Exam 1- Genes And Genetic Disease

Question 1

Codon

Answer 1

Sequence of 3 nitrogenous bases that specifies a particular amino acid. Triplets of based.

Question 2

Intron

Answer 2

Noncoding segment spliced out of mRNA

Question 3

Exon

Answer 3

Segment of mRNA that codes for proteins

Question 4

Mutation

Answer 4

Alteration of DNA capable of being passed to offspring.

Missense mutation
Nonsense mutation
Frameshift mutation

Question 5

Mutagen

Answer 5

Substance that alters genetic material (DNA)

Question 6

Gene

Answer 6

Segment of DNA that is the basic unit of inheritance

Question 7

Chromosome

Answer 7

Strand of condensed chromatin visible right before cell division. A somatic cell has 23 pairs of chromosomes. 1 sex chromosomes and 22 nonsectarian chromosomes (autosomes)

Question 8

Autosome

Answer 8

Chromosome that is not a sex chromosome. 1 pair of sex chromosomes and 22 pairs of autosomes.

Question 9

Allele

Answer 9

Different version of a paired gene at a given locus.

If 2 alleles are found together, the allele that is observable is the dominant, and the one whose effects are hidden is recessive.

Dominant allele: capital letter
Recessive: lowercase letter
Can be codominant

Ex: Hgb A vs Hgb S

Question 10

Frameshift mutation

Answer 10

A DNA mutation that involves an addition or deletion of a number of base pairs that is not a multiple of three, and thus alters all of the codons downstream from the site of insertion or deletion.

Question 11

Translocation

Answer 11

Interchanging of genetic material between nonhomologous chromosome. One chromosome breaks and becomes part of another chromosome.

Type of chromosomal aberration/ alteration.

Ex: Philadelphia chromosomal translocation. Increased chances of CML and ALL.

Question 12

Homozygous

Answer 12

Loci on a pair of chromosomes have identical genes (type O)

DD, dd affected or unaffected homozygous

Question 13

Heterozygous

Answer 13

Lock on a pair of chromosomes have different genes (Type AB)

Dd affected or unaffected heterozygous.

Question 14

Monosomy

Answer 14

One of the chromosomes in somatic cell has only one copy instead of 2 normal.

Question 15

Trisomy

Answer 15

One of the chromosomes in somatic cell has 3 copies instead of the normal 2.

Question 16

Genotype

Answer 16

The genetic material

Question 17

Phenotype

Answer 17

Expression of genes

Question 18

Mitosis

Answer 18

Diploid cell makes a copy of itself

Question 19

Meiosis

Answer 19

The process by which haploid cells are for from diploid

Question 20

Steps of protein synthesis

Answer 20

1) RNA polymerase binds to DNA promoter region
2) transcription
3) mRNA is spliced to remove noncoding sections
4) mRNA leaves the nucleus
5) translation

Question 21

Chromosomal disorder

Answer 21

Ex: Turner syndrome, Down syndrome, fragile X syndrome, klinfelter syndrome

Question 22

Diploid cell

Answer 22

A somatic cell that has 46 chromosomes in its nucleus

Question 23

Single gene disorder

Answer 23

Determined by one gene mutation. Autosomal dominant, autosomal recessive, or X-linked recessive.

Strongly determined by genes.

Ex: CF, hemophilia A, sickle cell

Question 24

X-linked disorders

Answer 24

Y chromosome only carries a few genes, so most sex-linked traits are X-linked.

More often seen in males than female, because they only have 1 X chromosome.

Dominant (rare) or recessive.

Question 25

Triploidy

Answer 25

Cells have 3 copies of each chromosome

Question 26

Barr body

Answer 26

Inactivated X chromosome that is seen in normal femal cells.

Question 27

Haploid cell

Answer 27

Has 23 chromosomes, one member of each pair. Will meet up with another haploid to make a diploid. Aka gamete.

Question 28

Homologous

Answer 28

2 of the same identical traits. In females, we have XX sex traits, a homologous pair. Males have a nonhomolygous pair.

Question 28

Polyploidy

Answer 28

More sets of chromosomes. In multiples of 23. Incompatible with life. More than 2 copies of each chromosome.
Triploidy- 3 sets of 23 chromosomes
Tetraploidy- 4 sets (92 chromosomes)

Question 29

Nondisjunction

Answer 29

Error during meiosis or mitosis. Homologous chromosomes fail to separate normally. Results in aneuploidy.

Question 30

Carrier

Answer 30

Have to have 2 recessive genes to have expressed trait (rr). Carriers have Rr so can still pass it on but don’t have the expressed trait.

Phenotypically normal. Carries disease causing alleles.

Question 31

Sex chromosomes

Answer 31

1 pair of sex chromosomes and 22 of autosomes.
XY- male
XX- female

Question 32

Aneuploidy

Answer 32

Abnormal number of single chromosomes. Loss of chromosome (monosomy) material more serious than duplicate.

23 pairs usually. On one pair you’re missing one chromosome and only have 1 (monosomy). On another pair you have 2 from one parent, for a total of 3 instead of 2 (trisomy). Autosomal aneuploidy usually lethal, but Can survive with trisomy13, 18, and 21.

Sex chromosomal aneuploidy is not lethal (except for monosomy (X): Y chromosome has little genetic info and extra X chromosome is usually inactive (fragile X). Having 1 X is lethal.

Question 33

Down Syndrome (Trisomy 21)

Answer 33

3 copies of the 21st chromosome.
Nondisjunction in egg.
Linked with maternal age.
Intellectual disability, poor muscle tone, increases congenital heart defects, increased risk for Alzheimer’s after age 40.

Question 34

Chromosomal deletion

Answer 34

Broken chromosomes or loss in DNA in 1 chromosome can have serious effect.

Cri du chat Syndrome- deletion of long arm of chromosome 5. Microcephalic, low birth weight.

Question 35

Chromosomal duplication

Answer 35

Multiple copies of DNA portion. Less serious than deletion. But when they have offspring, chromosomes don’t align and offspring can have issues.

Question 36

Autosomal dominant disorders

Answer 36

Single-gene disorders

Diseases are rare. Very rare for two affected people with the dominant trait to produce offspring. Dd if they have one capital D, they are effected. Only need to inherit a D from 1 affected parent to get the disease.
Genotype of affected person: DD or Dd
Genotype of unaffected person: dd

Males and female equally likely.
One of the patents has to have the disease.
Heterozygous individuals pass it on to 50% of their offspring. Does not skip generations because there are no carriers.

75% chance to pass on (recurrence rate) if both parents Dd (affected):
25% DD homozygous affected
50% Dd heterozygous affected
25% dd homozygous unaffected

Phenotype: observable effect

Ex: achondroplasia, Huntingtons

Question 37

Autosomal Recessive trait (d)

Answer 37

Single gene disorder

Disease: A person must have 2 recessive alleles. Must receive a a recessive gene from each parent. (dd) to get the disease. non sex-linked (same in M and F).

Rare, but number of carriers can be high.
Usually in children not parents.

If both parents heterozygous carriers (Dd) 25% of passing it on (recurrence rate). 50% that offspring will be phenotypically normal and 25% genetically normal.

Example: CF

Chances increase with consanguineous mating between relatives.

Question 38

Locus

Answer 38

Sections of chromosome. Each locus is responsible for different characteristics of a person. If same on both locus in a chromosome pair, it’s homozygous. If different, heterozygous.

Question 39

X-linked dominant disorders

Answer 39

Rare

Affected father will pass the condition on to daughters but not sons

Affected mother will pass on to 50% of children (50% of getting c chromosome from mom), both male and female

Question 39

X-linked recessive disorders

Answer 39

Affected fathers (XhY) will transmit the affected genes to all his daughters but not his sons (he gives his sons the Y gene).

Affected mothers (XhXh) will pass to all her sons and all her daughters will be carriers.

Carrier mothers (XhXH) will pass the condition to 50% of their sons (no 2nd X to counteract disease gene) and 50% of her daughters will be carriers.

Question 39

Expressivity

Answer 39

Variation in a phenotype linked to a particular genotype. Severity may vary. A parent with a mild expression of a disease (they may not even know that they have it) can transmit the gene to a child, who can the exhibit severe expression of the disease.

Ex: neurofibtomytosis

Question 40

Trisomy X

Answer 40

Female with 3 X chromosomes.
Sterility, menstrual irregularity, to mental retardation.
Worse with each additional X.
Trisomy on the X chromosome.

Question 41

Klinefelter Syndrome

Answer 41

Chromosomal disorder.

At least 2 Xs and 1 Y.

Male appearance, develop breasts, small testes, sparse body hair, long limbs.

Question 42

Chromosome fragile sites

Answer 42

Areas on chromosomes that develop distinctive breaks or gaps when cells are cultured. No apparent relationship to disease.

Question 43

Fragile X Syndrome

Answer 43

Chromosomal disorder

Site on long arm of the X chromosome.

Usually in men because only one X.

Associated with mental retardation, second in occurrence to Down Syndrome.

Question 44

Threshold model

Answer 44

Liability distribution. For multifactorial traits, as the number of multifactorial traits increases, the liability for that disease increases as well. As the factors reach the threshold, the person will definitely be effected.

Though liability may be the same between men and women, the threshold may be different.

Question 45

Karyotype

Answer 45

Complete set of chromosomes in an individual

Question 46

Penetrance

Answer 46

Penetrance of a trait is the percentage of the individuals with a specific genotype who also express the expected phenotype. Incomplete means that the person with the disease-causing allele may not exhibit the disease phenotype ally all, even though it might be transmitted to the next generation.