Studied by 1 personchromosome
A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins.
difference between dna in eukaryotes and prokaryotes
Prokaryotic- one chromosome, ring shaped, in cytoplasm, made of dna
Eukaryotic- many chromosomes, made of dna, in strands, in nuclei
what is sickle cell anemia
The hemoglobin molecule, resulting in crescent shaped RBCs which have a difficult passing through blood vessels. Occurs from a base substitution mutation where valine is produced instead of glutamine.
how to determine sex by karyogram
x is longer than y. if it is xx, it is female, if it is xy, then it is
describe first phase of meiosis
Interphase (s-phase)
In the S-phase of the interphase before meiosis begins, DNA replication takes place.
Chromosomes are replicated and these copies are attached to each other at the centromere.
The attached chromosome and its copy are known as sister chromatids.
Prophase I
DNA supercoils and chromosomes condense
-nuclear membrane dissolves
centrioles migrate to the poles of the cell.
Crossing-over between chrimosomes can take place. This results in recombination of alleles and is a source of genetic variation in gametes
Metaphase I
-bivalents line up at the equator
Random orientation occurs - each bivalent aligns independently and hence the daughter nuclei get a different mix of chromosomes.
This is a significant source of genetic variation: there are 2n possible orientations in metaphase I and II. That is 223 in humans - or 8,388,068 different combinations in gametes!
Anaphase I
Homologous pairs are separated and pulled to opposing poles.
Spindle fibres contract
This is the reduction division - the bivalent is split and half the chromosomes move towards each pole.
Telophase I
Cytokinesis
New nuclei membrane forms
Chromosomes decondense
how does down syndrome occur
3 copies of chromosomes on chromosome 21
genome size
The amount of DNA contained in one copy of a genome
difference of karyotype and karyogram
A karyogram is A diagram or photograph of the chromosomes present in a nucleus (of a eukaryote cell) arranged in homologous pairs of decreasing length
A karyotype is A property of the cell described by the number and type of chromosomes present in the nucleus (of a eukaryote cell)
Explain why meiosis is described as a reduction division.
because it reduces the number of chromosomes from 46 chromosomes or 2n to 23 chromosomes or n (n describes a single chromosome set).
why does crossing over occur
to create diversity, bigger allele pool
Disjunction
the separation of homologous pairs of chromosomes following meiotic synapsis
Compare and constrast between the outcomes of non-disjunction in anaphase I with anaphase II
-both spiral and use endoflagellum to cause diseas
Chorionic Villus Sampling
sampling of placental tissues for prenatal diagnosis of potential genetic defects
Amniocentesis
A technique of prenatal diagnosis in which amniotic fluid, obtained by aspiration from a needle inserted into the uterus, is analyzed to detect certain genetic and congenital defects in the fetus.
chromatid
one of two identical "sister" parts of a duplicated chromosome
symptoms of sickle cell anemia
Causes blood to sickle so it is unable to carry as much oxygen to the cells of the body and can get stuck in vessels. Pain in the hands, feet, anemia, fatigue, yellowing of skin and eyes, rediced life span
advantages in technology that made human genome project possible
¥ Biotechnology techniques such as PCR are used to prepare samples: the DNA needs to be copied to prepare a sufficiently large pure samples to sequence
¥ Computers automate the sequencing process
¥ Fluorescent labeling techniques enable all four nucleotides to be analysed together
¥ Lasers are used to fluoresce the dye markers
¥ Digital camera technology reads the dye markers
Computers are used to assemble the base sequence
John Cairn
grew bacteria in media containing radioactive nucleotides, isolated the dna, and placed it on a electron-microscope grid covered with photographic emulsion
chromosome
made of DNA and protein; contains genes; structural units that are made up of DNA and proteins; by coiling DNA around proteins many times, large amount of information can be stored inside nucleus
genes
heritable factors that control specific characteristics; various specific forms of a gene (ex: 2 forms of gene that influences height=tall or short); different alleles are due to a slight variation in the base sequence;
multiple alleles: more than 2 alleles for one gene (ex: blood type), occupy same locus on one chromosome
alleles
different forms of a specific gene
gene locus
specific position of a gene on a chromosome
What do all individuals of a species carry?
same genes at same loci on same chromosome
human body cell (somatic cells)
have 46 chromosomes
human sex cells (gametes)
have 23 chromosomes
members of a species have...
same number of chromosomes each with same genes in sane gene loci (number of chromosomes varies between species)
mutations
new alleles are formed by mutation--> random changes, base substitution (change in one base in sequence of a gene which may or may not change amino acid sequence), neutral or harmful, can be lethal, mutations in somatic cells are not passed on but mutations in gametes are
Sickle cell disease
single base substitution leads to production of valine instead of glutamine; leads to production of abnormal red blood cells
gene mutations (gene wrongly expressed)
mutation is a permanent change in the base sequence of DNA; it is cumulative effects of millions of mutations and natural selection that have allowed all organisms to evolve from simpler ancestors; not all mutations cause disease;
mutations more likely to occur when....
exposed to mutagens like radiation and some chemicals
malaria
parasitic disease caused by a plasmodium cell; cannot infect sickle cells so people with sickle cell trait are resistant to malaria (sickle cell more prevalent in areas where malaria is endemic=natural selection)
genome
whole of the genetic information of an organism; humans: all DNA in nucleus & mitochondria; plant: all DNA in nucleus, mitochondria, & chloroplast; prokaryotes: smaller circular DNA & plasmids
human genome project
23,000 protein encoding genes; highly repetitive sequences (satellite DNA) important to gene expression
bacterial chromosomes
circular DNA molecule consisting of one chromosome (not associated with proteins, one copy of each gene)
plasmids
some prokaryotes contain them; extra DNA molecules (small and circular), not associated with proteins, not needed for basic life functions, multiple copies may be present, not always passed on in cell division, can be transferred from one cell to another (transformation)
plasmid used in bacterial transformation
eukaryote chromosomes
linear DNA associated with histone proteins; different chromosomes carry different genes (different in size & location of centromere, 23 types of chromosomes in human cells, each chromosome can carry thousands of genes); homologous chromosomes (carry same gene sequences, but not necessarily same alleles, allows for interbreeding, 1 from mom & 1 from dad)
sister chromatids
exact replicas
haploid
one chromosome of each type, humans=23, ex: gametes, end result of meiosis (4 haploid cells)
diploid
pairs of homologous chromosomes-2 copies of every gene; humans 26 chromosomes, ex: somatic cells, end result of mitosis (2 genetically identical diploid cells)
sex chromosomes
XX=female (all offspring inherit one X chromosome from mother)
XY=male (offspring inherit either an X or a Y chromosome from their father; determines sex of offspring)
X Chromosome
carries genes essential for males and females; one X chromosome is silenced in females during embryonic development
Y Chromosome
mostly carries genes only necessary for male development; houses the SRY gene (initiates development of male features); smaller
Punnett square
karyograms
shows chromosomes of an organism in homologous pairs of decreasing length (chromosomes are best seen during metaphase with a stain, some stains provide distinctive banding pattern for each chromosome)
arrangement of chromosomes that allow for distinctions to be made
size and structure, position on centromere, pattern of banding
karyotypes
property of an organisms studied through observations of a karyogram (can determine sex, detect down syndrome and other chromosomal abnormalities in fetal cells); chromosomes arranged in pairs according to size and structure
Downs Syndrome karyogram
meiosis
two cycles of cell division (1 cell-->2 cells-->4 cells); reduces chromosome # by half (diploid-->haploid); reduction division
homologous chromosomes
in pairs (inherited maternally & paternally); have same genes (but may different alleles); will have same size, centromere location
non-disjunction
can happen in anaphase; spindle fibers fail to separate chromosomes (both go to one pole); results in abnormal chromosome # (too few/many)
trisomy 21
down syndrome is a chromosomal condition that is associated with intellectual disability
klinefelter syndrome
a chromosomal condition that affects male physical and cognitive development
turner's syndrome
chromosomal condition that affects development in females; most common feature is short stature
crossing over
occurs during prophase 1; equivalent pieces of chromosomes are traded; new combinations of alleles; genetic diversity
random orientation of maternal & paternal chromosomes
a maternal chromosome line up with the homologous paternal chromosome but the side of the cell is random
genetic diversity
recombination: combinations of alleles different from the parents'; due to: random orientation of chromosomes, crossing over; benefit because diversity leads to flexibility in a changing environment
Mendel's Laws
discovered the basic laws of genetics although no one knew the shape of DNA; wrote his laws based on the # and type of peas that each pea plant produced
traits are inherited as discrete units
law of segregation (each parent has two copies of each trait; each parent passes on one copy-caused by reduction division in meiosis)
independent assortment (allele inherited for one trait does not determine the alleles inherited for other traits-caused by random assortment and crossing over)
gametes
haploid cells that result from meiosis (contain one allele of each gene); sperm or egg (fuse to form a diploid cell)
zygote
start of life; fusion of gametes results in diploid #, 2 alleles of each gene present (same or different), 1 from mom and 1 from dad, combination of alleles depends on type and # of alleles present
genotype
combination of alleles present (TT, Tt)
phenotype
physical expression of genotype (tall, short)
codominant
two alleles are equally strong so both are expressed; ex: AB Blood
ABO blood system
controlled by tri-allelic gene; generates 6 genotypes; alleles control production of antigens on surface of red blood cells; allele I^A produces antigen A; I^B produced antigen B; I produced no antigen
Note
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