THE CHROMOSOMAL BASIS OF INHERITANCE CHAPTER 15 What

THE CHROMOSOMAL BASIS OF INHERITANCE CHAPTER 15

What you must know: • How the chromosome theory of inheritance connects the physical movement of chromosomes in meiosis to Mendel’s laws of inheritance. • The unique pattern of inheritance in sex-linked genes. • How alteration of chromosome number or structurally altered chromosomes (deletions, duplications, etc. ) can cause genetic disorders. • How genetic imprinting and inheritance of mitochondrial DNA are exceptions to standard Mendelian inheritance.

Chromosome theory of inheritance: • Genes have specific locations (loci) on _________ • Chromosomes segregate and assort _________ Chromosomes tagged to reveal a specific gene (yellow).

Thomas Hunt Morgan • Drosophila melanogaster – _______ – Fast breeding, 4 prs. chromosomes (XX/XY) • ________ gene: located on X or Y chromosome – Red-eyes = wild-type; white-eyes = mutant – Specific gene carried on specific chromosome

Sex determination varies between animals

Sex-linked genes • Sex-linked gene on ____ • Females (XX), male (XY) – Eggs = __, sperm = ____ • Fathers pass X-linked genes to _______, but not sons • Males express recessive trait on the single X (_______zygous) • Females can be affected or ______

Transmission of sex-linked recessive traits Affected __________ Daughter _______ Mother Affected __________ + Carrier ______ Daughter & Son

Sex-linked disorders • ____________ • Duchenne muscular dystrophy • ____________

X-Inactivation _________= inactive X chromosome in female somatic cells; regulate gene dosage in females during embryonic development • Cats: allele for fur color is on X chromosome • Only _____ cats can be tortoiseshell or calico.

Human development • • ___ chromosome required for development of testes Embryo gonads indifferent at 2 months _______gene: sex-determining region of Y Codes for protein that regulates other genes

Genetic Recombination: production of offspring with new combo of genes from parents • If offspring look like parents ________ • If different from parents ________

• If results do not follow Mendel’s Law of Independent Assortment, then _______________

Linked genes: located on ______ chromosome and tend to be inherited ________ during cell division

___________: explains why some linked genes get separated during meiosis • the further apart 2 genes on same chromosome, the higher the probability of ________ and the higher the ____________

How many chromosomes are there? How many chiasmata are there?

Calculating recombination frequency

__________: genetic map that is based on % of ________events • 1 map unit = _____________frequency • Express relative distances along chromosome • 50% recombination = far apart on _____ chromosome or on 2 __________ chromosomes

Review & Reflect 1. Re-read each slide. 2. Highlight key vocab in one color 3. Highlight key concepts or definitions in another color 4. Write at least 3 questions or connections in the margins.

Discuss 1. Who was Thomas Hunt Morgan and what did he contribute to our modern understanding of genetics? 2. What is X-inactivation and why does it occur? 3. What are linked genes? How can you tell if 2 genes/traits may be linked?

Exceptions to Mendelian Inheritance

Genomic Imprinting • Genomic ______: phenotypic effect of gene depends on whether the gene is inherited from M or F parent • Methylation: _______ genes by adding ______ groups to DNA

Non-Nuclear DNA • Some genes located in organelles – _______________, plastids – Contain small circular DNA • Mitochondria = ______ inheritance (eggs) Variegated (striped or spotted) leaves result from mutations in pigment genes in plastids, which generally are inherited from the maternal parent.

Genetic Testing Reasons for Genetic Tests: • ________ testing (genetic disorders) • Presymptomatic & ________ testing • ______ testing (before having children) • Pharmacogenetics (medication & dosage) • Prenatal testing • _________ screening • Preimplantation testing (________)

Prenatal Testing • May be used on a fetus to detect genetic disorders • ___________: remove amniotic fluid around fetus to culture for karyotype • _____________sampling: insert narrow tube in cervix to extract sample of placenta with fetal cells for karyotype

___________: ___________ chromosomes fail to separate properly in Meiosis I or Meiosis II

_________ can detect nondisjunctions. Down Syndrome = Trisomy ____

Nondisjunction _______ Syndrome: 47 XYY, 47 XXY

Nondisjunction ______ Syndrome = 45 XO

Chromosomal Mutations

Chromosomal Mutations

Nondisjunction • _________: incorrect # chromosomes – Monosomy (__ copy) or Trisomy (___copies) • _________: 2+ complete sets of chromosomes; 3 n or 4 n – Rare in animals, frequent in ______ A tetraploid mammal. Scientists think this species may have arisen when an ancestor doubled its chromosome # by errors in mitosis or meiosis.

Review Questions 1. What is the pattern of inheritance of the trait (shaded square/circle) shown in the pedigree? 1. How many chromosomes are in a human cell that is: a) Diploid? b) Triploid? c) Monosomic? d) Trisomic?

Chi-Square Analysis Practice • Two true-breeding Drosophila are crossed: a normal-winged, red-eyed female and a miniature-winged, vermillion-eyed male. The F 1 offspring all have normal wings and red eyes. When the F 1 offspring are crossed with miniature-winged, vermillion-eyed flies, the following offspring resulted: – 233 normal wing, red eye – 247 miniature wing, vermillion eye – 7 normal wing, vermillion eye – 13 miniature wing, red eye • What type of conclusions can you draw from this experiment? Explain your answer.