Changes in Chromosome Structure

Change in Chromosomes Often if the chromosome numbers or structures are changed a lot, there are lethal consequences. Plants tolerate changes better than animals

Polyploidy Having MORE than 2 sets of chromosomes – Triploidy (3N) Seedless fruit (pollen stimulates ovary to grow, but seeds do not. – Tetraploidy (4N) Produce larger flowers and fruits – Common in plants, not in animals, often result in larger flowers or fruits

How do we use this in plants

Parthenocarpy Development of the ovary of a flower into a fruit without fertilization

Abnormal Chromosome numbers Nondisjuction – Pairs of homologous chromosomes do not separate normally – RESULT: one gamete receives two of the same type of chromosome, while another receives no copy of that chromosome – Chromosome number would be 47 or 45, not 46

smeiosis.swf The link below will take you through non-disjunction in Meiosis I and Meiosis II

Aneuploidy DEFINITION: Having an abnormal number of only one type of chromosome Results from either the egg or sperm having extra or a missing chromosome. Monosomy – Zygote has only one copy of one type of chromosome Trisomy – Zygote has three copies of one type of chromosome

oOk Another video showing non-disjunction, but with music and not words.

Types of Chromosomal Mutations

EXAMPLE Cri-du-chat (“cry of the cat”) results from a specific deletion in chromosome 5 Severe intellectual disabilities Catlike cry Dies in infancy or early childhood

EXAMPLE Charcot-Marie-Tooth AKA: hereditary sensory and motor neuropathy Runs in families Nerves (axons and myelin) become damaged Muscles lose strength

Duplications Charcot-Marie-Tooth disease – most common inherited neurological disorder – CMT1A results from a duplication of a gene on chromosome 17 carries instructions for producing the peripheral myelin protenin-22. RESULT: peripheral nerves do not function correctly

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Inversions A single chromosome undergoes breakage and rearrangement within itself Often results in no effect to the individual

Certain cancers, including chronic myelogenous leukemia (CML) are caused by translocations of chromosomes

Robertsonian Translocation Acrocentric chromosomes – Short arms break – Long arms join – 13 and 14 – 14 and 21

Translocations Chronic myelogenic Leukemia Activated cancer Causing gene on Chromosome 22

XY recombination Abnormal recombination in the father of XX males, results in an X chromosome that carries the SRY gene (designated X*) Genetically female Phenotype: Male

Summary Structural changes can cause problems with growth, development, and function of the body’s systems. – These changes can affect many genes along the chromosome and disrupt the proteins made from those genes. Structural changes can occur – during the formation of egg or sperm cells, – in early fetal development, or – in any cell after birth.

Summary (cont) Pieces of DNA can be – rearranged within one chromosome – transferred between two or more chromosomes – Lost – Duplicated Effect of change depends on – Size, location, and what is lost or gained – Can have no effect or cause mild to severe medical problems. osomemutation.asp