Chapter 12 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. Section 1 Chromosomes and Inheritance

Chapter 12 Chromosomes Genes reside on chromosomes. Section 1 Chromosomes and Inheritance

Chapter 12 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. Section 1 Chromosomes and Inheritance

Chapter 12 Karyotypes: Male and Female Section 1 Chromosomes and Inheritance

Chapter 12 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 Section 1 Chromosomes and Inheritance

Chapter 12 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 red- eyed 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 Section 1 Chromosomes and Inheritance

Chapter 12 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 Section 1 Chromosomes and Inheritance

Chapter 12 Effects of Gene Location, continued Linked Genes –Pairs of genes that tend to be inherited together are called linked genes. Colorblindness is sex-linked Section 1 Chromosomes and Inheritance

Chapter 12 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. Section 1 Chromosomes and Inheritance

Chapter 12 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 Section 1 Chromosomes and Inheritance

Chapter 12 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 Section 1 Chromosomes and Inheritance

Chapter 12 Mutations Lethal mutation cause death, often before birth Effects of a mutation can be helpful, harmful, and/or neutral Section 1 Chromosomes and Inheritance

Chapter 12 Mutations, continued Chromosome Mutations –Chromosome mutations are changes in the structure of a chromosome or the loss or gain of an entire chromosome. Section 1 Chromosomes and Inheritance

Chapter 12 Chromosomal Mutations Section 1 Chromosomes and Inheritance Deletion: loss of a piece of a chromosome due to breakage 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 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 Section 1 Chromosomes and Inheritance

Chapter 12 Mutations, continued Gene Mutations –Gene mutations are changes in one or more of the nucleotides in a gene. Section 1 Chromosomes and Inheritance

Chapter 12 Gene Mutations Section 1 Chromosomes and Inheritance

Homework Section 12.1Review Pg 240 #1-9

Section 2 Human Genetics Chapter 12 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.

Section 2 Human Genetics Chapter 12 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 Section 2 Human Genetics Genetic Disorder: disease or disabling condition that have a genetic basis

Section 2 Human Genetics Chapter 12 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

Section 2 Human Genetics Chapter 12 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

Section 2 Human Genetics Chapter 12 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 Click below to watch the Visual Concept. Visual Concept Comparing Single Allele, Multiple Allele, and Polygenic Traits Section 2 Human Genetics

Chapter 12 Click below to watch the Visual Concept. Visual Concept Comparing Complete, Incomplete, and Co-Dominance Section 2 Human Genetics

Chapter 12 Genetic Traits and Disorders, continued X-Linked Traits –The gene for colorblindness, an X-linked recessive gene, is found on the X chromosome.

Section 2 Human Genetics Chapter 12 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 Click below to watch the Visual Concept. Visual Concept Comparing X-Linked and Sex-Influenced Traits Section 2 Human Genetics

Chapter 12 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.

Section 2 Human Genetics Chapter 12 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

Section 2 Human Genetics Chapter 12 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 Click below to watch the Visual Concept. Visual Concept Genetic Disorder Section 2 Human Genetics

Chapter 12 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.

Homework Section 12.2 Review Pg 248 #1-8