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NSG 530 STUDY GUIDE Patho Quiz 1.
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NSG 530 STUDY GUIDE Patho Quiz 1.STUDY GUIDE FOR QUIZ #1 Advanced Pathophysiology 2019
Study the process of meiosis – specifically what occurs when homologous chromosomes fail to separate
Human cell can be categorized into gametes (Sperm & egg cells) and somatic cells, which include all cells other than
gametes. Each somatic cell nucleus has 46 chromosomes in 23 pairs. These are diploid cells, and the individual’s father
and mother each donate on chromosome per pair. New somatic cells are formed through mitosis and cytokinesis.
Gametes are haploid cells: they have only 1 member of each chromosome pair, for a total of 23 chromosomes. Haploid
cells are formed from diploid cells by meiosis.
A somatic cell has 23 pairs of chromosomes
In meiosis I, chromosomes in a diploid cell resegregate, producing four haploid daughter cells. It is this step in meiosis
that generates genetic diversity. DNA replication precedes the start of meiosis I. During prophase I, homologous
chromosomes pair and form synapses, a step unique to meiosis.
In meiosis a haploid cell is created from a diploid cell.
What are the 8 stages of meiosis in order?
Aneuploidy is caused by nondisjunction, which occurs when pairs of homologous chromosomes or sister chromatids
fail to separate during meiosis. The loss of a single chromosome from a diploid genome is called monosomy (2n-1),
while the gain of one chromosome is called trisomy (2n+1).
Know the risk factors for down syndrome
Nondisjunction occurs when homologous chromosomes (meiosis I) or sister chromatids (meiosis II) fail to
separate during meiosis The most common trisomy is that of chromosome 21, which leads to Down
syndrome.
Down syndrome is a chromosomal
disorder Down syndrome
Best known example of
aneuploidy Trisomy 21
1:800 live births
Mentally retarded, low nasal bridge, epicanthal folds, protruding tongue, poor muscle tone
Risk increases with maternal age >35
People who have down syndrome are at a higher risk for developing Alzheimer disease because of involvement of
chromosome 21.
1 in 800 to 1 in 1000 live births are affected with Down syndrome.
RISK FACTORS – increases greatly with material age. Younger than 30 have a risk of 1 – 1000 to 1 in 2000. After 35 risk
increases greatly. By 45 and older a risk of 3% to 5% of children born will have down syndrome.
This increase in risk is caused by the age of maternal egg cells, which are held in an arrested state of prophase 1 from
the time they are formed in the female embryo until they are shred in ovulations. Thus, an egg cell formed by a 45-year
woman is inself 45 years old. This long suspended state may allow defects to accumulate in the cellular proteins
, responsible for meiosis, leading to nondisjunction. The risk of Down syndrome, as well as other trisomies, does not
increase with paternal age.
Genetic diseases caused by single genes usually are autosomal dominant, autosomal recessive or X-linked
recessive X-linked recessive disease are seen more often in males than in females.
If the cells have three copies of each chromosome triploidy is present.
Loss of chromosome material usually has more serious consequences than duplication of chromosome material.
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