Chapter 8 Gen Bio.pdf

Does the cell ever get tired of cycling/ retires? G0 Phase Resting phase The Cell exits Cell Cycle and stops dividing Also called Quiescent stage – for a long/ indefinite period Cells are differentiated – most human body cells – eg. Liver, Nerve, Muscle cells, etc. Some may be “c...

Does the cell ever get tired of cycling/ retires? G0 Phase Resting phase The Cell exits Cell Cycle and stops dividing Also called Quiescent stage – for a long/ indefinite period Cells are differentiated – most human body cells – eg. Liver, Nerve, Muscle cells, etc. Some may be “called back” to cell cycle  Controls of cell cycle G1 M G2 Factors that control cell cycle Cyclin + Cdk = Mitogens Active complex Cyclins – G1, G1/S, S, G2, M Cyclin Dependent Kinases (Cdks) Cdk Inhibitors (CKIs) Proteolysis Cyclin + Cdk + CKI = Inactive complex CKIs  Species Number of chromosomes in body cells Different Indian muntjac deer 6 individuals of Koala 16 a single Opossum 22 species have Giraffe 30 the same Mouse 40 Human 46 number and Duck-billed platypus types of 54 Bison 60 chromosomes. Dog 78 Red viscacha rat 102  How to visualize Homologous Chromosomes – Produce a karyotype – break open a human cell in metaphase of mitosis, – stain the chromosomes with dyes, – take a picture with the aid of a microscope, and – arrange the chromosomes in matching pairs by size.  Types of Homologous Chromosomes A Human body cell called Somatic Cell have 46 chromosomes: – 22 pairs of matching chromosomes, called Autosomes, and – two different Sex chromosomes, X and Y, In mammals, – males = 1 X and 1 Y – Females = 2 X chromosomes. Sexual Reproduction – Meiosis & Fertilization Figure 8.10  Haploid gametes (n = 23) Gametes and the n Egg cell Life Cycle of a n Sexual Organism Sperm cell MEIOSIS FERTILIZATION Multicellular Diploid diploid adults zygote (2n = 46) 2n (2n = 46) MITOSIS and development Key Haploid (n) Diploid (2n)  Gametes and the Life Cycle of a Sexual Organism Humans are said to be diploid (2n) organisms because all body cells contain pairs of homologous chromosomes. A haploid (n) cell has only one member of each pair of homologous chromosomes. All gametes are haploid (n) cells. © 2016 Pearson Education, Inc.  Gametes and the Life Cycle of a Sexual Organism In the human life cycle, a haploid sperm cell from the father fuses with a haploid egg cell from the mother in a process called fertilization. The resulting fertilized egg, called a zygote, is diploid, with two sets of chromosomes, one set from each parent. © 2016 Pearson Education, Inc.  The Process of Meiosis All sexual life cycles involve an alternation of diploid and haploid stages. Meiosis - the process of cell division that produces haploid gametes in diploid organisms. Prevents the chromosome number from doubling in every generation. © 2016 Pearson Education, Inc.  1 Chromosomes 2 Homologous 3 Sister chromatids duplicate. chromosomes separate. separate. Pair of A pair of Sister homologous homologous chromatids chromosomes chromosomes in diploid parent cell INTERPHASE BEFORE MEIOSIS MEIOSIS I MEIOSIS II  The Origins of Genetic Variation Meiosis produces genetic variations by – Crossing Over – Independent Assortment Offspring of sexual reproduction are genetically different from their parents and one another. © 2016 Pearson Education, Inc. Features of Prophase I Formation of tetrad Synapse of homologous chromosome Crossing Over and Chiasma formation Crossing Over It is the exchange of corresponding segments between non- sister chromatids of homologous chromosomes Thus, gametes arise with chromosomes that are partly from the mother and partly from the father. © 2016 Pearson Education, Inc.  Independent Assortment of Chromosomes Meiosis contributes to genetic variety. – When aligned during metaphase I of meiosis, the side-by- side orientation of each homologous pair of chromosomes is a matter of chance. – For a species with more than two pairs of chromosomes, such as humans, every chromosome pair orients independently of all the others at metaphase I. © 2016 Pearson Education, Inc. One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment Independent assortment produces 2n distinct gametes, where n = the number of unique chromosomes. In humans, n = 23 and 223 = 6,000,0000.  Independent Assortment of Chromosomes When aligned during metaphase I of meiosis, the side-by-side orientation of each homologous pair of chromosomes is a matter of chance. Independent Assortment of Chromosomes –For a human, n = 23, so there are 223, or about 8 million, possible chromosome combinations that can appear in gametes. –A single man and a single woman can produce zygotes with 64 trillion combinations of chromosomes! © 2016 Pearson Education, Inc. Figure 8.15 Parent cell Parent cell 2n = 4 2n = 4 MITOSIS MEIOSIS Prophase Prophase I MEIOSIS I Duplicated chromosome Homologous chromosomes Site of come together. crossing over Metaphase Metaphase I Chromosomes Homologous align. pairs align. Anaphase Anaphase I Telophase Telophase I Sister Homologous chromatids chromosomes separate. separate. Haploid 2n 2n n=2 Sister MEIOSIS II chromatids separate. n n n n Error in NONDISJUNCTION IN MEIOSIS I chromosome Meiosis I segregation or Homologous chromosomes Non-Disjunction fail to separate. the members of a Meiosis II chromosome pair fail to separate at anaphase, during meiosis I or II, Gametes producing gametes with abnormal numbers of n+1 n+1 n1 n1 chromosomes. Abnormal  NONDISJUNCTION IN MEIOSIS II Meiosis I Meiosis II Sister chromatids fail to separate. Gametes n+1 n1 n n Abnormal Normal How does Non-Disjunction Alter Chromosome Number When an abnormal gamete produced by nondisjunction unites with a normal gamete during fertilization – Trisomy & Monosomy – When a normal sperm fertilizes an egg cell with an extra chromosome, the result is a zygote with a total of 2n + 1 chromosomes.  Down Syndrome: An Extra Chromosome 21 In a condition called trisomy 21, there are three “21 no.” chromosomes, making 47 chromosomes in total. Most common abnormality. Condition is called Down syndrome Affects about 1/ 700 children Down Syndrome: An Extra Chromosome 21 Children/ Adults with Down syndrome have characteristic facial features, a life span shorter than normal exhibit varying degrees of developmental delays. Individuals may live to middle age or beyond, and can function well within society. Observed mostly in the fetuses of pregnant women age 35 and older – Why??  Autosomal Trisomy The only other human autosomal trisomics to survive to birth: – Trisomy 13 (Patau syndrome): The generalized phenotype of trisomy 13 includes a harelip; a small, malformed head; “rockerbottom” feet; and a mean life expectancy of 130 days. – Trisomy 18 (Edwards syndrome): includes “faunlike” ears, a small jaw, a narrow pelvis, and rocker-bottom feet; almost all babies with trisomy 18 die within the first few weeks after birth.  Abnormal Numbers of Sex Chromosomes Nondisjunction in meiosis can lead to abnormal numbers of sex chromosomes, X and Y. Non-disjunctions are mostly autosomal – Unusual numbers of sex chromosomes seem to upset the genetic balance less than unusual numbers of autosomes. © 2016 Pearson Education, Inc. Table 8.1 Klinefelter Syndrome = multiple non- disjunctions – XXY, XXYY, XXXY, XXXXY Video Cell Cycle Check Points  Abnormalities during cell cycle Mutation in genome  over- / under- expression of some proteins Epigenetic changes Damage of regulatory proteins Excessive use of mitogens Exposure to mutagens/ radiations Viral Infections Abnormal cell Division/ CANCER  What Is Cancer? Cancer is an anomaly/ disease of the cell cycle. Cancer cells – do not respond normally to the cell cycle control system, – divide excessively, and – may invade other tissues of the body. Cells cannot stop dividing and go through uncontrolled cell division becoming cancerous cells or tumors. Skin cancer  Types of Abnormal Growths Cancer cells can form tumors, abnormally growing masses of body cells. – benign tumor - The abnormal cells remain at the original site – Malignant tumors – Cell growth spreads into neighboring tissues and other body parts, forming new tumors, interrupting organ function. © 2016 Pearson Education, Inc. End of Lecture