Download Recessive Genetic Disorders

Genetic Diseases
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
Disorder
Cause
Cystic Fibrosis
Gene that codes for a
membrane protein is
defective
genetic disorder.
Effect
 Excessive mucus
production
 Digestive and
respiratory failure
Albinism
Genes do not produce
normal amounts of the
pigment melanin.
 No color in skin,
eyes, or hair
 Susceptible to UV
damage
 Vision problems
 No cure
 Skin protection
 Visual rehab
Galactosemia
Gene that codes for
enzyme that breaks
down galactose is
absent.
 Mental disabilities
 Enlarged liver
 Kidney failure
 No cure
 Restriction of
lactose/galactose in diet
Tay-Sachs
disease
Enzyme that breaks
down fatty substances
is absent.
 Build-up of fatty
deposits in brain
 Mental disabilities
 No cure or
treatment
 Death by age 5
Cure/Treatment
 No cure
 Daily mucus
cleaning
 Mucus-thinning
drugs
Genetic Diseases
Cystic Fibrosis
Galactosemia
Normal
Brain
(left)
Tay Sachs
Brain
(right)
Genetic Diseases
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
Huntington’s
A gene affecting
 Decline of mental
disease
neurological function is
and nerve function
defective.
 Ability to move
deteriorates
Achondroplasia A gene that affects bone  Short arms and legs
growth is abnormal.
 Large head
Cure/Treatment
 No cure or
treatment
 No cure or
treatment
Huntington’s
Disease
Achondroplasia
Pedigrees:
Genetic Diseases
8. Define pedigree: a diagram that traces the inheritance of a particular trait
through several generations
9. Know to read a pedigree key.
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.
Genetic Diseases
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.
Genetic Diseases
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.
Genetic Diseases
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
(monosomy)
Phenotype
Female with
Turner’s
syndrome
Characteristics Affects
growth and
development
of ovaries
XXX
(trisomy)
Nearly
normal
female
XXY
(trisomy)
Male with
Klinefelter’s
syndrome
Most are
sterile
XYY
(trisomy)
Nearly
normal
male
OY
(monosomy)
Results in
death