BIOL 313 | Ch5 - Chromosome Behavior

Karyotype

stained and photographed preparation of metaphase chromosomes arranged according to their size and position of centromeres

The amount of chromosomes humans contain

46

The amount of homologous autosomes humans have

22

Metacentric

Located in the middle of the chromosome

Submetacentric

Closer to one end of the chromosome

Acrocentric

near one end of the chromosome

Telocentric

centromere is continuous with telomere

Centromeres separate…

karyotypes

Arms

The nickname for the two regions a karyotypes is divided into

“p”

short arm (petit)

“q”

long arm (letter after p)

Barr body

inactive X chromosome in the nucleus of interphase cells

Dosage compensation

equalizes the number of active copies of X-linked genes in females and males

genetic mosaics

Females are this for genes on the X chromosome; only one X allele is active in each cell

heterochromatic

The Y chromosome is largely this.

pseudoautosomal regions

A homologous region of the Y-chromosome, which are between tips of X and Y.

26 - 70

The amount of proteins encoded on the Y chromosome

SRY

master sex controller gene that encodes testis determining factor (TDF) for male development

testis determining factor (TDF)

A protein encoded by the SRY gene that initiates male sex determination by triggering the development of testes.

Human populations

This can be traced via studies of Y-chromosome

Genghis Khan

The most successful reproducer in human history.

“-ploidy”

Word root from the Greek for, roughly, count or copy

Euploid

“good count” – the correct number of chromosome copies

Aneuploid

“not good count” – wrong number of chromosome copies

Haploid

“half count” – half the normal number of copies

Monoploid, diploid, triploid…

“one, two, three count” – tells the number of chromosome copies

Polyploid

“many count” – whole genome has been repeated numerous times

Aneuploidy

daughter cells with too many or too few of a particular chromosome

Nondisjunction

chromosomes that do not disjoin properly at the anaphase, resulting in aneuploidy daughter cells

Down syndrome

aneuploid condition that results from three copies of chromosome 21

an “overdose” of c21 gene products

The cause of Down Syndrome

Deletions

involve the loss of a chromosome segment, which can lead to various genetic disorders.

two double-stranded breaks, followed by rejoining of the wrong ends

the cause of deletions

ectopic recombination

a process where recombination occurs at non-homologous sites, potentially leading to genomic instability - between repeated or homologous sequences.

direct repeats

Ectopic recombination on the same chromosome results in formation of a circular DNA molecule

Duplications

genetic rearrangements in which a chromosome segment is present in multiple copies

Genes for red and green photopigments

…are close on the X-chromosome

Green-pigment genes

may be present in multiple copies on the chromosome due to mispairing and unequal crossing-over

Unequal crossing-over

can result in gene deletion and color-blindness

Inversions

when the order of genesI in a chromosome segment is reversed

inverted repeats

ectopic recombination between these things on the same chromosome

a “loop”

twisted chromosomes in the inverted region, when pairing

with their homologs in meiosis

translocation

Interchange of parts between nonhomologous

chromosomes

position effects

position effects:

Translocations may produce the following type of changes in gene function due to repositioning of a gene

Synapsis

the pairing of homologous chromosomes during meiosis, allowing for genetic recombination.

quadrivalent

four pairs of sister chromatids, formed via heterozygous reciprocal translocation

Robertsonian translocation

A type of nonreciprocal translocation, the fusion of two acrocentric chromosomes in the centromere region, that also results in the apparent loss of one chromosome in karyotype analysis.

Polyploid species

have multiple complete sets of chromosomes

Polyploidy plants

are advantageous in crops, because it typically increases the

size of individual plant cells

meiosis through unreduced gametes

a mechanism of polyploidization

endoreduplication

the doubling of the chromosome number takes place in mitosis, followed by failure to divide

monoploid

most are sterile; their chromosomes cannot pair up and

segregate normally in meiosis

Monoploid plants

are useful in selective plant breeding

auxin

a hormone that is used to treat monoploid cells, that can be grown in culture into a lump

colchicine

a chemical that inhibits tubulin polymerization. (Spindle fibers do not form, and no separation of chromosomes occurs in mitosis.)