ch8

Given that a human normally contains 46 chromosomes, give the chromosome number for each of the following conditions: Turner syndrome (female, no Barr bodies) Klinefelter syndrome (male, one Barr body) Triploid Down syndrome (trisomic) Trisomy 13

T. syndrome (female, no Barr bodies) 45 K. syndrome (male, one Barr body) 47 Triploid 69 Down syndrome (trisomic) 47 Trisomy 13 - 47

What is the leading cause of Down syndrome?

The nondisjunctional event that produces Down syndrome occurs more frequently during oogenesis in women older than age 35.

Trisomy 21, or Down syndrome, occurs when there is a normal diploid chromosomal complement but one (extra) chromosome 21. While there is reduced fertility in both sexes, females have higher fertility than males. Van Dyke et al. (1995; Down Syndrome Research and Practice 3(2): 65-69) summarize data involving children born of Down syndrome individuals. Given the fact that conceptuses with 48 chromosomes (four #21 chromosomes) are not likely to survive early development, what percentage of surviving offspring would be expected to have Down syndrome if both parents have Down syndrome?

Two-thirds of the surviving offspring would be expected to have Down syndrome.

What is the outcome of nondisjunction in meiosis I?

a resultant gamete that may harbor from one chromosome both sister chromatids or none at all

Although the most frequent forms of Down syndrome are caused by a random error, nondisjunction of chromosome 21, Down syndrome occasionally runs in families. The cause of this form of familial Down syndrome is ________.

a translocation between chromosome 21 and a member of the D chromosome group

Assume that an organism has a diploid chromosome number of 14. There would be ________ chromosomes in a tetraploid.

28

The condition known as cri-du-chat syndrome in humans has a genetic constitution designated as ________.

46, 5p-

Assume that an organism has a haploid chromosome number of 7. There would be ________ chromosomes in a monoploid individual of that species.

7

Inversion heterokaryotypes are often characterized as having reduced crossing over and reduced fertility. Assume that you were examining a strain of organisms you knew to be inversion heterokaryotypes and saw a relatively high number of double chromatid bridges extending between anaphase I nuclei, as indicated in the following drawing. What is the product of this type of inversion loop?

A four-strand double crossover in the inversion loop of a paracentric inversion (in the heterozygous state) would generate the double bridge and two acentric fragments (which would be lost).Section: 8.7

Name two methods used in genetic prenatal diagnostic testing in humans.

Amniocentesis and chronic villus sampling.

Colchicine is an alkaloid derived from plants. What is its effect on chromosome behavior?

By interfering with spindle formation, replicated chromosomes fail to migrate to the poles at anaphase; thus, sister chromatids end up in the same nucleus.

Which of the following statements is TRUE regarding Familial Down Syndrome?

Familial Down syndrome is caused by a translocation involving chromosome 21.

What experiment led to the identification of the DSCR (Down Syndrome Critical Region)?

Genetic dissection of the Down syndrome critical region

What explanation is generally given for lethality of monosomic individuals?

Monosomy may unmark recessive lethals that are tolerated in heterozygotes carrying the wild-type allele.

Trisomy 21, or Down syndrome, occurs when there is a normal diploid chromosomal complement but one (extra) chromosome 21. Although fertility is reduced in both sexes, females have higher fertility rates than males. Van Dyke et al. (1995; Down Syndrome Research and Practice 3(2): 65—69) summarize data involving children born of Down syndrome individuals. Assume that children are born to a female with Down syndrome and a normal 46-chromosome male. What proportion of the offspring would be expected to have Down syndrome?

One-half of the offspring would be expected to have Down syndrome.

A chromosome without a centromere is ________.

acentric

Describe double Bar mutations in Drosophila melanogaster.

an X chromosome with two duplications of the 16A region

The condition that exists when an organism gains or loses one or more chromosomes but not a complete haploid set is known as ________.

aneuploidy

Assume that a species has a diploid chromosome number of 24. The term applied to an individual with 25 chromosomes would be ________.

aneuploidy and trisomy

Recently, a gene located on chromosome 3 in humans, FHIT, has been shown to be associated with the significant human malady known as ________.

cancer

How do deletions and translocations in chromosomes often occur?

chromosomes will break and the sticky ends will rejoin

Having a complete set or sets of chromosomes is called ________.

euploid

What type of chromosomal configuration does the following diagram illustrate?

inversion (paracentric) heterozygote

Noninvasive prenatal genetic diagnosis is sometimes preferred to amniocentesis because ________.

it requires only a blood draw from the mother

________ is viewed as a major cause of aneuploidy

nondisjunction

A child is born with Turner's syndrome and she is red green color blind (recessive X-linked). Her father is red green color blind as well and her mother is homozygous dominant for color sight. What had to happen in order for this child to be born with this chromosomal complement?

nondisjunction in either meiosis I or meiosis II of the mother

A son is born with Kleinfelter's syndrome and hemophilia. His father was normal and his mother was a carrier for the recessive X-linked blood clotting disorder. What occurred in meiosis to produce this genetic outcome?

nondisjunction in meiosis II of the mother

A ________ inversion is one whose breakpoints do not flank the centromere.

paracentric

Provide an example of gene redundancy that occurs in both eukaryotes and prokaryotes

rDNA

An individual with Patau syndrome would be ________.

said to have a trisomy

The chromosomal aberration that causes cri-du-chat syndrome can be referred to as a(n) ________.

segmental deletion

What is a fragile site?

the chromosomal region susceptible to breakage

Haploinsufficiency refers to ________.

the condition whereby a single chromosome is insufficient to sustain life

Which of the following is not a potential outcome of a gene duplication?

they may lead to translocation cross formation during synapsis

Genetic anticipation is best described as ________.

trinucleotide repeats increase in future generations

An expected meiotic pairing configuration in a ________ would be a trivalent.

triploid

Assume that a species has a diploid chromosome number of 24. The term applied to an individual with 36 chromosomes would be ________.

triploid

What error of meiosis leads to both a duplication and a deletion?

unequal crossing over

A genomic condition that may be responsible for some forms of fragile X syndrome, as well as Huntington disease, involves ________.

various lengths of trinucleotide repeats