The Human Genome Chapter 14
Human Heredity • Human chromosomes – There are 23 pairs of chromosomes. Half the chromosomes are from each parent. • Autosomal chromosomes – Chromosome numbers 1 thru 22. • Sex Chromosomes – chromosome pair #23. There are two options XX for female or XY for male.
Human Chromosomes • Human Karyotype
Karyotype of Down syndrome (trisomy 21)
Nondisjunction (not coming apart) – Causes chromosomal disorders • Incomplete separation of chromosomes during anaphse (I or II) during meiosis.
Nondisjunction continued • Chromosomal Disorders: • Down Syndrome – Trisomey (3 copies of a chromosome) on chromosme 21. • Turner;s Syndrome – Females with only 1 X chromosome (females are sterile).
Males and females are born in a roughly 50 : 50 ratio because of the way sex chromosomes separate during meiosis.
Female X X X Male Y 50:50 XX:XY
All human egg cells carry a single X chromosome. Half of the sperm carry and X chromosome & half carry a Y chromosome.
Pedigree Patterns • A pedigree chart shows the relationships within a family.
Human Traits A square represents a male. A circle represents a female. A vertical line and a bracket connect the parents to their children. A horizontal line connecting a male and a female represents a marriage. A shaded circle or square indicates that a person expresses the trait. A circle or square that is not shaded indicates that a person does not express the trait.
Autosomal chromosomes (#1-22) • Dominant autosomal disorder • Disease is present in EVERY generation. • Equal chance for males or females to have the trait.
Autosomal continued • Recessive autosomal disorder • Disease skips generations. • Equal chance for male or female.
Sex-linked genes • Genes located on X & Y chromosomes are called sex-linked genes. • Most sex linked traits are linked to the X chromosome • Males have just one X chromosome. So all X-linked alleles are expressed in males, even if they are recessive.
X Chromosome Duchenne muscular dystrophy • The Y chromosome is much smaller than the X chromosome contains only a few genes. Melanoma X-inactivation center X-linked severe combined immunodeficiency (SCID) Colorblindness Hemophilia Y Chromosome Testis-determining factor
Colorblindness • Three human genes associated with color vision are located on the X chromosome. • In males, a defective version of any one of these genes produces colorblindness.
Father (normal vision) • Possible Inheritance of Colorblindness Allele