Chromosomes

Cairns' technique for measuring the length of DNA by autoradiography Outline conclusions drawn from the images produced using Cairn's autoradiography technique.

-> Cairns was able to produce images of DNA and found out that prokaryotic DNA is circular. -> They were able to produce (later) images of eukaryotic chromosomes (size and measurement). -> Observed DNA replication at the replication fork.

A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length Describe the process of creating a karyogram

1) cells are frozen in metaphase with the use of chemicals to stop spindle fibres from forming. it is stopped in metaphase because at this point the chromosomes are showing 2) hypotonic solutions are added so that the cell would swell up and burst 3) the chromosomes are now spread out from each other and stained to view from a microscope 4) the photograph is taken and cut out to be reorganised

State the number of nuclear chromosome types in a human cell.

23 chromosome in a human cell. This consists of 22 autosomes and 2 types of sex chromosomes.

Description of methods used to obtain cells for karyotype analysis e.g. chorionic villus sampling and amniocentesis and the associated risks Describe the two procedures for obtaining fetal cells for production of a karyotype.

Amniocentesis: needle is inserted into uterus though the stomach. Fluid is drawn containing fetus cells. Karyotype is done to make a karyogram. Chronic villus sampling: a thin tube is inserted into the vagina and into the uterus. small sample of DNA of the placenta is removed that contains baby cells, and karyotype.

In a eukaryote species, there are different chromosomes that carry different genes. List three ways in which the types of chromosomes within a single cell are different.

Chromosomes can differ in length. The type of gene in different chromosome can differ. Location of centromere can differ.

Diploid nuclei have pairs of homologous chromosomes Define diploid.

Diploid describes a cell that contain two copies of each chromosome. Nearly all the cells in the human body carry two homologous, or similar, copies of each chromosome.

Developments in research follow improvements in techniques- autoradiography was used to establish the length of DNA molecules in chromosomes Outline the advancement in knowledge gained from the development of autoradiography techniques.

Discovery of where specific substances were located in cells or tissues. Cairns obtained images of whole DNA molecules from E. Coli. Revealed forks in DNA for the first time Used to investigate structure of Eukaryotic chromosomes Ability to measure the length of eukaryotic chromosomes

Haploid nuclei have one chromosome of each pair List example haploid cells.

Female egg and male sperm.

Diploid nuclei have pairs of homologous chromosomes State the human cell diploid number.

For humans, the diploid chromosome number equation is 2n = 46 because humans have two sets of 23 chromosomes (22 sets of two autosomal or non-sex chromosomes and one set of two sex chromosomes).

Haploid nuclei have one chromosome of each pair Define haploid.

Haploid. of a cell or organism having a single set of chromosomes.

Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes Define homologous chromosome

Homologous chromosomes are chromosomes that share: The same structural features (e.g. same size, same banding patterns, same centromere positions) The same genes at the same loci positions (while the genes are the same, alleles may be different)

Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum Explain the relationship between the number of human and chimpanzee chromosomes

Humans have 46 chromosomes and chimpanzees have 48. Research have shown that it was possible that the cimpanzees' chromosome merged (chromosome #2) into 1 human chromosome.

Use karyograms to deduce sex and diagnose Down Syndrome in humans Describe the use of a karyogram to diagnose Down syndrome.

If a karyogram shows a trisomy on chromosome 21, meaning that there is three chromosomes in the set of 21 instead of 2 then it is diagnosable as down syndrome.

Use karyograms to deduce sex and diagnose Down Syndrome in humans Distinguish between a karyogram and a karyotype.

Karyotypes describe the number of chromosomes and what they look like (size bands and centromere placement). Karyograms are the study of the whole set of chromosomes arranged in pairs by size, and position of the centromere.

Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum Explain why the typical number of chromosomes in a species is always an even number.

Most eukaryotic species has an even number in the offspring because of sexual reproduction.• Each parent gives one set of chromosome, resulting in an even number in baby.

The number of chromosomes is a characteristic feature of members of a species State that chromosome number and type is a distinguishing characteristic of a species.

Organism with a different number of chromosome are unlikely to be interbred.• Therefore all interbreeding members of a species needs to have the SAME # of chromosomes.

Describe prokaryotic DNA

Prokaryotes have one Chromosome consisting of circular DNA. They DO NOT posses a nucleus, instead the genetic material is found free in the cytoplasm in a region called the nuclei. The genetic material of a prokaryote is naked and not associated with proteins for additional packaging.

Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes State a similarity and a difference found between pairs of homologous chromosomes.

Similarity: same gene loci, majority of DNA sequence is same, same length (bp), same centromere position, same banding patterns. Differences: 2 different origins, different alleles of genes.

Relationship between plasmids and prokaryotes

Some prokaryotes have plasmids but eukaryotes do not. Plasmids are small circular DNA molecules that contain only a few gens and are capable of self replication.

Haploid nuclei have one chromosome of each pair State the human cell haploid number.

The haploid number for humans is 23 n=23.

Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum State the minimum chromosome number in eukaryotes.

The minimum # of chromosomes in a eukaryote is 2n=2. The "Jack jumper ant".

The number of chromosomes is a characteristic feature of members of a species List mechanisms by which a species chromosome number can change.

The number of chromosome can change during evolution. Chromosomes numbers can decreased through fusing or can increase by splitting.

Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum Explain why the chromosome number of a species does not indicate the number of genes in the species.

The number of chromosomes does not indicate the number of genes. It's possible to have one large chromosome with many genes or many smaller chromosomes with fewer genes. Likewise, it's possible to have large chromosomes with relatively few genes or smaller chromosomes that are packed full of genes!

Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex Outline the structure and function of the two human sex chromosomes.

The x is chromosome is larger than the y chromosome.

A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length List the characterisitcs by which chromosomes are organized

They are matched by size, banding patterns, position of centromere, and ordered from longest to shortest.

Use karyograms to deduce sex and diagnose Down Syndrome in humans Deduce the sex of an individual given a karyogram.

XX female XY male

Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex Outline sex determination by sex chromosome

XX: Girl XY: Boy Due to the male having both chromosomes they have a higher of passing any of it which determines the offspring's gender

Diploid nuclei have pairs of homologous chromosomes State an advantage of being diploid.

You'd have a copy of each of your chromosome, therefore 2 copies of your genes. In any case that the chromosome is mutates or broken, the copy of the allele can prevent a negative effect.

Cairns' technique for measuring the length of DNA by autoradiography Describe Carin's technique for producing images of DNA molecules from E. Coli.

a) cells were grown in a culture with the presence of radioactive thymine. cells would replicate with thymine. b) cells were placed onto a dialysis membrane and cell would be slowly digested leaving only DNA. c) thin film of photographic envision was placed on top of the membrane and left in darkness for 2 months. d) after 2 months, the film is placed under a microscope, where the dark spots are (from radioactivity decay) was where the DNA was.e) image of DNA produced.

Diploid nuclei have pairs of homologous chromosomes Outline the formation of a diploid cell from two haploid gametes.

as sexually reproducing organisms receive genetic material from both parents, they have two sets of chromosomes (diploid cells)to reproduce these organisms must create sex cells (gametes) with half the number of chromosomes (haploid)when two haploid gametes fuse, the resulting diploid cell (zygote) can grow and develop into a new organism