NAME_________________________________ CLASS:_____________ Unit 4 - Genetics: The Science of Heredity Mendel’s Work Gregor Mendel was a priest in the 19th century who loved to garden. While tending his garden he wondered why some plants had traits similar to their parents, and some plants had different traits then those of their parents. _____________: Each different form of a characteristic that an organism can pass on to it’s offspring. NAME_________________________________ CLASS:_____________ Mendel decided to study _____________. His research would eventually earn him the nick name “the father of ______________”. _____________: the passing of physical characteristics from parent to offspring. _____________: the scientific study of heredity. Mendel started his experiments with ________________ plants. _____________: an organism that is the offspring of many generations that have the same trait. (purebred short pea plants come from short parents and short grandparents, and short great grandparents) Once Mendel had purebred plants, he crossbred plants with different traits with one another. In Mendel’s experiments, he called plants in the first cross the parental generation or ________________________. The offspring of the P genertation he called the _________________________. The offspring of the F1 generation he called the ________________________. NAME_________________________________ CLASS:_____________ Mendel’s Results In all of Mendel’s crosses only one form of the trait appeared in the F1 generation, however, in the F2 generation the lost form of the trait always reappeared in about__________ of the plants. Dominant and Recessive Alleles _________________: A section of the DNA that codes for a specific trait. (hair color gene) _________________: the different forms of a particular gene. (brown or blonde) An organisms traits are controlled by the alleles it inherits from it’s parents. Some alleles are dominant while other alleles are recessive. A _________________ allele is one whose trait always shows up in the organism when the allele is present.(written as a _______________ letter) A _________________ allele is one whose trait is hidden when the dominant allele is present. (written as a__________________ letter) NAME_________________________________ CLASS:_____________ Inheriting Alleles For every _____________ you have, your DNA is carrying 2 __________. One came from your _____________and one came from your _____________. If both are the _________________ version, you show the ______________ trait. If both are the ________________ version, you show the ______________ trait. If one is the ___________________ version and one is the _______________ version, you show the ___________________ trait. Genotypes and Phenotypes An organism that has two identical alleles for a trait is said to be _____________________. RR= homozygous _________________ rr= homozygous _________________ An organism that has two different alleles for a trait is said to be _____________________. Rr = heterozygous An organism’s__________________ is its physical appearance or visible traits. (tall, blonde, round seeds, brown eyes) An organism’s __________________ is its genetic makeup or allele combinations. (Tt, bb, RR, Bb) NAME_________________________________ CLASS:_____________ The Cell and Inheritance According to _____________________________________, genes are carried from their parents to their offspring on _____________________. Remember, humans have 46 chromosomes. Those chromosomes are in pairs. 23 come from the father’s ____________, and 23 come from the mother’s ______________. When the sperm and egg come together, the resulting ______________ has all 46 chromosomes. Meiosis How do sperm and eggs end up with only half the number of chromosomes? Instead of dividing by _________________, the parent cells of sperm and eggs divide by a process called _______________. During meiosis the chromosomes pairs separate and are distributed to two different cells. The resulting cells have only ____________ as many chromosomes as the other cells in the organism. When the chromosomes pairs separate and go into two different sex cells, so do the alleles carried on each chromosome. One allele from each pair goes to each sex cell. NAME_________________________________ CLASS:_____________ NAME_________________________________ CLASS:_____________ Probability and Heredity _________________is a number that describes how likely it is that an event will occur. Probability can be expressed as a ____________, or as a _______________. If you flip a coin, there is a one in two chance it will land on heads…. ½, or 50% If you roll a dice, there is a one in six chance you will roll a 5… 1/6, or about 17%. Independence of Events When you toss a coin more than once, the results of one toss do not affect the results of the next toss. Flipping a heads the first time, does not make you more likely to flip a tails the next time. Punnett Squares A _______________ _____________ is a chart that shows all possible combinations of alleles that can result from a genetic cross. NAME_________________________________ CLASS:_____________ NAME_________________________________ CLASS:_____________ Incomplete Dominance In __________________ _______________, neither allele is dominant or recessive to the other allele. As a result, the alleles ____________ and show a third possible phenotype in the offspring. Codominance In ________________, neither alleles is dominant to the other, so heterozygous organisms show __________ of the possible phenotypes at the same time. NAME_________________________________ CLASS:_____________ NAME_________________________________ CLASS:_____________ NAME_________________________________ CLASS:_____________ Sex Linked Traits The genes of some traits are carried on the sex chromosomes. These traits are called ________________ __________________. Because males only have one X chromosome, often even recessive alleles carried on the X chromosome will appear in the male phenotype. Hemophilia Colorblindness Many more males are colorblind than females. NAME_________________________________ CLASS:_____________ Pedigrees A pedigree is a chart that shows a family tree. Geneticists use pedigrees to track which members of a family have a particular trait and which people are “_______________”.