Chapter 3.6 - Chromosomes

heterochromatin

darker chromatin

euchromatin

lighter chromatin

histones and DNA

chromatin is made up of _____ and _____

p arm

the short arm of the chromosome

q arm

long arm of the chromosome

centromere

the largest constriction of the chromosome and where spindle fibers attach

heterochromatin

darkly staining, contains mostly repetitive DNA

euchromatin

contains more protein encoding genes

telomeres

chromosome tips composed of many repeats of TTAGGG and shorten with each cell division

subtelomeres

the chromosome region between the chromatin and telomeres

8,000 - 300,000 bases

the subtelomeres consist of _____ - _______ bases

500

subtelomeres includes at least ___ protein-encoding genes

subtelomeres

in this region there is a 6-base repeat similar to telomeres

multigene families

genes that are related in structure

pseudogenes

genes that have become inactive over time

subtelomeres

multigene families and psuedogenes are in what region of the chromosome?

False

True or False: Every chromosome has the centromere in the same place

telocentric

centromere position is at the tip

acrocentric

centromere position is close to the end

submetacentric

centromere position is displaced from the center

metacentric

centromere position is at the midpoint

True

True or False: chromosomes differ in size

satellite chromosome

there is a secondary constriction near the tip of the chromosome with a satellite structure attached at the end

46 chromosomes; 23 diploid chromosomes

a normal karyotype has…

diploid

two sets of each chromosome

haploid

one set of each chromosome

number of chromosomes or missing pieces of chromosomes

chromosome abnormalities can happen due to … (2)

polyploidy

addition of whole sets of chromosomes

17%; 3%

___% of all spontaneous abortions and ____% of all stillbirths and newborn deaths show polyploidy

triploid

three copies of each chromosome; produced by two sperm fertilizing one egg or a haploid sperm fertilizing a diploid egg

aneuploidy

cells with extra or missing chromosomes; gametes produced with one extra chromosome and another with one missing chromosome

nondisjunction

common cause of aneuploidy

Down Syndrome

Trisomy 21

Trisomy 21

most common trisomy

down syndrome

distinctive facial and physical problems, many medical problems (treatable), varying degrees of developmental disabilities, link with one form of Alzheimers disease, may also be produced by a translocation

True

True or False: maternal age is a risk factor for having a child with Down syndrome

edwards syndrome

trisomy 18

trisomy 18

most due to nondisjunction in meiosis II in oocyte and do not survive

trisomy 18

2nd most common trisomy

trisomy 18

80% of people with this trisomy are female

edwards syndrome

characterized by small head, malformed ears, widely spaced, eyes, clenched hands, heart abnormalities, and kidney malformations

patau syndrome

trisomy 13

patau syndrome

very rare and generally do not survive 6 months; medical and physical abnormalities (facial malformation and eye fusion)

aneuploidy

trisomy and monosomy are associated with what?

turners syndrome

only one copy of x chromosome; 1 in 2,500 female births; 99% of affected fetuses die in utero; absence of Y leads to development as a female; phenotypes include short statue, webbing at back of neck, incomplete sexual development (infertile), and hearing impairment

not in every cell

turners syndrome is mosaic meaning it is…

45

people with turners syndrome have ___ chromosomes

47

people with triplo-X aneuploidy have ___ chromosomes

triplo-X aneuploidy

1 in 1,000 female births; extra copy of every x-linked gene, few modest effects on phenotype include tallness, menstrual irregularities, and slight impact on intelligence; x inactivation of two X chromosomes occurs and the cells have 2 barr bodies

klinefelters syndrome

1 in 1,000 male births; extra copy of each x-linked gene; phenotypes include incomplete sexual development, rudimentary testes and prostate, long limbs, large hands and feet, some breast tissue development; some cases are not diagnosed until fertility problems arise or remain undiagnosed

47

people with Klinefelter syndrome have ___ chromosomes

XXYY sendrome

mistaken for Kleinfelters; associated with ADHD, OCD, learning disabilities, and infertile; treated with testosterone

XYY/Jacobs syndrome

1 in 1,000 male births, extra y chromosome, 96% phenotypically normal, modest phenotypic differences may include: tall, acne problems, minor speech and reading disabilities

47

people with XYY or Jacobs syndrome have ___ chromosomes

deletions

chromosomal ______ result in missing copies of genes; usually bad as it can allow recessive allele to dominate

duplication

chromosomal ______ result in extra copies of genes; unequal crossing over

True

True or False: larger regions of deletion or duplication increase the likelihood that there will be an associated phenotype

translocation

nonhomologous chromosomes exchange segments

derivative chromosomes

an abnormal chromosome formed from a rearrangement, such as a translocation or insertion, involving parts of two or more chromosomes or multiple aberrations within a single chromosome

robertsonian and reciprocal

what are the two types of translocation?

robertsonian translocation

where two nonhomologous acrocentric chromosomes break at the centromere and long arms fuse; the short arms are often lost

reciprocal translocation

two nonhomologous chromosomes exchange a portion of their chromosome arms; some individuals carry a translocation but are not missing any genetic material unless a translocation breakpoint interrupts a gene

inversion

these chromosomes have a region flipped in orientation; 5-10% of these cause health problems probably due to disruption of genes at the breakpoints; these may impact meiotic segregation

paracentric

inverted region does NOT include centromere

pericentric

inverted region includes centromere

isochromosomes

chromosomes with identical arms; form when centromeres divide along the incorrect plane during meiosis

ring chromosomes

chromosomes shaped like a ring; occur in 1 in 25,000 conceptions; may arise when telomeres are lost and sticky chromosome ends fuse; have phenotypes associated with the loss or addition of genetic material

uniparental disomy

inheritance of two chromosomes or chromosome parts from the same parent