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in the nucleus of every cell there are a number of long threads called chromosomes

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in the nucleus of every cell there are a number of long threads called chromosomes

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each chromosome contains one very long molecule of DNA

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each chromosome carries instructions for making many different proteins

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each chromosome carries instructions for making many different proteins

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the DNA molecule carries a code that instructs the cell about which kinds of proteins it should make

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is a part of a DNA molecule coding for one protein

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you inherited the genes from your parents

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you inherited the genes from your parents

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the genes on your chromosomes determine all sorts of things about you: physical characteristics or the risk to have a genetic disease

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humans have 46 chromosomes inside each cell, all with many genes on them

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humans have 46 chromosomes inside each cell, all with many genes on them

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every cell in the body has an exact copy of all genes

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there is no one else in the world with exactly the same combination of genes

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humans begin life as a single cell, a zygote-, formed by the fusion of an egg cell and a sperm cell

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humans begin life as a single cell, a zygote-, formed by the fusion of an egg cell and a sperm cell

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the nuclei of each of these gametes contained a single complete set of 23 chromosomes. when they fused together, they produced a zygote with 46 chromosomes

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the two chromosomes of a pair in diploid cells are called HOMOLOGOUS CHROMOSOMES

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the two chromosomes of a pair in diploid cells are called HOMOLOGOUS CHROMOSOMES

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one is from the person's mother and the other from their father

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chromosomes of humans arranged in order, largest first

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Soon after the zygote was formed, it began to divide over and over again, producing a ball of cells that eventually grew into you

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each time a cell divided by mitosis, the two new cells produced were provided with a perfect copy of the two sets of chromosomes in the original zygote

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each time a cell divided by mitosis, the two new cells produced were provided with a perfect copy of the two sets of chromosomes in the original zygote

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the new cells produced were all genetically identical

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mitosis is the way in which any cell divides when an organism is growing, or repairing a damaged part of its body

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mitosis is the way in which any cell divides when an organism is growing, or repairing a damaged part of its body

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after mitosis the two new cells contain the same information of the parent cell

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just before mitosis take place, the chromosomes in the parent cell are copied

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just before mitosis take place, the chromosomes in the parent cell are copied

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each copy remains attached to the original one,so each chromosome is made up of two identical threads -chromatids- and the point were they are held together is called the centromere

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meiosis: nuclear division giving rise to cells that are genetically different

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meiosis: nuclear division giving rise to cells that are genetically different

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human gametes are formed by meiosis, a cell division that occurs in the ovary and testes

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one of each pair of homologous chromosomes came from the mother, and one from the father

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one of each pair of homologous chromosomes came from the mother, and one from the father

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during meiosis the new cells get a mixture of these: a sperm could contain a chromosome 1 from the father and a chromosome 2 from his mother, and so on

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MEIOSIS PRODUCES GENETIC VARIATION: crossing over

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MEIOSIS PRODUCES GENETIC VARIATION: crossing over

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there are all sorts of different possible combinations, this is one of the reasons why gametes are genetically different from the parent cell

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shortly after a zygote is formed, it begins to divide by mitosis, so every new cell is genetically identical

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shortly after a zygote is formed, it begins to divide by mitosis, so every new cell is genetically identical

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this happens over the next few hours and days after fertilisation

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as the embryo develops, the cells begin to take on different roles

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every cell in the body has the same genes

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every cell in the body has the same genes

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but in each cell, only a particular set of these genes is switched on or expressed

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DIFFERENTIATION INVOLVES SWITCHING PARTICULAR SETS OF GENES ON OR OFF: .....example....

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DIFFERENTIATION INVOLVES SWITCHING PARTICULAR SETS OF GENES ON OR OFF: .....example....

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the cells in the hair follicle are the only ones that actually expresses the gene for hair colour; this gene is present in all cells of the body, but it is not expressed

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that are the cells in the very early embryio, and are capable to produce every kind of specialized cell in the body

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once a cell is differentiated, it cannot change its role

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once a cell is differentiated, it cannot change its role

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some stem cells remain in our body and are able to divide and to produce different types of specialised cells

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the range of different cells the adult stem cells can produce is limited

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the range of different cells the adult stem cells can produce is limited

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for example, bone marrow stem cells can divide to produce red blood cells, platelets and the different types of white blood cell, but they cannot produce nerve cells, or liver cells, or any other kind of specialized cell

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medical researchers are interested in finding out more about stem cells

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medical researchers are interested in finding out more about stem cells

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for example, if we could use stem cells to replace pancreatic cells that fail the secretion of insulin, then we could fight diabetes type 1

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about 20000 human genes are  carried on our two sets of 23 chromosomes

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about 20000 human genes are  carried on our two sets of 23 chromosomes

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in chinchillas there are several different forms of the fur colour gene, we can refer to these alleles using letters as symbols

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we can call the allele that gives grey fur G, and the allele that gives charcoal fur g

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we can call the allele that gives grey fur G, and the allele that gives charcoal fur g

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this means that there are three possible combination of alleles: GG, Gg, gg

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if the two alleles are the same, that is GG or gg, the chinchilla is said to be homozygous,  if the two alleles are different, that is, Gg, then it is heterozygous

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if the two alleles are the same, that is GG or gg, the chinchilla is said to be homozygous,  if the two alleles are different, that is, Gg, then it is heterozygous

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each cell has at least two alleles for any characteristic

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each cell has at least two alleles for any characteristic

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please, "translate" pure breeding as LINEA PURA (pure-breeding strains are always homozygous for the characteristic considered)

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eg. chinchillas genotype for fur color could be GG, Gg,gg; whereas how it looks like represents the phenotype

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sometimes other things can affect the phenotype

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sometimes other things can affect the phenotype

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for the moment, we don't worry about effects which the environment might have

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Dominant Alleles vs Recessive Alleles | Understanding Inheritance

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if the alleles show codominance (che poi per noi italiani sarebbe dominanza incompleta, ma tant'è), we will observe three genotypes and also three phenotypes

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a person with blood type AB shows on the surface of his red blood cells both antigens

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human and egg cells have 23 chromosomes, therefore

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human and egg cells have 23 chromosomes, therefore

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these cells carry only one of each pair of alleles of all the genes

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allows to test a suspected heterozygous by crossing it with a known homozygous recessive (for example the allele for tallness that is dominant to the allele for dwarfness in certain species of pea)

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in monohybrid inheritance

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with small numbers probabilities don't always match reality

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with small numbers probabilities don't always match reality

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the last pairs of chromosomes are responsible for determining sex

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the last pairs of chromosomes are responsible for determining sex

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sex chromosomes

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a woman's chromosome are both alike and are called X chromosomes, whereas a man has only one X chromosome, the other is the Y chromosome

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a woman's chromosome are both alike and are called X chromosomes, whereas a man has only one X chromosome, the other is the Y chromosome

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when I must expect barr body

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ma ho proprio la fissazione!!

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dna contains a code that determines exactly what sequence of aminoacids a cell should string together when it makes a particular protein

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dna contains a code that determines exactly what sequence of aminoacids a cell should string together when it makes a particular protein

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a gene determines what protein will be made, and the protein affects the feature of an organism

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a gene determines what protein will be made, and the protein affects the feature of an organism

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enzymes determine the metabolic reactions that take place, and therefore the substances that are made through these reactions

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a specific base sequence tells the cell to join a specific amino acid to another

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DNA is found in the nucleus, protein synthesis happens on the ribosomes in the cytoplasm

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DNA is found in the nucleus, protein synthesis happens on the ribosomes in the cytoplasm

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to carry information from the DNA to the ribosome. a messenger molecule called mRNA is used

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when a protein is to be made, an mRNA molecule is made in the nucleus, copying the base sequence from the appropriate length of DNA

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as the long, thin molecule of mRNA passes through ribosome, it links aminoacids together in the right order to make the desired protein, following the code contained on the mRNA molecule

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when an allele (eg. grey fur) is dominant to another (eg. charcoal fur) we can observe three possible genotypes (GG, Gg, gg) but only two phenotypes (grey or charcoal)

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when an allele (eg. grey fur) is dominant to another (eg. charcoal fur) we can observe three possible genotypes (GG, Gg, gg) but only two phenotypes (grey or charcoal)

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a recessive allele only affects the phenotype when there is no dominant allele present (homozygous recessive)

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Great revision sheets on inheritance for the new specifications! | Science | Gcse science revision, Science revision, Gcse science

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Great revision sheets on inheritance for the new specifications!

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Mitosis (video) | The cell cycle and mitosis | Khan Academy

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Mitosis is how cells divide! Learn what happens in all the phases of mitosis: prophase, metaphase, anaphase, and telophase.

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Meiosis - A Level Biology Revision Notes