1. Tracing the Inheritance of the Human Y Chromosome
Women have sex chromosomes of XX, and men have sex chromosomes of XY.
Which of a man's grandparents could not be the source of any of the genes on his Y-chromosome?
Father's Mother.
Mother's Father.
Father's Father.
Mother's Mother, Mother's Father, and Father's Mother.
Mother's Mother.

2. Tracing the Inheritance of the Human X Chromosome
Women have sex chromosomes of XX, and men have sex chromosomes of XY.
Which of a women's grandparents could not be the source of any of the genes on either of her X-chromosomes?
Mother's Father.
Father's Mother.
Mother's Mother.
Father's Father.
Mother's Mother and Mother's Father

4. Is there a special pattern of inheritance for genes located on the X or Y chromosome?
Yes, they are called sex-linked genes.
More than 100 sex-linked genetic disorders have been mapped on the X chromosome.
Y chromosomes are smaller than X chromosomes and appear to only contain a few genes.

5. Red-Green Colorblindness
The most common type of red-green color perception defect is due to a mutation on the X-chromosome (i.e. a red-green color blind allele). X-linked red-color blindness is a recessive trait. Females heterozygous for this trait have normal vision. The color perception defect manifests itself in females only when it is inherited from both parents. By contrast, males inherit their single X-chromosome from their mothers and become red green color blind if this X-chromosome has the color perception defect.

6. Hemophilia
Hemophilia in humans is due to an X-chromosome mutation. What will be the results of mating between a normal (non-carrier) female and a hemophilac male?
half of daughters are normal and half of sons are hemophilic.
all sons are normal and all daughters are carriers.

7. Chromosomal Disorders
In some disorders, entire chromosomes, or large segments of them, are missing, duplicated, or otherwise altered.
The most common error is nondisjunction, when homologous chromosomes fail to separate during meiosis.
If nondisjunction occurs, the number of chromosomes in the gametes can be abnormal, and a disorder may result.

8. Homologous chromosomes fail to separate
Nondisjunction
Section 14-2
Homologous chromosomes fail to separate
Meiosis I:
Nondisjunction
Meiosis II
Go to Section:

9. Homologous chromosomes fail to separate
Nondisjunction
Section 14-2
Homologous chromosomes fail to separate
Meiosis I:
Nondisjunction
Meiosis II
Go to Section:

10. Homologous chromosomes fail to separate
Nondisjunction
Section 14-2
Homologous chromosomes fail to separate
Meiosis I:
Nondisjunction
Meiosis II
Go to Section:

12. Down’s Syndrome Occurs in 1/800-1,000 births Caused by nondisjunction
Trisomy 21 = three copies of chromosome 21

13. Frequency of Down Syndrome Per Maternal Age
Age (years)
Frequency of Fetuses with Down Syndrome to Normal Fetuses at 16 weeks of pregnancy
Frequency of Live Births of Babies with Down Syndrome to Normal Births
----
1 / 1250
1 / 1400
1 / 1100
1 / 900 32
1 / 750 33
1 / 420
1 / 625 34
1 / 325
1 / 500 35
1 / 250
1 / 350 36
1 / 200
1 / 275 37
1 / 150
1 / 225 38
1 / 120
1 / 175 39
1 / 100
1 / 140 40
1 / 75 41
1 / 60
1 / 85 42
1 / 45
1 / 65 43
1 / 35
1 / 50 44
1 / 30
1 / 40
45 and older
1 / 20
1 / 25
Return to Prenatal Testing for Down Syndrome Return to Down Syndrome: Health Issues Homepage

14. Down’s Syndrome
The image shows a karyotype of a person with Down’s Syndrome, Trisomy 21

15. Sex Chromosome Disorders
Turner’s Syndrome (XO)
underdeveloped ovaries, short stature, webbed neck, and broad chest. Individuals are sterile, and lack expected secondary sexual characteristics. Mental retardation typically not evident.

17. Sex Chromosome Disorders
Klinefelter’s Syndrome (XXY)
Nondisjunction in males
Some development of breast tissue, little body hair is present; typically tall, with or without evidence of mental retardation. Males with XXXY, XXXXY, and XXXXXY karyotypes have a more severe presentation, and mental retardation is expected.

19. Some Autosomal Disorders in Humans
Type of Disorder
Disorder
Major Symptoms
Disorders caused by recessive alleles
Albinism
Lack of pigment in hair, skin, and eyes
Cystic Fibrosis
Excess mucus in lungs, digestive tract, liver; increased susceptibility to infections; death in childhood unless treated
Phenylketonuria
Accumulation in brain cells; lack of normal pigment; mental retardation
Tay-Sachs Disease
Lipid accumulation in brain cells; mental deficiency; blindness; death in early childhood
Disorders Caused by dominant alleles
Achondroplasia
Dwarfism (one form)
Huntington’s Disease
Mental deterioration and uncontrolled movements; appears in middle age
Disorders caused by codominant alleles
Sickle Cell Anemia
Sickled red blood cells; damage to many tissues

20. Albinism

21.                                                                     
Phenylketonuria

22.                           
Achondroplasia

23. Sickle Cell Anemia

24. Causes of Genetic Disorders
Dominant Alleles
Recessive Alleles
Sex-linked genes
Autosomal genes
Nondisjunction
Gene mutations
Chromosomal mutations

25. Gene Mutations
Changes in the DNA sequence that affect genetic information.
Result from changes in one gene.
Types:
Point mutations
Frameshift mutations

26. Chromosomal Mutations
Mutations involving changes in whole chromosomes.
Changes in the number of copies or structure of a chromosome.
Types:
Deletions
Duplications
Inversions
Translocation

27. Deletion
Duplication
Inversion
Translocation