4.3 Alterations in Chromosome Structure and Number

Question 1

What is a chromosomal mutation?

Answer 1

-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

Question 2

What is a karyotype?

Answer 2

number and visual appearance of the chromosomes in the cell nuclei of an organism or species

Question 3

Describe two conditions that result from
chromosome changes.

Answer 3

Down Syndrome - trisomy on chromosome 21
Patau Syndrome - trisomy on chromosome 13

Question 4

Trisomy 13 + symptoms

Answer 4

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

Question 5

Trisomy 18 + symptoms

Answer 5

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

Question 6

Deletion on short arm of chromosome 5 + symptoms

Answer 6

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

Question 7

XXY + symptoms

Answer 7

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

Question 8

Trisomy 21 + symptoms

Answer 8

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

Question 9

XO + symptoms

Answer 9

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

Question 10

Primary benefits of CVS?

Answer 10

-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

Question 11

What are the primary benefits of prenatal
genetic testing?

Answer 11

-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

Question 12

Which two genetic conditions are often screened for using prenatal genetic testing?

Answer 12

Spina Bifida and Down’s Syndrome

Question 13

What are some risks associated with the CVS
procedure?

Answer 13

-maternal bleeding
-miscarriage
-premature birth.

Therefore, these procedures are usually conducted only if there is a high risk of genetic disorder

Question 14

Give an example of a genetic disorder that can be detected through newborn screening and explain.

Answer 14

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

Question 15

What are some of the characteristics of
Prader-Willi syndrome?

Answer 15

-developmental delays
-learning disabilities
-behavioural problems
-obesity
-short stature
-decreased muscle tone
-sex glands that produce little or no hormones

Question 16

Give an example of a genetic condition that
can result from errors in meiosis

Answer 16

Non-Disjunction
-Patau Syndrome
-Prader-Willi Syndrome
-Down Syndrome

Question 17

What is the karyotype of an individual with
Klinefelter syndrome?

Answer 17

Extra chromosome on the sex chromosome X for males (XXY)

Question 18

What are the main differences between the
tests done in carrier testing and in newborn
screening?

Answer 18

-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)

Question 19

Presymptomatic testing

Answer 19

-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

Question 20

Diagnostic genetic testing

Answer 20

-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

Question 21

Which type of genetic testing could be used to confirm Huntington’s disease? Why?

Answer 21

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

Question 22

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?

Answer 22

presymptomatic testing

Question 23

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?

Answer 23

Amniocentesis

Question 24

List four types of damage to chromosome structure that can cause disorders

Answer 24

-translocation
-inversion
-deletion
-duplication

Question 25

There’s a genetic accident in which 2 resulting gametes are normal, 1 gametes has an extra chromosome and 1 gamete is missing a chromosome, when did it occur?

Answer 25

during meiosis ll
(sister chromatids failed to separate properly)

Question 26

What populations in Canada are most affected
by Tay-Sachs disease?

Answer 26

-most common among French Canadians and certain Jewish populations
-attacks an infant’s nervous system and results in death by five years of age.

Question 27

How is a mother’s age related to the
probability of non-disjunction of
chromosomes in her egg cells?

Answer 27

-direct correlation between them
-meiosis begins in the female’s ovaries before she is born but is not completed until meiosis resumes during ovulation
-since only one egg is released each month, egg cells may remain stopped in the middle of meiosis for
decades
-some research suggests that damage to the cell during this lag time may contribute to errors in meiosis.

Question 28

Describe what happens during non-disjunction in meiosis l.

Answer 28

If homologous chromosomes fail to separate during meiosis I, the result is two gametes that lack that chromosome and two gametes with two copies of the chromosome

Question 29

Describe what happens during non-disjunction in meiosis ll?

Answer 29

If sister chromatids fail to separate during meiosis II, the result is one gamete that lacks that chromosome, two normal gametes with one copy of the chromosome, and one gamete with two copies of the chromosome.

Question 30

Why might non-disjunction be less likely
in a male?

Answer 30

-in humans, nondisjunction in meiosis is much more common in egg production than in sperm production
-the reason is that human oocytes remain arrested before completing meiosis I from before birth until ovulation

Question 31

What is the relationship between Down
syndrome and the karyotype trisomy 21?

Answer 31

The karyotype trisomy 21 is for down syndrome

Question 32

Describe how meiosis can lead to
trisomy 21

Answer 32

-usually caused in meiosis ll by an error in cell division called nondisjunction
-nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two
-prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate.

Question 33

What are some ethical considerations related to
advancements in genetic screening technology?

Answer 33

-how can “good” and “bad” uses of these technologies be distinguished
-who decides which traits are normal and which constitute a disability or disorder
-may cause stigmatization, family discord and psychological distress

Question 34

Suppose an animal has a diploid number of
6 chromosomes (2n=6). If a trisomy were to
occur in one of this animal’s gametes, how many
chromosomes would that gamete contain?

Answer 34

gametes(n=3)
-trisomy= n+1
=4

Question 35

An individual with more than the correct number of chromosome sets is called …

Answer 35

polyploid

Question 36

Suppose an individual has the karyotype
XXX. Explain what might have occurred in
her parents’ gametes that resulted in this
karyotype.

Answer 36

?
-non-disjunction would have occurred in her parent’s gametes (specifically a trisomy on the sex chromosomes)

Question 37

Explain why problems might arise
in meiosis in an individual with a
chromosomal inversion

Answer 37

-inversion= damage to chromosomal structure
-this can cause diseases (muscular dystrophy, walker-warburg syndrome)
-sometimes when an inversion occurs, it also results in missing or extra copies of genetic material
-when this happens, the genetic code can be so
hard to decode that the resulting offspring will
not survive or will have significant
abnormalities

Question 38

Why are current treatments for Klinefelter
syndrome successful?

Answer 38

?
-many new treatment options available (testosterone replacement therapy)
-can start it from a young age