Karyotypes

Karyotype = A display (picture) of all the chromosomes in the nucleus of a cell. A display (picture) of all the chromosomes in the nucleus of a cell.

How do you make a karyotype? 1. Cell cycle is stopped in mitosis 1. Cell cycle is stopped in mitosis Why? Why? –So you can see the chromosomes 2. Put cells on microscope slide 2. Put cells on microscope slide 3. Stain cells so the chromosomes can be seen 3. Stain cells so the chromosomes can be seen 4. Take a picture of what is seen under the microscope 4. Take a picture of what is seen under the microscope 5. Enlarge picture 5. Enlarge picture

What do Doctors do with karyotypes? Cut out chromosomes Pair up homologous chromosomes –according –according to size starting with the largest, position of centromere and banding pattern Glue them down with their homologous partner

Enlarged picture of chromosomes in prophase Completed karyotype

Remember... Normal humans have 2 of each chromosome Normal humans have 2 of each chromosome No more -- no less No more -- no less

Sex chromosomes the X & Y the X & Y –Always the last set of chromosomes Males = XY Males = XY Females = XX Females = XX

Autosomes - All chromosomes except for the X & Y (sex chromosomes) All chromosomes except for the X & Y (sex chromosomes) Pairs 1-22 Pairs 1-22

What can a Dr. determine from a karyotype?

¶ Sex of a person ¶determined by the 23rd pair of chromosomes (in humans) ^ Females have 2 “large” X chromosomes ^Chromosomes will be the same size Males have 1 “large” X and a smaller y chromosome Males have 1 “large” X and a smaller y chromosome –Chromosomes will not be the same size

What else can a doctor determine? · The presence of a chromosomal number defect …

Disjunction Normal separation of Chromosomes and Chromatids during Meiosis I and Meiosis II (Anaphase I & II)

Normal Karyotypes Has 46 chromosomes for humans Arranged in 23 pairs

Nondisjunction- failure to separate

What does nondisjunction cause? Missing Chromosomes – Monomy Embryo/Fetus will not survive Means 45 chromosomes Exception is this can occur on 23 rd chromosome pair Extra Chromosomes – Trisomy Means 47 chromosomes –Down Syndrome (Trisomy 21) –Patau Syndrome (Trisomy 13) –Klinefelter’s Syndrome (XXY) –Turner’s Syndrome (X-) –XYY Syndrome –And many more………….

47, XX or XY, +13 Serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months. Serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months. Patau Syndrome Patau Syndrome

Cleft Palate

Klinefelter’s Syndrome

Symptoms of Klinefelters Sterile male Sterile male Testes abnormally small Testes abnormally small Later in life feminine contours may develop Later in life feminine contours may develop

Characteristics of Cri-du-chat Has only 1 chromosome at locus 5 Has only 1 chromosome at locus 5 Mentally retarded Mentally retarded Small head Small head

Characteristcs of Cri-du-chat Unusual facial features Unusual facial features Cry sounds like a cat meowing Cry sounds like a cat meowing

Characteristics of Turner Syndrome Only 1 X no y Female Sex organs and secondary sex characteristics do not develop

Sterile Sterile Short of stature Short of stature Mentally “normal” Mentally “normal”

Characteristics of Down Syndrome Has 3 chromosomes at locus 21 Has 3 chromosomes at locus 21 Characteristic facial features Characteristic facial features Mentally retarded Mentally retarded short short

Characteristics of Down Syndrome Heart defects Heart defects Webbed fingers Webbed fingers Generally do not live to be much older than 30 Generally do not live to be much older than 30

Amniocentesis