3.2 Syllabus
U1. Prokaryotes have one chromosome consisting of a circular DNA molecule.
-Circular DNA contains all the genes needed for the basic life processes of the cell. DNA in bacteria not associated with protein so sometimes described as naked.
-Only 1 chromosome in prokaryotic cell = only single copy of each gene
=Prokaryotes do not have nucleus so genetic material found free in cytoplasm in a region called nucloeid
-2 identical copies are present briefly after chromosome has been replicated but it’s a preparation for cell division. These identical chromosomes are moved to opposite poles and the cell then splits in two.
-Prokaryotes have two types of DNA: • single chromosome • plasmids
-A copy of the chromosome is made just before cell division (by binary fission).
-Only 1 chromosome in prokaryotic cell = only single copy of each gene
=Prokaryotes do not have nucleus so genetic material found free in cytoplasm in a region called nucloeid
-2 identical copies are present briefly after chromosome has been replicated but it’s a preparation for cell division. These identical chromosomes are moved to opposite poles and the cell then splits in two.
-Prokaryotes have two types of DNA: • single chromosome • plasmids
-A copy of the chromosome is made just before cell division (by binary fission).
U2. Some prokaryotes also have plasmids but eukaryotes do not.
-Plasmid: small extra DNA molecules that are commonly found in prokaryotes and are circular and naked which contains few genes that may be useful to the cell. It’s Not responsible for normal life processes –these are controlled by the nucleoid chromosome
=These genes beneficial only when antibiotic is present in environment
-Plasmid not always replicated at the same time as chromosome of prokaryotic cell or at same rate. So there are multiple copies of plasmids in cell and plasmid may not be passed to both cells formed by cell division
-Copies of plasmids passed from one cell to another which allows to spread through population. It’s even possible for plasmids to cross the species barrier.
=Happens if plasmid that’s released when prokaryotic cell dies is absorbed by cell of
by different species.
=Natural method of gene transfer between species.
-Also used by biologists to transfer genes between species artificially.
-Can be incorporated into the nucleoid chromosome
=These genes beneficial only when antibiotic is present in environment
-Plasmid not always replicated at the same time as chromosome of prokaryotic cell or at same rate. So there are multiple copies of plasmids in cell and plasmid may not be passed to both cells formed by cell division
-Copies of plasmids passed from one cell to another which allows to spread through population. It’s even possible for plasmids to cross the species barrier.
=Happens if plasmid that’s released when prokaryotic cell dies is absorbed by cell of
by different species.
=Natural method of gene transfer between species.
-Also used by biologists to transfer genes between species artificially.
-Can be incorporated into the nucleoid chromosome
U3. Eukaryote chromosomes are linear DNA molecules associated with histone proteins.
-Chromosome in eukaryotes composed of DNA and protein
→ DNA is single immensely long linear DNA molecule and is associated with histone
histone proteins. Histones are globular in shape and wider than DNA. There r many histone molecules in chromosome with DNA molecule wound around them.
→Adjacent histones in chromosome are separated by short stretches of the DNA molecule that are not in contact with histones.
= Gives a eukaryotic chromosome the appearance of a string of beads during interphase
-Eukaryotic chromosomes may be up to 85mm in length. To fit such a length of DNA into a nucleus with a diameter of 10 μm it has to be coiled in a predictable fashion that still allows for processes, such as replication and protein synthesis, to occur.
-Nucleosomes are formed by wrapping DNA around histone proteins
→ DNA is single immensely long linear DNA molecule and is associated with histone
histone proteins. Histones are globular in shape and wider than DNA. There r many histone molecules in chromosome with DNA molecule wound around them.
→Adjacent histones in chromosome are separated by short stretches of the DNA molecule that are not in contact with histones.
= Gives a eukaryotic chromosome the appearance of a string of beads during interphase
-Eukaryotic chromosomes may be up to 85mm in length. To fit such a length of DNA into a nucleus with a diameter of 10 μm it has to be coiled in a predictable fashion that still allows for processes, such as replication and protein synthesis, to occur.
-Nucleosomes are formed by wrapping DNA around histone proteins
U4. In a eukaryote species there are different chromosomes that carry different genes.
-Eukaryote chromosome: too narrow to be visible with light microscope during interphase
-During mitosis, meiosis: chromosome become much shorter and fatter by supercoiling so become visible if stains that bind either DNA or proteins are used.
→ 1st stage of mitosis: chromosome can be seen to be double. There are 2 chromatids,
with identical DNA molecules produced by replication
-Chromosome examined during mitosis: Different types can be seen:
→ Differ both in length and in the position of centromere where the 2 chromatids are
held together. Centromere can be positioned anywhere from close to an end to the
centre of the chromosome.
-Every gene in eukaryotes occupy a specific position on 1 type of chromosome: locus of gene.
Each chromosome type therefore carries specific sequence of genes arranged along the linear DNA molecule and in many chromosomes this sequence contains over thousand genes
-Having the genes arranged in a standard sequence along a type of chromosome allows parts of chromosomes to be swapped during meiosis.
-Eukaryotes possess multiple chromosomes. All individuals of a species possess the same chromosomes, with the same gene loci. For example all humans have twenty three pairs.
-Chromosomes can vary by:
• Length – the number of base pairs in the DNA molecule
• Position of the centromere
• Genes occur at a specific locus (location), i.e. it is always found at the same position on the same chromosome (the locus and genes possessed vary between species)
-During mitosis, meiosis: chromosome become much shorter and fatter by supercoiling so become visible if stains that bind either DNA or proteins are used.
→ 1st stage of mitosis: chromosome can be seen to be double. There are 2 chromatids,
with identical DNA molecules produced by replication
-Chromosome examined during mitosis: Different types can be seen:
→ Differ both in length and in the position of centromere where the 2 chromatids are
held together. Centromere can be positioned anywhere from close to an end to the
centre of the chromosome.
-Every gene in eukaryotes occupy a specific position on 1 type of chromosome: locus of gene.
Each chromosome type therefore carries specific sequence of genes arranged along the linear DNA molecule and in many chromosomes this sequence contains over thousand genes
-Having the genes arranged in a standard sequence along a type of chromosome allows parts of chromosomes to be swapped during meiosis.
-Eukaryotes possess multiple chromosomes. All individuals of a species possess the same chromosomes, with the same gene loci. For example all humans have twenty three pairs.
-Chromosomes can vary by:
• Length – the number of base pairs in the DNA molecule
• Position of the centromere
• Genes occur at a specific locus (location), i.e. it is always found at the same position on the same chromosome (the locus and genes possessed vary between species)
U5. Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes.
-If 2 chromosomes have same sequence of genes = homologous
→Homologous chromosomes are not identical to each other since for at least some of genes on them, the alleles (alleles carried at each locus may vary) are different but in same size and structure (one from mom, one from father). They carry same genes at same loci
-If 2 eukaryotes are member of same species -> each of chromosomes in 1 of them to be homologous with at least one chromosome in the other. This allows members of a species to interbreed.
-Somatic cell nuclei(body cell) = diploid 2n
-Homologous chromosomes must be separated in gametes (via meiosis) prior to reproduction, in order to prevent chromosome numbers continually doubling with each generation
→Homologous chromosomes are not identical to each other since for at least some of genes on them, the alleles (alleles carried at each locus may vary) are different but in same size and structure (one from mom, one from father). They carry same genes at same loci
-If 2 eukaryotes are member of same species -> each of chromosomes in 1 of them to be homologous with at least one chromosome in the other. This allows members of a species to interbreed.
-Somatic cell nuclei(body cell) = diploid 2n
-Homologous chromosomes must be separated in gametes (via meiosis) prior to reproduction, in order to prevent chromosome numbers continually doubling with each generation
U6. Haploid nuclei have one chromosomes of each pair.
-Haploid nucleus has 1 chromosome of each type. It has 1 full set of chromosomes that r found in its species. Haploid nuclei in humans: 23
-Gametes are sex cells that fuse together during sexual reproduction. Gametes have haploid nuclei, so in humans both egg and sperm cells contain 23 chromosomes.
-Possess a single gene copy (allele) for each trait
-Haploid cells are also present in bacteria (asexual) and fungi (except when reproducing)
-Gametes are sex cells that fuse together during sexual reproduction. Gametes have haploid nuclei, so in humans both egg and sperm cells contain 23 chromosomes.
-Possess a single gene copy (allele) for each trait
-Haploid cells are also present in bacteria (asexual) and fungi (except when reproducing)
U7. Diploid nuclei have pairs of homologous chromosomes.
-Diploid nucleus has 2 chromosomes of each type so it has 2 full sets of chromosomes that are found in its species. Diploid nuclei in human: 46 chromosomes
-When haploid gametes fuse together during sexual reproduction, zygote with diploid nucleus is produced. When this is divided by mitosis more cells with diploid nuclei are produced. Many living organisms cells consist entirely diploid cells except for the cells that they r using to produce gametes for sexual reproduction
-Diploid nuclei have 2 copies of every gene apart from genes on sex chromosomes.
-> Advantage: Effects of harmful recessive mutations can be avoided if a dominant allele is also present.
-When haploid gametes fuse together during sexual reproduction, zygote with diploid nucleus is produced. When this is divided by mitosis more cells with diploid nuclei are produced. Many living organisms cells consist entirely diploid cells except for the cells that they r using to produce gametes for sexual reproduction
-Diploid nuclei have 2 copies of every gene apart from genes on sex chromosomes.
-> Advantage: Effects of harmful recessive mutations can be avoided if a dominant allele is also present.
U8. The number of chromosomes is a characteristic feature of member of a species.
-Karyotype is a property of the cell described by the number and type of chromosomes
present in the nucleus (of a eukaryote cell).
-Chromosomes of an organism are visible in cells that are in mitosis, with cells in metaphase giving the clearest view.
-Stains have to be used to make chromosomes show up. -> Some stains give each chromosome type of distinctive banding pattern
-If dividing cells are stained and placed on microscope slide and are then burst by pressing on the cover slip, chromosomes become spread. They often overlap each other, but careful searching a cell can usually be found with no overlapping chromosomes. Micrograph can be taken of stained chromosomes.
-More cells are diploid, chromosomes are usually in homologous pairs. They are arranged by size, starting with longest pair and end with the smallest.
-They are determined via a process that involves:
->Harvesting cells (usually from a foetus or white blood cells of adults)
->Chemically inducing cell division, then arresting mitosis while the chromosomes are condensed
The stage during which mitosis is halted will determine whether chromosomes appear with sister chromatids or not
present in the nucleus (of a eukaryote cell).
-Chromosomes of an organism are visible in cells that are in mitosis, with cells in metaphase giving the clearest view.
-Stains have to be used to make chromosomes show up. -> Some stains give each chromosome type of distinctive banding pattern
-If dividing cells are stained and placed on microscope slide and are then burst by pressing on the cover slip, chromosomes become spread. They often overlap each other, but careful searching a cell can usually be found with no overlapping chromosomes. Micrograph can be taken of stained chromosomes.
-More cells are diploid, chromosomes are usually in homologous pairs. They are arranged by size, starting with longest pair and end with the smallest.
-They are determined via a process that involves:
->Harvesting cells (usually from a foetus or white blood cells of adults)
->Chemically inducing cell division, then arresting mitosis while the chromosomes are condensed
The stage during which mitosis is halted will determine whether chromosomes appear with sister chromatids or not
U10.Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex.
-Two chromosomes in humans that determine sex: (XX: female, XY: male)
1. X chromosome relatively large and has its centromere near the middle
2. Y chromosome is much smaller and has its centromere near the end
-Only sex chromosome determines the gender of a fetus.
-X chromosome has many genes that are essential in both males and females so all humans must have x chromosome.
-Y chromosome only has a small number of genes. Small part of the y chromosome has the same sequence of genes as a small part of the X chromosome, but the genes on the remainder of Y chromosome are not found on X chromosome and are not neede for female.
-> 1 Y chromosome gene in particular causes a fetus to develop as a male which is called
either SRY/TDF.
=Initiates the development of male features, including testes and testosterone production. Because of this gene a fetus with 1 X and 1 Y chromosome develops as male.
-Females have 2 X chromosomes. Females pass on one of their X chromosomes in each egg cell, so all offspring inherit an X chromosome from their mother. The sex chromosomes are homologous in females (XX) but are not homologous in males (XY)
-Gender of human is determined as the moment of fertilization by 1 chromosome carried in the sperm. This can either be an X or Y Chromosome. When sperm are formed, half contain the X chromosome and half the Y chromosome.
-Daughters inherit their father’s X chromosome and sons inherit his Y chromosome.
1. X chromosome relatively large and has its centromere near the middle
2. Y chromosome is much smaller and has its centromere near the end
-Only sex chromosome determines the gender of a fetus.
-X chromosome has many genes that are essential in both males and females so all humans must have x chromosome.
-Y chromosome only has a small number of genes. Small part of the y chromosome has the same sequence of genes as a small part of the X chromosome, but the genes on the remainder of Y chromosome are not found on X chromosome and are not neede for female.
-> 1 Y chromosome gene in particular causes a fetus to develop as a male which is called
either SRY/TDF.
=Initiates the development of male features, including testes and testosterone production. Because of this gene a fetus with 1 X and 1 Y chromosome develops as male.
- A fetus that that has 2 X chromosomes and no Y chromosome does not have TDF gene so ovaries develop instead of testes and female sex hormones are produced, not testosterone.
-Females have 2 X chromosomes. Females pass on one of their X chromosomes in each egg cell, so all offspring inherit an X chromosome from their mother. The sex chromosomes are homologous in females (XX) but are not homologous in males (XY)
-Gender of human is determined as the moment of fertilization by 1 chromosome carried in the sperm. This can either be an X or Y Chromosome. When sperm are formed, half contain the X chromosome and half the Y chromosome.
-Daughters inherit their father’s X chromosome and sons inherit his Y chromosome.