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Chromosomes and Inheritance

Chromosomes and Inheritance. Chapter 12-1. Objectives. Distinguish among inheritance patterns D ominant , recessive, codominant , sex-linked, polygenic, incomplete dominance, multiple alleles Explain how mutations in the DNA sequence can sometime result in change of an organism

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Chromosomes and Inheritance

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  1. Chromosomes and Inheritance Chapter 12-1

  2. Objectives • Distinguish among inheritance patterns • Dominant, recessive, codominant, sex-linked, polygenic, incomplete dominance, multiple alleles • Explain how mutations in the DNA sequence can sometime result in change of an organism • Explain how mutations in gametes can result in change in the offspring

  3. Vocabulary • Amniocentesis • Carrier • Chromosome map • Deletion • Frame shift mutation • Genetic disorder • Germ-cell mutation • Inversion • Lethal mutation • Monosomy • Nondisjunction • Pattern of inheritance • pedigree • Point mutation • Polygenic trait • Sex-influenced trait • Sex linkage • Single-allele trait • Somatic mutation • Substitution • Translocation • Trisomy

  4. Sex Determination • X is female and Y is male (smaller chromosome) • After meiosis II, one cell gets X and one get Y (from male parent) • 50% chance of being male or female

  5. Sex Linkage • Sex linkage is on sex chromosome • More genes on X chromosome than on Y • When on X, called X-linked genes • When on Y, called Y-linked genes

  6. Linkage Groups • Genes located on one chromosome and are inherited together • Crossing over is the exchange of genes • Causes new gene combinations

  7. Chromosome Mapping • The farther apart on the chromosome, the likelier crossover will happen • Chromosome map shows the linear sequence of genes on the chromosome through breeding experiments • One map unit are 2 genes separated by crossing over 1% of the time (closer together, less likely to be seperated)

  8. Mutation • Change in DNA of an organism • Germ mutation- no affect, in gametes (offspring?) • Somatic mutations- in body cells, do not affect offspring • Lethal mutations- cause death usually before birth • Some mutations are beneficial

  9. Chromosome Mutations • Deletion is the loss of a piece of chromosome • Inversion is when a piece breaks off and reattaches backwards • Translocation is when a breaks off and reattaches to another nonhomologous chromosome • Nondisjunction is when the chromosome doesn’t separate and the gamete gets an extra

  10. Gene Mutations • Point mutation-substitution, addition, or removal of a nucleotide • Substitution- one nucleotide is replaced with another and makes a new codon • Sickle cell anemia- adenine is substituted for thymine • Insertion is when a nucleotide is added and deletion is when one is lost • Both are serious and cause frame shift mutation (all codons moved)

  11. HumanGenetics Chapter 12-2

  12. Studying Human Inheritance • Geneticists focus on disease • Usually study phenotype of members of the same family and make a pedigree • Patterns of inheritance are predictable patterns throughout generations • Carriers do not express allele but can pass it on to offspring (recessive)

  13. Pedigree Chart

  14. Genetic Traits and Disorders • Genetic disorders are diseases or debilitating conditions that have genetic basis

  15. Traits Controlled by a Single Allele • Single allele traits controlled by a single allele of a gene • Huntington’s Disease controlled by a dominant allele • Most people do not know they have the disease until after they have children (in their 30s or 40s) • Discovered genetic marker (short section of DNA that is known to have association with nearby gene) • Others are controlled by homozygous recessive traits • Cystic fibrosis and sickle-cell anemia

  16. Traits Controlled by Multiple Alleles • 3 or more alleles of the same gene for a single trait • ABO blood type (IA, IB, i) • A has A antigen, B has B antigen, AB has both, O has none • A person with Rh- blood cannot receive Rh+ blood Blood Typing

  17. Polygenic Traits • Controlled by 2 or more genes • Show many degrees of variation • Also influenced by environment (ex: height)

  18. X-Linked Traits • Found on the X chromosome • Colorblindness, Hemophilia, Duchenne muscular dystrophy • Not all are diseases, mostly code for protein

  19. Sex-Influenced Traits • The presence of male or female sex hormones influence traits • Ex: male pattern baldness • Both male and female homozygous will lose hair • Heterozygous males will lose hair, female will not

  20. Disorders Due to Nondisjunction • Usually causes death • Monosomy -1, trisomy +1chromosome • Down Syndrome (trisomy-21) has an extra chromosome 21 • Klinefelter’s Syndrome (XXY) has feminine characteristics, mental retardation, infertile • Turner’s Syndrome (X) is female but does not mature, infertile • Just Y does not survive

  21. Detecting Human Genetic Disorders • Genetic screening examines the genetic make-up through karyotype or blood tests (+ or – proteins) • Genetic counseling is medical guidance for people at risk

  22. Can also test fetus • Amniocentesis removes fluid from around fetus • Chorionic villi sampling removes tissue from between the uterus and placenta • Or immediately after birth • Some babies have phenylketonuria (PKU) which prevents the digestion of phenylananine and can cause brain damage • Can be prevented by removing from the diet

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