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Chapter 3 part 1 Heredity and Genetics Section 3-1 Turn to page 64 in your book. At the top of the page, look for the blue box that says Investigate. Work with the students in your table row. Kyle and Isaac work with the students to your right Jazlyn and Brian work with the students to your left On a piece of paper, list the 5 characteristics that describe your appearance. Ex.) hair color, eye color, and height. Compare your list with others in your group Think about it - Does anyone in your group have the same exact characteristics as you? Are any of them common? Section 3-1What is heredity? Key terms Trait- characteristic Inherited trait – a trait that is passed from parents to their offspring Heredity- passing of traits from parents to offspring Genetics- study of heredity Traits You can make a list of characteristics about yourself. This list includes things about yourself such as Eye color Height Hair color It is very unlikely another student in the class or school will have the same traits that you have. This is because the combination of traits that you have are very unique. There is only one you. These characteristics are called traits. Traits Identifying Traits Have you ever noticed that you look like your parents? Siblings? Children often look like their parents or even grandparents. There is a reason for this: During fertilization (the making of you) male and female sex cells join. Each cell contains a unique set of material that affects the development of their offspring (children) Traits are passed from parents to children. These traits are called inherited traits. Ex.) eye color Heredity The passing of traits from parents to offspring is called heredity. The field of biology that studies heredity is called genetics. Why might we study genetics? 1.) 2.) 3.) Heredity Gregor Mendel was an Austrian monk who was one of the first people to study genetics. He used pea plants for this studies. He is also often referred to as the “Father of Genetics”. The Heredity of Twins Twins are siblings that are born at the same time. There are 2 types of twins 1.) Identical develop from 1 egg fertilized by 1 sperm cell, that splits in 2. These 2 cells become 2 individuals They are genetically the same; they have the same exact traits, which makes them hard to tell apart. They are ALWAYS the same sex (either both boys or both girls) 2.) Fraternal Develop from 2 eggs fertilized by 2 sperm cells at the same time. These twins are genetically different from each other, just like regular siblings. They CAN be 1 boy, and 1 girl, or both boys or both girls. They are more common What you need to do now… For Homework: On Pg. 65, Answer questions #1-12 on a piece of paper. DUE TOMORROW!!! Take your time, make your answers and work NEAT!!! If you are struggling, READ the section over again. If you are still struggling come see me during HOMEROOM TOMORROW. Tomorrow bring with you… Your homework, and turn it in the bin at the beginning of class. Also bring your Chapter 3 note packet A sharpened pencil What you should be doing… Turning in your COMPLETED homework from yesterday. Pg. 65, #1-12 Get out your CHAPTER 3 note packet and a pencil Place everything else on the floor! 3-2 What is meiosis? Key Terms sperm cells – male reproductive cell Egg cells- female reproductive cell Gamete- reproductive cell Meiosis- type of cell division that produces gametes Gametes Every body cell of an animal has the same number of chromosomes. However, there are special cells in an animals body that only have ½ the number that the other cells have. These cells are called gametes They are used only in reproduction. Egg- female reproductive cell Sperm – male reproductive cell These develop from special cells in the body. When they are formed, the number of chromosomes is cut in ½. This process is called Meiosis. Gametes contain half the number of chromosomes as body cells. Not all organisms have the same number of chromosomes. Number of Chromosomes in various organisms Organism Body Cells Gametes Fruit Fly 8 4 Bull Frog 26 13 Human 46 23 Meiosis Type of cell division that produces gametes. It occurs in two parts Meiosis I Meiosis II These phases are similar to mitosis (cell division). At the end of meiosis II there are 4 daughter cells, which contain half the number of chromosomes as the original cell. The steps of Meiosis What you should do now… Answer Questions 1-9 on page 67 in your book for homework. It is due tomorrow. Take your time and make sure that your answers are neat and correct. Begin your Meiosis II drawing with the time remaining in class. I will assign you a due day, and you will have only 1 day in class to work on this assignment. You will be graded on NEATNESS!! If you need someone to help you write out the labels I will help you! What you should be doing… Get out your Chapter 3 Guided Note packet and a pencil or pen Put everything else on the floor. 3-3 What is DNA? Key terms DNA – large molecule contained in chromosomes Replication- process by which DNA is duplicated Protein Synthesis- process by which proteins are made RNA- molecule used in the making of proteins Discovery of DNA After the discovery of chromosomes, scientists began to question what they were made of. They discovered that chromosomes are made up of a large molecule called DNA, which stands for deoxyribonucleic acid. James Watson and Francis Crick are credited with the discovery of DNA’s structure in 1953. Structure of DNA The model used to describe the structure of DNA is called a double helix and looks like a twisted ladder. The sides of the ladder are made up of sugars and phosphates. The steps of the ladder are made up of 4 different nitrogen bases. Each base pairs with only 1 other base. Adenine (A) can only bond with Thymine (T) Guanine (G) can only bond with (C) Let’s try a couple stands… Write the complimentary strand (or the one that each base would pair with) for the strands below. REMEMBER! A=T and G=C 1.) GGTACATCGAT 2.) TGATCGATCAG Replication During Mitosis, the chromosomes replicate so that each new daughter cell get’s a copy. For this to happen, DNA must also replicate. This process is called replication. The DNA ladder breaks itself in half, like unzipping a zipper. Then new bases are added to each half of the zipper. The new DNA is an exact copy of the old DNA The role of DNA A single strand of DNA can have THOUSANDS of steps or base pairs. The arrangement of these pairs will code for a specific code, with determine what gene will be formed. Different genes determine the different kinds of inherited traits of an organism. How long is an actual gene? Protein Synthesis DNA controls organism’s traits by producing certain proteins at certain times. This is called protein synthesis. Proteins are made of molecules called amino acids, which are made by the ribosomes in a cell. DNA is found inside the nucleus, which is where protein synthesis begins. DNA is too big to fit through the nuclear membrane, so a special molecule is needed to take the code from the nucleus to the ribosome. This molecule is called RNA (ribonucleic acid). RNA is a little different than DNA It is single stranded (one side of the ladder) Instead of Thymine (T) it has Uracil (U) It copies the code from DNA then carries it to the ribosome. There it acts like a pattern where proteins can be built from. Ribosome reads the RNA and attaches the correct amino acids, which link together forming a protein. Protein synthesis summary… What you should do now… Complete Worksheet 3-3 for homework and turn it in tomorrow. What you should be doing… Get out your Chapter 3 Guided Note packet and a pencil or pen Put everything else on the floor. 3-4 What are Chromosomes? Key Terms Karyotype – organized display of an organism’s chromosomes Centromere – point of a chromosome where two parts meet Gene- parts of a chromosome that control inherited traits Allele- one of two or more forms of a particular gene Chromosomes The fine, threadlike structures called chromosomes are found in the cell’s nucleus. They control heredity Scientists study chromosomes using something called a karyotype. Karyotype – is a display of an organism’s chromosomes It is organized by shape and size The chromosomes are often numbered. Chromosome Structure Chromatin is a long thin strand of DNA that makes up chromosomes When a cell is getting ready to divide, the chromatin condenses and wraps around special proteins to give it an X shape. Each side of a chromosome is called a chromatid, and two chromatids are exact copies of each other. They are held together by a centromere. Genes Gene- a special part of the chromosome that controls inherited traits. It is found on a specific part of the chromosome. Gene determine hair color, eye color, ear shape, etc. They also control processes in your cells. Chromosome Pairs For organisms that carry out life through sexual reproduction (2 parents), chromosomes exist as pairs. An organisms gets 1 set from mom, and 1 set from dad. Ex.) 23 from mom, 23 from dad, give us our full 46. Chromosome pairs are often very similar in size and shape. Alleles Alleles are different versions of the same trait. Ex.) Trait – hair color Allele – brown hair vs. blonde hair Alleles for the same trait are ALWAYS found at the same place on the same chromosome What you should do now… What you should be doing… Get out your Chapter 3 Notes, and something to write with. Put everything else on the floor 3-5 Why can offspring differ from their parents? Key terms Homozygous – having 2 like genes for the same trait Heterozygous- having 2 unlike genes for the same trait Dominate gene- gene whose trait always shows itself Recessive gene- gene whose trait is hidden when the dominate trait is present Genes and Traits Gregor Mendel, the “Father of genetics” studied pea plants During his study he noticed that there must be a factor that affected how a plant was going to look. These factors are now called, “genes”. For example, he noticed that some of his plants were tall, and some where short. He then decided that there must be a gene for height. The height of a pea plant must be determined by 2 genes, one from each parent. Each trait of an organism must be determined by at least one gene from each parent. Homozygous Plants Mendel noticed that one kind of tall pea plant always had tall offspring. These plants have 2 tall genes, one from each parent. He also noticed that one kind of short pea plant always had short offspring. These plants have 2 short genes, one form each parent. These plants were homozygous. Heterozygous plants Mendel then tested to see what the offspring of a homozygous tall and a homozygous short would look like. They were also all tall. He called them heterozygous because he knew that had 2 unlike genes for a trait. Dominate Genes When you cross 2 different organisms, one trait always shows itself, and one is always hidden. Mendel then coined the terms: Dominate gene- a gene that always shows itself Recessive gene – a gene that is hidden when the dominate gene is present. What you should do now… What you should be doing… Get out your Chapter 3 Notes, a calculator and something to write with. Put everything else on the floor 3-6 How do genes combine in offspring? Key terms Punnett square – chart that shows possible gene combinations. Gene Symbols Organisms have at least 2 genes for most traits They receive at least one kind from each parent. Letters are used to represent combinations of genes. The dominate is always capital The recessive is always lower case Ex.) If we say that brown hair color is dominate over blonde hair color, it would look like this: B – brown b- blonde Let’s try a couple If brown eyes are dominate over green eyes If attached ear lobs are dominate over unattached Predicting Traits Suppose you have a father that is homozygous dominate for black hair (BB), and a mother who is homozygous recessive for brown hair (bb). How could you predict what color hair their children will have? A tool that is used to predict traits is called a Punnett square. It is a chart used to show possible combinations for offspring. Constructing a Punnett Square Step 1 – draw a square with 4 boxes in it. Step 2 – put the parents on the sides of the Punnett square Step 3 – fill in each square with the dominate gene Step 4- fill in each box with the recessive gene Your finished Punnett square should look like this: B b b B Bb Bb Bb Bb So what will the offspring look like? Every box of that Punnett square was Bb, so: It was 4/4 Bb, which is the same as 100% So all of the children will have black hair. They will all be heterozygous dominate, because they have both kinds of genes. Combining heterozygous genes When both parents are heterozygous (Bb) for a gene, the Punnett square will always show the same results: It looks like this: B b B BB Bb b Bb bb BB - ¼ = 25% Bb - 2/4 = 50% Bb – ¼ = 25% Let’s practice If you have a purple flowering plant that is homozygous dominate for it’s flower color is crossed with a homozygous recessive yellow flowering plant, what will the resulting offspring look like? If you cross 2 heterozygous purple flower plants, what will the resulting generations be? What you should do now… What you should be doing… Get out your Chapter 3 Notes, a calculator and something to write with. Put everything else on the floor 3-7 What are incomplete dominance and co-dominance? Key terms Incomplete dominance – pattern of inheritance in which alleles from both parents are blended Codominance - pattern of inheritance in which both alleles of a gene are expressed Incomplete Dominance Usually if an allele is dominant over another allele, the dominate one is the only that shows up in an offspring This type of inheritance is called incomplete dominance. In this case the offspring will show a blending of traits from each parent.