Introduction To Genetics PDF

Dr. Osama Essawi 24-25 Molecular Biology & Genetics 6105221 Dr. Osama Essawi Office : HC 105 G Office hours: Mon/Wed 11:00 – 12:30 Tues 11:00 – 12:00  Dr. Osama Essawi 24-25 Text Book Gene...

Dr. Osama Essawi 24-25 Molecular Biology & Genetics 6105221 Dr. Osama Essawi Office : HC 105 G Office hours: Mon/Wed 11:00 – 12:30 Tues 11:00 – 12:00  Dr. Osama Essawi 24-25 Text Book Genetics A conceptual Approach 7th Edition  Dr. Osama Essawi 24-25 INTRODUCTION TO GENETICS GENETICS is the scientific study of genes, heredity, and the variation of organisms. It explores the principles governing the transmission of traits from one generation to the next. Genetics provides insights into how traits are inherited, offering a window into the mechanisms that shape the characteristics of living organisms. From eye color to disease susceptibility, genetics unravels the mysteries of heredity. Heredity refers to the passing of genetic information “genes” from parents to offspring or from one generation to the next. Inheritance is how traits, or characteristics, are passed on from generation to generation.  Dr. Osama Essawi 24-25 The Cell Theory Cell theory is one of the unifying theories in biology, and one that is universally accepted by all biologists. The theory states that: All living organisms are made of one or more cells. All Cells arise from other preexisting cells.  Dr. Osama Essawi 24-25 Cells, DNA, Genes, and Chromosomes: Exploring the Essence of Life Cells - The Basic Units of Life: - Cells are the smallest structural and functional units of living organisms. DNA - The Molecular Blueprint: - Deoxyribonucleic Acid (DNA) is the hereditary material that encodes the genetic instructions for the development and functioning of all known living organisms. Genes - Blueprint to Traits: - Genes are segments of DNA that contain the instructions for building and maintaining an organism. Chromosomes - Genetic Packaging: - Chromosomes are structures composed of DNA and proteins found in the nucleus of eukaryotic cells.  Dr. Osama Essawi 24-25 Chromosome Structure Each chromosome consists of two chromatids known as ‘sister chromatids’ connected by a centromere. The chromatids contain identical DNA sequences and are formed during the process of DNA replication. Each chromatid is made up of one very long, condensed DNA molecule, which is made up of a series of genes. Genes carry the genetic information. The ends of the chromatids in chromosomes are ‘sealed’ with protective structures called telomeres. The p arm is the shorter of the two arms of a chromosome. It is named "p" for "petit," meaning small. While the q arm is the longer of the two arms.  Dr. Osama Essawi 24-25 Fertilization and Chromosome Count Dr. Osama Essawi 24-25  Dr. Osama Essawi 24-25 Chromosome Types Eukaryotic chromosomes can be divided into four major types based on the position of the centromere. - Submetacentric chromosome: the centromere is located a little above the center. - Metacentric chromosome: the centromere is located at the center. - Telocentric chromosome: the centromere is located at the terminal end of the chromosome. - Acrocentric chromosome: the centromere is located almost near one end of the chromosome.  Dr. Osama Essawi 24-25 Karyotyping Karyotyping is a technique that involves arranging and visualizing an individual's chromosomes to analyze their number, size, and structure. Karyotyping is used to detect chromosomal abnormalities, such as aneuploidy (abnormal number of chromosomes), translocations, and deletions. Cells, often obtained through amniocentesis, chorionic villus sampling (CVS), or blood samples, are cultured and then arrested at metaphase to capture the condensed chromosomes.  Dr. Osama Essawi 24-25 Karyotyping Process 1- Cell Culture: Cells are cultured to stimulate their division, allowing for the observation of chromosomes in a condensed state. 2- Metaphase Arrest: Chemicals are used to arrest cells at metaphase, the stage where chromosomes are most condensed and visible. 3- Chromosome Staining: Chromosomes are stained with a dye, typically Giemsa stain, to create distinct banding patterns, facilitating identification.  Dr. Osama Essawi 24-25 Identifying Chromosomes Chromosomes are identified based on three key features: 1- Size - Distinguishing between two different chromosomes is most easily accomplished by comparing their sizes. 2- Banding pattern - The size and location of Giemsa bands on chromosomes make each chromosome pair unique. 3- Centromere position - Centromeres are regions in chromosomes that appear as a constriction.  Dr. Osama Essawi 24-25 G-Banding G Banding is a cytogenetic technique that involves staining chromosomes with Giemsa dye, creating characteristic bands along the chromosomes. These bands result from the preferential binding of the dye to regions of the chromosomes with different DNA base pair compositions. G Banding produces distinct dark and light bands along each chromosome, subdividing it into regions. The banding patterns are unique to each chromosome and serve as a "fingerprint" for identification. q24 The combination of numbers and letters allows us to indicate the exact position of any gene on a chromosome. The notation is typically in the format "qXY," where "X" represents the region and "Y" represents the band. For example: 1q24 represents region 2 and band 4 on the long arm of chromosome 1. The position 1q24 is closer to the centromere than 1q25  Dr. Osama Essawi 24-25 G-Banded Metaphase Chromosomes  Dr. Osama Essawi 24-25 Karyotype: Autosomes Vs sex chromosome A normal male chromosome pattern would be described as: 46,XY 46 = total number of chromosomes XY = sex chromosome constitution Any further description would refer to any abnormalities or variants found  Dr. Osama Essawi 24-25 Reasons for a Karyotype Analysis Issues with early growth and development, such as failure to thrive, developmental delays, and short stature. Cases of stillbirth and neonatal death. Fertility challenges, especially in couples with a history of infertility or multiple pregnancy loss. Family history considerations, particularly when there's a known or suspected chromosomal abnormality in a first-degree relative. Pregnancy in a woman of advanced age (over 35 years).  Dr. Osama Essawi 24-25 Genotype vs Phenotype Many phenotypes are influenced by environmental factors. A person’s phenotype is determined by both the genomic makeup (genotype) and the environmental factors. The most common phenotype in a natural population is Known as Wildtype  Dr. Osama Essawi 24-25 Homozygous genotype: - Occurs when a person inherits identical alleles from both parents for a gene. - Both alleles can be dominant (XX) or recessive (xx). Heterozygous genotype: - Occurs when a person inherits different alleles for the same gene from both parents. - Heterozygosity is indicated by a capital letter for the dominant allele and a lowercase letter for the recessive allele (e.g., Bb for eye color).  Dr. Osama Essawi 24-25 Influence of Environmental Factors on Phenotype Himalayan rabbits possess a temperature-sensitive tyrosine gene that affects the production of pigments in their fur. The fur color of Himalayan rabbits is influenced by temperature during growth. Cooler areas, such as the extremities, result in darker pigmentation, while warmer areas, like the body core, lead to lighter pigmentation. The fur color changes in response to variations in temperature, darkening as it gets colder and lightening as temperatures rise. The Himalayan rabbit's coloration is an example of phenotypic plasticity, where the environment influences the expression of genetic traits.  Dr. Osama Essawi 24-25 Genes and Traits Genes are the hereditary unit that is transmitted from one generation to the next. Each gene carries instructions for the development and expression of specific traits in an organism. Genes are diverse, and variations lead to trait diversity. Alleles, different versions of a gene, contribute to the variability observed in traits among individuals. Every cell activates only a portion of its genes, while the remaining genes are suppressed or deactivated. The mechanism responsible for activating and deactivating genes is referred to as gene regulation.  Dr. Osama Essawi 24-25 The Complexity of Genetic Information Each gene has the potential to generate several proteins through alternative splicing enhancing the variety of protein products. Proteins undergo various modifications such as phosphorylation, methylation, acetylation, and glycosylation. These modifications amplify the functional diversity of proteins beyond the gene level. Modified proteins can participate in various protein complexes, further expanding their functional roles.  Dr. Osama Essawi 24-25 Epigenetics Epigenetics explores heritable changes in gene function and expression that do not involve alterations to the underlying DNA sequence. It encompasses modifications to DNA and histone proteins, influencing gene expression. Epigenetic changes can be influenced by environmental factors, like diet, stress, and exposure to toxins.  Dr. Osama Essawi 24-25 Epigenetic gene regulation. Histone modification is a crucial aspect of epigenetic regulation. It involves chemical alterations, such as methylation and acetylation, to histone proteins associated with DNA. Histone methylation involves the addition of methyl groups to histones, which can either activate or repress gene expression. Histone acetylation involves the addition of acetyl groups to histones, which leads to an open chromatin structure, promoting gene expression.  Dr. Osama Essawi 24-25 Glossary TABLE 3.1 Summary of important genetic terms Term Definition Gene An inherited factor (encoded in the DNA) that helps determine a characteristic Allele One of two or more alternative forms of a gene Locus A specific place on a chromosome occupied by an allele Genotype A set of alleles possessed by an individual organism Homozygote An individual organism possessing two of the same alleles at a locus Heterozygote An individual organism possessing two different alleles at a locus Characteristic or character An attribute or feature possessed by an organism Phenotype or trait The appearance or manifestation of a characteristic  Dr. Osama Essawi 24-25 Thank you