Human Genetics 3

Chromosome Review Remember that a chromosome is a piece of tightly coiled DNA. Chromosomes occur in pairs. Example: The chromosome 1 that you inherited from mom has the same types of genes as chromosome 1 you inherited from dad. Both chromosome 1s pair together. Genes are in the DNA on a chromosome. When genes occur together on a chromosome they are linked.

Chromosome Mutations Mutation: any change in one’s DNA An alteration of a chromosome may change the DNA sequence contained within. Lethal Mutation: a deadly mutation Germ Cell Mutation: mutation in a gamete that does not affect parent but will affect offspring Ex: an egg with too many chromosomes Somatic Cell Mutation: mutation in an parent’s body cells that is not passed onto an offspring Ex: Cancer

Detecting Chromosome Mutations Karyotype A photograph of an organism’s chromosomes Used to diagnose disorders related to physically noticeable chromosomal mutations

Types of Chromosome Mutation Deletion (http://learn.genetics.utah.edu/content/begin/traits/predictdisorder/flash/deletions.swf) A section of a chromosome breaks and is lost Consequence: genetic information is lost Loss of information in a germ cell will likely affect the offspring; loss could be lethal

Survey of Genetic Disorders Cri du Chat Syndrome Caused by a deletion of a section of chromosome #5 Phenotype: Cat-like (mewing) cry Broad face Small head Severe retardation & behavioral disorders

Types of Chromosome Mutation Inversion Piece of a chromosome breaks off and reattaches in reverse order Consequence: reordering of genes Often harmless, but certain genes when reordered will not produce surviving offspring

Types of Chromosome Mutation Translocation (http://learn.genetics.utah.edu/content/begin/traits/predictdisorder/flash/translocations.swf) Piece of a chromosome breaks off and reattaches elsewhere Consequence: reordering of genes Most often a lethal chromosome mutation

Types of Chromosome Mutation Nondisjunction During meiosis, chromosomes fail to separate properly into gametes Consequence: too many or too few chromosomes in a gamete

Monosomy vs. Trisomy Monosomy Trisomy http://learn.genetics.utah.edu/content/disorders/chromosomal/turner/flash/monosomy.swf Trisomy http://learn.genetics.utah.edu/content/disorders/chromosomal/down/flash/trisomy.swf

Monosomy vs. Trisomy Monosomy & Trisomy result from nondisjunction Monosomy: baby after fertilization has only 1 chromosome instead of the normal pair Trisomy: baby after fertilization has 3 of the same chromosome

Survey of Genetic Disorders Turner’s Syndrome Cause: missing X chromosome in egg (monosomy) Phenotype: Occurs in females Will not mature sexually (sterile) Short body with webbed neck May have kidney and heart defects

Survey of Genetic Disorders Down Syndrome A.k.a. Trisomy 21 Caused by inheriting 3 of chromosome 21 1/660 births Phenotype: Small head, flattened nose, protruding tongue, eyes slant up Mental disability Stunted growth

Survey of Genetic Disorders Klinefelter’s Syndrome Present in males with XXY genotype 1/850 men affected Phenotype: Often not noticed Show fewer secondary sex characteristics Infertility Mental disability

Survey of Genetic Disorders XYY or “Supermale” ~1/1000 men Phenotype: Wiry build, elbows turned out, increased acne, not usually athletic Higher than average testosterone Evil stereotypes claim XYY’s more likely to be violent or have behavioral problems

Survey of Genetic Disorders XXX or “Superfemale” ~1/1000 women Phenotype Pretty normal May have lower IQ XXXX Mild mental disability XXXXX Severely disabled May or may not survive…

Detecting Genetic Disorders There are several methods used to diagnose genetic disorders before a baby is born. Sometimes prevention is possible through: Genetic Counseling Proper pre-natal care Good parental health before and during conception After birth, there is no cure for a genetic disease, only medical and psychological therapies to help children and their families cope with a disorder.