Genetics Chapter 8

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Are chromosome aberrations passed to offspring in a predictable manner

yes

define aneuploidy

abnormal number of chromosOmes

what do you call the loss of a single chromosome from an otherwise diploid genome

monosomy

what do you call the gain of one chromosome

trisomy

define euploidy

a complete haploid set of chromosomes is present

what do you call the condition where more than two haploid sets of chromosomes is present

polyploidy

what do you call organisms with three sets of chromsomes

triploid

what do you call an organism with four sets of chromosomes

tetraploid

what are three ways in which a normally diploid individual could have a variation on the precisely two haploid chromosome sets

change in total number of chromosomes
deletion or duplication of genes or chromosome segments
rearrangement of genes on chromosome or between chromosomes

in terms of n, gieve monosomy, disomy, trisomy, tetrasomy

2n-1, 2n, 2n+1, 2n+2

in terms of n give diploidy, triploidy

2n, 3n

what is autopolyploidy

multiples of the same genome

if nondisjunction occurs between the P and F1 generation, what will be the n numbers for the offspring of the F2 generation when mated with a haploid gamete; how is this different than if the nondisjunction occurs between the F1 and F2 generations?

2 trisomic and 2 monosomic ; 2 disomic (normal) and one trisomic and one monosomic

what is the name for a 2n-1 individual and is this condition tolerated if the -1 is an autosome

monosomy; no, if autosome, poorly tolerated in animals

what is an example of an animal tolerating monosomy of an autosome

drosophila; small chromosome 4, though they develop more slowly, are smaller and have impaired viability

where do we see animals tolerating monosomy

sex chromosomes (x)

what are two causes for autosomal monosomic inviability

1) unmasks recessive lethals otherwise tolerated in heterozygotes
2)single copy of a recessive gene may be insufficient to provide adequate function for sustaining individual: HAPLOINSUFFICIENCY

what is haploinsufficiency?

when single copy of a recessive gene is insufficient to provide adequate function for sustaining individual

trisomy can be somewhat more tolerated than monosomy in individuals if _____

the chromosome involved is relatively small

trisomy for the sex chromosomes has a _____ dramatic phenotype than trisomies for autosomes, which are often lethal

less

what is the symbol for down syndrome

47, 21+

what is the main phenotypic similarity among people with down syndrome

prominent epicanthic fold

in trisomy, at any particular region along the chromsome length only ___ of the 3 homologs may _____, though different regions of the trio may be _____

2, synapse, paired

the hypothetical portion of chromosome 21 that is thought to contain the genes that are dosage sensitive and responsible for many phenotypes associated with the syndrome is called

down syndrome critical region

when three copies of a chromsome are synapsed, the configuration si called a

trivalent

in some cases, prior to the first division, one bivalent and one ____ (an unpaired chromosome) may be present instead of a trivalent

univalent

down syndrome is usually the result of nondisjunction of the _____ chromosome 21 during meiosis in anaphase 1

maternal

what are three techniques for determining if a fetus has down syndrome

amniocentisis: fetal cells obtained from amniotic fluid
chorionic villus sampling (CVS) fetal cells obtained from chorion of placenta
noninvasive prenatal diagnosis 10 mL maternal blood sample

does Down Syndrome typically run in families? can it?

no; yes

what is it called when down syndrome runs in families? what does this involve?

familial down syndrome: translocation of chromosome 21

what are two other human trisomies that survive to term

patau syndrome (trisomy 13) and edwards syndrome (trisomy 18)

what percent of all conceptions terminate in spontaneous abortion

20%

what percent of spontaneously aborted fetuses demonstrate some form of chromosomal imbalance

50%

what percent of all fertilized eggs in humans contain some error in chromosomal number

10-30%

what percent of all chromsomal anomalies are spontaneously terminated before birth?

90%

what is one piece of evidence that monosomic gametes may be very functionally impaired compared to trisomic?

trisomies are often found in spontaneously aborted fetuses with monosomies are hardly found at all

in what organisms is polyploidy very common

lizards, amphibians, fish, plants (Very common)

what is more common 4n or 3n how about 4n or 5n

4n in both cases even numbers favored

in what two ways can polyploidy originate? what are two words associated with theses ways?

the addition of one or more extra sets of chromosomes identical to the normal haploid complement of the same species: AUTOPLOIDY
and combination of chromosome sets from different species occurring as a consequence of hybridization resulting in ALLOPLOIDY

in autopolyploidy, is each additional set of chromosomes identical to the parent species?

yes

what are several ways in which autotriploids arise?

failure of all chromosomes to segregate during meiotic divisions producing a diploid gamete
two sperm may fertilize an ovum resulting in a triploid zygote
cross a diploid with a tetraploid

which are more common, autotetraploids or autotriploids

autotetraploids

define allopolyploidy

the combination of chromsome sets from different species as a consequence of interspecific matings

what effect does Colchicine have on the cell cycle?

it interferes with spindle formation and thus replicated chromosomes cannot separate at anaphase and do not migrate to te poles. Wen colchicine is removed, the cell can reenter interphase. When the paired sister chromatids separate and uncoil, the nucleus contains twice the diploid number of chrom0somes and is therefore 4n.

are autopolyploids typically smaller or larger than their diploid relatives

larger

what are several examples of large autopolyploids

winesap apples, seedless watermelon, commerical bananas.

the commercial strawberry is an ___ploid

octa

an allotetraploid arises from ______ of two closely related ____

hybridization; species

what is an amphidiploid

it four haploid genomes are derived from two KNOWN species (but remember, the species ARE different)

are amphidiploid plants often found in nature

yes

what is endopolyploidy?

the condition in which only certain cells in an otherwose diploid organism are polyploid

Cotton is a good example of what?

amphidiploidy; a cross between Old world cotton and wild american strain and treated with colchicine, we saw how this could happen and produce fertile offspring

do amphidiploids often exhibit traits of just one parental species?

no; both

in the case of endopolyploidy, these cells replicate and segregate chromosomes without _____ _____

nuclear division

what are several examples of endopolyploidy:

vertebrate liver cell nuclei
stem and parenchymal tissue of apical regions of flowering plants
cells lining gut of mosquito larvae

what do the endopolyploid cells have in common? what is an example of this?

the proliferation of chromsome copies often occurs in cells where high levels of certain gene products are required. Ribosomal and transfer RNA genes are examples of multiple-copy genes

exchanges and transfers of genes within the genome is are called

translocations

what are five types of rearrangements of chromosome segments?

deletions, duplications, inversions, nonreciprocal translocations, reciprocal translocations

how are structural alterations in the location of genes on a chromosome most often caused?

breaks along the axis of a chromosome and the ends produced at points of breakage are sticky and can rejoin other broken ends

if one of the homologs has been broken and put back together, and the other homolog is fine, the inidividual is called heterozygous for the aberration. In this case is the individual typically affected?

no

a _____ is a missing region of a chromosome

deletion or deficiency

what do you call a deletion near either end of the chromosome?

terminal deletion

what do you call a deletion in the interior of the chromosome?

intercalary or interstitial deletion

in the case of a deletion, the portion of the chromosome that retains the _____ region is usually maintained when the cell divides, whereas the segment without the ______is eventually lost in progeny cells following mitosis and meiosis

centromere; centromere

for synapsis to occur between a chromosome with a large intercalary deletion and a normal homolog, the unpaired region of the normal homolog must "buckle out" into a ______ or ______ _______

deletion; compensation loop

in cases of deletions often times, if one is good and one is not, the bad one is

looped out

in humans, cri du chat syndrome results from the deletion of a small terminal portion of chromosome ; what arm

5; small arm p

what type of deletion do those with cri du chat syndrome exhibit on chromosome 5?

segmental deletion

what is the symbol for cri du chat?

46,5p- (meaning that the individual has all 46 chromosomes, but that some or all of the chromosome 5 short arm p is missing)

what is the set of signs and symptoms of cri du chat syndrome?

GI and Cardiac complications, mentally retarded, abnormal development of the glottis and larynx leading to the characteristic cry

what is the incidence of cri du chat syndrome worldwide

1 in 25,000-50,000

is cri du chat syndrome an inherited condition? what happens?

no; results from the sporadic loss of chromosomal material in gametes

what gene is on the p arm of chromosome 5; what does it do?

TERT gene: telomerase reverse transcriptase and enzyme essential for the maintenance of telomeres during DNA replication

what are three causes for abnormal phenotypes resulting from heterozygote deletions?

haploinsufficiency: if one copy is present it is not performing optimally
Gene imbalance
pseudodominance

what are the two components of telomerase

RNA and TERT (telomerase reverse transcriptase)

when any part of the genetic material-a single locus or a large piece of a chromosome-is present more than once in the genome it is called a

duplication

do we see formation of a compensation loop in heterozygotes with a duplication as well as deletion?

yes

what are two possible causes for a duplication of a part of a chromosome?

-unequal crossing over during meiosis
-replication error prior to meiosis

if there is unequal crossing over between synapsed chromosomes during meiosis, what type of chromosomal abnormality do we see?

a deletion and a duplication arise

what is an example of duplication, specifically gene redundancy, that greatly favors us?

organisms have multiple copies of ribosomal RNA genes; the rDNA that codes for rRNA is often very duplicated in favor of us

in what cells do we see the highest number of ribosomes

oocytes

describe gene amplification

basically, in the case of rRNA, if you have a case of gene redundancy for a processing selectively replicated rDNA, a new set of genes is released from its template/ Because each new copy is equivalent to one NOR, multiple micronucleoli are formed. If we then multiply the number of micronucleoli by the number of gene copies in each NOR, we see that amplification in the cells is amazing.

what is an example of a duplication in Drosophila

bar eye: wild type B+B+ 800 facets; B+B 350 facets, B/B bar 70 facets and double bar BdB+ even fewer results from a duplication in one copy of the region called 16A on the X chromosome

talk a bit about the role of gene duplication in evolution

it is thought that there are some genes in whihc a mutation could not be tolerated, however, if this essential gene is duplicated, major mutational changes will be tolerated throughout generations because one copy is alright. This duplicated copy is free to undergo mutation over time. This mutating duplicated copy may have anew function that imparts an adaptive advantage to organisms

what are two examples of gene duplication in evolution? (two examples of genes that have a substantial amount of their DNA sequence in common, but whose gene products are distinct)

trypsin and chymotrypsin
myoglobin and hemoglobin

what are gene families?

groups of contiguous genes whose products perform the same function

what is an example of a gene family

the various genes encoding for the various types of human hemoglobin polypeptide chains

an _____ is a type of chromosomal aberration in which a segment of a chromosome is turned around 180 degrees in a chromosome

inversion

an inversion requires ____ at two points along the length of the chromosome and subsequent _____ of the inverted segment

breaks; reinsertion

by forming a chromosomal loop prior to breakage the newly created sticky ends are brought close together and _____

rejoined

if the centromere is not part of the rearranged chromosome segment in the case of inversion it is called

paracentric inversion (think A=non) involved

if the centromere is part of the rearranged chromosome segment in the case of inversion it is called

pericentric inversion (think I=in)involved

does an inversion involve loss of genetic material

no, not technically, however often genes do get lost

an inversion may arise from chromosomal _____

looping

the major histocompatibility complex is a group of three genes, MHC 1, MHC2, MHC3, which code for glycoprotein found in all ____cells ( so all but red blood cells)

nucleated

when determining the tissue compatibility of individuals, they can look at the the _____ compatibility; must individuals be 100%compatible

MHC; no

which type of inversion does not result in a change in the relative lengths of the two arms of the chromosome? which does result in such

paracentric; pericentric

if only one member of a homologous pair of chromosomes has an inverted segment, is normal linear synapsis possible?

no

what do you call organisms with one inverted chromosome and one noninverted homolog

inversion heterozygotes

what is the only way that pairing between inversion heterozygotes can occur?

inversion loop

if a single crossover occurs between nonsister chromatids we we see two parental chromatids and two recombinant chromatids. if the SCO occurs within a paracentric inversion, one recombinant _____ chromatid, and one recombinant _____ chromatid will be produced

dicentric; acentric

is an acentric chromatid viable

no

both dicentric and acentric chromatids in the case of a single crossover in a paracentric inversion we see both ____ and _____, thus they are not viable

duplication and deletion

so basically, big picture with outcomes of inversions, any cross over whatsoever results in insertion and deletion and a non-viable chromosome in 50% of the chromosomes; true or false

true

does inversion suppress crossing over, or does the inversion have the effect of suppressing the recovery of crossover products when chromosome exchange occurs within the inverted region?

the latter

______ is the movement of a chromosomal segment to a new location in the genome

translocation

reciprocal translocation involves the exchange of segments between _____

two nonhomologous chromosomes.

what is the easiest way for reciprocal translocation to occur?

for two nonhomologous chromosome arms to come close to each other so that an exchange is facilitated

is genetic material lost or gained during reciprocal translocations

neither

does the presence of a translocation directly alter the viability of individuals bearing it?

no

how do homologs that are heteroxygous for a reciprocal translocation undergo synapsis during meiosis

in a cruciform or crosslike configuration

what are the two possible segregation patterns in the case of translocation? what yields what product

alternate segregation (leads to normal and balanced gamete) and adjacent segregation (leads to duplications and deficient gamete)

what do you call a common type of translocation that involves breaks at the extreme ends of the short arms of two nonhomologous acrocentric chromosomes, producing a new large submetacentric or metacentric chromosome?

Robertsonian translocation

what is an example of robertsonian translocation

familial down syndrome

in familial down syndrome, one of the parents contains a ____,___ translocation; is this parent normal phenotypically; how many chromosomes does he or she have; what do you call him or her

14/21, D/G; meaning one parent has the majority of the G-group chromsome 21 translocated to one end of the D group chromosome 14; yes; 45; balanced translocation carrier

when you mate a normal individual with a translocation carrier for down syndrome what are the resulting offspring

one normal two translocation carriers and one monosomic lethal

does familial down syndrome show familial anticipation

yes

____ _____ are more susceptible to chromosome breakage when cells are cultured in the absence of certain chemicals such as folic acid

fragile sites

what is fragile X syndrome i

it is the most common form of inherited mental retardation (also called martin bell syndrome) and is far more common in males and is a dominant trait

something about gene defective fragile x sydnrome FMR that codes for rna carrying memory and learning protein; if trinucleotide repeat number is 0-54 normal, 55-230 carrier
>230 disease fragile X

just need to know that CGG is repeated a ton in fragile x syndrome

1) When an organism gains or loses one or more chromosomes but not a complete haploid set, the condition is known as;

aneuploidy

2) Cri-du-chat syndrome has a genetic composition designated as,

45,5p-

3) A genomic condition that may be responsible for some forms of fragile-X syndrome as well as Huntington's disease, involves

various lengths of trinucleotide repeats

4) Recently, a gene located on chromosome 3 in humans, FHIT has been shown to be associated with

cancer

5) In Trisomy 21 or Down syndrome, although there is reduced fertility in both sexes females are more fertile than males. Assume that children are born to female with Down syndrome and a normal male. What proportion of children would be expected to have Down syndrome?

1/2

1) Nondisjunction is considered as a major cause of aneuploidy. T/ F
2)

T

Familial Down syndrome can be caused by a translocation between chromosome 1 and 14. T/ F
3)

F

A deletion may set up a genetic circumstance known as overdominance. T/ F
4)

F; pseudodominance

A pericentric inversion includes the centromere. T/ F
5)

T

Assume that an organism has a diploid chromosome number of 14. There would be 56 chromosomes in a tetraploid. T/ F
6)

F; 28

A position effect occurs when a gene's expression is altered by virtue of a change in the position. Position effects occur with inversions and translocations. T/ F
7)

T

rDNA in eukaryotes is typically redundant. T/ F
F

T

when you think Allopolyploid

think chromosome sets from different species

when you think Acentric chromatid

think lacks centromere

when you think familial down syndrome think

Translocation between chromosome 14 and 21

when you think ) Patau syndrome

think trisomy 13

when you think edwards syndrome think

trisomy 18

when you think williams syndrome think

deletion in chromosome 7

when you think Prader-Willie syndrome

think deletion on chromosome 15

when you think bar mutation think

x-linked trait

how do translocations cause phenotypic defects

if the translocation breakpoint disrupts the gene or if the gene near the breakpoint is altered in its expression because of relocation to a different chromosomal environment (position effect).

3) What is the difference between primary and familial Down syndrome? How does each type arise?

3) Primary Down syndrome is caused by spontaneous, random nondisjunction of chromosome 21, leading to Trisomy 21. Familial DS arises from Robertsonian translocation between chromosome 21 and 14. Translocation carriers do not have DS, but their children have an increased incidence of it. If the translocated chromosome segregates with a normal 21, the gametes will have two copies of chromosome 21 and result in DS.

4) Why do extra copies of genes sometimes cause drastic phenotypic effects?

4) The expression of some genes is balanced with the expression of other genes. The ratio of different gene products should be maintained within a range to ensure proper cellular function. Extra copies of one of the genes results in over expression of the gene product and throws off the balance.

which type of chromosome mutations Increase the amount of genetic material in a particular chromosome?

duplication

which type of chromosome mutations Increase the genetic material in all chromosomes?

polyploidy

which type of chromosome mutation Decreases the amount of genetic material in a particular chromosome?

deletion

which type of chromosome mutations Change the position of DNA sequence without changing the amount of genetic material?

inversion

which type of chromosome mutations Move DNA from one chromosome to a nonhomologous chromosome?

translocation

A chromosome has the following sequence where represents the position of the centromere; A B C D E F G.
What types of mutations are necessary to change this chromosome into each of the following? A) A B E * F G

deletion

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