Genetics exam 2

Metacentric

Metacentric

centromere in middle

Submetacentric

centromere slightly off center

Acrocentric

centromere close to end

Telocentric

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

Why is the banding of eukaryotic chromosomes useful?

1. Individual stained chromosomes can be distinguished from each other

2. Banding structures are used to detect changes in chromosome structure

3. Chromosome banding is used to asses evolutionary relationships between species

Numerical abnormalities

have added or missing chromosomes (polyploidy, aneuploidy)

Structural abnormalities

deletions, duplications, translocations, inversions

Cytogenetic nomenclature

First: number of chromosomes Second: what sex chromosomes present Third: If there are abnormalities

Euploid

Balanced chromosome condition

Polyploidy

condition in which an organism has extra sets of chromosomes

Aneuploid

An extra or missing chromosome

Which monosomy or trisomy are viable?

13, 18, 21, X and monosomy X

How do aneuploidies arise?

Mitotic non-disjunction or chromosome loss

Mitotic non disjunction

Sister chromatids don't separate properly (leads to trisomic and monosomic daughter cells)

Chromosome loss

One sister chromatid does not go to a pole (normal and monosomic daughter cells)

Mosiacism

a condition in which cells within the same person have a different genetic makeup. Happens after fertilization

Patau Syndrome

Trisomy 13

Edward syndrome

Trisomy 18

Down syndrome

Trisomy 12

Describe meiotic chromosome segregation in a trisomic cell

1. Chromosomes form a trivalent

2. Two centromeres go to one pole and one centromere goes to the other OR

3. Chromosomes form one bivalent and one univalent

4. Two centromeres go to one pole and one centromere goes to the other

Klinefelter syndrome

XXY (sexual immaturity)

Jacobs syndrome

XYY (tall and thin)

Triple X

XXX (tall and thin, menstrual irregularity)

Turner syndrome

X0 (Short stature, webbed neck, sexually undeveloped)

Balanced rearrangements

Abnormality of chromosome structure that results in a normal chromosome compliment. Ex. Inversion, simple translocation, reciprocal translocation

Unbalanced rearrangement

Abnormality of chromosome structure that results in an abnormal chromosome compliment. Ex. Deletion and duplication

Interstitial

A type of deletion that occurs in the middle of the chromosome

Terminal

A type of deletion that occurs at the end of the chromosome

Tandem duplications

Repeated segments are adjacent and face in the same direction

Copy number variation (CNV)

A segment of DNA that varies in copy number among members of the same species

Paracentric

A type of inversion that does no include the centromere

Pericentric

A type of inversion that does include the centromere

Translocation

Exchange of DNA between 2 different chromosomes

Reciprocal

A type of translocation where 2 chromosomes exchange with no apparent loss of DNA

Explain 2 mechanisms that cause reciprocal translocation

1. Environment causes 2 chromosomes to break

2. DNA repair recognizes reactive ends and connects them incorrectly OR

3. Crossover between homologous chromosomes