Section 1 Chromosomes and Inheritance Chapter 12 Objectives • Distinguishbetween sex chromosomes and autosomes. • Explainthe role of sex chromosomes in sex determination. • Describehow an X- or Y-linked gene affects the inheritance of traits. • Explainthe effect of crossing-over on the inheritance of genes in linkage groups. • Distinguishbetween 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.

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.

Section 1 Chromosomes and Inheritance Chapter 12 Effects of Gene Location, continued • Linked Genes • Pairs of genes that tend to be inherited together are calledlinked genes.

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 Mutations • Germ-cell mutationsoccur in gametes and can be passed on to offspring. • Somatic-cell mutationsoccur in body cells and affect only the individual organism.

Section 1 Chromosomes and Inheritance Chapter 12 Mutations, continued • Chromosome Mutations • Chromosome mutationsare 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 Chapter 12 Mutations, continued • Gene Mutations • Gene mutationsare changes in one or more of the nucleotides in a gene.

Section 1 Chromosomes and Inheritance Chapter 12 Gene Mutations

Section 2 Human Genetics Chapter 12 Objectives • Analyzepedigrees to determine how genetic traits and genetic disorders are inherited. • Summarizethe different patterns of inheritance seen in genetic traits and genetic disorders. • Explainthe inheritance of ABO blood groups. • Comparesex-linked traits with sex-influenced traits. • Explainhow 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.

Section 2 Human Genetics Chapter 12 Pedigree for Cystic Fibrosis

Section 2 Human Genetics Chapter 12 Some Important Genetic Disorders

Section 2 Human Genetics Chapter 12 Genetic Traits and Disorders • Polygenic Inheritance • Polygenic characters, such as skin color, are controlled by two or more genes.

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.

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.

Section 2 Human Genetics Chapter 12 Genetic Traits and Disorders, continued • X-Linked Traits • The gene forcolorblindness, 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.

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.

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.

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.

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