Genetics lecture 2- chromosome structure&abnormalities.

winniesmith1's version from 2017-06-11 15:22

Section 1

Question Answer
What proteins are DNA associated withhistones
What is chromatinDNA helix tightly coiled around histones
What does a nucleosome consist ofone histone with (nearly) 2 turns of DNA around it
What is euchromatina lightly packed region of chromatin, often under active transcription
What is heterochromatinChromatin further coiled to form solenoids which form loops and minibands.
When is DNA visibleonly when chromosomes condense during cell division

Section 2

Question Answer
How many chromosomes do human somatic cells contain46 (44 autosomes and 2 sex chromosomes)
How many chromosomes in gametic cells23
What are centromereswhere spindle fibers attach during cell division. Divide chromosomes into 2 arms (p and q)
What does centromere location givechromosome characteristic shape, useful for identification.
Describe centromere position: metacentriccenter, such that both sections are of equal length
Describe centromere position: Submetacentricslightly offset from the center leading to a slight asymmetry in the length of the two sections.
Describe centromere position: Acrocentricseverely offset from the center leading to one very long and one very short section.
Describe centromere position: Telocentriccentromere at the very end of the chromosome. (q arm only not p)
What is a satellitea chromosome segment that is separated from the main body of the chromosome by such a secondary constriction.

Section 3

Question Answer
Interphase-G1 phases involves rapid growth, organelle synthesis, centriole replication (8-10hrs). -S phase involves duplication of chromosomes (6-8hrs).-G2 involves further protein synthesis. (4-6 hrs)
Prophase-Chromatin coils and thickens. -Sister chromatids joined by centromere become visible. -Nucleolus disappears and nuclear membrane breaks down. -Spindle fibres form in cytoplasm
Metaphase -Chromosomes move to equatorial plane of cell. -Centromeres attach to spindle fibres
Anaphase-Centromeres divide splitting the sister chromatids. -Spindle fibres shorten and chromosomes move to opposite poles of the cell
Telophase-Nuclear membrane forms. -Chromosomes uncoil and nucleoli forms.-Spindle fibres break down.
Cytokinesis-Cell furrow formation and constriction of cell membrane splits cell in two

Section 4

Question Answer
Describe cell cycle: MeiosisGerm cell division. 2 rounds of division with only 1 round of DNA synthesis. Results in 4 haploid cells (gametes). Reduction in chromosome number.
What is crossing over and where does it occurOccurs during prophase 1. Homologous chromosomes pair up (synapsis), form chiasma (chromatids intertwine) and exchange chromosomal regions.
What happens in Prophase lChromatin condenses. Spindle organisation takes place. Synapsis and crossing over occurs (recombination)
What happens in Metaphase lHomologous chromosomes align at equatorial plane of cell.
What happens in Anaphase lHomologous pairs separate and move to opposite poles of cell with sister chromatids remaining together attached at centromere (random assortment)
What happens in Telophase lCytokinesis results in two daughter cells, each containing one chromosome of the homologous pair.
What happens in Prophase llChromatin condenses. Spindle forms. Chromatids joined by centromere
What happens in Metaphase llChromosomes align at equator. Centromeres attach to spindle fibres
What happens in Anaphase llCentromeres divide and chromatids migrate to opposite poles of cell
What happens in Telophase llCytokinesis results in four daughter cells, each containing one copy of each chromosome (not genetically identical).

Section 5

Question Answer
One division Mitosis
Two divisionsMeiosis
Daughter cells genetically identical Mitosis
Daughter cells genetically differentMeiosis
Chromosome nm same for daughter and parent cells (2n)Mitosis
Chromosome nm of daughter half that of parent (1n)Meiosis
Daughter cells have one each of maternal and paternal chromosomesMitosis
Daughter cells have combination of maternal and paternal chromosomesMeiosis
Occurs in somatic cells Mitosis
Gives rise to genetic variation Meiosis
Used for growth,repair and asexual reproductionMitosis
Occurs in germline cells Meiosis

Section 6

Question Answer
How many live births will have a chromosome abnormality1 in every 150
What is cytogenetics the study of chromosomes and their abnormalities.
What is a karyotypean organized profile of a person's chromosomes.
What does a karyotype involvemicroscopic examination of chromosome length, position of the centromere and banding pattern.
How do you create a karyotype5mL venous blood > Add phytohemagglutinin and culture medium > Culture at 37 degrees for 3 days > Add colchicine and hypotonic saline > cells fixed > spread cells onto slide by dropping > Digest with trypsin and stain with Giemsa > analyze "metaphase spread" > Karyotype.
What do you look for when matching chromosomes in a karyotypesize of chromosome, centromere position, banding pattern

Section 7

Question Answer
When do chromosomal abnormalities occurWhen number of chromosomes is not 46 (numerical) or when individual chromosomes have missing genetic material (structural)
What are numerical aberrations-Polyploidyaddition or loss of complete set of chr. -Aneuploidyaddition or loss of individual chr.
What are structural abberrations -Translocation -Rearrangements -Deletion
What is a triploid set of chromosomes(3n) 3 of each chromosome. 15-18 % of miscarriages, often due to dispermy, 69 XXY
What is a tetraploid set of chromosomes(4n) 4 of each chromosome. 5 % of miscarriages, caused by post-fertilization mitotic errors
What is Aneuploidy-addition or loss of individual chromosome - monosomy (2n-1) or trisomy (2n+1). -typically due to abnormal meiotic division

Section 8

Question Answer
Cause of down's syndrome47XX/XY (+21). 1 in 800-1000 live births.
symptoms of down's syndrome-Characteristic facial features: low nasal root, extra fold on eyelid, low ears and enlarged tongue. -Short in stature, single palmar crease. -Congenital heart defects, GI tract obstruction and respiratory infections. -Mental retardation. -Prone to developing early Alzheimer’s and leukaemia. -Often infertile. -wide variation in severity.
Cause of klinefelter's syndrome 47XXY 1 in 500 to 1 in 1000 male births
symptoms of klinefelter's syndrome-Individuals taller than average with long arms and legs. -Generally male phenotype. -Decreased facial and pubic hair, 30 % develops breasts (gynecomastia). -Typically diagnosed after puberty. -Might have reduced IQ.
Cause of turner's syndrome45X, single X chromosome. Female phenotype. 1 in 5,000 to 1 in 10,000 live female births.
symptoms of turner's syndrome -Short stature, broad shield-like chest. -Extra skin on lateral neck - “webbed neck”. -Congenital heart and kidney defects. -Underdeveloped ovaries, lack of secondary sex characteristics, infertile. -Normal intelligence.
Other sex chromosome aneuploidies47 XXX-1 in 1000 -Tall, Menstrual irregularities -Mostly normal -Increased number of X chromosomes (4 or 5 X chr. ) leads to mental retardation and physical abnormality
Other sex chromosome aneuploidies47XYY-1 in 1000. -Tall, acne, speech and reading problems
Cause of cri-du-chat syndrome46XX/Y, del(5p). Deletion of chort arm (p) of chromosome 5. 1 in 50,000 live births.
symptoms of cri-du-chat syndrome-High pitched cat-like cry, caused by abnormal larynx development. -Mental retardation. -Poor muscle tone. -Small head (microcephaly), wide-set eyes (hypertelorism) .

Section 9

Question Answer
Structural aberrations: Deletion a portion of a chromosome is missing or deleted
Structural aberrations: Duplication a portion of a chromosome is duplicated, resulting in extra genetic material
Structural aberrations: Rearrangementsa portion of a chromosome has broken off and turned upside down and reattached (inversions), or formed a circle (rings).
Structural aberrations: Translocation a portion of one chromosome is transferred to another chromosome