Karyotyping

Karyotypes Chromosomes are distinguished by their appearance –size –position of centromere –pattern of bands (when stained) Karyotypes show us there are 2 of each type of chromosome

Karyotypes What is a karyotype? –Micrograph (picture) of chromosomes entered into computer –Chromosomes electronically arranged into pairs based on appearance (reference above) –The resulting picture is a karyotype

Chromosome Pair 23: Sex chromosome Chromosome Pairs 1-22: Autosomes Note: Exception to rule is chromosome pair 23 if the person is male (XY).

The Human Genome (I) Consists of 23 pairs of chromosomes. Chromosomes 1 through 22 are called autosomes. The X and Y chromosomes are the sex chromosomes. –Males are XY. –Females are XX.

Karyotyping As a Laboratory Technique for Disease Diagnosis Typical human cells contain 23 pairs of chromosomes. Variations in the number or structure of human chromosomes can cause a variety of genetic disorders. Variations in the number of chromosomes within a cell are called aneuploidies.

Non-Disjunction Incorrect separation of chromosomes or chromatids in meiosis known as non- disjunction Most embryos arising from gametes with abnormal chromosome numbers abort spontaneously (are miscarried) Some combinations of abnormal chromosome number survive to birth or beyond

Down Syndrome Trisomy 21 –3 copies of chromosome 21 Characteristics –facial features –short stature –heart defects –mental disabilities Statistics –1 in 800 –f increases w/age Autosomal Nondisjunction

Incidence of Down Syndrome Age of Mother (years) N u m b e r p e r B i r t h s

Sex Chromosome Nondisjunction **this table will be in the lab today to help you determine each karyotype GenotypeGenderSyndromePhysical Traits XYMaleNone-normal XXY XXYY XXXY MaleKlinefelter’s Syndrome sterility, small testicles, breat enlargement XYYMaleXXY Syndromenormal male traits XXFemaleNone-normal XOFemaleTurner Syndrome sex organs don’t mature at adolescence, sterility, short stature XXXFemaleTrisomy Xtall stature, learning disabilities, limited fertility

Fetal Testing TestBenefitRisk AmniocentesisDiagnosis of: chromosome abnormalities other defects discomfort infection miscarriage Chorionic villus sampling Diagnosis of: chromosome abnormalities genetic defects miscarriage infection newborn limb defects Fetal blood sampling Diagnosis of: genetic or chromosome abnormality fetal blood problems and O2 levels medications to fetus before birth bleeding from sample site infection amniotic fluid leak fetal death