lecture 1 chromosomes.pptx11111111111111
- 1. Chromosomes and Genes Edited by Dr. Mohammed Mohammed Nabil Lecturer in faculty of Veterinary medicine Sphinx University
- 2. Chromosome: Tightly coiled strands of DNA ●Form when cells divide ●Chromosomes created for the new cells ●2 Parts: ○1) Chromatids: two identical parts of a chromosome ○2) Centromere: Joins chromatids together
- 3. Identifying chromosomes Chromosomes can be identified by: ●Their size ●Their shape (the position of the centromere) NB Chromosomes are flexible ●Banding patterns produced by specific stains (Giemsa) Chromosomes are analysed by organising them into a KARYOTYPE © 2007 Paul Billiet ODWS © Biologyreference.com
- 4. ●Defined: Picture of an individuals chromosomes ○Help identify sex & chromosome defects ●First 22 pairs = autosomes ●Size of final pair identifies sex ○Same size: XX = female ○Different size: XY = male ●Normal human will have 46 chromosomes KARYOTYPE
- 5. Numbers of chromosomes ● Constant for each cell in the body except sex cells which only have half sets ● Constant throughout the life of an individual (you don’t lose or gain chromosomes) ● Constant for all members of a species ○ Humans have 46 chromosomes ○ Chimpanzees have 48 ○ Maize (corn) has 20 © 2007 Paul Billiet ODWS
- 6. ●Diploid Cells = Cells with the full set of chromosomes ○Paired chromosomes ●Half of our chromosomes come from each parent (23 from each parent) ●Somatic (non-sex) cells are diploid ●Created by mitosis ●Ex: Skin, Muscle, Nerve, Blood Cells
- 7. ●Haploid Cells = Cells with ½ the total number of chromosomes ●Gametes (sex cells) are the only haploid cells ○Ex: Sperm, Egg, Pollen ●Created by meiosis ○Chromosome number reduced by 1/2 How do humans get 46 chromosomes? Haploid sperm cell (23) + Haploid egg cell (23) = Diploid zygote (46)
- 9. Chromosomes in eukaryotes and prokaryotes are different PROKARYOTES EUKARYOTES single chromosome plus plasmids many chromosomes circular chromosome linear chromosomes made only of DNA made of chromatin, a nucleoprotein (DNA coiled around histone proteins) found in cytoplasm found in a nucleus copies its chromosome and divides immediately afterwards copies chromosomes, then the cell grows, then goes through mitosis to organise chromosomes in two equal groups
- 10. Chromosomes in eukaryotes ●Found in the nucleus ●Condensed and visible during cell division ●At the beginning of mitosis they can be seen to consist of two threads (sister chromatids) joined by a centromere ●The sister chromatids are identical copies ●During mitosis the sister chromatids separate and are placed into two nuclei © 2007 Paul Billiet ODWS Image believed to be in the Public Domain
- 11. How many chromosomes are in brain cells? Remember…Brain cells are non-sex cells… …Somatic cells are non-sex cells… …Somatic cells are diploid… …Diploid cells have the full set of chromosomes Answer = 46
- 12. What is the human haploid chromosome number? Remember…Haploid = half number of chromosomes Answer = 23 chromosomes
- 13. How many chromosomes are in female egg cells? Remember…Egg cells are sex cells… …Sex cells are gametes… …Gamete cells are haploid… …Haploid cells have ½ the set of chromosomes Answer = 23
- 14. What is the human diploid chromosome number? Remember…Diploid = total number of chromosomes Answer = 46
- 15. What is the human gamete chromosome number? Remember…Gamete cells are sex cells… …Sex cells are haploid… …Haploid cells have ½ the set of chromosomes
- 16. What is the human somatic chromosome number? Remember…Somatic cells are non-sex cells… …Somatic cells are diploid… …Diploid cells have the full set of chromosomes Answer = 46
- 17. Genes
- 18. Genes biochemical units of heredity that make up the chromosomes a segment of DNA capable of synthesizing a protein A gene is a locus (or region) of DNA that encodes a functional RNA or protein product, and is the molecular unit of heredity. [Some genetic traits are instantly visible, such as eye colour or number of limbs, and some are not, such as blood type, risk for specific diseases, or the thousands of basic biochemical processes that comprise life. Genome the complete instructions for making an organism consisting of all the genetic material in its chromosomes
- 19. Genes ● Genes - are the basic units of heredity located on chromosomes which contain threadlike strands of DNA. ● Egg and Sperm contain 23 chromosomes each.
- 20. Genes – Our Code for Life Chromosomes Strands of DNA (deoxyribonucleic acid) that carry genetic information; located in the nucleus of every human cell Humans: 46 chromosomes (23/23) Genes DNA segments; key functional units in hereditary transmission Can be active (expressed) or inactive Autosomes Sex Chromosomes
- 21. Genes & DNA- Parts of a Cell
- 22. Genes ● Like chromosomes, genes operate in pairs, with one gene in each pair coming from each parent ○ Homozygous Condition ■ Paired genes are the same ○ Heterozygous Condition ■ Paired genes are different ■ In this case, one gene in the pair masks the other
- 23. Genes – Our Code for Life ● Genotype للشخص الجيني التركيب ○ A person’s genetic makeup; determined at pregnancy and fixed forever ● Phenotype ○ The ways in which a person’s genotype is manifested in observable characteristics; may change over time ■ **Different genotypes can yield the same phenotype ■ **Genes are flexible ● Polygenic Inheritanceالجينات متعدد ○ Characteristics that are influenced by more than one pair of genes
- 24. Genotypes ●A gene for a particular character or trait may exist in two forms; one is dominant (E) and the other is recessive (e).
- 25. Dominant and Recessive Genes ●Dominant Genes ○ One gene overshadows the other. ●Recessive Gene ○The gene that is overshadowed by a dominant gene.
- 26. Examples of Genotypes ●There are three basic genotypes for a particular character: ○AA = homozygous dominant ○Aa = heterozygous ○aa = homozygous recessive
- 27. Phenotypes ●Phenotype is the physical appearance or other characteristic of an organism as a result of the interaction of its genotype and the environment. Some examples would be: • Size • Shape • Color
- 28. Genetic & Chromosomal Problems Chromosomal deletion: • when cells go through meiosis, portions of the chromosome are lost. Chromosomal inversion: • when cells go through meiosis, parts of the chromosome are flipped. Chromosomal translocation: • when cells go through meiosis, parts of the chromosomes stick together and switch. Chromosomal non-disjunction: • when cells go through meiosis the chromosomes don’t separate correctly and either too many or not enough are passed on.
- 29. Basics: Genes – Our Code for Life ● Genetic & Chromosomal Problems ○ Cystic Fibrosis ■Two recessive genes; respiratory & digestive tract ○ Sickle Cell Anemia ■Two recessive genes; blood disorder ○ Tay-Sachs Disorder ■Two recessive genes; fatal neurological disorder ○ Phenylketonuria ■Two recessive genes; difficulty digesting a certain amino acid – phenylalanine
- 30. Basics: Genes – Our Code for Life ● Genetic & Chromosomal Problems ○ Down Syndrome ■ Extra chromosome (21st pair) ○ Klinefelter’s Syndrome male ■ Extra X chromosome; reduced masculine characteristics (e.g. enlarged breasts, obesity, etc.) ○ Turner’s Syndrome female ■ Missing X chromosome (e.g. infertility, sexually underdeveloped, etc.)
- 32. 1- Identical or monozygotic twins, one fertilized egg (ovum) splits and develops into two babies with exactly the same genetic information. 2- Fraternal or dizygotic twins, two eggs (ova) are fertilized by two sperm and produce two genetically unique children. Dizygotic
- 33. Questions ● True or false : 1. In KARYOTYPE the Size of final pair identifies sex ( ) 2. Diploid Cells are Cells with the full set of chromosomes ( ) 3. Somatic (non-sex) cells are diploid ( ) 4. Haploid Cells are Cells with ½ the total number of chromosomes ( ) 5. Hershey & Chase experiments confirmed that DNA is a genetic material ( ) 6. Gametes (sex cells) are the only haploid cells ( ) 7. Diploid zygote are 46 chromosome ( ) 8. The human gamete chromosome number are 23 ( ) 9. Genetic information transmitted only by DNA ( ) 10.DNA replication Occurs in S phase of cell cycle ( )
- 34. Complete the following sentence : 1. How many chromosomes are in brain cells……………. 2. How many chromosomes are in female egg cells……….. 3. What is the human somatic chromosome number…………….. 4. A gene for a particular character or trait may exist in two forms ………… ● Write short notes in Genetic & Chromosomal Problems
Editor's Notes
- #17: Genes biochemical units of heredity that make up the chromosomes a segment of DNA capable of synthesizing a protein Genome the complete instructions for making an organism consisting of all the genetic material in its chromosomes A gene is a locus (or region) of DNA that encodes a functional RNA or protein product, and is the molecular unit of heredity.[1][2]:Glossary The transmission of genes to an organism's offspring is the basis of the inheritance of phenotypic traits. Most biological traits are under the influence of polygenes (many different genes) as well as the gene–environment interactions. Some genetic traits are instantly visible, such as eye colour or number of limbs, and some are not, such as blood type, risk for specific diseases, or the thousands of basic biochemical processes that comprise life. Genes can acquire mutations in their sequence, leading to different variants, known as alleles, in the population. These alleles encode slightly different versions of a protein, which cause different phenotype traits. Colloquial usage of the term "having a gene" (e.g., "good genes," "hair colour gene") typically refers to having a different allele of the gene. Genes evolve due to natural selection or survival of the fittest of the alleles. The concept of a gene continues to be refined as new phenomena are discovered.[3] For example, regulatory regions of a gene can be far removed from its coding regions, and coding regions can be split into several exons. Some viruses store their genome in RNA instead of DNA and some gene products are functional non-coding RNAs. Therefore, a broad, modern working definition of a gene is any discrete locus of heritable, genomic sequence which affect an organism's traits by being expressed as a functional product or by regulation of gene expression.[4][5]
- #21: Chromosomes threadlike structures made of DNA that contain the genes DNA (deoxyribonucleic acid) complex molecule containing the genetic information that makes up the chromosomes has two strands-forming a “double helix”--held together by bonds between pairs of nucleotides James Watson and Francis Crick are given credit for developing the three-dimensional structural model of DNA used today. However, they were not the first to ask the question, “How is hereditary information carried from one generation to the next?” or “How does it work?” Throughout history, our understanding of science changes as small modifications are made to what is known. Each discovery makes it possible for the next step in our understanding of scientific concepts to occur. The Watson and Crick model of DNA would not