Biology 121 Chapter 5
Biology 121 Chapter 5 121
University of Louisiana at Lafayette
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This 10 page Study Guide was uploaded by Maria Luisa Cepeda on Wednesday February 10, 2016. The Study Guide belongs to 121 at University of Louisiana at Lafayette taught by Dr. Jeffrey Spring in Fall 2015. Since its upload, it has received 38 views.
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Date Created: 02/10/16
Chapter 5: Chromosomes and Inheritance 5.1- Cell division provides for reproduction, growth, and repair Cell Theory: all life is cellular and all cells arise from preexisting cells Through cell division cells are able to generate more cells. Two offspring cells are genetically identical to each other and parent cell. Prior to cell division, original cell copies its chromosomes, structures that contain most of the organism’s DNA. 1 set of chromosomes is distributed to each offspring cell. Sexual Reproduction: formation of genetically unique offspring. Begins with fertilization joining of gametes (23 chromosomes from dad’s sperm and 23 chromosomes of mom’s egg) to form a single original cell called zygote. Development: occurs through repeated rounds of cell division, the zygote develops into embryo, then fetus, then baby. Growth & repair: body grows; cell division provides new cells needed to expand tissues and organs. In adultsmillions of cells divide each second to replace damaged cells (heal a wound) Asexual Reproduction: creation of a new individual by 1 parent w/o sperm and egg. Only 1 set of chromosomes passed down Offspring genetically identical to each other and parent Binary fission: single-celled organisms reproduce by splitting into two. Plant Reproduction: sprouting or by sending out runners Regeneration: some animals can regenerate lost limbs The trillions of cells in our bodies are identical because they all formed via cell division from a single original cell called the zygote. 5.2- Chromosomes are associations of DNA and Protein DNA, the genetic material may contain a great number of genes-units of inheritance made from DNA that code for proteins. Almost all the genes in a eukaryotic cell are found on chromosomes located in nucleus. Different species have different numbers of chromosomes in nucleus Each human body cell contains 46 chromosomes in its nucleus. # of chromosomes does not correspond to the size or complexity of an organism. DNA of 2 humans of the same sex is about 99.5% identical. DNA wrapped around protein form package called chromatin. Proteins help keep DNA tightly organized in nucleus. Cell division: cell replicates (copies) its chromosomes and compacts them into sister chromatids that stay joined at the centromere. Then sister chromatids separate, each going to each offspring cell. Gene: a small segment of DNA. Hundreds or thousands of genes in a chromosome. Contains info to build 1 or more strands of protein or 1 or more molecules of RNA. Every eukaryotic cell contains chromosomes in nucleus. Each chromosome consists of 1 long piece of DNA associated with proteins that help to compact and organize it. Together, the DNA and protein form chromatin. 5.3- Cells have regular cycles of growth and division Cell cycle: lifetime of a cell organized in sequence of events from time cell is created until its division into 2 cells. 1. Interphase: 90% of the cell cycle, most of cell’s lifetime is spent during interphase. Cell performs its normal functions, duplicates the chromosomes, doubles in size, builds organelles, chromosomes remain uncondensed. By end of interphase, every chromosome in nucleus has a duplicate called a sister chromatid. Mitotic Phase: Mitosis and Cytokinesis Nucleus along with its already duplicated chromosomes divides and is distributed to the 2 offspring cells Cytokinesis-cytoplasm is divided and distributed Result: 2 genetically identical offspring cells that begin their own cell cycles. 5.4- During mitosis, the nucleus is duplicated Mitosis, the division of the nucleus into two offspring nuclei. The duplicated chromosomes are organized and separated At the start of mitosis, nuclear membrane dissolves o Chromosomes condense (w/ help of proteins) o Protein tracks called mitotic spindle appearused to organize chromosomes. Chromosomes align o Pairs of sister chromatids line up in center of cell o Each chromosome attached to a separate track of mitotic spindle Chromosomes split Sister chromatids split apart and dragged by mitotic spindle towards opposite sides. Nuclear membrane reforms Chromosomes uncondense Nucleusduplicated into 2 nuclei 5.5- During cytokinesis, the cell is split in two Cytokinesis the distribution of the cytoplasm to the 2 offspring cells Cleavage furrow in an animal cell Indentation around the equator of cell Proteins form cleavage furrow Cell plate in a plant cell Cytoplasm is divided forming a cell plate, a strip of membrane and cell wall materials that forms along center line of cell. 5.6- Gametes have half as many chromosomes as body cells Human Life Cycle Each gamete has a single set of chromosomeshaploid(n) Only gametes are haploid When gametes fusediploid (2n) zygote. Somatic cells (body cells other than reproductive games) are diploid. In gonads (testes in males and ovaries in females) a special kind of cell division produces gametes. Male gametesperm; Female gameteegg Inventory of chromosomes Karyotype-photographic inventory of chromosomes in person’s cells Homologous chromosomes-2 chromosomes in a matching pair o Carry genes controlling same inherited characteristics o Versions of genes may be different on chromosomes Sex chromosomes o2 of the 46 chromosomes determine sex oHuman females (XX); Human males (XY) oThe other 44 chromosomes are called autosomes The human life cycle involves fertilization (fusion of haploid gametes to produce a diploid zygote), growth and development via cell division, and then the production of gametes in the gonads. All human body cells have 46 chromosomes organized as 23 homologous pairs of chromosomes. 5.7- Meiosis produces gametes Meiosis- type of cell division that produces gametes (sperm and egg) from cells in gonads. 2 rounds of cell division Chromosomes double, then are divided in half, then in half again. Interphase Chromosomes duplicate within nucleus Meiosis I Chromosomes condense and line up by homologous pairs Nuclear membrane dissolves Chromosomes pairs separate 1 member of each pair heading to opposite end of cell Cytokinesis After chromosome pairs separate, cell divides into 2 cells. Nucleus reforms and now 2 offspring cells get ready for Meiosis II Meiosis II Chromosomes condense and line up in center of cell Sister chromatids split apart Cytokinesis II Produces a total of 4 offspring cells, nuclear enveloped reforms, chromosomes uncondense. Meiosis is a type of cell division that produces haploid gametes from diploid body cells. One round of chromosome duplication is followed by two rounds of division. The result is 4 offspring cells, each with half the number of chromosomes as the starting cell. 5.9 Several Processes produce genetic variation among sexually reproducing organisms 3 ways sexual reproduction produces variations in organisms Independent assortment Each homologous pair in Meiosis I contains 1 maternal chromosomes and 1 paternal chromosome 8 million possible arrangements of chromosomes Random fertilization 1 gamete with random chromosomes fertilizes another gamete with random chromosomestremendous variation in the 46 chromosomes that end up in zygote Crossing over Chromosomes are not passed on intact when you produce gametes Homologous chromosomes lined up during meiosis swap pieces This produces hybrids that are partially paternal and maternal 5.10 Mistakes during meiosis can produce gametes with abnormal numbers of chromosomes Nondisjunction: chromosomes fail to separate properly. Result: gametes with unusual # of chromosomes (usually 1 too few or 1 too many) Usually fatal but can occasionally produce adult w/ syndrome Trisomy 21 Most common chromosomal abnormality Condition in which person has 3 copies of chromosome 21 for a total of 47 chromosomes Produces Down syndrome Sex chromosome abnormalities Nondisjunction affects sex chromosomes as well as autosomes Klinefelter, Jacob, Triple X, and Turner Syndrome. 5.11- Mendelian Genetics Heredity: transmission of traits from one generation to the next. Character inherited feature, varies from individual to another Each comes in 2 or more variationstraits Alleles: alternate forms of a particular gene 2 identical alleles homozygous Different heterozygous Dominant Allele usually determines organism’s appearance (represented by uppercase letter) Recessive Allele may be passed on to offspring. Only expressed in individual who is homozygous recessive. (Lowercase letter) Phenotype: physical traits Genotype: underlying genetic makeup. Causes phenotype in combination w/ environment through action of genes. An organism’s physical traits (phenotype) are caused by its genetic makeup (genotype). Most characters are controlled by two copies of a gene called alleles. The two alleles for a trait may be identical (homozygous) or they may be different (heterozygous) 5.12- A punnet square can be used to predict the results of a genetic cross Genetic cross- 2 individuals of the P generation (parents) are crossed to produce the F1 generation (first-generation offspring) Monohybrid Cross is a genetic mating that follows just one trait of the two parents. Law of Segregation During gamete formation: the two alleles for any given character separate, one allele going into half the gametes and the other allele going into the other half of the gametes. 5.13-Mendel’s law of independent assortment accounts for the inheritance of multiple traits Dihydrid Cross is one in which two separate characters are studied. Law of independent assortment states that each pair of alleles separates independently of the alleles for other characters. Inheritance of one character has no effect on the inheritance of another. Ex: seed color has no effect on which allele inherited for seed shape Principle applies to all sexually reproducing species 5.14- Pedigrees can be used to trace traits in human families The dominant trait is not necessarily “normal” or more common than the recessive trait. Carrier- heterozygous individual who has a recessive disease- causing allele but does not display the disease. 5.15- The inheritance of many traits is more complex than Mendel’s Laws Classic Mendelian geneticsinheritance of many characters, but others require extensions to the simple rules Incomplete Dominance Intermediate appearance Multiple Alleles Human blood types determined by a gene with 3 alleles I, Ia, Ib Pleitropy 1 gene influences many characters 1 single mutationmany physical changes Ex: sickle cell anemia (mutation of red blood cells)anemia and weakness. Polygenic Inheritance Effect of many genes on a single character. Ex: human height and skin color are each affected by several genes. Environment vs. Genetics Only genetic influences are inherited; effects on environment not passed on to next generation. 5.16- Linked genes may not obey the law of independent assortment Linked genes- genes located near each other on same chromosome are often inherited together. Genetic Recombination Movement of chromosomes controls the inheritance of genetic traits. Crossing over (during gamete formation where homologous chromosomes pair up in meiosis) Produces hybrid chromosomes called recombinant chromosomes that contain parts of both original chromosomes 2 genes located very near each otherlittle chance that crossover will occur. 5.17-Sex-linked genes display unusual inheritance patterns -Of the 46 human chromosomes, 44 are called autosomes. The other 2 are the sex chromosomes. Sex Chromosomes 1 X chromosome + 1 Y chromosomeMale ; XXFemale Each sperm by a male22 autosomes and 1 sex chromosome. Half will have an X chromosome, and half will have the Y. Each body cell of male44 autosomes + XY Each egg produced by female22 autosomes and 1 X chromosome. Each body cell 44 autosomes + XX Offspring’s sex determined by whether sperm cell that fertilizes the egg bears and X or Y chromosome. Sex-Linked Inheritance Sex-linked genes- single genes located on the X chromosome that control several human characters. Human cells contain 44 autosomes and 2 sex chromosomes. If a person has 2 X sex chromosomes, she is female; males have 1 X and 1 Y. Because they are located on the X chromosome, sex linked genes display unusual inheritance patterns. 5.18-Nuclear transfer can be used to produce clones -Biologists have learned to artificially manipulate the natural process of cell division in order to produce clones-genetically identical individuals born of a single parent. Nuclear transplantationanimals Procedure in which a nucleus is removed from an adult donor cell, injected into a nucleus-free egg cell, and then induced to grow into an embryo that may produce a new organism through cell division. The resulting individualclone of animal that provided the nucleus/ Plant Cloning Widely used in agriculture. Small plant samples placed into growth liquid. Reproductive Cloning Embryo produced through nuclear transplantation. If animal is a mammal, the embryo must be injected into uterus of a mother Stem cells Embryowhether natural or produced via nuclear transplantation is rich in stem cells. In therapeutic cloning stem cells are harvested from the cloned embryo Embryonic stem cells have potential to develop into every cell type in the body Other stem cell sourcesadult bone marrow + umbilical cord blood. Cannot be grown into a variety of cells but are easier to collect.
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