s Notes:

Karyotypes

Human Chromosomes- what you know…• Humans have 46 chromosomes

(diploid-2N)• 2 of them are sex chromosomes (X

and Y) they determine what sex you are– XX = female– XY = male

• 44 of them are autosomes they do not determine the sex of an individual.

Sex chromosomes

How is a KARYOTYPE Made?1. Collect sample:

a. Fetus: amniotic fluid collected during an amniocentesis or a piece of the placenta collected during a chorionic villi sampling test (CVS).

b. Newborn: white blood cells

2. Separate dividing & non-dividing cells using chemicals3. Culture the dividing cells to get a lot of cells4. Add chemical to stop cell division when chromosome is

compacted5. Lyse the cells6. Stain the chromosomes (stain sticks to regions with a lot of

“A” and “T” bases7. Analyze!

How is a KARYOTYPE Analyzed?• Use computers to match the homologous pairs.• We will cut out the chromosomes from a

chromosome spread then arrange them to match the banding patterns of the homologous pairs– Use banding patterns, size of chromosome, and

position of centromere• This type of picture is called a

KARYOTYPE

Chromosome Spread

Karyotype

What does a Karyotype tell you?

– Sex (male or female)– Irregular numbers of chromosomes– Any mutations in the chromosomes

• Basically: all the chromosomes in a cell are displayed and can be examined for abnormalities

Is this offspring a girl or boy? How do you know?

Are there any abnormalities in this offspring?

Chromosomal Disorders• Most of the time, the mechanisms that separate

human chromosomes in meiosis work very well, but things can go wrong

• The most common error: NONDISJUNCTION– The chromosomes fail to separate in Anaphase I or II – The result? Abnormal numbers of chromosomes in

gametes.

Nondisjunction

Prefixes: dis = absence of / opposite of non = not

Root Word:Junction = joining together

• disjunction = the act of separating• nondisjunction = the act of not

separating

Figure 14-15page 352

Nondisjunction(after anaphase I)

Metaphase I

“Trisomy” = 3 copies of a chromosome

End of Meiosis—4 gametes produced

Examples of Chromosomal Disorders

• Down Syndrome (3 #21 chromosomes)• Klinefelter’s Syndrome (XXY)• Turner’s Syndrome (XO)• Triple X Syndrome (XXX)

                

• Down's Syndrome: 47 chromosomes with 3 #21 chromosomes.

• Triple-X Syndrome: 47 chromosomes caused by 3 X chromosomes.

• Klinefelter's Syndrome: 47 chromosomes caused by 2 X chromosomes and 1 Y chromosomes.

• Turner's Syndrome: 45 chromosomes with 1 X chromosome (caused by the absence of one of the X chromosomes or a Y chromosome).

Examples of Nondisjunction resulting in Chromosomal

Disorders

Chromosomal Mutations

• Chromosomal Mutations

– Deletion

– Duplication

– Inversion

– Translocation

Chromosomal Mutation (change in number)

• If an organism is born with the incorrect number of chromosomes– Ex: 47 human

chromosomes instead of 46

• Result of nondisjunction

Down Syndrome

• 3 copies of chromosome #21 • 1 in 800 babies in the US is born with this

disease• produces mild to severe mental

retardation • May not live as long

Klinefelter’s Syndrome

• This is a sex chromosomal disorder associated with males.

• Nondisjunction causes an extra X chromosome to be passed

along during meiosis (XXY). • Resulting male cannot reproduce • Cases have been found in which

individuals were (XXXY) or (XXXXY)

• Decrease muscle mass and body hair

Turner’s Syndrome

• This is a sex chromosomal disorder associated with females.

• Nondisjunction causes offspring to inherit only one X chromosome (genotype = XO).

• Resulting female is sterile due to underdeveloped sex organs.

• 1/2500 females

Review question..Who determines the sex of a child?

The mother or the father?

THE FATHER!!!!Why?

Why does the father determine the sex of the offspring???

• Mom is XX: she can donate either one X chromosome or the other X chromosome to the offspring

(mom can only donate an X)• Dad is XY: he can donate either an

X chromosome or a Y chromosomes.– If the offspring receives an X from

dad, it is female – If the offspring receives a Y from dad,

it is male