Human Genetic Diseases Flashcards
What is nondisjunction?
When chromosomes don’t break away like they are supposed to.
What is aneuploidy?
The occurrence of one or more extra or missing chromosomes leading to an unbalanced chromosome complement. The most common type of chromosomal abnormality. Most people with aneuploidy have trisomy (three copies of a chromosome) instead of monosomy (single copy of a chromosome). aneuploid cells have an abnormal number of chromosomes.
What are trisomies?
3 copies of chromosomes. Downs syndrome.
What are monosomies?
Turner syndrome.
What are translocations?
A chromosomal abnormality where part or all of a chromosome is transferred to another non-homologous chromosome. There are three types of translocation: balanced, robertsonian, and reciprocal.
What are deletions?
A genetic change that involves the absence of a segment of DNA. DiGeorge syndrome is a disorder caused due to the deletion of a small segment of chromosome 22.
What are duplications?
a mutation where one or more copies of a DNA segment is produced and duplicated. A certain chromosome can duplicate causing too much of one protein.
Explain reciprocal translocation vs. robertsonian translocation?
In a reciprocal translocation, two different chromosomes have exchanged segments with each other. In a Robertsonian translocation, an entire chromosome attaches to another at the centromere.
How do pedigree analysis work with DNA genetics?
It’s a way we can see how things are passed down through families.
Define autosomal Dominant inheritance
– these traits are inherited equally in males and females and do not skip generations.
Define autosomal recessive
these traits are inherited equally in males and females and can skip generations.
Define x-lined dominant inheritance
these traits are more common in females than males and do not skip generations. Affected fathers will always pass the trait to daughters but never to sons. Affected mothers will pass the trait to both daughters and sons.
Define X-linked recessive inheritance
these traits are more common in males than females and can skip generations. Affected fathers cannot pass the traits to sons but the daughters will at least be carriers of the condition. Affected mothers will always pass the trait to sons and daughters will at least be carriers.
Define y-linked inheritance
these traits are not common. Women are never affected. Affected fathers will pass the trait to all of their sons.
define mitochondrial inheritance
although these traits are not common, they affect both males and females. Mitochondria which are the powerhouses of the cell have their own DNA which can be passed on. However, the trait is only passed from mothers to their offspring. Fathers can be affected but will not be able to pass the trait to offspring.
define mitochondrial inheritance
although these traits are not common, they affect both males and females. Mitochondria which are the powerhouses of the cell have their own DNA which can be passed on. However, the trait is only passed from mothers to their offspring. Fathers can be affected but will not be able to pass the trait to offspring.
What is a zygote?
a diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum. contains the human genome.
What are chromosomes?
Chromosomes are the structures that hold genes.
What are genes?
Genes are the individual instructions that tell our bodies how to develop and function
T or F: Many chromosomes have two segments, called “arms,” separated by a pinched region known as the centromere. The shorter arm is called the “p” arm. The longer arm is called the “q” arm.
True
What is the typical number of chromosomes in a human cell?
46, 23 pairs
The first 22 pairs of chromosomes are called what?
Autosomal
The final pair of chromosomes is called
Sex Chromosomes.
A picture or chromosome map is called a
A karyotype
T or F: n the past decade, newer techniques have been developed that allow scientists and doctors to screen for chromosomal abnormalities without using a microscope. These newer methods compare the patient’s DNA to a normal DNA sample. The comparison can be used to find chromosomal abnormalities where the two samples differ. One such method is called noninvasive prenatal testing. This is a test to screen a pregnancy to determine whether a baby has an increased chance of having specific chromosome disorders. The test examines the baby’s DNA in the mother’s blood.
True
Explain the difference between numerical abnormalities and structural abnormalities
Numerical Abnormalities is when an individual is missing one of the chromosomes from a pair, the condition is called monosomy. When an individual has more than two chromosomes instead of a pair, the condition is called trisomy but these are both numerical abnormalities.
Explain the difference between monosomy and trisomy
monosomy is when you are missing on one of the chromosomes and trisomy is when an individual has more than a pairs, such as 3 chromosomes. Examples for trisomy is having more than one pair. Monosomy is when missing a chromosome.
Name some trisomy abnormalities
Down syndrome, also known as Trisomy 21, Edward syndrome, and Patau syndrome.
Name a monosomy abnormality that could occur
Turner syndrome. Monosomies are missing one chromosome. Cells are sensitive to the loss of a chromosome. The only viable loss of a chromosome is on the sex chromosome for Turner syndrome. Turner’s syndrome is significantly lower than that of sex chromosome trisomies, suggesting that a single X chromosome is insufficient for optimum cell function. These individuals are usually mosaics.
What are structural abnormalities?
When a chromosomes structure are altered. This can be from deletions, translocations, duplications, inversions, or rings.
Most chromosome abnormalities occur as an accident in the egg or sperm. Some abnormalities, however, happen after conception; T or F
True
Chromosome abnormalities can be inherited from a parent (such as a translocation) or be “de novo” (new to the individual). This is why, when a child is found to have an abnormality, chromosome studies are often performed on the parents.
True
T or F: As paternal age increases, it can increase the chance of having children with chromosome abnormalities.
False. Maternal Age can because Women are born with all the eggs they will ever have. Some researchers believe that errors can crop up in the eggs’ genetic material as they age. Older women are at higher risk of giving birth to babies with chromosome abnormalities than younger women. Because men produce new sperm throughout their lives, paternal age does not increase risk of chromosome abnormalities.
T or F: Chromosomal abnormalities can also cause miscarriage, disease, or problems in growth or development.
True
the major chromosomal aneuploidies seen in live-born babies are:
trisomy 21 (Down syndrome), trisomy 18; trisomy 13; 45, X (Turner syndrome); 47, XXY (Klinefelter syndrome); 47, XYY; and 47, XXX.
what are the rings in chromosomal abnormalities?
when a chromosome undergoes two breaks and the broken ends fuse into a circular chromosome
What is an isochromosome?
An isochromosome can form when an arm of the chromosome is missing and the remaining arm duplicates.
explain balanced rearrangements
Balanced rearrangements include inverted or translocated chromosomal regions. Since the full complement of DNA material is still present, balanced chromosomal rearrangements may go undetected because they may not result in disease. A disease can arise as a result of a balanced rearrangement if the breaks in the chromosomes occur in a gene, resulting in an absent or nonfunctional protein, or if the fusion of chromosomal segments results in a hybrid of two genes, producing a new protein product whose function is damaging to the cell.
Most aneuploids are lethal. True or false.
True. Researchers now appreciate that aneuploid gametes are produced at surprisingly high rates in human meioses, and that very few aneuploid embryos are able to survive. In fact, trisomies represent about 35% of spontaneous abortions. Indeed, the only other autosomal trisomies besides 21 that are detected in any appreciable numbers among newborns involve chromosomes 13 and 18, but affected babies rarely survive beyond the first few months of life (Hassold & Hunt, 2001).
Who was John Langdon Down?
Viable trisomies are restricted to only a few human chromosomes. The most common human trisomy involves chromosome 21 and is known as Down syndrome (DS), named for John Langdon Down, the physician who first described the condition in 1866. Interestingly, almost a century elapsed between the clinical description of DS and its association with trisomy 21.
Why do sex chromosome abnormalities seem to do better than autosome abnormalities?
Humans are much more able to tolerate extra sex chromosomes than extra autosomes. Thus, after DS, the most common human aneuploidy is the condition known as Klinefelter’s syndrome (Jacobs & Strong, 1959). Klinefelter’s males have a total chromosome number of 47, which includes two X chromosomes and one Y chromosome. According to convention, these males are designated as 47,XXY individuals. Other configurations of the sex chromosomes have been observed in 47,XXX females and 47,XYY males. Compared to autosomal trisomies, these sorts of sex chromosome trisomies are fairly benign. Affected individuals generally show reduced sexual development and fertility, but they often have normal life spans, and many of their symptoms can be treated by hormone supplementation. The ability of humans to tolerate supernumerary sex chromosomes is quite remarkable, as individuals can survive with as many as four sex chromosomes. This tolerance most likely relates to both X inactivation and to the small number of genes on the Y chromosome. In fact, when cells from individuals with more than one copy of the X chromosome are analyzed under a microscope, all but one of the X chromosomes appear as condensed Barr bodies, the cytological manifestations of X-chromosome inactivation. Supernumerary copies of the Y chromosome may be tolerated because the few gene products of the Y chromosome are not required for survival.
What is mosaicism in turner syndrome?
When the chromosome is partially missing rather than fully missing. In mosaic Turner syndrome, an X chromosome is missing in some cells in people assigned female at birth.
What is G-banding?
When reading a karyotype, The dye stains regions of chromosomes that are rich in the base pairs Adenine (A) and Thymine (T) producing a dark band. A common misconception is that bands represent single genes, but in fact the thinnest bands contain over a million base pairs and potentially hundreds of genes. For example, the size of one small band is about equal to the entire genetic information for one bacterium.
What is a genetic disorder?
A genetic disorder is a condition that is caused by an abnormality in an individual’s DNA. Abnormalities can be as small as a single-base mutation in just one gene, or they can involve the addition or subtraction of entire chromosomes.
Explain the general issues that arise with chromosomal abnormalities?
A lot of times issues arrive with entire sections of chromosomes such as deletion, or duplication, or translocation. Sometimes this wont show until later down the line.
When does Robertsonian translocation cause problems?
Usually the affect happens down the line when you pass down the section because it is missing a part.
