Recessive Genetic Disorders:



Recessive Genetic Disorders:

1. What kind of genotype is necessary to express a recessive genetic disorder?

Homozygous recessive

2. What is an individual that is heterozygous for a recessive genetic disorder called?

carrier

3. Which of these recessive genetic disorders is most common in the US? Tay-sachs

least common? Galactosemia

4. Know the information for each recessive genetic disorder.

|Disorder |Cause |Effect |Cure/Treatment |

|Cystic Fibrosis |Gene that codes for a membrane protein is |Excessive mucus production |No cure |

|[pic] |defective |Digestive and respiratory failure |Daily mucus cleaning |

| | | |Mucus-thinning drugs |

|Albinism |Genes do not produce normal amounts of the |No color in skin, eyes, or hair |No cure |

|[pic][pic] |pigment melanin. |Susceptible to UV damage |Skin protection |

| | |Vision problems |Visual rehab |

|Galactosemia |Gene that codes for enzyme that breaks down |Mental disabilities |No cure |

|[pic] |galactose is absent. |Enlarged liver |Restriction of lactose/galac-tose in |

| | |Kidney failure |diet |

|Tay-Sachs disease |Enzyme that breaks down fatty substances is |Build-up of fatty deposits in brain |No cure or treatment |

|[pic] |absent. |Mental disabilities |Death by age 5 |

Cystic Fibrosis

Galactosemia

Normal Brain (left)

Tay Sachs Brain (right)

Dominant Genetic Disorders:

5. What kinds of genotypes must an individual have in order to express a dominant

genetic disorder? Homozygous dominant or heterozygous

6. Which of these 2 dominant genetic disorders is more common in the US?

Huntington’s disease

7. Know the following information for each genetic disorder.

|Disorder |Cause |Effect |Cure/Treatment |

|Huntington’s disease |A gene affecting neurological function is |Decline of mental and nerve function |No cure or treatment |

| |defective. |Ability to move deteriorates | |

|Achondroplasia |A gene that affects bone growth is abnormal. |Short arms and legs |No cure or treatment |

| | |Large head | |

Huntington’s

Disease

Achondroplasia

Pedigrees:

8. Define pedigree: a diagram that traces the inheritance of a particular trait

through several generations

9. Know to read a pedigree key.

[pic]

Notes on reading a pedigree:

• An individual heterozygous for a recessive trait is a carrier.

• An individual heterozygous for a dominant trait is affected.

• If the trait is hidden for generations, it is most likely a recessive trait.

• If males are affected more often than females, and females are carriers, the trait is most likely sex-linked.

Complex Pattern Inheritance: Codominance Genetic Disorders

10. Describe the inheritance pattern of codominance.

Both alleles are expressed in a heterozygous individual

11. What is the condition that demonstrates codominance discussed in class?

Sickle cell trait

12. What is the phenotype of an individual heterozygous for the sickle cell trait?

AS

13. How does the mutated shape of red blood cells affect an individual’s health?

The sickled cells get trapped in blood vessels and block the flow of blood. Also,

the sickled cells die sooner than normal resulting in a low red blood cell count.

14. What is the name of the protein inside red blood cells? hemoglobin

15. What is the function of hemoglobin? Oxygen attaches to the heme in the

hemoglobin to be carried from the lungs to all other parts of the body.

16. What causes the production of mutated hemoglobin molecules?

A change in the 6th amino acid in the beta chain of hemoglobin causes the mutation. Normal hemoglobin has glutamic acid; sickle cell has valine.

17. Why do the mutated hemoglobin molecules cause the cell to change shape?

When there is no oxygen attached to the hemoglobin, the hemoglobins stick

together forming long fibers that elongate the cell into a sickle shape.

18. What is the allele for normal red blood cells? A

19. What is the allele for sickled red blood cells? S

20. Fill in the chart: This chart refers to the sickle cell trait, which is an example of

codominance.

|Genotype |Phenotype |

|AA |Normal red blood cells are produced. (Healthy person) |

|AS |Both normal red blood cells AND sickled red blood cells are produced. Person experiences symptoms under low oxygen conditions. |

|SS | Production of ONLY sickled red blood cells. Person has sickle cell anemia and experiences symptoms all of life. |

21. What are some of the symptoms experienced by an individual with sickle cell

disease (SS)? Pain in bones and joints

possible stroke

possible blindness

damage to lungs, kidneys, and heart

22. What is life like for AS genotype individuals? They have a normal life but

experience symptoms of sickle cell anemia under conditions of low oxygen levels

such as high elevation.

23. What is malaria? An infectious disease caused by the parasite Plasmodium that is

carried in the salivary glands of mosquitoes.

24. What is the relationship between individuals heterozygous for sickle cell disease

and their susceptibility to malaria?

Individuals heterozygous for sickle cell disease are less likely to become sick

with malaria.

25. What makes this relationship possible? Because sickled red blood cells die within

10-20 days, the parasite does not have time to replicate and invade other cells.

Sex-Linked Disorders

26 What is a sex-linked trait? Traits controlled by genes located on the X chromosome.

27. What are 2 examples of disorders that are carried on the X chromosome?

Hemophilia

Red-green color blindness

28. How is the gender of a baby determined? An X chromosome is given by the

mother and an X OR Y chromosome is given by the father. The combination

results in the following:

XX= female

XY= male

29. What are the chances of a couple having a boy or girl? 50% boy / 50 % girl

30. If a sex-linked trait is recessive, why will it be more likely for males to

express the trait?

A male only has one X chromosome and will express the trait if he inherits it. A

female has 2 X chromosomes, so she would have to inherit 2 copies of the

mutated X in order to express the disease.

31. What is hemophilia? A disorder characterized by delayed blood clotting.

Nondisjunction:

32. Define nondisjunction:

Cell division during which homologous chromosomes or sister chromatids fail to separate properly

33. What is the result of nondisjunction?

Gametes, and therefore, offspring will have an extra copy or only one copy of a chromosome.

34. What is having an extra copy of a chromosome (set of 3) called?

Trisomy

35. What is having only one copy of a chromosome called?

Monosomy

36. What is one of the earliest known human nondisjuction chromosomal disorders?

Down syndrome: results from an extra copy of chromosome 21

37. What are the conditions resulting from nondisjunction of sex chromosomes?

|Genotype |XO |XXX |XXY |XYY |OY |

| |(monosomy) |(trisomy) |(trisomy) |(trisomy) |(monosomy) |

|Phenotype |Female with Turner’s |Nearly normal female |Male with Klinefelter’s |Nearly normal male |Results in death |

| |syndrome | |syndrome | | |

|Characteristics |Affects growth and | |Most are sterile | | |

| |development of ovaries | | | | |

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