1. The Human Genome
Chapter 14

2. 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.

3. Human Chromosomes Human Karyotype
These human chromosomes have been cut out of a photograph and arranged to form a karyotype. Photo credit: ©CNRI/Science Photo Library/Photo Researchers, Inc.

4. Karyotype of Down syndrome
(trisomy 21)

5. Boy with Down syndrome

6. Girl with Cri-du-Chat syndrome

7. Nondisjunction Trisomy
Nondisjunction causes gametes to have abnormal numbers of chromosomes. The result of nondisjunction may be a chromosome disorder such as Down syndrome.
Trisomy

8. Nondisjunction (not coming apart) – Causes chromosomal disorders
Incomplete separation of chromosomes during anaphse (I or II) during meiosis.

9. 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).

10. Nondisjunction

11. Human Sex Determination

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

13. Female X X XX XY X
Male Y
50:50
XX:XY

14. All human egg cells carry a single X chromosome
All human egg cells carry a single X chromosome. Half of the sperm carry and X chromosome & half carry a Y chromosome.

15. Pedigree Patterns
A pedigree chart shows the relationships within a family.

16. Human Traits A square represents A circle 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.
This drawing shows what the symbols in a pedigree represent.

17. Autosomal chromosomes (#1-22)
Dominant autosomal disorder
Disease is present in EVERY generation.
Equal chance for males or females to have the trait.

18. This table shows the major symptoms of some well-known genetic disorders.

19. Autosomal continued
Recessive autosomal disorder
Disease skips generations.
Equal chance for male or female.

21. 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.

22. 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
Genes on X and Y chromosomes, such as those shown in the diagrams, are called sex-linked genes.
Y Chromosome
Testis-determining
factor

23. 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.

24. Father (normal vision)
Possible Inheritance of Colorblindness Allele
Father (normal vision)
X-linked alleles are always expressed in males, because males have only one X chromosome. Males who receive the recessive Xc allele all have colorblindness. Females, however, will have colorblindness only if they receive two Xc alleles.