CH 16 Inheritance IGCSE Biology PDF

BY CELL :00201110983031 00201110983031 [email protected]  5 State that the sequence of bases in a gene determines the sequence of...

BY CELL :00201110983031 00201110983031 [email protected]  5 State that the sequence of bases in a gene determines the sequence of amino acids used to make a specific protein (knowledge of the details of 1 State that chromosomes are made of DNA, nucleotide structure is not required) which contains genetic information in the form 6 Explain that different sequences of of genes amino acids give different shapes to 2 Define a gene as a length of DNA that codes for a protein molecules. protein 7 Explain that DNA controls cell 3 Define an allele as an alternative form of a gene function by controlling the production 4 Describe the inheritance of sex in humans with of proteins, including enzymes, reference to X and Y chromosomes. membrane carriers and receptors for 1 Describe inheritance as the transmission neurotransmitters of genetic information from generation to 8 Explain how a protein is made, generation limited to: 2 Describe genotype as the genetic make-up of an the gene coding for the protein organism and in terms of the alleles present remains in the nucleus 3 Describe phenotype as the observable features of messenger RNA (mRNA) is a copy of a an organism gene 4 Describe homozygous as having two identical mRNA molecules are made in the alleles of a particular gene nucleus and move to the cytoplasm 5 State that two identical homozygous individuals that breed together will be pure-breeding the mRNA passes through ribosomes 6 Describe heterozygous as having two different the ribosome assembles amino acids alleles of a particular gene into protein molecules 7 State that a heterozygous individual will not be the specific sequence of amino acids pure-breeding is determined by the sequence of bases 8 Describe a dominant allele as an allele that is in the Mrna (knowledge of the details expressed if it is present in the genotype of transcription or translation is not 9 Describe a recessive allele as an allele that is only required) expressed when there is no dominant allele of 9 Explain that most body cells in an the gene present in the genotype organism 10 Interpret pedigree diagrams for the inheritance of a given characteristic 11 Use genetic diagrams to predict the results of monohybrid crosses and calculate phenotypic CELL :00201110983031 00201110983031 [email protected]  DEOXYRIBONUCLEIC ACID DNA Formed of two strands that twist together forming a spiral known as double helix.  Each strand is formed of sequence of bases.  Bases of one strand form hydrogen bonds with bases of the other strand. There are four types represented by A,T,C and G. A and T are joined together by two hydrogen bonds. C and G are joined together by three hydrogen bonds. Importance of DNA bases  The sequence of bases provides codes for the types of proteins that have to be made in the cells.  The different types of proteins lead to development of characteristics, for example black hair is a protein while yellow hair is other protein.  The different types of proteins may be enzymes or hormones that affect activity of the body or maybe antibodies for immunity. body or maybe antibodies for immunity. CELL :00201110983031 00201110983031 [email protected]  Explain how protein is made 1. The gene coding for the protein remains in the nucleus. 2. mRNA molecules carry a copy of the gene to the cytoplasm. 3. the mRNA passes through ribosomes. 4. the ribosome assembles amino acids into protein molecules. 5. the specific order of amino acids is determined by the sequence of bases in the mRNA. It is the transmission of genetic information from generation to generation. Chromosome - A coiled thread of DNA and protein found in the nucleus of cells, it is made up of string of genes. - Every species is characterized by having a certain number of chromosomes. Example: humans have 46 chromosomes in every cell of the body except for gametes (gamete has only 23 chromosomes.) - Chromosomes can be seen clearly in the cell by the light microscope only when the cell is dividing because at this stage, they become shorter and fatter. - Chromosomes carry genes. CELL :00201110983031 00201110983031 [email protected]  Explain that the sequence of bases in a gene is the genetic code for putting together amino acids in the 1. correct order to make a specific protein (knowledge of the details of nucleotide structure is not required). 2. DNA has only four bases but proteins have 20 different amino acids. This means that the four DNA 'letters'. 3. have to be combined to make different 'words', each one signifying a particular amino acid. Explain that DNA controls cell function by controlling the production of proteins (some of which are enzymes), antibodies and receptors for neurotransmitters Controls functions in the cell 1. DNA molecule carries a code that instructs the cell about which kinds of proteins should make. 2. Each chromosome carries instructions for making many different proteins. A part of DNA molecule coding for one protein is called a gene. Protein is made up of long chains of amino acids. There are 20 different amino acids. 3. The sequence of these amino acids in a protein molecule determines the final shape of the molecule and this shape also affects how the protein works. 4. DNA contains a code that determines exactly what sequence of amino acids a cell should string together when its making a particular protein. 5. This is how genes affect an organism's features. A gene determines what protein will be made, and protein affects a feature of the organism. 6. Many proteins do this by acting as enzymes. Other proteins have different functions, such as antibodies and receptors for neurotransmitters. CELL :00201110983031 00201110983031 [email protected]  Types of nuclei HAPLOID DIPLOID A nucleus which has one set of unpaired A nucleus which has two sets of chromosomes. chromosomes EX In gametes EX In all body cells except gametes. Types of chromosomes AUTOSOMES SEX CHROMOSOMES Are the chromosomes responsible for Are the chromosomes responsible for sex different characteristics except sex. determination. - Are represented by X and Y. (Y is shorter than X). - In males X and Y chromosomes are present. - In females two X chromosomes re present Homologous chromosomes Chromosomes which carry genes for the same characteristics in the same position. - Have the same position of centromere. - One comes from the father (paternal) while the other comes from the mother ( maternal). CELL :00201110983031 00201110983031 [email protected]  Important definitions SCIENTIFIC TERM DEFINITION GENES -A specific length of DNA occupying a position called locus in a chromosome which codes for making a particular protein. ALLELES Allele is one of two or more different forms of a gene. INHERITANCE is the transmission of genetic information from generation to generation CHROMOSOME is a thread-like structure of DNA, carrying genetic information in the form of genes HAPLOID NUCLEI is a nucleus containing a single set of unpaired chromosomes, e.g. in gametes DIPLOID NUCLEI is a nucleus containing two sets of chromosomes, e.g. in body cells GENOTYPE is the genetic make-up of an organism in terms of the alleles present (eg. Tt or GG). PHENOTYPE is the observable features of an organism HOMOZYGOUS is having two identical alleles of a particular gene HETEROZYGOUS is having two different alleles of a particular gene DOMINANT ALLELE is an allele that is expressed if it is present RECESSIVE ALLELE is an allele that is only expressed when there is no dominant allele of the gene present Example : The gene which codes for fur colour in an animal may have two forms (alleles), a form (an allele) codes for white colour and a form ( an allele) codes for black colour. CELL :00201110983031 00201110983031 [email protected]  SEX DETERMINATION EXPLAIN WHY THE MALE IN HUMANS DETERMINE THE SEX Males because they produce gametes that contain the chromosome Y. TYPES OF INHERITANCE MONOHYBRID DIHYBRID Means that cross between organisms which Means that cross between organisms which show contrasting variations of only one show contrasting variations of TWO characteristic characteristic Example Black animal crossed with a white one. If all their offspring is black, the allele for black is said to be dominant and is represented by a capital letter (A) while the allele for white is ressisive and is represented by the same letter but small (a) CELL :00201110983031 00201110983031 [email protected]  Types Of Alleles Dominant Recessive The allele which is expressed always The allele which is expressed in the absence Can be classified into of the dominant one. 1. Homozygous 2. Heterozygous Each individual receives two alleles for each characteristic - One from the father and one from the mother. - If the two alleles are identical for example AA or bb the individual is called homozygous. - If the two alleles are different for example Aa the individual is called heterozygous Inheritance examples 1- If two homozygous individuals with different phenotypes are crossed The result is 100% heterozygous dominant. Example Parental phenotype Genotype GG gg Gamete G g F1 genotype Gg Phenotype green Phenotype ratio green: 100% Genotype ratio Gg : 100% PUNNET SQUARE CELL :00201110983031 00201110983031 [email protected] 2- If two heterozygous individuals with the same phenotype Red white Example Parental phenotype Genotype Rr Rr Gametes R r R r F1 genotype RR Rr Rr rr Phenotype 3 red : 1 white 3- If a heterozygous dominant and homozygous recessive are crossed Example Parental phenotype Genotype Rr rr gametes R r r r F1 genotype Rr rr Phenotype 1 RED : 1 WHITE 50% : 50 % CELL :00201110983031 00201110983031 [email protected]  TEST CROSS THE PROCESS OF BREEDING BETWEEN TWO INDIVIDUALS, ONE DOMINANT AND ONE RECESSIVE TO CHECK IF THE DOMINANT IS HETEROZYGOUS OR HOM0ZYGOYS. SEX INHERITANCE Each human body cell has 46 chromosomes. There a 22pairs of chromosomes plus another two chromosomes. which may not look alike. These are the sex chromosomes. female cell has two sex chromosomes that are alike (called XX) and male cells have two sex chromosomes that are not alike (XY). CELL :00201110983031 00201110983031 [email protected]  SEX LINKED GENES A characteristic in which the gene responsible is located on a sex chromosome, which makes it more common in one sex than in the other. Example colour blindness, haemophilia. Any gene carried on the sex chromosomes is sex linked Example : Colour blindness. It is a disease caused due to a recessive alleleof a sex linked gene. In this disease the person cannot distinguish the green, yellow , orange and red colours. This disease can be detected by using a card contains the above colours in a certain pattern and so the infected person cannot detect this pattern. It is due to a defect in one of the three groups of colour sensitive cones. A person who is homozygous for this allele can't tell the difference between red & green. CELL :00201110983031 00201110983031 [email protected]  Example: affected female (mother) with normal male(father) PUNNET SQUARE The ratio in the offspring is different in genotype and phenotype Genotype 1 female homozygous healthy :1 carrier female :1 healthy male :1 affected male CO DOMINANCE a situation in which both alleles in heterozygous organisms contribute to the phenotype, two alleles, both are expressed, where neither is dominant over the other, when found in as heterozygous. ex. Blood group: The three alleles IA, IB, O. CELL :00201110983031 00201110983031 [email protected] If a plant with red flowers and a plant with white flower re crossed together and the produced offspring has pink flowers. CELL :00201110983031 00201110983031 [email protected]  Key for solving problems Any offspring contains trait which is not found in the parents, it means that then parents are heterozygous (dominant) for this trait and the child is recessive. NOTICE Breeding true or pure breading means homozygous individual TYPES OF NUCLEAR DIVISION MITOSIS MESIOSIS Nuclear division giving rise to Reduction division in which DEFINITION genetically identical cells. chromosome number is halved from diploid to haploid, resulting on genetically different cells PLACE All body cells (forms body Reproductive organs (forms cells) gametes) NUMBER OF CELLS Gives 2 daughter cells Gives 4 daughter cells. PRODUCED produced Identical to each Non identical other & to the parent cell. ( variation) ( no variation) NUMBER OF Each nucleus has the diploid Each nucleus has the haploid CHROMOSOMES number of chromosomes number of chromosomes. PRODUCED IMPORTANCE 1-Growth of living organisms. 1.Formation of gametes for 2-Asexual reproduction. sexual reproduction. 3-Healing and replacement of 2. thus reduces/ halves the damaged cells. number of chromosomes, so By producing diploid identical number of chromosomes cells doesn't double each generation. * CAUSES variation CELL :00201110983031 00201110983031 [email protected] EXPLAIN Why are gametes genetically different from the parent cell? Because They are produced by meiosis (reduction division) at which. The homologous pair of chromosomes in parent cells which came from the person's mother& one from their father, during meiosis, the new cells get a mixture of these, So a sperm cell could contain a chromosome r from the man's father and a chromosome from his mother, and so on , There are all sorts of different combinations. How meiosis leads to variation By forming new combinations of alleles from maternal and paternal chromosomes stem cells as unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions. CELL :00201110983031 00201110983031 [email protected]