Lecture 7_Introduction to Genetics_25.pdf
- 1. Dr. Osama Essawi 24-25 Molecular Biology & Genetics Dr. Osama Essawi
- 2. 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.
- 3. 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.
- 4. 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.
- 5. Dr. Osama Essawi 24-25 Fertilization and Chromosome Count
- 6. Dr. Osama Essawi 24-25
- 7. 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.
- 8. 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.
- 9. 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.
- 10. 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.
- 11. 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. • 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 q24
- 12. Dr. Osama Essawi 24-25 G-Banded Metaphase Chromosomes
- 13. 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
- 14. 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).
- 15. 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
- 16. 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).
- 17. 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.
- 18. 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.
- 19. 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.
- 20. 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.
- 21. Dr. Osama Essawi 24-25 Glossary 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 TABLE 3.1 Summary of important genetic terms
- 22. Dr. Osama Essawi 24-25 Thank you