Chapter 11.3

Chromosomes and Human Heredity

Karyotype Studies

• A Karyotype is an array of chromosomes created by photographing the metaphase chromosomes from one cell, cutting out the individual chromosomes from the photograph and lining them up in order from largest to smallest, pairing the appropriate homologous chromosomes. ...

Karyotype Studies

• Notice on this Karyotype there are 3 copies of the 21st set of chromosomes

• This results in downs’ syndrome (trisomy 21)

Nondisjunction at M1Nondisjunction at M2

• Non-disjunction occurs when chromosomes in the developing gamete (sex cell) fail to separate during one of the divisions of meiosis. The result is a sperm or egg cell with either an additional chromosome, or one that lacks one chromosome. When this sex cell combines with one from the opposite sex, the resulting fetus will have cells with an extra, or one chromosome that is lacking. Generally, such fetus' will not develop properly and we would say that the resulting baby would have a birth defect.

Animation of Non-Disjunction

Changes in Numbers of Sex Chromosomes

Turners Syndrome (0X)

• Turner syndrome is a genetic disorder that affects a girl's development. The cause is a missing or incomplete X chromosome. Girls who have it are short, and their ovaries don't work properly. Most are infertile.

XXX female

• Triple X syndrome is a form of chromosomal variation characterized by the presence of an extra X chromosome in each cell of a human female.

• Usually these woman are undiagnosed and function normally

XXY male – Klinefelter’s Syndrome

• Chromosomal defect in males in which there is an extra X chromosome; manifestations may include underdeveloped testes, physical feminization, sterility, and mental retardation.

XYY Male

• Most often, this chromosomal change causes no unusual physical features or medical problems.

• XYY boys and men are usually taller than average and several centimeters taller than their parents and siblings

• XYY males have normal sexual development and usually have normal fertility. Since XYY is not characterized by distinct physical features, the condition is usually detected only during genetic analysis for another reason.

OY Chromosome

• A person with only one Y chromosome (45,Y) could not survive or be born alive. The X chromosome has important genes on it that would be completely missing in such a person.

Fetal Testing - amniocentesis

• A sample of amniotic fluid can be withdrawn and analyzed (fluid contains fetal cells). It is useful for

• Diagnosing sex linked disorders

• Chromosomal defects• Sex can also be

determined

Fetal Testing – Chorionic villus sampling

• Tissue is taken from membrane surrounding the fetus. Can test for:

• (1) Chromosomal abnormalities.

• (2) Some inherited disorders. Dominant, Recessive and X-linked patterns of inheritance.

Fetal Testing – Fetal Blood sampling

• A fetal blood sample may be taken to:

• diagnose genetic or chromosome abnormalities.

• check for and treat severe fetal anemia or other blood problems such as Rh disease.

• check for fetal oxygen levels.

• check for fetal infection.

• give certain medications to the fetus.

Extra Review

• REVIEW: Nondisjunction can be caused by _____ .

• Answer: Failure of the chromosomes to separate during meiosis

• REVIEW: A gamete affected by nondisjunction would have _____ .a. a change from the normal chromosome number b. one extra or one missing chromosome c. the potential for a genetic disorder d. all of the above

More questions

• Amniocentesis involves sampling• Fetal cells in amniotic fluid• The condition occurring when an organism

has a 2n + 1 chromosome composition is known as

• Trisomy• The sex chromosome composition of a

person with Turner syndrome is• XO

Assessment

• 1. Sex of individual and whether the proper number of chromosomes are there

• 2. In homologous pairs from largest to smallest.

3.

4.

• Males only receive on X and one Y so missing sections could contain vital genes . With females having 2 XX deletion in one X could be made up for by the other

Further study

• Really interesting information on human genetics