Identify the composition of chromosomes in eukaryotes.
They consist of DNA and proteins.
Experiments by Oswald Avery and his co-workers in 1943, showed that if extracts from the genetic material from bacteria were treated with enzymes that broke down carbs, proteins or lipids, then the bacteria were still able to 'transform' (the genetic mate
They drew the conclusion that the main chemical compound of genetic material was DNA.
Distinguish between a gene and an allele.
A gene a heritable factor that determines a specific characteristic. Ex: Gene for eye color An allele is one form of a gene that can occupy the locus for the characteristic. Ex: Blue eye color (b) Brown eye color (B)
Define Genome.
The complete genetic information of an organism.
Define Gene Mutation.
A permanent change in the genetic info in a gene. It can involve one or more base pairs.
Spontaneous Mutation
The causative agent can't be identified.
Induced Mutation
The causative agent can be identified. Ex: x-rays, gamma rays, or certain chemical substances such as benzene.
Base Substitution Mutation
A point mutation where one base is substituted for another in the genetic code for a particular gene.
Identify the mutation involved in our favorite disease that we always seem to talk about, sickle-cell anemia.
A point mutation to an adenine on the beta chain of hemoglobin chromosome 11.
Explain how the mutation in sickle-cell anemia affects transcription and translation.
The gene mutation GAG to GTG causes the amino acid glutamic acid to be a valine in transcription and translation. The expression of the slightly different amino acid changes the properties ... I think I'll come back to this one because I fell asleep writi
The diagram shows the structure of normal red blood cells and sickle-shaped red blood cells. Describe how sickling affects the functioning of red blood cells.
Sickling decreases the elasticity and flexibility of red blood cells making them more rigid and unable to flow through narrow capillaries. The sickle cells clump together causing vessel occlusion. This deprives the body's cells of oxygen and cellular meta
Explain why sickle-cell trait is advantageous in some regions of the world.
Sickle-cell trait refers to the heterozygous condition where a person has 1 defective gene for sickle-cell anemia and 1 gene for normal red blood cells. Due to incomplete dominance, heterozygotes (carriers of sickle cell gene) show some signs of sickling
Non-Disjunction
a mistake driving cell division when homologous chromosomes fail to separate properly or sister chromatids fail to separate. It can occur in either meiosis or mitosis and leads to one daughter cell missing a chromosome and one with an additional chromosom
Meiosis
A type of cell division that results in haploid daughter cells. It is only found in sexually reproducing organisms and is a reduction division with the diploid number of (2n) as found in body cells and a haploid number (n) for the gametes.
Homologous Chromosomes
The corresponding pairs that look the same except for the sex chromosomes X and Y. They have the same length, genes for the characteristics at corresponding loci, same centromere position and in sexually reproducing organisms one is inherited from each pa
Crossing Over
The exchange of certain sections of chromosomes when the homologous chromosomes are paired in the tetrad in meiosis.
Chiasma (Plural Chiasmata)
The point at which the chromosomes cross and break.
Define aneuploidy
Is a genetic condition where there is a abnormal chromosome number, e.g there are 1 more copy of chromosomes or there is a deficiency in 1 or more chromosomes.
What is Down syndrome
is a genetic condition caused by the presence of additional genetic info from chromosome 21
describe main cause of down syndrome
The main cause around 96% of cases, is the presence of a complete extra copy of chromosome 21, called trisemy 21, trisemy 21 is mainly caused by non-disjunction of chromosomes during meiosis in the formation of the gamete. This means that after fertilizat
Outline how translocation can lead to down syndrome.
translocation occurs when genetic material from 1 chromosome attaches to another chromosome. in down syndrome, genetic material from #21 attaches to another chromosome, e.g from the 13-15 group or the 11-22 group. the most common form of trans location th
explain how non-disjuction can lead to mosaic down syndrome
mosaic down syndrome refers to a genetic condition where some cells show trisomy 21 while other cells have the normal 46 chromosomes. if a non-disjuction occurs after conception when the embryo is undergoing early mitotic divisions, some cells will be aff
Define karyotype
is an arrangement of chromosome pairs ascending to size A shape
Outline how karyotypes are prepared
its prepared by collecting cells, culturing them and then halting cell division at metaphase. the cells are stained and then the chromosomes are sorted accordingly to size and structure
identify cells likely to be collected for karyotyping.
Cells likely to be collected for karyotyping include embryonic cells collected by amniocentesis or chorionic villus sampling to check for abnormalities in the developing child. Blood cells from adults or children are collected for diagnosis of chromosomes
interphase
chromosomes replicates forming identical sister chromatids joined by centromere
prophase 1
diploid $ of chromosome appear as long, then threads shorten, thickened and homologous chromosomes pair with each other. crossing over can occur. Nuclear membrane disappears
metaphase 1
pairs of homologous chromosomes in the form of tetrads lined up at the equator with 1 chromatid of each pair facing each pole.
anaphase 1
chromosomes move towards the poles pulled by spindle fibers. sister chromatids stay attached.
telophase 1 and cytokinesis
each half of cell complete haploid set with 2 sister chromatids. Cytokinesis and divisions of cytoplasm occurs of the same time. 2 haploid daughter cells are formed.
prophase 2
spindle aparatus forms.
metaphase 2
Sister chromatids line up equator and attach to spindle fibers
anaphase 2
centromeres seprate and sister chromatids are pulled apart and move to opposite poles.
telophase 2 and cytokinesis
Nuclei form, chromosomes begin condensing and cytokinesis occcurs leading to 4 daughter cells.
Identify Down Syndrome and sex in a human karyotype.
If the child has three copies of chromosome 21 the genetic disorder is down syndrome or trisomy 21. If the child has an X and Y chromosome then the child is male.
Identify sex in a human karyotype.
A female has two X chromosomes. Male has one X and one Y.
Genotype
The genes present or the set of alleles present, whether they produce an effect or not.
Phenotype
The appearance and functioning of an organism from the genes present and due to the effect of the environment.
Dominant Allele
The form of a gene that will determine the resulting appearance in a heterozygous genotype.
Recessive Allele
The form of a gene that is masked by the dominant allele in a heterozygous genotype.
Codominant Alleles
The forms of genes that have equal influence in a heterozygous genotype.
Locus
The location on a chromosome for a particular gene.
Homozygous
Both alleles for a particular gene are identical.
Heterozygous
The two alleles for a particular gene are different.
Carrier
A person heterozygous for a trait with a harmful recessive gene and not showing the characteristic though able to pass the allele to offspring.
Test Cross
Breeding sequence with a homozygous recessive to determine the genotype of an individual- whether the individual showing the trait is homozygous or heterozygous.