3 Karyotypes Definitions Uses Karyotype – a picture of an individual’s chromosomes.Karyotyping - A technique that uses a picture of an individual’s chromosomes to analyze and detect chromosomal abnormalities.To detect possible fetal abnormalities.Form of genetic screening conducted on potential parents.
4 Methods for Preparing a Karyotype IndividualsFetusPre-natal diagnosisAmniocentesis- a small amount of amniotic fluid, which contains fetal tissues, is sampled from the amniotic sac surrounding a developing fetus, and the fetal DNA is examined for genetic abnormalities.(see diagram)2. Chorionic villi sampling- entails sampling of the placental tissue and testing it for chromosomal abnormalities.Postnatal diagnosisWhite blood cell test
6 Arrangement of a Karyotype Humans have 23 pairs (46) of chromosomes22 pairs of autosomes (body cells)1 pair of sex chromosomes – which determine the sex of the individualFemales are XX; males are XYArranged by size from largest to smallest1 pair of homologous chromosomes at each site
7 Types of Chromosome Abnormalities Nondisjunction – failure of homologous pairs of chromosomes to separate during meiosis.Results in trisomy – 3 chromosomes instead of a pair at a given site.Deletion – missing segment of a chromosome.monosomy – missing a whole chromosomeTranslocation – segment of one chromosome is attached to another chromosome.Crossing over – exchange of parts between two homologous chromosomes.Inversion – genes switch loci (places) on a chromosome.Syndrome – a group of symptoms.
23 Carriers – individuals that have the gene for a trait but do not have the condition; heterozygous
24 Patterns of Inheritance Autosomal DominantDoes not skip generationsAffects males and females equallyApproximately ½ the offspring of a person with the trait will be affectedThe affected person is usually heterozygous2. Autosomal RecessiveBoth parents and grandparents of an affected person are usually normal.¼ of the siblings of an affected person will also be affected.Affects males and females equally.
25 Patterns of Inheritance 3. X-linked DominantAffects females more than malesAffected males have no normal daughters and no affected sonsAffected females who are homozygous transmit the trait to all childrenDoes not skip generations4. X-linked RecessiveSkips generationsAffects males more than femalesTrait is transmitted by “carrier” femalesAn affected male will pass the carrier status to all of his daughters so ½ of their sons will be affected.
26 X-linked InheritanceGenes on the X chromosome have no counterpart on the Y chromosome, therefore, characteristics determined by a gene on the X chromosome are always expressed in males.
27 How many males are affected? How many females are affected?What is the pattern of inheritance?