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Chapter 15: Chromosomal Basis of Inheritance

Chapter 15: Chromosomal Basis of Inheritance (Link between Meiosis or cellular processes and Genetics) Objectives Mendelian Genetics is based on the physical behavior of chromosomes Sex linked genes have unique inheritance patterns

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Chapter 15: Chromosomal Basis of Inheritance

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  1. Chapter 15: Chromosomal Basis of Inheritance • (Link between Meiosis or cellular processes and Genetics) • Objectives • Mendelian Genetics is based on the physical behavior of chromosomes • Sex linked genes have unique inheritance patterns • Linked genes are often inherited together due to physical proximity on the chromosome • Alterations of chromosome number or structure results in genetic disorders • There are some exceptions to the inheritance patterns

  2. Chromosome Theory Chromosomes are what segregates and undergo independent assortment.

  3. Chromosomal Behavior determines sex of organism -There is a sex determining region on the Y chromosome. -Gonads are generic until about 2 months -SRY gene is responsible for the formation of the testes

  4. Sex Linked Genes -Sex linked recessive genes for color blindness -homozygous recessive females have the trait -males that get the recessive allele from mom will have the disease • X Chromosome Inactivation • One of the X chromosomes in females becomes in active. • Barr Bodies are the inactive version of the X chromosome • Inactivation doesn’t happen right away • Females that are heterozygous for a certain X chromosome trait can express both traits during development. • Inactive versions produce the same in active versions during mitosis.

  5. Linked Genes and Recombinant Chromosomes -Parental types vs Recombinants p. 294 -Recombinations can happen when chromosomes segregate indpendently or after crossing over has occurred -Crossing over is responsible for recombinant genes if they are located on the same chromosome Location of genes on a chromosome

  6. Chromosomal Dissorders -Nondisjunction – homologous chromosomes don’t move apart -Aneuploidy – when a zygote has an abnormal chromosome amount -monosomic one less -trisomic one extra (polyploidy) -Downs Syndrome (trisomy 21) – the older the woman is the greater the odds of having a baby with Downs -Sex Chromosomes dissorders (Most are normal) Klinefelters syndrome XXY – male is sterile Turnner syndrome XO only known viable monosomy in humans – Females are sterile *Barr Bodies are reason success of individuals

  7. Alterations of Chromosome Structures *Many cases cause severe problems – most don’t make it to birth

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