Karyotype and Nondisjunction

Chromosome vs Autosome

autosome (22 pairs or 44 total) have the DNA for most of your physical and chemical traits (hair, height, eyes, skin color, etc)

sex chromosomes (one pair or 2 total) have DNA which says if you're male/female

*if autosomes aren't specifically mentioned then the word "chromosome" includes sex chromosomes and autosomes

Sex Chromosome to gender ?

you get one sex chromosome from each parent, males have XY and women have XX
- to be a male your dad has to give u the Y and your mom give you the X
- to be a female your dad and mom both give one X chromosome each

Nondisjunction

When the cell doesn't divide correctly in mitosis or meiosis, causes daughter cells to have one more or one less chromosome than they should

Is Nondisjunction harmful?

Not if it happens in somatic cells (mitosis)
YES if it happens in gametes
^^ can cause children to have genetic mutations

What happens if an egg is fertilized with a nondisjuncted sperm?

EVERY cell in the child's body will have the mutation
ex. if the zygote has an extra chromosome, then every cell in its body will

Trisomy

if a homologous pair has an extra chromosome
ex. down syndrome is if someone has a trisomy on pair 21
(tri means 3 (three) some...)

Monosomy

if there is a chromosome missing and there can't be a homologous pair for it
(poor chromosome has to third-wheel all of the others now)

Nondisjunction Disorders (only 6 we gotta know)

Klinefelter syndrome
Turner syndrome
Triple X syndrome
Down Syndrome
Edward Syndrome
Patau Syndrome

Klinefelter syndrome

- male trisomy
- the child has an extra X sex chromosome (total 47)
- XXY

Symptoms for Klinefelter syndrome

small testes, developing of breasts, infertile

Turner syndrome

- female monosomy
- the child is missing a X sex chromosome (total 45)
- XO (if there is just one then they put O)

Symptoms for Turner Syndrome

infertile, short, webbed neck, broad chest

Triple X syndrome

- female trisomy
- the child has an extra X sex chromosome (total 47)
- XXX
*no symptoms or problems, child can live a normal life

Down Syndrome

- trisomy 21
- child has an extra chromosome at pair 21 (total 47)
- XX/XY, +21

Down Syndrome symptoms

intellectually disabled, flat face/nose, heart problems

Edward Syndrome

- trisomy 18
- child has an extra chromosome at pair 18 (total 47)
- XX/XY, +18

Edward Syndrome symptoms

intellectually disabled, fisted hands, heart problems

Patau Syndrome

- trisomy 13
- child has an extra chromosome at pair 13 (total 47)
- XX/XY, +13

Patau Syndrome symptoms

cleft palate (upper mouth I think), intellectually disabled, small eyes, and malformed ears

Karyotype notation

its how karyotypes are written

ex. Down syndrome has an extra chromosome on the 21st pair
so 47 (for # of chromosomes), XX (male), and +21 (for location)
Notation: 47, XX, +21

Don't need to write number after if sex chromosome
ex. Klinefelter's syndrome has an extra X chromosome
Notation 47, XXY

Age on disorders

older the man or woman is, the higher the risk for a child with mutation
40 yr old woman has 1:100 chance of Down Syndrome baby
30 yr old woman has 1:800 chance of down Syndrome baby
20 yr old woman has 1:1500 chance of down syndrome baby

Karyotype

a photograph of your chromosomes from a sample of your DNA is taken from a powerful microscope, then they are sorted in their homologous pairs from tallest to shortest

What can a karyotype tell?

the karyotype can tell the child's gender as well as any genetic disorders, like having or missing an extra chromosome
* VERY useful for couples who are expecting a baby

Two ways to get DNA for a Karyotype

Amniocentesis and CVS

Amniocentesis

- a long needle is inserted into the mother's womb and amniotic fluid (fluid around the baby) is taken
- can only be performed after 15 weeks of pregnancy
*risk that the hole might not fix itself and the baby could die

CVS

- Chorionic Villi Sampling
- a needle is inserted into the mother's womb and a sample of the placenta from around the baby is taken
- can be performed after 11th week of pregnancy