Chapter 8 Part 1

Question 1

Metacentric

Answer 1

The centromere is located exactly in the middle

Question 2

Submetacentric

Answer 2

The centromere was displaced towards one location

Question 3

p-arm

Answer 3

The shorter arm of the chromosome

Question 4

q-arm

Answer 4

The longer arm of the chromosome

Question 5

Acrocentric

Answer 5

The centromere is near one end, producing a long arm and a knob, or satellite, at the other end

Question 6

Telocentric

Answer 6

The centromere is at or very near the end of the chromosome

Question 7

Karyotype

Answer 7

The complete set of chromosomes passed by an organism
– usually presented in metaphase

Question 8

Colchicine ** extra not too important

Answer 8

Prevents chromosomes to go to anaphase to see karyotypes

Question 9

Extra Stuff – Click on to see what it is!

Answer 9

Giesma – reveals G bands which distinguish areas of DNA that are rich in adenine-thymine base pairs

Q-bands – reveal by staining chromosomes with quinacrine mustard

C-bands – which are regions of DA occupied by centromeric heterochromatic

R-bands –which are rich in cytosine-guanine base pairs

Question 10

What are the different types of chromosome mutations?

Answer 10

1. Chromosome Rearrangement
2. Aneuploidy
3. Polyploidy

Question 11

Chromosome rearrangement

Answer 11

Mutations that change the structure of the chromosome

There are four basic types of rearrangements:
1. Duplication
2. Deletions
3. Inversions
4. Translocations

Occur…when double stranded breaks occur in the DNA molecule found within a chromosome

Question 12

Aneuploidy

Answer 12

The number of chromosomes is altered: one or more individual chromosomes are added or deleted

For example…
- Trisomy 21 which results from adding have three 21 chromosomes
- People with this issue get Down syndrome

Question 13

Polyploidy

Answer 13

One or more complete sets of chromosomes are added

A polyploidy is any organism that has more than two sets of chromosomes
– 3n,4n,5n, and more

Question 14

How does double-strand repair and mutation occur?

Answer 14

Double-stranded breaks in DNA often cause cell death

If the two broken ends are rejoined correctly, the original chromosome is restored

Sometimes the wrong ends are connected…this causes mutations

Chromosome rearrangements cal also rise through errors in crossing over or when crossing over occurs between repeated DNA sequences

Question 15

Chromosome Duplication

Answer 15

Is a mutation in which part of the chromosome has been doubled….

Consider a chromosome with segments AB*CDEFG
* = centromere

A duplication of the allele E and F can result in

AB*CDEFEFG –> So notice that the chromosome is larger in this case

Question 16

Tandem Duplication

Answer 16

This type of duplication, in which the duplicated segments is immediately adjacent to the original segment

Ex. EFEF

Question 17

Displaced Duplication

Answer 17

If the duplicated segment of alleles of one chromosomes are located some distance away from the original location on the same chromosome

Ex. ABEF*CDEFGH

Question 18

Reverse Duplication

Answer 18

A duplication where the orientation of the alleles has been inverted

AB*CDEFFEG
EF switched to FE

Question 19

Unequal Crossing Over

Answer 19

Chromosomes misalign during crossing over and results in duplication and deletions

Ex. Human colour Blindness

Question 20

Abnormal gene dosing

Answer 20

The amount of a particular protein synthesized by a cell is often directly related to the number of copies of that gene

Question 21

Pseudo-dominance

Answer 21

Normally recessive mutations on the homologous chromosomes lacking the deletion maybe expressed when the wild-type allele has been deleted and no longer masks the recessive allele

Question 22

Haplo-insuffiecient

Answer 22

Some genes must be present in two copies for normal function, and this situation occurs when we are missing the other gene

Question 23

Paracentric Inversion

Answer 23

Inversions that occur before or after the centromere

AB*DCEFG

Question 24

Pericentric Inversion

Answer 24

Inversion that occur between the centromere

ADB*CEFG

Question 25

Dicentric Chromatid

Answer 25

Chromatid that has two centromeres; produced when crossing over takes place within a paracentric inversion

Question 26

Acentric Chromatid

Answer 26

Chromatid that lacks a centromere; produced when crossing over takes place within a paracentric inversion

Question 27

Dicentric Bridge

Answer 27

Structure produced when the two centromeres of a dicentric chromatid are pulled toward opposite poles, stretching the dicentric chromosomes across the centre of the nucleus…

Eventually, the dicentric bridge breaks as the two centromeres are pulled farther apart

Question 28

How do individuals heterozygous for inversions cross over during prophase I of meiosis? – paracentric

Answer 28

1. The heterozygous chromosomes – homologous pairs or homologs – posses one wild type – the correct sequence – and one chromosome with a paracentric inversion
2. In prophase I, an inversion loop forms when a single crossing over occurs within the inverted region
3. This results in an unusual structure…where two chromosomes form with four chromatids and two centromeres…and one chromosome that lacks a centromere –> formation of dicentric chromatids
4. In anaphase I, the centromeres separate stretching the dicentric chromatid, which breaks…the chromosome lacking a centromere is lost into the cytoplasm
5. The two gametes contain non-recombinant chromosomes one wild type – normal and one with inversion…the other two contain recombinant chromosomes that are missing some genes; these gamester will not produce viable offspring

Question 29

How do individuals heterozygous for inversions cross over during prophase I of meiosis? – pericentric

Answer 29

1. The heterozygote possesses one wild-type chromosome and one chromosome with a pericentric inversion
2. In prophase I, an inversion loop forms…if crossing over takes place within the inverted region…two of the resulting chromatids have too many copies of some genes and no copies of others
3. Unlike in paracentric, we still have two chromosomes each with two chromatids and one centromere
4. The chromosomes separate in Anaphase I, and than later in Anaphase II
5. Four gametes are produced:
   - Normal non recombinant gamete
   - Nonviable recombinant gametes X 2
   - Nonrecombinanat gamete with pericentric inversion

Question 30

Nonreciprocal translocation

Answer 30

Movement of a chromosomes segment to a non homologous chromosome or chromosomal region without any – or with unequal – reciprocal exchange of segments

ABCDEFG and MNOPQRS

ABCDG and MNOPEFQRS

Question 31

Reciprocal Transaction

Answer 31

Reciprocal exchange of segments between two non homologous chromosomes

ABCDEFG and MNOPQRS

ABCDQRS and MNOPEFG

Question 32

What are the effects of a phenotype in translocation?

Answer 32

1. They can physically link genes that were formerly located on different chromosomes…these new linkage relations may affect gene expression – a position effect – as genes translocated to new position effect, as genes translocated to new locations may come under the control of different sequences or other genes that affect their expression
2. Second, chromosome breaks that bring about translocations may take place within a gene and disrupt its function –

Ex. Neurofibromatosis, a genetic disease characterized by numerous fibrous tumours of the skin and nervous tissue, results from an autosomal dominant mutation.

Question 33

Robertsonian Translocation

Answer 33

The long arms of two afrocentric chromosomes become joined to a common centromere, generating a metacentric chromosome with two long arms and another chromosome with two very short arms

– some causes of Down syndrome disorder
– the short arm is a fragment that often fails to segregate and is lost

Question 34

Which type of segregation in reciprocal or non-reciprocal translocation produce viable gametes?

Answer 34

Alternate Segregation

N1,N2 || T1,T2.

Question 35

Which types of segregation in reciprocal or non-reciprocal translocation produce inviable gametes?

Answer 35

Adjacent-1 Segregation and Adjacent-2 Segregation

missing genes or too many genes occur on the gene

Adjacent-2 gametes are rare because homologous chromosomes with adjacent centromere do not segregate

Adjacent-1 gametes are often found too…but they produce 50% viable and 50% non-viable offspring

Question 36

Alternate Segregation

Answer 36

Type of segregation that takes place in a heterozygote for a translocation:

If the original, non-translocated chromosomes are N1 and N2 and the chromosomes containing the translocated segments are T1 and T2, then alternate segregation takes place when N1 and N2 move toward one pole and T1 and T2 move towards the opposite pole

Question 37

Adjacent-1

Answer 37

One translocated and one non-translocated chromosomes separate…

***Homologous chromosomes segregate in Meiosis I

Question 38

Adjacent-2

Answer 38

One translocated and one non-translocated chromosomes separate…

***Homologous chromosomes DO NOT segregate in Meiosis II

Question 39

How does reciprocal transformation occur in meiosis?

Answer 39

1. An individual heterozygous for the reciprocal translocation possesses one normal copy of each chromosome and one translocated copy
2. Because each chromosome has sections that are homologous to two other chromosomes, a cross like configuration forms in prophase I of meiosis
3. In anaphase I, the chromosomes separate in three different ways
4. Alternate Segregation
5. Adjacent-1 and Adjacent-2 Segregation

Question 40

Fragile Sites

Answer 40

Sites that develop constrictions or gaps when the cells are grown in culture and that are prone to breakage under entrain conditions

Ex. Common health condition as a result is fragile-X syndrome