Lecture 7

Question 1

mutation

Answer 1

any permanent change in the DNA

Question 2

chromosome mutation

Answer 2

is a change in the structure or arrangement of the chromosomes

Question 3

Aneuploidy

Answer 3

excess or deficiency in a single chromosome. The name refers to the number of copies of the abnormal chromosome

2n+1=7

Question 4

Polyploidy

Answer 4

addition of one of more complete sets of chromosomes

3n=9

Question 5

Duplication mutation

Answer 5

• a portion of the chromosome has been doubled. -Duplicated region can be on the same chromosome or a different chromosome.

Question 6

tandem mutation

Answer 6

the duplicated region is immediately adjacent to the original region

Question 7

displaced mutation

Answer 7

the duplicated segment is located some distance from the original segment, on the same chromosome, or a different chromosome

Question 8

reverse duplication

Answer 8

the inverted orientation of a duplication

Question 9

homozygous individual for a mutation

Answer 9

carries it on both homologous chromosomes

Question 10

heterozygous individual for a mutation

Answer 10

there is one normal chromosome and one with the duplication

Question 11

What happens to the duplicated chromosome during pairing in prophase 1?

Answer 11

it loops out so that the homologous regions align

Question 12

imbalances in the amounts of gene products

Answer 12

abnormal gene dosage

Question 13

deletion mutation

Answer 13

the loss of a chromosomal segment

Question 14

If the deletion includes the centromere

Answer 14

the chromosome will not segregate during mitosis or meiosis and will be lost

Question 15

psuedominance

Answer 15

normally recessive mutations on the homologous chromosome lacking the deletion may be expressed when the wild type allele has been deleted (and no longer masks the recessive allele’s expression).

Question 16

Haploinsufficient gene

Answer 16

When a single copy of a gene is not sufficient to produce a wild type phenotype

Question 17

Inversion

Answer 17

• a chromosome region is flipped 180 degrees
• individuals have not lost or gained genetic information
• may break a gene into 2 parts or move to a new location
• can cause position effects. If position is altered it can cause inappropriate temporal or spatial expression.

Question 18

Pericentric

Answer 18

inversions that include the centromere

- one centromere will appear on each product

Question 19

Paracentric

Answer 19

inversions that occur outside of the centromere

- the product will be a chromatid with two centromeres and one with none

Question 20

Heterozygous for paracentric inversion

Answer 20

• two gametes contain wild-type non recombinant chromosomes
• the other two contain recombinant chromosomes that are missing some genes; these gametes will not produce viable offspring

Question 21

heterozygous for pericentric inversion

Answer 21

• recombinant gamers are nonviable because genes are either mission or present in too many copies.

Question 22

Translocation

Answer 22

a segment of a chromosome moves from one chromosome to a nonhomologous chromosome or to another place on the same chromosome

Question 23

Nonreciprocal (Unbalanced) Translocations

Answer 23

• loss of DNA

- A chromosomal segment moves from one chromosome to another without any reciprocal exchange

Question 24

Reciprocal (Balanced) Translocations

Answer 24

• no loss of DNA
• two way exchange of segments between chromosomes
• cause problems if the breakpoints are in the middle of a gene or if position effects places genes under different regulation

Question 25

Meiosis in a heterozygote for a reciprocal translocation

Answer 25

- because each chromosome has sections that are homologous to two other chromosomes, a crosslike configuration forms in prophase 1 - in anaphase I the chromosomes separate in one of three different ways (alternate segregation, adjacent-1 segregation, and adjacent-2 segregation)

Question 26

Gametes resulting from adjacent-1 and adjacent-2 segregation

Answer 26

are nonviable because some genes are present in two copies, whereas others are missing

Question 27

Robertson translocation

Answer 27

- the long arms of two chromosomes with centromeres near -the end become joined to a common centromere through a translocation - generates a long chromosomes with a centromere near the middle and another chromosome with two very short arms.

Question 28

Nullisomy

Answer 28

loss of both members of a homologous pair of chromosomes 2n-2

Question 29

Monosomy

Answer 29

loss of a single chromosome 2n-1

Question 30

Trisomy

Answer 30

gain of a single chromosome 2n+1

Question 31

Tetrasomy

Answer 31

gain of a pair of homologous chromosomes 2n+2

Question 32

nondisjunction

Answer 32

- the failure of homologous chromosomes or sister chromatids to separate in mitosis or meiosis - usually alters the phenotype drastically - most mutations are lethal, most likely due to abnormal gene dosage

Question 33

Aneuploidy through nondisjunction in Meiosis

Answer 33

- Nondisjunction in Meiosis 1 results in two trisomic and two monosomic - Nondisjunction in Meiosis 2 results in trisomic, monosomic, and two normal diploid - the earlier it happens the more severe it will be

Question 34

The most common aneuploidy in humans

Answer 34

Trisomy 21 or Down syndrome

Question 35

Down Syndrome

Answer 35

- arises from nondisjunction in egg formation

Question 36

Familial Down syndrome

Answer 36

- not trisomic for a complete chromosome 21 - they have 45 chromosomes but an extra copy of part of chromosome 21 is attached to another chromosome through a translocation - tends to run in families - arises in offspring whose parents are carriers of chromosomes that have undergone a robertson translocation between chromosomes 21 and 14. The long arm of 21 and the short arm of 14 exchange places

Question 37

Nondisjunction in a mitotic division

Answer 37

may generate patches of cells in which every cell has a chromosome abnormality and other patches in which every cell has a normal karyotype

Question 38

mosaicism

Answer 38

regions of tissue with different chromosome constitutions

Question 39

polyploidy

Answer 39

- the presence of more than two sets of chromosomes | - common in plants is a major mechanism by which new plant species have evolved.

Question 40

autopolyploidy

Answer 40

- chromosome sets are from a single species - due to accidents of meiosis or mitosis that produce extra sets of chromosomes - the chromosomes are homologous and attempt to align in prophase I of meiosis, which usually ends in sterility.

Question 41

allopolypoloidy

Answer 41

- chromosome sets are from two or more species - poloidy involves non homologous sets of chromosomes - arises from hybridization between two species - hybrid chromosomes are not homologous, so they will not pair and segregate in meiosis. - hybrid functionally haploid and sterile - can be fertile if nondisjunction occurs at an early mitotic cell division

Question 42

Steps for doing an inversion problem

Answer 42

1. decide if it pericentric or paracentric 2. draw the prophase 1 loop - line up letters that are the same - label the centromeres 3. Draw an X where there recombination event has occurred 4. Determine the chromatids by following each line - make sure you have one of each chromatid end (label the end or check off each time you use an end) - after recombination chromatids may or may not have a single copy of each gene

Question 43

duplications usually arise from

Answer 43

unequal crossing over during meiosis

Question 44

Individuals homozygous for translocation

Answer 44

meiosis is normal

Question 45

Klinefelter

Answer 45

XXY | aneuploidy in sex chromosomes

Question 46

Turner

Answer 46

single X | aneuploidy in sex chromosomes