8.3 Human Genetics and Mutations Key Concepts: How do chromosomes help determine gender? How do chromosome mutations occur? Different genetic diseases How can scientists test for genetic disease? Key Vocabulary: Autosome Nondisjunction Monosomy Trisomy Karyotype Amniocentesis

The 23rd pair are sex chromosomes that determine an person’s gender Human Chromosomes How many pairs of chromosomes do human diploid cells have? 23 pairs (46 total) The first 22 pairs of chromosomes are autosomes (=body/self) that do not determine sex The 23rd pair are sex chromosomes that determine an person’s gender X codes for female Y codes for male

Sex Determination Female cells have two X chromosomes - XX Male cells have one X and one Y chromosome - XY In meiosis, the chromosome number is reduced in cells when pairs of chromosomes split What sex chromosome will females contribute to offspring? ONLY an X What sex chromosomes will male sperm contribute to offspring? X or a Y

Sex Determination **If an X chromosome sperm fertilizes an egg, what will the sex of the offspring be? FEMALE **If a Y chromosome sperm fertilizes an egg, what will the sex of the offspring be? Male

Chromosome Mutations Changes the number of chromosomes in a cell What is the normal number of chromosomes in a body cell? A sex cell? 46 23 Monosomy occurs when a fertilized egg has only 1 copy of a chromosome Trisomy occurs when a fertilized egg has 3 copies of a chromosome

Nondisjunction Nondisjunction occurs when chromosomes don’t separate properly during meiosis What phase of meiosis do the chromosomes separate? ANAPHASE Causes fertilized eggs to have an abnormal number of chromosomes

Nondisjunction

Chromosome Diseases Down’s syndrome – AKA TRISOMY 21 3 chromosomes on 21st pair instead of 2 Kleinfelter syndrome – XXY Syndrome 3 sex chromosomes (this person is male with female characteristics) Turner syndrome – Monosomy X One sex chromosome (this person is female)

Karyotype Picture of a person’s chromosomes Arranged from largest to smallest Genetic test done with high-risk pregnancies Used to diagnose genetic diseases and abnormal numbers of chromosomes Made using a sample of amniotic fluid from mothers womb Amniocentesis is used to extract the fluid

Amniocentesis – a procedure done to extract DNA from the fetus.

Amniocentesis

Karyotype Is this karyotype from a male or female? Female

Karyotype Is this karyotype from a male or female? Male

Karyotype What mutation and disease does this karyotype show? Down Syndrome

Karyotype What mutation and disease does this karyotype show? Turner Syndrome

Turner Syndrome

Karyotype What mutation and disease does this karyotype show? Kleinfelter Syndrome

Kleinfelters