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Concept Dis. Ch 3

Chromosomes, Genes & Cell Division

activities of cells controlled by chromosomes present in nucleus
chromosomes exist in pairs in all somatic cells
genome is ___ for every cell within an individual identical
___ chromosome in females will differ randomly from cell to cell inactive X
types of cells that do not divide nerve, skeletal, & cardiac
spermatogenesis is ___ continuous
spermatogenesis produces more ___ cells from each precursor useful
recessive gene can only be expressed through a heterozygous pairing
HLA haplotypes combine in such a way that ___ are possible for any combination of 2 parents 4 separate pairings
diseases caused by a failure of mitochondrial DNA are usually transmitted from the mother
Gene therapy typically uses a virus to introduce desirable genetic material into the patient
practice of inserting genetic material into bacterium/yeast to synthesize desired pharmaceutical products is called recombinant DNA technology, genetic engineering &/or gene splicing
somatic cells are cells other than those giving rise to eggs/sperm
one member of each paired chromosome is derived from the male and female parent, respectively
homologous chromosomes matched pair of chromosomes, derived from each parent
in humans the normal chromosome component is 22 pairs of autosomes
autosomes chromosome other than a sex chromosome
sex chromosomes X & Y chromosomes that determine genetic sex
genes units of inheritance & segments of DNA chain determining some property of the cell
genes are arranged along the chromosome like "beads on a string"
sum total of all the genes contained in a cell's chromosomes, & is same for all cells, is its genome
genes sometimes code for specific enzymes/other proteins need for cell function
genes are also known to code so that they can act as regulators controlling activities of neighboring genes
gene product protein/enzyme specified (coded) by a gene
only a small % of total DNA in genome consists of genes
it is not yet known the functions of DNA remaining, which are interspaced between genes
exons part of chromosome DNA chain coded for specific protein/enzyme
intron non coding part of chromosomal DNA chain
when makes gene product both exons & introns are transcribed
removed from cytoplasm, when making gene product, before RNA leaves nucleus introns
only coding sequences that specify ___ to be constructed delivered to ribosomes by mRNA protein
genes expressed in given cell determine both its structure & function
Human Genome Project international collaboration of scientists who mapped nucleotide sequence of entire human genome
genomics study of gene structure
attempts to correlate structure of genes with effects of genes on individual genomics
gene expression process, or regulation of process, by which effects of a gene are manifested
single nucleotide polymorphism (SNP) genetic polymorphism between 2 genomes that based on deletion/insertion/exchange of single nucleotide
SNPs are pronounced as "snips"
may effect how genes function single nucleotide variation
sex cells of normal female contain two X chromosomes
sex cells of normal male contain 1X and 1Y chromosome
female sex cells function as though they contain genetic material equivalent to 1 X chromosome
genetic activity of both X chromosomes, in a female, is only essential during first wk of embryonic development
inactivated X chromosome appears as a small mass of chromatin attached to nuclear membrane of somatic cells
Barr body inactivate X chromosome applied to nuclear membrane in female
also called sex chromatin body Barr body
Lyon hypothesis X-chromosomes in excess of 1 inactivated on random basis at an early stage of embryonic life, leading to mosaicism for X linked genes in female, since paternal X chromosome inactivated in some cells & maternal 1 in remainder
mosaicism presence in an individual of two or more cell lines that are karyotypically or genotypically distinct and are derived from a single zygote
combination of staining & ultraviolet light makes it possible to determine X & Y chromosomes composition of intact cells
during process of staining, cells of normal male posses florescent spot but lack sex chromatin body
during process of staining, cells of normal female posses sex chromatin body but lack florescent spot
cell division in which chromosomes duplicated in daughter cells are identical to those in parent cell mitosis
characteristic cell division found in all cells of human body except in gametes
meiosis special type cell division occurring in gametes in which # chromosomes reduced by 1/2 in ovum & sperm
gametogenesis development of mature eggs & sperm from precursor cells
daughter cell cell resulting from division of single cell (called parent cell)
mitosis is characteristic of all___ however not all mature cells are able to divide somatic cells
divide as needed to replace lost/damaged cells, or to heal an injury liver & connective tissues cells
rate of cell division is controlled closely to match body's need and excess cells are not normally produced
growth factors soluble growth promoting substance produced by cells attached to receptors on cell membrane of other cells
activates receptors & initiates events leading to growth/division of target cells growth factors
depending on biochemical signals sent to "machinery" inside cell it will either grow & divide or growth is inhibited
cells are programmed to undergo ____ number of cell division and then they die a limited
chromatids one of two newly formed chromosomes held together by centromere
the process by which chromatids separate mitosis
each chromosome duplicates itself before cell division, so in a somatic cell just before cell division there are actually 96 chromosomes
when chromosomes shorten during cell division, term chromatid is applied to still-joined chromosomes
as soon as chromatids separate they are called chromosomes again
during prophase each chromosome thickens & shortens
centrioles migrate to opposite poles of cell forming mitotic spindle during prophase
mitotic spindle consists of small fibers radiating in all directions from centrioles
some of the ____ attach to chromatids during prophase mitotic spindle fibers
the nuclear membrane breaks down towards the end of prophase
during metaphase the chromosomes line up in the middle of the cell
during metaphase, chromatids are partially separated but still remained joined at the centromere
centromere structure that joins each pair of chromatids formed by chromosome duplication
site where spindle fibers are attached during metaphase centromere
chromatids constituting each chromosome separate & are pulled to opposite poles of cell by spindle fibers during anaphase
nuclear membranes of 2 daughter cells reform & cytoplasm divides forming 2 daughter cells during telophase
synapse paring of homologous chromosomes in meiosis
crossover interchanging of genetic material between homologous chromosomes during synapse & meiosis
pairing of homologous chromosomes & interchange of genetic material during prophase is the characteristic feature of meiosis
in female, 2 X chromosomes synapse in same way as autosomes
in male, X & Y chromosomes synapse end to end & do not exchange segments
each daughter cell created during meiosis contains only one member of each homologous pair of chromosomes & chromosomes are not exact duplicates of parent
during 2nd meiotic division 2 chromatids composing each chromosome separate, 2 daughters formed each containing 1/2 of normal # of chromosomes
1st meiotic division daughter cells receive 23 chromosomes
2nd meiotic division daughter cells receive 23 chromosomes because 2nd division is similar to mitotic division
gonads testes & ovaries
contain precursor cells/germ cells capable of developing into mature sperm/ova
mature germ cells are called gametes
gametogenesis process by which gametes are formed
spermatogenesis process by which sperm form
oogenesis process by which ova form
spermatogonia precursor cells in testicular tubules
singular term for spermatogonia spermatogonium
each spermatogonium contains 46 chromosomes
spermatogonia divide by mitosis to form spermatocytes
spermatocytes contain ___ chromosomes 46
primary spermatocytes divide by meiosis
spermatids germ cells in late stage of sperm development just before complete maturation to form mature sperm
after 1st meiotic division two 2ndary spermatocytes divide by 2nd meiotic div. forming 2 spermatids containing 23 chromosomes
entire process of spermatogenesis takes about 2 months
sperm are produced continually
precursor cells of ova are called oogonia
singular term for oogonia is oogonium
each oogonia contains 46 chromosomes & continually divide in fetal ovaries before birth into oocytes containing 46 chromosomes
oocytes become surrounded by granulosa cells
granulosa cells cells lining ovarian follicle
primary oocytes in follicles begin prophase of 1st meiotic division during fetal life but do not follow the division through to completion
large number of primary follicles are formed, but many degenerate during infancy & early childhood
cyclic ovulation begins under influence of pituitary gonadotrophic hormones, follicle-stimulating hormone & luteinizing hormone
when oocyte is discharged it completes its first meiotic division, giving rise to 2 daughter cells-unequal in size
after oocyte completes 1st meiotic division one daughter cell receives 1/2 of chromosomes & almost all of cytoplasm
daughter cell receiving 1/2 of chromosomes & almost all of cytoplasm is called secondary oocyte
daughter cell receiving 1/2 of chromosomes & almost none of cytoplasm is called first polar body
first polar body is discarded
2ndary oocyte begin 2nd meiotic division leading to formation of mature ovum & 2nd polar body - each containing 23 chromosomes
unless ovum is fertilized meiotic division is not completed
each precursor cell, in spermatogenesis, produces four spermatozoa
each precursor cell, in oogenesis, produces one ovum
oocytes are not produced continually; all oocytes present in ovaries were formed before birth
oocytes remain in a prolonged prophase of meiotic division from fetal life until ovulated
presence of abnormalities in chromosome number/structure can be detected by culturing cells in suitable medium
in order to study chromosomes, lymphocytes can be induced to undergo mitotic division
chemicals are added to lymphocytes to stop the mitotic division once the chromosomes have become separate & distinct, which causes accumulation of cells arrested in mitosis in the culture medium
normal dividing cell arrested in mitosis contains 46 chromosomes, each consisting of chromatids joined at their centromeres
size, location of centromere, arms of chromosome, & pattern of light/dark bands along chromosomes are classifications of chromosomes
karyotype arrangement of chromosomes from single cell arrangement in pairs in descending order according to size of chromosomes & position of centromeres
locus position of gene on chromosome
one of several related genes that may occupy same locus on a homologous chromosome alleles
alleles are always found on the same ___ of the gene locus
if both alleles are the same an individual is homozygous
if both alleles are different an individual is heterozygous
expression of the gene manifestation of a heritable trait in individual carrying gene(s) that determine it
a recessive gene expresses a trait only when present in the homozygous state
gene that expresses a trait in either the heterozygous/homozygous state dominant gene
sex-linked gene present on X chromosome
term applied to genes located on X chromosome in male hemizygous
when both alleles of a pair are expressed the alleles are called codominant
gene imprinting modification of gene during spermatogenesis or oogenesis
gene imprinting does not change the structure of the gene only the way the gene is expressed in offspring
mitochondria have small amounts if DNA that contain some of genes required for synthesis of energy-generating mitochondrial proteins
in mitochondria genes determine various enzymes & other proteins that produce ATP-generating machinery
mutations to mitochondrial DNA may take place during duplication/replication
transmission of abnormal mitochondrial DNA is almost always from the mother, because ovum contains large number of mitochondria
antigens present on cells are determined by cluster of genes on chromosome 6
major histocompatibility complex MHC group of genes on chromosome 6 that determine antigens on surface of cells
MHC, in humans these cell surface proteins/antigens were 1st identified on peripheral blood leukocytes
designations HLA complex & HLA antigen and MHC complex & MHC antigen are used interchangeably
self-antigens, which set us apart from one another HLA complex & HLA antigen and MHC complex & MHC antigen
antigenicity of HLA complex/antigens depends on whether one's own proteins or HLA proteins of another person
self-antigens are unique for person possessing them & are recognized by immune system as being a part of that person, or not foreign
non-self antigens foreign proteins
non-self antigens in another person for whom they are antigenic cause an immune response
cells containing MHC proteins different from transplant recipients caused rejection of transplanted organ unless immune system is suppressed
there are 1200 different allelic genes that can occupy gene loci with HLA system
each allele, in a locus, is designated specific letter to identify locus and number to indicate allele
haplotype set of HLA genes on one chromosome that is transmitted in a set
each person has two haplotypes, each consisting of four HLA genes
two haplotypes together determine a total of eight HLA proteins on the cell
during HLA typing of organ donors, one attempts to match major antigens of donor as closely as possible, so graft has better chance to survive
MHC Class I proteins are determined by HLA-A, HLA-B & HLA-C genes
present on all nucleated cells & blood platelets MHC Class I proteins
platelets cytoplasmic fragments of large nucleated bone marrow cells
because cells lack nuclei, MHC Class I proteins are not found on surface of red blood cells
MHC Class II proteins are determined by HLA-D genes
only found on macrophages (and related cells having same functions) & some types of lymphocytes MHC Class II proteins
child will only have ___ haplotype in common with each parent one
from each parent, a children will inherit one of two possible haplotypes
due to way chromosomes inherited from parent to chil, a child can have any of four possible combinations of haplotypes
presence of this HLA gene indicates a predisposition to an arthritis of spine & sacroiliac joints HLA-B27
certain HLA-D types have been associated with type 1 diabetes & Rheumatoid Arthritis
reason for association of specific disease with certain HLA type in related to association of HLA gene complex to genes controlling immune system response
those with certain HLA types appear to have genes less capable of regulating immune responses when subjected to antigenic stimulation
autoimmune diseases disease associated with formation of cell-mediated/humoral immunity against one's own cells/tissue components
recombinant DNA technology methods for combining gene from one organism, such as specifying insulin synthesis, with gene's from another organism, such as bacterium
genetic engineering genes being manipulated; same as recombinant DNA technology
gene splicing piece of genetic material being cut open & another piece of genetic material being spliced into it
plasmid small, circular DNA molecule separate from main bacterial chromosome
circular plasmids are opened, during recombinant DNA technology, by means of enzyme that "cuts" plasmid DNA so desired gene can be inserted btwn cuts end of plasmid
DNA tech has been source of insight into molecular basis of genetic diseases by increasing understanding of normal gene structure & function
possible to identify mutation of gene in fetal cell DNA obtained from amniotic fluid
gene therapy normal gene inserted into defective cell, inserted gene compensates for missing/dysfunctional gene
successful application of gene therapy requires identify/select correct gene to insert, choose proper cell to receive gene, effective means of inserting gene into cell, ensure inserted gene able function long enough for desired effects
the agent used to introduce gene into selected cell, in gene therapy, is called vector
vector in gene therapy is usually a virus, coupling to lipid or other material taken into cell by endocytosis
gene therapy targets somatic cells
lymphocytic leukemia was a side effect of gene therapy because gene inserted into lymphocyte-producing stem cell which disrupted function of other cells regulating growth & function
alternate forms of the same gene are called alleles
being characteristic of germ cells, chromosomes reduced by half, & entails two separate divisions vs.being characteristic of somatic cells, no loss of chromosomes, & only one division major differences between meiosis vs. mitosis
Created by: lfrancois