Lecture 13a

Question 1

What is a chromosome mutation?

Answer 1

Changes in a chromosome region encompassing multiple genes

Question 2

What are euploid organisms?

Answer 2

Organism with the normal number chromosome sets.

Question 3

What is an aberrant euploid?

Answer 3

Organism that has more or fewer than the normal number of sets.

Question 4

What is polyploidy?

Answer 4

Organisms that have more than two chromosome sets. It is better tolerated than aneuploidy and is common among plants. Polyploids tend to be proportionally bigger.
Ex. triploid (3n), tetraploid (4n), etc.

Question 5

What is monoploid?

Answer 5

A haploid set in a diploid species

Question 6

What are autopolyploids?

Answer 6

Multiple chromosome sets originating from within one species

Question 7

What are allopolyploids?

Answer 7

Chromosome sets from two or more different species (form only between closely related species)

Question 8

What is aneuploidy?

Answer 8

Extra/missing chromosomes from a full set.

Question 9

What does it mean to be trisomic? monosomic? nullisomic?

Answer 9

Trisomic: 1 extra copy of 1 chromosome in a diploid (2n+1)
Monosomic: 1 fewer copy of 1 chromosome in a diploid (2n-1)
Nullisomic: 2n-2

Question 10

When is a polyploidy organism stable vs unstable?

Answer 10

Stable (fertile): ploidy is even

Unstable: ploidy is odd –> messes up lining up of homologs in Meiosis 1 (gametes and offspring are aneuploid)

Question 11

What are autotetraploids?

Answer 11

Arise by the doubling of a 2n to 4n. Can have regular meiosis if chromosomes pair as two bivalents or one quadrivalent. Nonfunctional aneuploid gametes form if a trivalent + univalent occur.

Question 12

How do polyploids arise?

Answer 12

1) Natural accident: Ex. 2n gamete + n gamete = 3n offspring or 2n gamete + 2n gamete = 4n offspring
2) Colchicine treatment: prevents microtubule formation in mitosis –> doubled chromosome complement in cells

Question 13

What is allopolyploidy?

Answer 13

Combining chromosomes from gametes of two species. The species must be closely related. Possibility of being sterile if the chromosomes are not homologous enough to properly segregate in meiosis

Question 14

What is amphiploidy?

Answer 14

First allo then auto. Organism has a diploid set of chromosomes from each parent.

Question 15

What is aneuploidy?

Answer 15

Chromosome number is different than the WT number.. Mostly due to nondisjunction in M1 or M2. Nondisjunction causes the gamete to be n+1 or n-1. Then, the consequence is felt in offspring when aberrant gamete combines w/ normal gamete to make 2n+1 or 2n-1 offspring.

Question 16

What is nondisjunction?

Answer 16

Failure of normal segregation of homologous chromosomes or chromatids to opposite poles at meiotic or mitotic divisions.

Question 17

What does nondisjunction at M1 lead to?

Answer 17

n+1
n+1
n-1
n-1

Question 18

What does nondisjunction at M2 lead to?

Answer 18

n+1
n-1
n
n

Question 19

Why is nondisjunction bad?

Answer 19

1) missing a copy of a chromosome means missing those chromosomes genes –> less mRNA –> less protein
2) Recessive alleles on other chromosome copy take full effect
3) Extra copies of a chromosome –> more protein –> can screw up rxn balance in cell
4) Most trisomes lead to miscarriage

Question 20

What are the 4 types of chromosomal rearrangements?

Answer 20

Deletion, Deletion&Duplication, Inversion, Translocation

Question 21

What are the two ways in which chromosomal rearrangements arise?

Answer 21

1) Breakage and rejoining

2) Crossing over between repetitive DNA

Question 22

What is deletion?

Answer 22

A chromosome segment is lost. Breakage in DNA can be caused by X ray or gamma rays. Crossing over occurs on same chromosome (loop forms).

Question 23

What is deletion & duplication?

Answer 23

Generally occurs because of unequal crossing over between homologous chromosomes. One chromosome has parts deleted and the other chromosome has those parts added on to it. Severity depends on gene function and length of deletion/duplication. It creates partial aneuploidy.

Question 24

What is inversion?

Answer 24

The orientation of a segment on a chromosome is reversed. Usually has no effect but if breakage occurs in the middle of a gene then effect is negative.

Question 25

What is translocation?

Answer 25

A chromosome segment is moved to a different chromosome. Occurs between non-homologous chromosomes. Gametes will not carry even diploid set of genes.