Things to Know for the Test

Things to Know for the Test – Human Genetics

1. How many pairs of autosomes are in a human cell? 22 2. What is the most common fatal genetic disease? Cystic fibrosis 3. How many c’somes does a human sperm cell contain? 23 4. Genetic disorder that is written as 47XXY? Kleinfelter’s syndrome 5. Metabolic disorder that every newborn in PA is screened for? Phenylketonuria (PKU) 6. What is used to follow a trait through a series of generations? Pedigree 7. If a female is a hemophiliac and a male is normal, what are the chances of them having a kid with hemophilia? Overall 50% (0% of girls, 100% of boys) XH Y Xh XHXh XhY Xh XHXh XhY

8. What sex-linked disorder causes a person to lose control of their muscles? Duchenne muscular dystrophy 9. What is a characteristic of an autosomal dominant genetic disorder? Just need one bad allele to get it; no difference between males and females in inheritance; doesn’t skip generations (see also Q29) 10.What are the sex chromosomes of a female? XX 11.How many sex chromosomes are in a human cell? 2 12.Disorder in which a person has an extra copy of chromosome #21? Down syndrome 13.If a female is a carrier for colorblindness and the male is colorblind, what are the chances that they will have a colorblind girl? 50% of the girls (25% of all children will be colorblind girls) Xc Y XC XCXc XCY Xc XcXc XcY

14.Genetic disorder in which a person lacks skin pigment? albinism 15.Defective gene that causes most cases of cystic fibrosis? CFTR 16.Genetic disorder that attacks the nervous system and is prevalent in Jewish and French Canadian populations? Tay-Sachs 17.Two disorders caused by excessive repeats of three nucleotides? Huntington’s disease; fragile X syndrome 18.What symbol in a pedigree is used to represent a normal male? □ 19.What symbol in a pedigree is used to represent a female that is heterozygous? Half-filled circle 20.What symbol is used to represent two people that are married? Connect with horizontal line 21.Disorder when a person has skin spots that develop into benign tumors? Neurofibromatosis 22.Genetic disorder when a person is missing a sex c’some? Turner syndrome 23.What process causes chromosome number disorders? nondisjunction 24.If a father has a sex-linked disorder, what is true of his kids? Daughter gets the gene and will be carrier or affected, depending on gene from mother; son doesn’t get gene 25.If a mother has a sex-linked disorder, what is true of her kids? Can pass on gene to sons and daughters. If it is a recessive disorder, all sons will get it, daughters will be carriers or affected. 26.What must be true if an offspring has an autosomal recessive disorder? Both parents must have the gene (carrier or affected) 27.An autosomal dominant disorder in which symptoms don’t show until the 30s or 40s? Huntington’s disease 28.Disorder where a thick mucous builds up in the lungs? Cystic fibrosis 29.What are the chances that someone with an autosomal dominant genetic disorder will have a kid with the disorder? If the person is heterozygous (and other parent normal): 50%. If the person is homozygous: 100% 30.What type of disorder is illustrated by the karyotype below? XXY = Kleinfelter’s

31.What disorder is illustrated by the karyotype below? Three copies of #21 = Down syndrome

32. What inheritance pattern is illustrated by each of the pedigrees below? The two on the left below (A & C on the question sheet) are autosomal dominant: similar numbers of male and female affected; doesn’t skip generations; male to male transmission. Upper right (B on question sheet) is sex-linked recessive: more males than females affected; skips generations; no male to male transmission; females are shown as carriers (circle with dot in center). Lower right (D on question sheet): autosomal recessive. A male and female are affected, no evidence of the condition in previous generations. Parents must be carriers.

33. On what chromosomes are most of the genetic disorders located? autosomes 34. Determine if the genetic disorders below are sex-linked, autosomal dominant or recessive, the result of a c’some number disorder, or the result of excessive trinucleotide repeats.

a. cystic fibrosis autosomal recessive b. hemophilia sex-linked recessive c. Huntington’s disease autosomal dominant, trinucleotide repeat d. Duchenne muscular dystrophy sex-linked recessive e. PKU autosomal recessive f. Tay-Sachs autosomal recessive g. Down syndrome chromosome number h. Kleinfelter’s syndrome chromosome number i. neurofibromatosis autosomal dominant j. albinism autosomal recessive k. galactosemia autosomal recessive l. colorblindness sex-linked recessive m. fragile X sex-linked recessive, trinucleotide repeat

35. What antigens are present for the following blood types: A, AB, O, B+? A, A and B, none, B and Rh 36. Is it OK to give an Rh- person receive Rh+ blood? Why or why not? It might not be safe. If the person has previously been exposed to the Rh antigen, would have antibodies against Rh, and these would attack the blood. 37. What type of blood can you safely give someone who is type: A? O? AB? A or O; O; any 38. What is the difference between an antigen and an antibody? Antigen is a molecule on a cell that antibodies recognize; antibodies are proteins that stick to antigens as part of the defense against foreign invaders. 39. Can an AB mother have an O child? Why or why not? No. The child must inherit either the A or B allele. Type O blood has neither A nor B allele. 40. What is X-inactivation? Does it occur in males, females, or both? Inactivation of the genes on one of the X chromosomes; occurs in females 41. Describe the inheritance of mitochondrial diseases. Inherited from mother 42. What is a chromosome translocation? A piece of a chromosome breaks off and gets attached to another chromosome.

Short Answers.

43. Explain what happens if a mother has a sex-linked disorder and why? If it is a recessive disorder: she has two bad genes. All the sons will get the gene and will get the disorder (since they have only one X). All the daughters will get the gene and will either be carriers or will have the disease (depending on what they inherit from father). If it is a dominant disorder: she may have one or two bad genes. If just one, sons and daughters each have a 50% chance of getting the bad gene and getting the disorder. If she has two bad genes, all the children must inherit it and will get the disorder.

44. What is the difference between an autosomal genetic disorder and a sex-linked disorder? Which is more common and why? Do any of the disorders affect males more than females or vice versa? If so, why? Autosomal is on autosomes, sex-linked on X chromosome. Autosomal is more common since most chromosomes are autosomes. Sex-linked recessive affects males more than females, since they only have one X chromosome and there can’t be a good gene on another chromosome to protect. (Sex-linked dominant is rare, but would be expected to affect females more than males, since they have two X chromosomes and thus more chance to get a bad gene.)

45. Construct a pedigree for the scenario below. Include proper symbols and genotypes.

 Joe and Lisa Smith are married and have 4 daughters.  Susan, the oldest is married and has 2 boys, Dave and John. John has cystic fibrosis.  Kristin, the second oldest is married and has a normal daughter.  Taryn, the third oldest is married and has 3 boys and the oldest has cystic fibrosis.  Tracy, the youngest isn’t married but has cystic fibrosis.

Cystic fibrosis is autosomal recessive. The three individuals with CF must have two recessive alleles. Since they have children with CF, Joe and Lisa; Susan and her husband; and Taryn and her husband must all be carriers (one good and one bad gene). The other individuals must have at least one good gene (since they do not have CF), but we do not know if they are carriers.