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Mizzou BIO_SC 1010 - Heredity

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Biology 1010 1st Edition Lecture 10Outline of Last Lecture I. What is a Somatic Cell?II. Cell DivisionIII. Stages of the Cell CycleIV. Cell Division is tightly regulatedV. What is Cancer?VI. Fighting CancerOutline of Current Lecture I. Genes are the units of inheritanceII. Humans are diploid organismsIII. How do you get one from two?IV. MeiosisV. Meiosis vs. MitosisVI. How unique are you?VII. How can Y chromosomes be used to trace paternity and ancestry?VIII. Errors in meiosisIX. Fetal chromosomal abnormalitiesX. Understanding of genetics XI. Meiosis can have mishapsCurrent LectureGenes are the units of inheritance• Genes are physically transmitted from parents to children• The alleles of genes from your parents are the reason you resemble your mother, father, and other family members• Not every child of a couple receives the exact same parental genes• Most genes have several alleles, each created by a genetic mutation These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-a mutation is a change in the nucleotide sequence of DNA, which creates alternative alleles of agene-cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane regulator gene on chromosome 7Humans are diploid organisms• Diploid- two copies of every chromosome -one from the biological mother-the other is inherited from the biological father• Genes located on the X and Y chromosome in males do not have a second copy• The two pairs have the same general function• The nucleotide sequence of each copy can differ-a person can carry two different alleles of the same gene-one of which functions differently from the other • A person’s phenotype includes the visible or measurable features of an individual• A person’s genotype is the particular genetic makeup of an individualHow do you get one from two? (5.6)• Most of the cells in your body are diploid; they have two copies of each chromosome • Sexually reproducing organisms need to make cells with a single set of chromosomes • Gametes, or sex cells, are haploid: they contain only one copy of each chromosome • Male gametes are called sperm• Female gametes are called eggs• One pair of chromosomes makes you male or female -the 46 chromosomes in your body are organized as 23 homologous pairs-of these, 22 pairs are autosomes-one pair is your sex chromosome (females are XX, males are XY)• Karyotypes are photographic inventories of chromosomes -chromosomes are organized I homologous pairsMeiosis• Meiosis is the production of gametes -gametes (sperm and egg) are formed by a special type of cell division, meiosis -cells produced from meiosis are haploid-like mitosis, meiosis occurs in stages • Meiosis occurs in stages-meiosis (like mitosis) starts with chromosome duplication before division-in meiosis, there are then two rounds of cell division -the result of meiosis is four haploid offspring cells, all with one-half the number of chromosomes Meiosis vs. Mitosis How unique are you?• Unless you have an identical twin, you are genetically different from any human that has ever lived• Sexual reproduction leads to variation-three major processes mean variation is the norm for sexual reproduction 1. Independent assortment2. Random fertilization3. Crossing over • Independent assortment of chromosomes leads to variation-chromosomes line up by homologous pairs during meiosis 1-maternal and paternal chromosomes are shuffled randomly• Random fertilization by sperm and egg leads to variation-the probability that any one sperm will fertilize any particular egg is extremely small• Crossing over during meiosis leads to variation -chromosomes can “swap” genetic material, creating new, unique combinations -crossing over occurs when homologous chromosomes line up during meiosis 1How can Y chromosomes be used to trace paternity and ancestry?• Sons inherit their Y chromosome from their biological fathers• No homologous pairing in Y chromosomes• Rarely undergoes genetic recombination Errors in meiosis• Nondisjunction is a failure of chromosomes to separate accurately during cell division• Aneuploidy- an abnormal number of one or more chromosomes• When an aneuploidy gamete is fertilized by a normal gamete, the resulting zygote can have an abnormal number of chromosomes Fetal chromosomal abnormalities• In most cases, fetal chromosomal abnormalities are so severe the zygote spontaneously aborts• In some cases, the abnormality is not life-threatening but does cause a severe disability • Down syndrome and other chromosomal abnormalities ca be diagnoses by amniocentesis, a procedure that removes fluid surrounding the fetus to obtain and analyze fetal cells to diagnose genetic disorders • Technicians analyze the fetal karyotype (the chromosomal makeup of cells) using the amniotic fluid that contains fetal cells with the fetus’ DNA Meiosis can have mishaps • Non-disjunction is when chromosomes fail to separate properly• Resulting gametes will have too few or too many chromosomes-zygotes with abnormal chromosome numbers will usually of develop or will have abnormalities• Examples of nondisjunction -trisomy 21 is a condition in which a person receives three copies of chromosome 21 -the resulting condition is called down syndrome -sex chromosome nondisjunction can also occur -each combination of extra or missing sex chromosomes produces its own syndromesUnderstanding of genetics • Gregor Mendel was the first to deduce the basic principles of inheritance • Heredity is the transmission of traits from one generation to the next• Genetics is the study of heredity• Character and traits are inherited -human eye color is a character, or a inherited feature that varies among individuals -each possible variation of a character is a trait • Alleles are the individual units of inheritance-traits derive from


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