.

Huntington's Disease

Autosomal dominant disorder caused by a mutation in the HTT gene. Results in the progressive degeneration of nerve cells in the brain. Symptoms include motor, cognitive, and psychiatric disturbances.

Duchenne Muscular Dystrophy (DMD)

X-linked recessive disorder caused by mutations in the DMD gene. Leads to progressive muscle weakness and wasting. Typically affects boys, with symptoms appearing in early childhood.

Tay-Sachs Disease

Autosomal recessive disorder caused by mutations in the HEXA gene. Results in the accumulation of harmful substances in the brain and nervous system. Symptoms include developmental regression, loss of motor skills, and early death.

Turner Syndrome (Monosomy X)

Caused by the presence of only one X chromosome of the sex chromosomes (45, X). Results in short stature, infertility, heart defects, and other physical characteristics.

Klinefelter Syndrome (47,XXY)

Caused by an extra X chromosome in males (47, XXY). Leads to hypogonadism, infertility, and physical traits such as tall stature and reduced body hair.

Population genetics

is the study of genetic variation and its changes within populations over time. It involves understanding how genetic factors interact with evolutionary forces such as natural selection, genetic drift, gene flow, and mutation.

The Hardy-Weinberg equilibrium

is a principle in population genetics that describes the conditions under which allele frequencies in a population remain constant from generation to generation. It serves as a null model, providing a baseline against which to compare real-world population data and detect evolutionary forces.

The Hardy-Weinberg equilibrium assumes five conditions:

a large population size, random mating, no mutation, no gene flow, and no natural selection.

In the Hardy-Weinberg equilibrium, allele frequencies can be calculated using the formula:

p2 + 2pq + q2 = 1 (genotype frequency) and p + q = 1 (allele frequency). Whereareas, p = dominant; q = recessive

Evolution

is the process of change in the genetic composition of a population over time. It occurs through the mechanisms of natural selection, genetic drift, gene flow, and mutations.

Natural selection

is a key mechanism of evolution proposed by Charles Darwin.

The central idea of natural selection is "______________________" where individuals with advantageous traits have a higher chance of survival and

reproduction.

survival of the fittest

Natural selection can lead to the formation of new species through the process of _____________.

speciation

Genetic drift

is the random change in allele frequencies due to sampling effects in small populations.

Two main types of genetic drift are the:

bottleneck effect and the founder effect

Bottleneck Effect

Occurs when a population undergoes a sharp reduction in size due to a catastrophic event (e.g., natural disaster, disease outbreak) or intense selective pressure. The surviving individuals may have different allele frequencies than the original population.

Founder Effect

Occurs when a small group of individuals establishes a new population in a different geographic area. The new population may have different allele frequencies than the source population due to the limited genetic diversity of the founding individuals.

Gene flow, also known as gene migration or allele flow

is the transfer of genetic material (alleles) between populations of the same species. It occurs when individuals or gametes (e.g., pollen, seeds) move from one population to another and interbreed with members of the new population.

Genetic mutations

are alterations or changes in the DNA sequence of an organism's genome.

Mutations

provide a source of new genetic variation, which can be subject to selection or drift. For example, Fixed mutations often provide a significant advantage to individuals carrying the mutated allele in their specific environment. The mutation may confer an adaptive trait, enhancing the survival and reproductive success of individuals carrying the mutation.