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Chapter 12 Section 1 Chromosomes and Inheritance Objectives • Distinguish between sex chromosomes and autosomes. • Explain the role of sex chromosomes in sex determination. • Describe how an X- or Y-linked gene affects the inheritance of traits. • Explain the effect of crossing-over on the inheritance of genes in linkage groups. • Distinguish between chromosome mutations and gene mutations. Chapter 12 Section 1 Chromosomes and Inheritance Chromosomes • Genes reside on chromosomes. Chapter 12 Section 1 Chromosomes and Inheritance Chromosomes, continued • Sex Chromosomes and Autosomes – Sex chromosomes contain genes that determine an organism’s sex (gender). – The remaining chromosomes that are not directly involved in determining the sex of an individual are called autosomes. Chapter 12 Section 1 Chromosomes and Inheritance Karyotypes: Male and Female Chapter 12 Section 1 Chromosomes and Inheritance Chromosomes, continued • Sex Determination – In mammals, an individual carrying two X chromosomes is female. – An individual carrying an X and a Y chromosome is male. • Sex of an offspring is determined by the male/father Chapter 12 Section 1 Chromosomes and Inheritance Genetic Research – Early Work • Thomas Hunt Morgan – early 1900’s – Compiled research by using small fruit fly Drosophila melanogaster – While conducting his research he crossed a white-eyed (recessive) male with a normal red-eyed female. • The F1 generation all had red eyes, but when the F1 generation were crossed together the ratio became 3 redeyed to 1 white-eyed – This shows evidence of crossing-over, but it doesn’t show until the F2 generation – Exactly like Mendel’s pea plant diagram pg. 175 Chapter 12 Section 1 Chromosomes and Inheritance Effects of Gene Location • Sex-Linked Genes and Traits – Genes found on the X chromosome are X-linked genes. – A sex-linked trait is a trait whose allele is located on a sex chromosome. – Because males have only one X chromosome, a male who carries a recessive allele on the X chromosome will exhibit the sex-linked trait. • If a characteristic is sex-linked is occurs mostly in males Chapter 12 Section 1 Chromosomes and Inheritance Effects of Gene Location, continued • Linked Genes – Pairs of genes that tend to be inherited together are called linked genes. • Colorblindness is sex-linked Chapter 12 Section 1 Chromosomes and Inheritance Effects of Gene Location, continued • Chromosome Mapping – The farther apart two genes are located on a chromosome, the more likely a cross-over will occur. – Researchers use recombinant percentages to construct chromosome maps showing relative gene positions. Chapter 12 Section 1 Chromosomes and Inheritance Effects of Gene Location, continued • Chromosome Maps: – Depict the linear sequence of genes on a chromosome – Are constructed using crossing-over data from mating experiments – Are practical with species having only a few chromosomes Chapter 12 Section 1 Chromosomes and Inheritance Mutations • Germ-cell mutations occur in gametes and can be passed on to offspring. • Somatic-cell mutations occur in body cells and affect only the individual organism. ex. Certain types of human skin cancers and leukemia result from somatic-cell mutations, but can’t be passed on to offspring to be inherited Chapter 12 Section 1 Chromosomes and Inheritance Mutations • Lethal mutation cause death, often before death • Effects of a mutation can be helpful, harmful, and/or neutral Chapter 12 Section 1 Chromosomes and Inheritance Mutations, continued • Chromosome Mutations – Chromosome mutations are changes in the structure of a chromosome or the loss or gain of an entire chromosome. Chapter 12 Section 1 Chromosomes and Inheritance Deletion: loss of a piece of a chromosome due to breakage Chromosomal Mutations Inversion: chromosomal segments break off, flips around backward, and reattaches Translocation: piece of one chromosome breaks off and reattaches to a nonhomologous chromosome Fig 12-6 pg 239 Chapter 12 Section 1 Chromosomes and Inheritance Mutations, continued • Nondisjunction: a chromosome fails to separate from its homologue during meiosis. One gamete receives an extra copy of a chromosome and another gamete receives no copies. • This occurs with Down syndrome, a person with it has 3 copies of chromosome #21, which gives them 47 chromosomes total instead of 46 http://img.dailymail.co.uk/i/pix/2007/07_02/gardinerDM1907_468x380.jpg Chapter 12 Section 1 Chromosomes and Inheritance Mutations, continued • Gene Mutations – Gene mutations are changes in one or more of the nucleotides in a gene. Chapter 12 Gene Mutations Section 1 Chromosomes and Inheritance Chapter 12 Section 2 Human Genetics Objectives • Analyze pedigrees to determine how genetic traits and genetic disorders are inherited. • Summarize the different patterns of inheritance seen in genetic traits and genetic disorders. • Explain the inheritance of ABO blood groups. • Compare sex-linked traits with sex-influenced traits. • Explain how geneticists can detect and treat genetic disorders. Chapter 12 Section 2 Human Genetics Inheritance of Traits • Pedigrees – Geneticists use pedigrees to trace diseases or traits through families. – Pedigrees are diagrams that reveal inheritance patterns of genes. Chapter 12 Section 2 Human Genetics Pedigree for Cystic Fibrosis Chapter 12 Some Important Genetic Disorders Genetic Disorder: disease or disabling condition that have a genetic basis Section 2 Human Genetics Chapter 12 Section 2 Human Genetics Genetic Traits and Disorders • Single genes having 2 or more alleles can determine traits, such as blood type or cystic fibrous • Polygenic Inheritance – Geneticists have learned that most human characteristics are polygenic characteristics (they are influenced by several genes) – Ex. Skin color results from additive effect of 3-6 genes – Other Ex. Eye color, height, and hair color Chapter 12 Section 2 Human Genetics Genetic Traits and Disorders, continued • Complex Characters – Complex characters, such as polygenic traits, are influenced by both genes and environment. – Ex. Skin color is influenced by genes and if person lives in area with a lot of sun, the skin will naturally be darker – Ex. Height is influenced by genes and if the person has good nutrition and no diseases they should be taller than someone who has poor nutrition and diseases Chapter 12 Section 2 Human Genetics Genetic Traits and Disorders, continued • Multiple Alleles – Multiple-allele characters, such as ABO blood groups, are controlled by three or more alleles of a gene. » Look at top of page 244 Chapter 12 Section 2 Human Genetics Comparing Single Allele, Multiple Allele, and Polygenic Traits Click below to watch the Visual Concept. Visual Concept Chapter 12 Section 2 Human Genetics Comparing Complete, Incomplete, and Co-Dominance Click below to watch the Visual Concept. Visual Concept Chapter 12 Section 2 Human Genetics Genetic Traits and Disorders, continued • X-Linked Traits – The gene for colorblindness, an X-linked recessive gene, is found on the X chromosome. Chapter 12 Section 2 Human Genetics Genetic Traits and Disorders, continued • Sex-influenced Trait – A sex-influenced trait, such as pattern baldness, is expressed differently in men than in women even if it is on an autosome and both sexes have the same genotype. • The difference is due to higher levels of testosterone in men, which interacts with genotype to produce pattern baldness Chapter 12 Section 2 Human Genetics Comparing X-Linked and Sex-Influenced Traits Click below to watch the Visual Concept. Visual Concept Chapter 12 Section 2 Human Genetics Detecting Genetic Disease • Genetic screening examines a person’s genetic makeup and potential risks of passing disorders to offspring. • Amniocentesis and chorionic villi sampling help physicians test a fetus for the presence of genetic disorders. Chapter 12 Section 2 Human Genetics Detecting Genetic Disease, continued • Genetic Counseling – Genetic counseling informs screened individuals about problems that might affect their offspring. – Process uses family pedigree to look at family history of disease and can assist parents in deciding whether or not to have children Chapter 12 Section 2 Human Genetics Treating Genetic Disease • Genetic disorders are treated in various ways. • Among the treatments are symptom-relieving treatments and symptom-prevention measures, such as insulin injections for diabetes. Chapter 12 Section 2 Human Genetics Genetic Disorder Click below to watch the Visual Concept. Visual Concept Chapter 12 Section 2 Human Genetics Treating Genetic Disease, continued • Gene Therapy – In gene therapy, a defective gene is replaced with a copy of a healthy gene. – Somatic cell gene therapy alters only body cells. – Germ cell gene therapy attempts to alter eggs or sperm.