4.3 Alterations in Chromosome Structure and Number Flashcards
What is a chromosomal mutation?
-mutation of the chromosomal segments of the DNA
strands
-can occur when the number of chromosomes or chromosome sets (ploidy) increases or decreases in a genome as well as when changes in chromosomes structure occur
What is a karyotype?
number and visual appearance of the chromosomes in the cell nuclei of an organism or species
Describe two conditions that result from
chromosome changes.
Down Syndrome - trisomy on chromosome 21
Patau Syndrome - trisomy on chromosome 13
Trisomy 13 + symptoms
Patau Syndrome
-polydactyl
-cleft lip + palate
-severe mental disabilities
-small head
-cardiac + other organ abnormalities
-cyclopia may result (fusion of eyes)
-approx 90% of children DON’T survive
-1/16,000 births
Trisomy 18 + symptoms
Edwards Syndrome
-babies have small heads with a prominent back to it
(occipital bone) + scalp lesions
-ears are malformed
-jaw is small
-child may have cleft lip or palate
-hands typically clenched in fists
-clubfeet can be present with webbing
-approx 90% of children DON’T survive this
-1/5000 births
Deletion on short arm of chromosome 5 + symptoms
Cri du Chat Syndrome
-child has a distinctive cry (sounds like a cat)
-cry caused by abnormal larynx development
-low birth weight + may have respiratory problems
-abnormal chromosome carrying the deletion comes
from father in about 80% of all cases
-some have a shortened life span
-1/50,000 births
XXY + symptoms
Klinefelter’s Syndrome
-males develop with female characteristics
-often tall with narrow shoulders
-usually don’t go through puberty or develop other hair (facial, underarm, pubic, etc)
-altered fat distribution (breasts)
-testicular degeneration
-half of all cases, extra X comes from mom or dad
-1/500-1000 births
Trisomy 21 + symptoms
Down’s Syndrome
-most common imbalance in the # of autosomes in
people
-intellectual disabilities + heart defects
-slanted eyes
-widely separated big toes
-prominant creases on hands are more typical
-90% of all cases, extra chromosome comes from mom
-1/800 births
XO + symptoms
Turner’s Syndrome
-girls with this don’t go through puberty
-don’t develop breasts or “other” hair
-typically infertile
-have only ONE chromosome (monosomy)
-single X chromosome comes from mom in about 80%
of all cases
-father that fertilizes egg, MISSING a sex chromosome
-1/2000-2500
Primary benefits of CVS?
-A sample can be taken after the 8th to 10th week of
pregnancy
-Karyotyping and biochemical tests can be performed
on the fetal cells immediately, providing results within
a day or so.
-This procedure can be conducted as early as the
8th week of pregnancy, enabling earlier detection
than amniocentesis
What are the primary benefits of prenatal
genetic testing?
-detect small-scale mutations or chromosomal alterations in a fetus
-help identify certain genetic diseases
-detect if there are extra or missing chromosomes or if any have significant changes to their structures
-these types of chromosomal changes can lead to birth defects and other problems
Which two genetic conditions are often screened for using prenatal genetic testing?
Spina Bifida and Down’s Syndrome
What are some risks associated with the CVS
procedure?
-maternal bleeding
-miscarriage
-premature birth.
Therefore, these procedures are usually conducted only if there is a high risk of genetic disorder
Give an example of a genetic disorder that can be detected through newborn screening and explain.
Phenylketonuria (PKU)
-shortly after birth, newborns are
screened for PKU
-inherited disorder that results in the inability of children to break down the naturally occurring
amino acid phenylalanine
-an accumulation of phenylalanine may lead to
severe developmental delays
-detection of this condition in a newborn can prevent retardation
What are some of the characteristics of
Prader-Willi syndrome?
-developmental delays
-learning disabilities
-behavioural problems
-obesity
-short stature
-decreased muscle tone
-sex glands that produce little or no hormones
Give an example of a genetic condition that
can result from errors in meiosis
Non-Disjunction
-Patau Syndrome
-Prader-Willi Syndrome
-Down Syndrome
What is the karyotype of an individual with
Klinefelter syndrome?
Extra chromosome on the sex chromosome X for males (XXY)
What are the main differences between the
tests done in carrier testing and in newborn
screening?
-Carrier testing can determine if an individual carries a
copy of a mutation that his or her children could inherit (before child is born)
-Newborn screening can detect some genetic disorders at birth through simple tests performed in hospitals(after child is born)
Presymptomatic testing
-a person with a family history of a genetic condition may want to undergo genetic testing to find out his or her risk of developing the condition
-usually done for disorders that appear after birth or later in a person’s life
Diagnostic genetic testing
-used to confirm a diagnosis when symptoms for a particular genetic condition are present
-slurred speech and shaking, for example, are symptoms of many unrelated conditions, including Huntington’s disease
-could be used to confirm that Huntington’s disease is the cause
-this type of testing can be conducted at any time during a person’s life
Which type of genetic testing could be used to confirm Huntington’s disease? Why?
Diagnostic genetic testing
-used to confirm a diagnosis when symptoms for a particular genetic condition are present
-slurred speech and shaking, for example, are symptoms of many unrelated conditions, including Huntington’s disease (helps to narrow down the disease)
-this type of testing can be conducted at any time during a person’s life
A woman with no breast cancer symptoms undergoes genetic testing for the presence of a mutation on chromosome 17. What is this kind of test an example of?
presymptomatic testing
A medical procedure is used in prenatal diagnosis to diagnosis chromosomal abnormalities. Small amounts of fluid are extracted from the amnion. What is the name of this prenatal testing?
Amniocentesis
List four types of damage to chromosome structure that can cause disorders
-translocation
-inversion
-deletion
-duplication
