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Name ________________ Test Date ___________UNIT 8 – Meiosis & Genetics Although the resemblance between generations of organisms had been noted for thousands of years, it wasn’t until the 1800s that scientific studies were carried out to develop an explanation for this. Today we know that we resemble our parents because of _______________, which is the set of characteristics we receive from ______________________. The study of heredity is known as _________________. What type of cells undergoes Meiosis? What type of cells undergoes Mitosis? What is a gamete? Give examples. If 2n= 800, than n=________ What are homologues pairs of chromosomes? What is the end result of Meiosis? How is Meiosis different compared to Mitosis? What is crossing over? What is a benefit to crossing over? I. SEXUAL REPRODUCTION & MEIOSIS (pp. 275-278) In sexual reproduction, an egg and sperm cell fuse together to create a fertilized egg or _______________. Egg and sperm cells are known as _____________. Gametes are the only cells in the body that are not produced by ________________. Instead gametes are created through a special process of cell division called ___________________ which ______________ the chromosome number. Meiosis only occurs in the _____________ of females and the ___________ of males. A. Chromosome Number 1. Human _____________ cells, or body cells, contain ________ chromosomes. Somatic cells are ____________ or ________ because these cells contain a ____________ set of chromosomes – half (______) from __________ and half (______) from __________. These “matching” chromosomes are known as ________________________________. A homologous pair is a pair of chromosomes – one from each parent, with the same ____________________ or ____________. 2. Human gametes (___________ and ____________) contain _______ chromosomes. They are _________________________ or ___________. These cells contain __________ the total number of chromosomes, a ______________ set of chromosomes. When the gametes fuse together in _____________________, the resulting _______________ has _______ chromosomes. B. Meiosis Gametes are formed in meiosis – a special type of cell division that only occurs in the _______________ of females and ______________ of males. In meiosis, DNA is replicated once in ______ of _____________, but the cell goes through two cell divisions, resulting in ______ cells with _______ the original chromosome number. Meiosis occurs in two stages: 1. Meiosis I - Prior to meiosis I, the DNA is replicated in _____ of ____________________. When the chromosomes, each consisting of 2 ________________________ line up in the middle of the cell in ________________ I, they line up in __________________ pairs. In anaphase I and telophase I, the homologous pairs _______________, but the sister chromatids and __________________ are still intact. Two cells are formed, each with _______ pairs of __________________________ making up _______ chromosomes, but there are no longer any ______________________________ present, so the two cells are _________________ or ______. 2. Meiosis II - The process continues with the two cells formed moving directly into prophase II without any further ____________________________. After the chromosomes align in the middle of the cell in _________________ II, this time the sister chromatids are pulled apart in _______________ II. Two new cells are formed from each of the two cells formed in Meiosis I, resulting in a total of ___________ new cells, each with ____________the original number of chromosomes. The cells produced are called ____________________. C. Crossing Over Crossing over occurs during ________________ when __________________ pairs of chromosomes come together. A portion of one __________________________ may be broken off and exchanged with the corresponding portion of a sister chromatid of the homologous chromosome. Crossing over is very common and _____________________ the genetic variability in offspring. Unit 8- HISTORY OF GENETICS Why is Gregor Mendel known as the “Father of Genetics”? Define & Give an example of a trait. What is the difference between crosspollination and self – pollination? If your parents were the F1 generation, who would be the P generation, and who would be the F2 generation? Read about Gregor Mendel (pp. 263-270) and write at least 8 characteristics about him around his picture. A. Gregor Mendel – Known as the “Father of _______________”, Mendel is famous for his experiments with ________ plants. He used true-breeding pea plants, which means _________________________ and characteristics always show. This generation of true-breeding plants is known as ______ generation. Mendel studied seven ______________, including plant height, seed color, flower color, etc. A trait is an ________________________________. Pea plants cross-pollinate, meaning pollen from one plant fertilizes an egg from another, but they can also self-pollinate, meaning pollen can fertilize egg from ______________ plant. Mendel controlled the fertilization process of the pea plants by preventing __________________________________ and controlling ___________________________________. B. Mendel’s Results 1. P generation – Crossed __________________ plants with one trait with ________________ plants with the other. For example, _____________________________________________ 2. F1 generation – Offspring produced from _________________. In F1, one trait seemed to _____________. For example, tall plants X short plants = __________________________. 3. F2 generation – Offspring produced from _________________. In F2, trait that disappeared in F1 reappeared in __________ of the offspring; the other ¾ showed _____________________________. C. Mendel’s Principles – After analyzing his results carefully, Mendel formed conclusions that increased understanding of inheritance and opened the door for the study of genetics. What are alleles? 1. Individual units called ___________ determine inheritable characteristics. A gene is a portion of ___________ that codes for a specific ____________. If you have 2 of the SAME alleles you are considered _______________, if you have 2 DIFFERENT alleles, you are ___________ 2. For each gene, an organism inherits two alleles, one from each __________________. Alleles are different forms or ____________________ of a ___________. a. If the two alleles are the same, the organism is said to be _________________ for that trait and the allele will be expressed. What is the difference between dominant & recessive traits? What terminology would be described if I said “The dog was black” ? What terminology would be descried if I said “ The dog was BB”? Describe the Principle of Segregation in your own words. b. If the two alleles differ, the organism is said to be ___________________ for that trait and only one allele will be expressed. The expressed allele is the ______________ allele, designated by an __________-case letter. The allele that is not expressed in a heterozygous trait is _________________, designated by a _____________-case letter. A recessive allele is only expressed when an organism is ________________. 3. In meiosis, the two alleles for a trait segregate (_______________). Each egg or sperm cell receives a copy of one of the two alleles present in the somatic cells of the organism. Due to the random separation of chromosomes in meiosis, there is a _________ chance that a copy of that allele will end up in the gamete produced. This is known as the principle of segregation. D. Genetics Terminology 1. Phenotype - ________________ description of trait; for example, ______________ 2. Genotype – Genetic make-up of an organism or set of alleles; for example, ________________ 3. Application of Terminology - If round pea seeds are dominant to wrinkled pea seeds, round is designated _____ and wrinkled is designated ______. a. Homozygous dominant for pea seed shape is written ______. Seed shape? __________ Genotype = _____________; Phenotype = __________________ b. Heterozygous for pea seed shape is written _______. Seed shape? _______________ Genotype = _____________; Phenotype = __________________ c. Homozygous recessive for pea seed shape is written _______. Seed shape? _________ Genotype = _____________; Phenotype = __________________ III. ANALYZING INHERITANCE (pp.135-137) A. Probability Due to the law of segregation, if you know the genotype of the parents, you can predict the likelihood of a trait occurring in the offspring. Probability can be written 3 ways. The probability of a coin coming up heads after being flipped is (fraction) _____, (ratio) ________, or (percent) _______. B. Punnett Squares A Punnett square is a tool used to predict the possible outcomes of _______________ and ____________________; in other words, a Punnett square is used to determine the probability of certain traits appearing in offspring. IV. PUNNETT PRACTICE **Please note: To earn full credit, you must include a key and cross with each problem!** A. Construct a Punnett square to determine the probability of white flowers if a heterozygous purple (Pp) flower is crossed with a homozygous white (pp) flower. Key: ____________________________ Cross: _________________________ Genotype ratio: = ___________________ Phenotype ratio:= ___________________ B. Construct a Punnett square to determine the probability of short pea plants if a homozygous tall (TT)plant is crossed with a heterozygous tall (Tt) plant. Key: _____________________ Cross: ___________________ Genotype ratio: = ___________________ Phenotype ratio:= ___________________ V. DIHYBRID CROSSES (pp. 270-271) The Punnett squares we have been doing are known as ___________________________________, meaning that only one trait has been considered at a time. In a dihybrid cross, ________ different ____________ on 2 different _____________________ are analyzed. A. If a pea plant with genotype RRYy (round, yellow peas) is crossed with a pea plant with genotype rrYy (wrinkled, yellow peas), what would the results be? Key: R = round, r = wrinkled; Y = yellow, y = green Cross: ________________________________________ Genotype ratio: ______________________________________________ Phenotype ratio: ______________________________________________ B. Key: G = gray body g = black body R = red eyes r = black eyes Cross: GGRr X Ggrr What are the phenotypes of the parent fruit flies? ________________________________ Cross: ___________________________________ Genotype ratio: ___________________________________________ Phenotype ratio: __________________________________________ VI. A CLOSER LOOK AT HEREDITY (pp. 272, 273) A. Incomplete Dominance – Neither allele has “complete” dominance over the other - heterozygous phenotype is a ____________________________________________________ For example, in snapdragons, ____________________________________________________ Cross: _______________________ Genotype ratio: __________________ Phenotype ratio: _________________ B. Codominance – Both alleles _____________ dominance and are always __________________ if present. For example, ________________________________________________________________________ Cross: ________________________________________ Genotype ratio: ________________ Phenotype ratio: _______________ C. Polygenic Traits – “_________________________” Many traits are controlled by more than one gene. Examples include _____________________________________________________ D. Multiple Alleles – Many genes have more than ___________ alleles, although an individual only has _____ alleles for the gene. An example is _______________. There are _______ possible alleles for this gene. Suggested Study Questions p. 283 (1-5, 11, 12, 17-20)