DNA and Genes Science 9 PDF

DNA and Genetics Science 9 Genetics - what do we know? Certain traits (characteristics) are heritable or inherited from our parents Because we are products of sexual reproduction there is a lot of variation in how our genes are expressed… but how does this happen?  S...

DNA and Genetics Science 9 Genetics - what do we know? Certain traits (characteristics) are heritable or inherited from our parents Because we are products of sexual reproduction there is a lot of variation in how our genes are expressed… but how does this happen?  Section 3.0 DNA – inherited material which results in variation Double-helix structure, found in the nucleus of all of your cells  DNA – Transmitter of Genetic Code Offspring resemble their parents due to characteristics that are passed on from generation to generation Long before we knew about DNA we knew about patterns of inheritance and used it to bring out the characteristics we most want.. Breeding Programs – used genetic information to produce breeds of plants and animals that have the best characteristics of the parents to allow the offspring to have desired and specific characteristics (Example:  DNA and Genetic Code -In 1953, James Watson and Francis Crick, explained that DNA has chemical building blocks carrying a wide range of instructions causing great diversity. They accomplished this based on the X-ray photographs taken by Rosalind Franklin  Construction of the DNA Molecule A ladder that has been twisted! Sides of the ladder are the same The steps or (pieces in between) are the components that are different Four Chemicals: The composition Guanine (G) (arrangement) of Cytosine (C) these chemicals is Adenine (A) the code the cells can read Thymine (T) Known as “GENETIC CODE” (arrangement into instructions to make a particular organism look the way it does) “BLUEPRINT” DNA is found in the nucleus of both animal and plant cells The reason so much DNA can fit into a cell nucleus is that it is exquisitely thin. You would need twenty billion strands of DNA laid side by side to make the width of the finest human hair. DNA is found in the nucleus of both animal and plant cells A length of DNA is divided into segments called chromosomes and shorter individual units called genes. The sum of all your genes is the genome. Chromosomes: Large pieces of DNA that contain MANY genes. The terms base pair and nucleotide are often used interchangeably but they have slightly different meanings. A nucleotide is the entire structure of C, A, G or T attached to the deoxyribose sugar (S) and the phosphate(P), whereas a base is just the C, A, G or T. Since A always pairs with T, and G always pairs with C, we refer to them as base pairs. Here are the complete structures of the bases, cytosine, thymine, guanine, and adenine.  DNA large molecule found in cells’ nuclei that is responsible for storing information and passing it on to the offspring NAMED: Deoxyribonucleic Acid Humans have 46 chromosomes that contain all of the genetic information, and there are over 25,000 genes in the human genome. Genes are composed of DNA, over 3 billion base pairs in the human genome. You have meter of it packed into every cell, and so many cells that if you formed all the DNA in your body into a single strand, it would stretch ten billion miles, to beyond Pluto. Chromosomes Because DNA is responsible for an organism's physical and chemical characteristics, there is a lot of DNA in a cell (approx. 2 meters in length) which is 1 000 000 times larger than the cell it fits into, therefore DNA arranges itself into small packages called “CHROMOSOMES” Each cell nucleus contains 46 chromosomes (23 pairs of chromosomes) Role of Sex Chromosomes (chromosome pair number 23): X Chromosome: Common in both males and females, carries genes vital for various body functions, including vision. Y Chromosome: Only in males, contains the gene that triggers male development. How Genetic Sex is Determined: From Mother: Always an X chromosome. From Father: Either an X (resulting in a girl) or a Y (resulting in a boy).  Genes Definition: DNA segment that contributes to phenotype (exterior look/function), and occupies a fixed position (locus) on a chromosome Offspring will inherit genes from both parent (ie. Hair Color), however the gene is represented in two possibilities (not always the same) Possible forms are known as “ALLELES” Alleles: different ‘versions’ of the same gene (we get one from each parents) CHROMOSOMES Made of many genes GENES Made of DNA DNA Made of nucleotides Instructions for all characteristics Homework Check and Reflect p.45  Section 3.2 – Cell Division Somatic cells are regular body cells, not reproductive cells. They all have a full set of How is the Genetic Information chromosomes Passed on? 2 Forms of Cell Division Mitosis: produces two new cells with same number of chromosomes. This type of cell division is used for growth and repair, and to replace dead cells. 50-70 billion cells die in your body every day. Mitosis essentially produces more of the same cells. Meiosis: cell division producing half the DNA of a normal cell (GAMETE “sex cell”). Meiosis is used exclusively for sexual reproduction.  Mitosis Produces 2 new cells with the SAME Pair up number of chromosomes Meet in the Occurs in Middle body cells of multicellular Pull organisms Apart - Responsible Now for growth and there are cellular repair of Two multi cellular organism  Meiosis Produces cells with only HALF the DNA, that is, half the chromosomes of a normal cell Gametes (Male & Female) Mules are hybrids between horses and donkeys. Horses have 64 chromosomes and donkeys have 62. As a result, mules, get only 63, an odd number. Viable gametes, normally, cannot be produced from a cell with an odd number of chromosomes. Hence, mules are mostly sterile, they cannot produce their own offspring. Homework – Check and Reflect pg.48 Q’s1-­4  Section 3.3 – Patterns of Inheritance Trait: genetically determined characteristic Purebred vs. Hybrid Purebred: organism with identical alleles/genes Hybrid: organism that the offspring is genetically dissimilar from the parents Dominant Traits trait expressed preferentially over another trait Why do all the kittens have a black coat? Are the kittens purebred or hybrid? Explain Alleles: different ‘versions’ of the same gene (we get one from each parent) Recessive Traits trait that is preferentially masked (not expressed, not visible) Look at Figure 3.14 pg. 51 If both parents are black why is there one white kitten? Homozygous and Heterozygous Zygote - a cell that results from the fusion of the male and female gametes. It has a full set of chromosomes, all chromosomes are paired. Homozygous - same alleles. If both chromosomes from a pair have the same version of the gene. For example if both parents pass on the blue eye gene to the child. The child is a homozygous individual. Heterozygous - different alleles. For example, if one parent passes on the allele for the blue eyes, and the other passes on the allele for broun eyes. This is a heterozygous individual. Homozygous can be dominant or recessive, depending on which allele is passed. Heterozygous has both versions, it cannot be called dominant or recessive. Example: Blue eye color is a recessive trait, brown eyes is dominant. If the mother has only the blue eye alleles, she is homozygous recessive. If the father has both alleles for the brown eye color, he is homozygous dominant. The children will receive both versions, therefore the children will all be heterozygous. What eye color will all children have? Brown. Why? Look at the Punnett square below to see all possible combinations. The alleles for the father are in the column on the left, the alleles for the mother are in the row at the top. The children’s allele combinations are listed as either BB, Bb, or bb b b B Bb Bb B Bb Bb  How do we make and use a PUNNETT SQUARE? Choose a letter from the alphabet that corresponds with the first letter of the DOMINANT TRAIT. For example, if the dominant trait is brown hair, then use letter B Upper case, or capital letter (or “BIG”) letter is used for the DOMINANT trait and the Lower Case letter (or small) letter is used for the recessive trait.  Example: Dad is Dominant for Brown hair (B) and Mom is recessive for Blond hair (b) 3 combinations: A) Homozygous Dominant BB B) Heterozygous Bb C) Homozygous Recessive bb  Try this!! Dad is Homozygous Dominant for Brown Eyes and Mom is Homozygous recessive for blue eyes. Draw the Punnett Square! HOW??? An individual’s genotype is the genetic code they carry in their cells that provides information for a particular trait. Their phenotype is the visible, expressed trait, such as hair color. The phenotype depends upon the genotype but can also be influenced by environmental factors. Dihybrid cross Punnett square. Take a look at this example of a Punnett square that involves two traits. One is the color, it can be yellow or green. Yellow is dominant and we use the letter Y. The other one is the shape, either round or wrinkled. Round is dominant, so we use the letter R. There are up to 4x4=16 possible genotypes. There are only 4 possible phenotypes: yellow round, yellow wrinkled, green round, You won’t need to be able to produce a dihybrid green wrinkled. Punnett square on a test.  Other Patterns of Inheritance Incomplete Dominance: intermediate inheritance resulting in a combined “phenotype” (outer appearance) Example: Red Flowers with White Flowers If the offspring turns red then that shows Red being a dominant trait If the offspring is white then White is the dominant trait If the offspring is PINK, that is the result of INCOMPLETE DOMINANCE (b/c neither red nor white was expressed in dominant form)  GENE ALLELE GENOTYP PHENOT E YPE HOMOZYGOUS DOMINANT HETEROZYG OUS HOMOZYGOUS RECESSIVE 13 HOMOZYGOUS DOMINANT HETEROZYG OUS HOMOZYGOUS RECESSIVE 13  Check and Reflect pg.54 Questions 1-­6  Assess Your Learning pg.55 Questions 1,2,4,5,6­-9