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Name __________________________________________________________ Study Guide – Chapter 6 Meiosis, Mendel and Punnett Squares 6.1 Define the following. Somatic cell – body cells, make up most of your body tissues and organs. Example: spleen, kidneys, eyeballs Gamete – sex cells, Example: eggs, sperm Homologous chromosome – 2 chromosomes – one inherited from the mother, one from the father – that have the same length and look – they have copies of the same genes although the copies may differ Diploid – 2n – a cell that has 2 copies of each chromosome – one from the mom and one from the dad Haploid – n – a cell that has only one copy of each chromosome Meiosis – cell division that divides a diploid cell into a haploid cell – necessary for sexual reproduction. Fertilization – the fusion of an egg and sperm Think about it and complete the following questions FULLY!!! Where are the germ cells located in the human body? In the reproductive organs – the ovaries and testes Is the cell that results from fertilization a haploid or diploid cell? Explain why. Diploid – the combination of 23 chromosomes from the mom and 23 chromosomes from the dad restores the diploid number to 46. Does mitosis or meiosis occur more frequently in your body? Explain why. Mitosis occurs throughout an organisms lifetime throughout many cells of the entire body, compared to meiosis, which only occurs at certain times and only in the reproductive organs. Do you think the Y chromosome contains genes that are critical for an organism’s survival? Explain your reasoning. No, females do not have a Y chromosome, and they are able to survive 6.3 Define the following Trait – distinguishing characteristics that are inherited such as eye color, tail length, leaf color Genetics – the study of biological inheritance patterns and variation in organisms Purebred – A uniform, genetic line (example: a line of plants that has self-pollinated for long enough) Cross – the mating of two organisms Law of Segregation – states that 1. organisms inherit two copies of each gene, one from each parent 2. organisms donate only one copy of each gene in the gametes, thus the two copies of each gene segregate, or separate during gamete formation Answer the following questions in complete sentences. Who is Mendel? What did he study? Mendel was an Austrian monk in the 1800’s - laid the groundwork for genetics. He is called the “father of genetics.” He revealed patterns of inheritance. Why is it important that Mendel began with purebred plants? The units of color (purple and white) were both individually present. They had neither blended together nor vanished. Practice Complete the following problems. A heterozygous, smooth pea pod plant is crossed with a wrinkled pea pod plant. Predict the offspring from this cross. a. What is the genotype of the parents? Ss and ss b. Set up a Punnett Square with possible gametes. c. Fill in the Punnett square. 6.4 d. What is the predicted genotypic ratio for the offspring? Ss:ss 2 :2 e. What is the predicted phenotypic ratio for the offspring? Smooth : Wrinkled 2 : 2 Define the following Gene – a piece of DNA that provides a set of instructions to a cell to make a certain protein. Allele – any alternative forms of a gene that may occur at a specific locus Homozygous – two of the same allele at a specific locus Heterozygous – two different alleles at a specific locus (example: one codes for white flowers while the other codes for purple flowers) Genotype – the genetic makeup of a specific set of genes – the LETTERS Phenotype – the physical characteristics, or traits, of an individual organism – WHAT IT LOOKS LIKE Dominant – the allele that is expressed when two different alleles or two dominant alleles are present Recessive – the allele that is only expressed when two copies are present Answer the following questions in complete sentences. How are the terms genes, locus and allele related? All have something to do with a particular segment of DNA, or nucleotides. A gene is a region of DNA, a series of nucleotides that codes for a protein. It can come in different forms, called alleles, that code for the same general type of information but the specific vary. The locus tells where a particular gene or allele is located on a chromosome. Explain why an organism’s genotype may be homozygous dominant, homozygous recessive or heterozygous, but never heterozygous recessive. The only way a phenotype or genotype can be recessive is if both alleles are recessive. Explain the difference between phenotype and genotype. Phenotype is the physical characteristics – or what you see – genotype are the letters representing the alleles. A purebred tall plant is crossed with a purebred short plant. All the F1 offspring are tall. What can you say about the allele for tallness? The tallness is the dominant gene. Practice. In humans, widow’s peak (W) is dominant over straight hairline (w). A heterozygous man for this trait marries a woman who is also heterozygous. a. What are the parents genotypes? Ww and Ww b. List possible genotypes of their offspring WW and Ww and ww c. List the phenotypic ratio for their children Widow’s Peak : Straight hairline 3 : 1 6.5 Define the following Punnett square – a grid system for predicting possible genotypes of offspring Monohybrid cross – cross that examines the inheritance of only one trait Dihybrid cross – cross that examines the inheritance of two different traits Law of Independent Assortment – that allele pairs separate independently of each other during gamete formation, or meiosis. Probability – the likelihood, or the chance, that a particular event will happen. Answer the following questions. F = purple f = white From an FF x FF cross, what percent of offspring would have purple flowers? 100% What do the grid boxes in a Punnett square represent? The possible offspring How did Mendel’s dihybrid crosses help him develop his second law? Mendel was able to observe that the inheritance of one trait did not influence the inheritance of a second trait. A fruit fly has diploid cells with 8 chromosomes. Explain how many chromosomes are in it haploid gametes. 4 chromosomes = half = haploid Meiosis is a continuous process, but we can think of it as taking place in 2 stages, Meiosis I and Meiosis II. Describe the products of each stage. How do the products of Meiosis I differ from those of Meiosis II? Meiosis I divides homologous chromosomes, produces diploid cells Meiosis II divides sister chromatids., produces haploid cells Gametes Each of the arrows is pointing to a different part of the Punnett square, what do those letters represent? Possible offspring REMEMBER TO GET MORE PRACTICE USING THE DIRECTIONS BELOW!! Please go to www.classzone.com - choose High School Science and New Jersey - choose Biology 2010 Book - Under “Assessment,” Select “Section Quizzes” - Choose Unit 3: Genetics on the left hand column - Take the quizzes for the Chapter 6.1 – Chapter 6.4