Human Heredity: Karyotypes and Pedigrees Mrs. Kooiman LSHS09-10

Vocabulary karyotype sex chromosome autosome pedigree

Human Chromosomes  By taking a look at the nucleus, we will see chromosomes of a human cell.  To analyze chromosomes, cell biologists photograph cells in mitosis, when the chromosomes are fully condensed and easy to see.  The biologists then cut out the chromosomes from the photographs and group them together in pairs.  A picture of chromosomes arranged in this way is known as a karyotype (KAR-ee-uh-typ).

Karyotype  These human chromosomes have been cut out of a photograph and arranged to form a karyotype.

TTTThere are 46 chromosomes in this karyotype of somatic cells TTTThere are 23 pairs of somatic cells TTTThe first 22 pairs are called autosomes

 The last pair are called sex chromosomes  XX = Female  XY = Male  What is the gender of this karyotype?

 Males and females are born in a roughly 50 : 50 ratio because of the way in which sex chromosomes segregate during meiosis.  Males and females are born in a roughly 50 : 50 ratio because of the way in which sex chromosomes segregate during meiosis.

 All human egg cells carry a single X chromosome.

 However, half of all sperm cells carry an X chromosome and half carry a Y chromosome.

This ensures that just about half, 2 out of 4, of the zygotes will be XX

 This ensures that just about half, 2 out of 4, of the zygotes will be XY

Pedigree Charts  Human genes are inherited according to the same principles that Gregor Mendel discovered in his work with garden peas.  However, in order to apply Mendelian genetics to humans, biologists must identify an inherited trait controlled by a single gene to ensure that the trait is actually inherited and not the result of environmental influences.

 A pedigree chart shows the relationships within a family

AAAA CIRCLE represents a Female,  AAAA SQUARE represents a Male, ■ AAAA HORIZONTAL line represents a marriage

AAAA VERTICAL line and a BRACKET connect the parents to their children GGGGeneration 1 had 5 children HHHHow many sons? HHHHow many daughters?

TTTThe children are listed from LEFT to RIGHT TTTThe OLDEST child is first TTTThe YOUNGEST child is last

AAAA SHADED circle or square means the person expresses the trait. AAAAn OPEN circle or square means the person does not express the trait.