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Transcript
Heredity Vocabulary Heredity Big Ideas Heredity and Reproduction Understand and explain that every organism requires a set of instructions that specifies its traits, that this hereditary information (DNA) contains genes located in the chromosomes of each cell, and that heredity is the passage of these instructions from one generation to another. Heredity Is the passing of physical characteristics, or traits, from parents to offspring Genetics is the study of heredity Parents are referred to as the P generation The first offspring are referred to as F1 The offspring of the F1 generation are the F2 generation Note: F stands for “filial”, or son Gregor Mendel, a monk living in the mid nineteenth century, discovered the principles of heredity through his experiments breeding pea plants and noticing which traits were passed from parent to offspring Mendel’s work was unknown during his lifetime, but was rediscovered during the early 1900s Mendel is known as the Father of Genetics Heredity Different forms of the same gene are called alleles During fertilization, sperm from the male parent and eggs from the female parent join to form new offspring An organism’s traits are controlled by the alleles it receives from its parents Heredity In the system of complete dominance, alleles can be dominant or recessive A dominant allele’s traits always show up in the offspring A recessive allele’s traits is hidden whenever the dominant allele is present Heterozygous means that the two inherited alleles are different. An organism with heterozygous traits is called a hybrid Homozygous means that the two inherited alleles are the same (either both dominant or both recessive). An organism that is homozygous is called a purebred Heredity Dominant versus recessive traits in humans Trait eye coloring Dominant brown eyes Recessive grey, green, hazel, blue hair dark hair non-red hair curly hair widow's peak blonde, light, red red hair straight hair normal hairline facial features dimples freckles no dimples no freckles Heredity Using Punnett squares to predict inherited traits – – – – A Punnett square shows how dominant and recessive traits combine Capital letters stand for dominant traits Lowercase letters stand for recessive traits Example: Brown eyes (B) are dominant over blue eyes (b) Heredity Using Punnett squares – – If one parent is a hybrid brown-eyed (Bb), and the other parent is a pure blue-eyed (bb), this is how the Punnett square would look. First, write the alleles of one parent on the side and the other on the top of the square b B b b Heredity Using Punnett squares – Rewrite each allele straight across or straight down – By convention, capital letters go first – Remember, B (brown eyes) dominates b (blue eyes). What you will see is the offspring’s genotype, or actual genes. Let’s see what the eye colors are Mother’s traits Father’s traits b b B Bb Bb b bb bb Heredity Using Punnett squares – – Remember, B (brown eyes) dominates b (blue eyes). So, in this Punnett square, the possible offspring (on average) will be 50% brown and 50% blue. The actual appearance of the organism is its phenotype. b b B Bb Brown Bb Brown b bb Blue bb Blue Heredity Using Punnett squares – – Let’s try again with two parents who are both hybrids for eye color First, write the alleles of on parent on the side and the other on the top of the square B B b b Heredity Using Punnett squares – – – – Rewrite each allele straight across or straight down By convention, capital letters go first Remember, B (brown eyes) dominates b (blue eyes). Now lets see what the eye colors are B b B BB Bb b Bb bb Heredity Using Punnett squares – Remember, in humans, B (brown eyes) dominates b (blue eyes). So the possible offspring (on average) will be 75% brown and 25% blue. b b B BB Brown Bb Brown B Bb Brown bb Blue Heredity Using Punnett squares – Another way to look at this is that the offspring, on average, will be 25% homozygous dominant (BB), 25% homozygous recessive (bb) and 50% heterozygous (Bb) b b B BB Brown Bb Brown B Bb Brown bb Blue Heredity Using Punnett squares – – – Let’s try some Punnett square problems Write them on your own paper In humans, brown eyes (B) is dominant over blue eyes (b). One parent is pure brown eyes, and the other parent is pure blue eyes, create the Punnett square to determine the average of each eye color Heredity Using Punnett squares – A brown-eyed man marries a blue-eyed woman and they have three children, two of whom are brown-eyed and one of whom is blueeyed. Draw the Punnett square that illustrates this marriage. Heredity Using Punnett squares – In fruit flies, gray body color is dominant (G), and ebony body color is recessive (g). What happens when a pure gray fruit fly has offspring with an pure ebony fruit fly? Heredity Using Punnett squares – – In a species, tall (T) is dominant and short (t) is recessive. If a pure short parent (tt) mates with a tall parent (TT or Tt), what would the percentages of tall and short offspring be? You will need to draw two Punnett squares to answer this one Heredity Using Punnett squares – There is a second system you need to know, called co- dominance – In this system, more than two alleles exist. – For example, with blood types, there are A alleles, B alleles and b alleles (recessive) Heredity Using Punnett squares – “Could a man with type B blood and a woman with type AB produce a child with type O blood?" – The woman must be AB, and the man may be either BB or Bb. Draw the two Punnett squares and see if any of the offspring could have type O (bb). Note: the only possible outcomes for blood type are Bb (Type B), bb (Type O), Ab (Type A) and AB (Type AB) Heredity Using Punnett squares – There is a third system you need to know, called incomplete dominance – In this system, neither trait dominates, the offspring’s traits are a mixture of both. – For example, red ( R) and white (W) would combine to form pink (RW) R R W RW RW W RW RW Chromosomes and Inheritence Chromosomes exist in pairs – – – In the early 1900s, Walter Sutton, an American geneticist, looked at chromosomes in grasshoppers His hypothesis was that chromosomes are the key to understanding how traits are passed from parents to offspring Sutton discovered that sex cells in grasshoppers (sperm and egg cells) only had half the number of chromosomes as regular body cells Chromosomes and Inheritence Chromosomes exist in pairs – – – – In an organism’s body cells, chromosomes exist in pairs In an organism’s sex cells, chromosomes exist alone These sex cells are called sperm in males, ova or egg cells in females During fertilization, chromosomes in sperm and egg cells merge to form a cell with chromosomes in pairs One half of each pair came from the male parent One half of each pair came from the female parent Chromosomes and Inheritence Chromosomes and Inheritance How do sex cells form? – – – – – Meiosis is the process through which sex cells are formed During meiosis, chromosome pairs separate into two cells The sex cells that form later have only half as many chromosomes as the other cells in the organism Note: females have two X chromosomes Note: males have one X and one Y chromosome Chromosomes and Inheritance Before meiosis Chromosomes and Inheritance After meiosis Sex cells Sexual versus asexual reproduction Reproduction – – – During sexual reproduction, two parents contribute different DNA This results in a new organism with traits of both parents Sex cells are formed through the process of meiosis Sexual versus asexual reproduction Reproduction – – During asexual reproduction, one parent produces an identical offspring New cells are created through the process of mitosis Sexual versus asexual reproduction Advantages Disadvantages Asexual Can quickly produce many offspring No variation in offspring, may not survive in a new environment Sexual Variation in offspring, some may survive if environment changes Finding mate, waiting for offspring to develop Classwork 1 - Heredity 1. 2. 3. 4. 5. 6. 7. Different forms of the same gene are called The study of heredity The “Father of Genetics” Define dominant allele Define recessive allele Define Heterozygous Define Homozygous Classwork 1 – Heredity (continued) 8. In __________ dominance, neither trait dominates, and the offspring’s traits are a mixture of both. 9. In __________ dominance, dominant triats mask recessive traits 10. In __________, more than two alleles are present Human Genetics Pedigree: A family tree that shows the presence or absence of a trait according to family relationships over several generations Human Genetics Humans inherit 23 pairs of chromosomes (46 total): 23 from Mom and 23 from Dad There is no noticeable genetic differences between different “races” There is no gene for alcoholism. There IS a gene that, when not properly functioning, gives a greatly increased likelihood that the person will develop alcoholism IF certain circumstances occur (like the person drinks alcohol) – A dysfunction on the gene BRAC1 causes one type of breast cancer. That does not mean that everyone with BRAC1 is destined to have breast cancer. Also, there are plenty of people without any dysfunction on BRAC1 that have breast cancer. Human Genetics Some human diseases are caused by genetic disorders – Hutchinson's Disease (dominant) – Sickle Cell (recessive) – Cystic Fibrosis (recessive) Some diseases are X-linked (only found on the X chromosome) – Hemophilia Some diseases are caused by having an extra chromosome – Down’s syndrome (extra chromosome #21) Sickle Cell Disease An altered hemoglobin protein (red blood cells) allows the red blood cells to change shape when under pressure or stress (like during exercise). This recessive disorder has remained in constant levels in the population because it makes the person immune to malaria Sickle Cell Disease An altered hemoglobin protein A homozygous person for the disease frequently dies younger than normal. A heterozygous person for the disease can lead a normal life and be immune to malaria; the heterozygous person has both sickle shaped red blood cells and round shaped red blood cells. What type of dominance is shown? X-linked diseases If the defective gene only occurs on the x chromosome then it is called an x-linked disease. In this case, women may be unaffected carriers while all men will be affected (as they only have one x chromosome). In pedigrees, these conditions are passed from mother to son. -Ex. Color blindness and male pattern baldness (not diseases but still x-linked) X-linked diseases An example of an x-linked disease is Hemophilia. In this condition, the person affected has platelets that do not function normally. When cut, the hemophiliac will bleed without clotting. These individuals used to always die young but new modern technology has allowed them to live longer lives. About 1/6000 people in America has hemophilia Classwork 2 – Human Genetics 1. 2. Define pedigree Humans inherit __ pairs of chromosomes, half from each parent This gene causes one type of breast cancer This genetic disorder affects red blood cells In this x-linked disease, the person affected has platelets that do not function normally, which means they may bleed to death without clotting. Even though her great-great grandmother Queen Victoria was a carrier of hemophilia, the children of this queen do not have the genetic disorder Genetics