IGCSE Biology Chapter 16 Chromosomes, Genes and Proteins PDF

CHAPTER 16 CHROMOSOMES, GENES IGCSE Biology AND PROTEINS INHERITANCE Inheritance is the transmission of genetic information from generation to generation. The Inheritance of such characteristics is called heredity and the branch of biology that studies how heredity works is call...

CHAPTER 16 CHROMOSOMES, GENES IGCSE Biology AND PROTEINS INHERITANCE Inheritance is the transmission of genetic information from generation to generation. The Inheritance of such characteristics is called heredity and the branch of biology that studies how heredity works is called genetics.  16.1 CELL DIVISION MITOSIS ▪nuclear division giving rise to genetically identical cells ▪mitosis is needed for processes of growth repair, replacement and asexual reproduction in some organism.  16.1 CELL DIVISION MITOSIS ▪When an organism grow their cells increase in number by dividing. ▪Each cell divides to produce two daughter cells. ▪One of the cells will grow and changes its shape and structure and becomes adapted to do one particular job, it becomes specialized ▪At the same time it loses its ability to divide any more. ▪The other cell is still able to divide and so continue the growth of the tissue.  16.1 CELL DIVISION MITOSIS mitosis produces two genetically identical cells in which the number of chromosomes is the same as in the original cell https://www.youtube.com/watch?v=RHyZVmbiA78 16.1 CELL DIVISION MITOSIS: ANIMAL AND PLANT  16.1 CELL DIVISION, MITOSIS SQUASH PREPARATION OF CHROMOSOMES USING ACETIC ORCEIN https://www.amybrownscience.com/2014/09/preparation-of- chromosome-squashes.html  16.1 CELL DIVISION STEM CELLS Stem cells are unspecialized cells in the body that have retained their power of division Examples: the basal cells of the skin, which keep dividing to make new skin cells cells in the red bone marrow, which constantly divide to produce the whole range of blood cells  16.1 CELL DIVISION STEM CELLS Cells taken from early embryos (embryonic stem cells) can be induced to develop into almost any kind of cell, but there are ethical objections to using human embryos for this purpose. 16.1 CELL DIVISION MEIOSIS ▪nuclear division, which gives rise to cells that are genetically different. ▪a reduction division, in which a diploid cell divides to produce haploid cells. ▪forms gametes (sperm and egg cells in mammals). Gametes are different from other cells because they have half the normal number of chromosomes (they are haploid).  16.1 CELL DIVISION MEIOSIS ▪ Meiosis produces four genetically different haploid cells. Unlike mitosis, meiosis is a reduction division – the chromosome number is halved from diploid ▪ As a result of meiosis and fertilisation, the maternal and paternal chromosomes meet in different combinations in the zygotes. Consequently, the offspring will differ from their parents and from each other in a variety of ways. https://www.youtube.com/watch?v=micUPynqx9k 16.1 CELL DIVISION MITOSIS VS MEIOSIS https://www.youtube.com/watch?v=zrKdz93WlVk  16.1 CHROMOSOMES Chromosomes are long strands of DNA, which contain genetic information in the form of genes. Each gene codes for the production of a particular kind of protein. 16.1 CHROMOSOMES 16.1 CHROMOSOMES 16.1 CHROMOSOMES KARYOTYPE ▪the number and appearance of chromosomes in the nucleus of a eukaryotic cell. ▪human somatic cell contains 23 pairs of chromosomes.  16.1 CHROMOSOMES NUMBER OF CHROMOSOMES ▪There is a fixed number of chromosomes in each species. ▪The number of chromosomes in a species is the same in all of its body cells. ▪The chromosomes are always in pairs, because when the zygote is formed, one of each pair comes from the male gamete and one from the female gamete. 16.1 CHROMOSOMES NUMBER OF CHROMOSOMES ▪Haploid: has one set of chromosomes, Example: gamete cells (sperm and egg cells has 23 chromosomes) ▪Diploid nucleus: has two sets of chromosomes, Example: somatic cells (body cells has 46 chromosomes or 23 pairs)  16.2 INHERITING GENES GENES AND LOCUS ▪Genes: a length of DNA that codes for a protein ▪Locus: the position of a gene 16.2 INHERITING GENES ALLELES ▪ Allele is a version of a gene. ▪ We can use letters to represent the alleles of a gene. ▪ The alleles of a gene that an organism has are its genotype, and the features produced by those alleles are its phenotype  16.2 INHERITING GENES ALLELES ▪Homozygous: two identical alleles of a particular gene. Homozygous organisms are pure-breeding. ▪Heterozygous: two different alleles of a particular gene. ▪Dominant: An allele that has an effect even when a different allele is present, represented with a capital letter. ▪Recessive: An allele that only has an effect when no other allele is present, represented by a small letter.  16.2 INHERITING GENES DETERMINATION OF GENDER ▪A pair of chromosomes in human karyotype controls whether offspring are male or female: ▪males have two different sex chromosomes, X and Y ▪females have two X chromosomes, XX ▪The ratio of female to male offspring is 1:1 – on average, half of the offspring will be girls and half will be boys  16.2 INHERITING GENES PEDIGREE DIAGRAMS ▪Pedigree diagrams can be used to demonstrate how genetic diseases can be inherited ▪They include symbols to indicate whether individuals are male or female and what their genotype is for a particular genetic characteristic  16.2 INHERITING GENES PUNNET SQUARES square diagram that is used to predict the genotypes of a particular cross or breeding experiment https://www.youtube.com/watch?v=Mehz7tCxjSE 16.2 INHERITING GENES PUNNET SQUARES 25% homozygous dominant 50% heterozygous 25% homozygous recessive  a way to explore the genotype of an organism 16.2 INHERITING GENES TESTCROSS ▪if ANY offspring show the recessive trait, the unknown genotype is heterozygous ▪if ALL the offspring have the dominant trait, the unknown genotype is homozygous dominant *large numbers of offspring are needed for reliable results  16.2 INHERITING GENES CO-DOMINANCE When both genes of an allele pair produce their effects in an individual (ie. neither allele is dominant to the other) the alleles are said to be co- dominant. 16.2 INHERITING GENES CO-DOMINANCE 16.2 INHERITING GENES INCOMPLETE DOMINANCE When both genes of an allele pair produce their effects in an individual but strictly applies to a case where the effect of the recessive allele is not completely masked by the dominant allele.  16.2 INHERITING GENES SEX LINKAGE Sex-linked characteristic ▪the gene responsible is located on a sex chromosome ▪more common in one sex than the other. 16.2 INHERITING GENES SEX LINKAGE Hemophilia is a rare disorder in which your blood doesn't clot normally because it lacks sufficient blood-clotting proteins (clotting factors) 16.3 GENES AND PROTEIN SYNTHESIS THE GENETIC CODE ❑DNA are made of nucleotides molecules. ❑A nucleotide is a 5- carbon sugar molecule joined to a phosphate group (–PO3) and an The nucleotides are joined by their organic base phosphate groups to form a long chain 16.3 GENES AND PROTEIN SYNTHESIS THE GENETIC CODE ❑Each DNA strand has chemical bases that pairs together. ❑A (adenine) always pairs up with T (thymine) ❑C (cytosine) always pairs up with G (guanine)  16.3 GENES AND PROTEIN SYNTHESIS THE GENETIC CODE ▪each nucleotide carries one of four bases (A, T, C or G). ▪a string of nucleotides holds a sequence of bases that forms a code which instructs the cell to make particular proteins. 16.3 GENES AND PROTEIN SYNTHESIS THE GENETIC CODE ▪the sequence of bases in the DNA decides which amino acids are used and in which order they are joined ▪each group of three bases stands for one amino acid ▪a sequence of triplets of the four bases specifies an entire protein can be called a gene 16.3 GENES AND PROTEIN SYNTHESIS THE GENETIC CODE ▪genetic code of DNA determines which proteins, particularly enzymes, are produced in a cell. Hence its also determines the cell’s structure and function ▪in this way, the genes also determine the structure and function of the whole organism ▪other proteins coded for in DNA include antibodies and the receptors for neurotransmitters 16.3 GENES AND PROTEIN SYNTHESIS MANUFACTURE OF PROTEIN IN CELLS ▪DNA molecules remain in the nucleus, but the proteins they carry the codes for are needed elsewhere in the cell ▪messenger RNA (mRNA) is used to transfer the information from the nucleus ▪mRNA is much smaller than a DNA molecule and made up of only one strand. Also it contains slightly different bases (A,C,G and U). Base U is uracil 16.3 GENES AND PROTEIN SYNTHESIS MANUFACTURE OF PROTEIN IN CELLS  16.3 GENES AND PROTEIN SYNTHESIS MANUFACTURE OF PROTEIN IN CELLS: TRANSCRIPTION ▪To pass on the protein code, the double helix of DNA unwinds to expose the chains of bases. ▪One strand acts as template. ▪mRNA is formed along part of this strand, made up of a chain of nucleotides with complementary bases to a section of the DNA strand.  16.3 GENES AND PROTEIN SYNTHESIS MANUFACTURE OF PROTEIN IN CELLS: TRANSLATION ▪mRNA carrying the protein code passes out of the nucleus, through a nuclear pore to the cytoplasm, then it attaches itself to a ribosome. ▪ribosomes make proteins. The mRNA molecule instructs the ribosomes to put together a chain of amino acids in a specific sequence, thus making a protein. https://www.youtube.com/watch?v=gG7uCskUOrA 16.3 GENES AND PROTEIN SYNTHESIS GENE EXPRESSION ▪specialized cells all contain the same genes but only the genes needed to code for the specific proteins are switched on (expressed) ▪this enables the cell to make only the proteins it needs to fulfill its function ▪example: ▪some cells in the stomach is to make the protein pepsin. ▪bone marrow cells make the protein haemoglobin, but do not need digestive enzymes.