Chapter 11 Notes Meiosis
Chapter 11 Notes Meiosis BIOL 04102-03
Northwest Missouri State University
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Date Created: 10/06/16
CHAPTER 11 SINGLE GENE INHERITANCE AND MEIOSIS: ROCK FOR A CAUSE INTRODUCTION I. Mutation a. A change in the nucleotide sequence of DNA, which creates a new allele of a gene. b. Allele i. Alternative nucleotide sequences of the same gene. HOW IS CF INHERITED I. Genes a. Provide instructions for making proteins b. Units of inheritance II. Diploid a. Having two copies of every chromosome. b. Each body cell carries two copies of each chromosome c. Homologous chromosomes i. A pair of chromosomes that both contain the same genes. ii. In a diploid cell, one chromosome in the pair is inherited from the mother, the other from the father. III. Human cells have 23 pairs of homologous chromosomes. a. One chromosome from each parent. i. Diploid. b. The two copies (alleles) can either be identical or different. IV. Phenotype a. The visible or measurable features of an individual. b. Observable or measurable traits. V. Genotype a. The particular genetic makeup of an individual. b. Genes. VI. Sexual reproduction a. Gametes i. Specialized reproductive cells that carry one copy of each chromosome. 1. Haploid. ii. Sex cells iii. Egg and sperm cells iv. Haploid 1. One copy of each chromosome. b. Meiosis i. A specialized type of nuclear division that generates genetically unique haploid gametes. ii. Cell division for haploid cells. iii. Halves the number of chromosomes from 46 to 23. c. Zygote i. A cell that is capable of developing into an adult organism. 1. The zygote is formed when an egg Is fertilized by a sperm. ii. When a haploid sperm fertilizes a haploid egg. iii. Now carries two copies of every gene. 1. 46 chromosomes. iv. Divides by mitosis to become an embryo. 1. An early stage of development reached when a zygote undergoes cell division to form a multicellular structure. 2. Eventually grow into a human child. INFOGRAPHIC 11.3 d. Diploid organisms produce specialized sex cells. i. Gametes ii. Haploid 1. One copy of each chromosome. e. When a sperm fertilizes an egg… i. The resulting diploid zygote divides. 1. Mitotic cell division. ii. Creates a baby. 1. Diploid. VII.Meiotic cell division a. Produces haploid sperm and egg. b. Similar to mitotic division i. Except there are two separate divisions. 1. First separates homologous chromosomes. 2. Second separates sister chromatids. INFOGRAPHIC 11.4: MEIOSIS PRODUCES HAPLOID EGG AND SPERM. c. Cell cycl begins i. Each chromosome is replicated. ii. A diploid cell carrying 23 pairs of chromosomes replicates. iii. Each chromosome now consists of two identical sister chromatids. iv. Prepares to divide and enters the first of two divisions. d. Meiosis 1 i. Homologous chromosomes separate, halving the chromosome number. ii. Homologous chromosomes pair and line up in the middle of the cell. iii. The chromosomes of each pair separate and move to opposite sides. iv. Although each daughter cell is haploid, each chromosome still has two sister chromatids. e. Meiosis 2 i. Sister chromatids separate. ii. Creating four haploid daughter cells. iii. Each daughter cell will develop into egg or sperm. VIII. Meiosis contributes to the genetic diversity of offspring in other ways. a. Recombination 2 i. An event in meiosis during which maternal and paternal chromosomes pair and physically exchange DNA segments. ii. Homologous maternal and paternal chromosomes pair up and physically swap genetic information by exchanging DNA segments. iii. Crossing over. iv. Maternal chromosomes actually contain segments from paternal chromosomes and vice versa. b. Independent assortment i. The principle that alleles of different genes are distribute independently of one another, not as a package. INFOGRAPHIC 11.5 MEIOSIS PRODUCES GENETICALLY DIVERSE EGG AND SPERM. c. Recombination i. Before separating at meiosis 1, 1. Maternal and paternal chromosomes line up next to each other. 2. Physically exchange segments of DNA. 3. Maternal chromosomes contain segments from paternal chromosomes, and vice versa. d. Independent assortment i. Maternal and paternal chromosome pairs separate according to how they have randomly lined up in the cell. ii. Each time meiosis occurs, the chromosome pairs line up differently. 1. Different chromosome combination is produced in resulting gametes. iii. When all 23 chromosome pairs are considered, there are more than 8 million unique chromosome combinations possible. LIVING WITH THE DISEASE I. Recessive a. An allele that reveals itself in the phenotype only if a masking dominant allele is not present. b. When one allele masks the effect of another. c. This is the hidden allele. d. Lower-case letter. II. Dominant allele a. An allele that can mask the presence of a recessive allele. b. The normal allele, which conceals the recessive allele. c. Capital letter. III. Heterozygous a. Having two different alleles. b. A dominant and recessive allele. c. Mixed alleles IV. Homozygous 3 a. Having two identical alleles. b. Same alleles. c. Homozygous dominant i. Two dominant alleles. d. Homozygous recessive i. Two recessive alleles. V. Punnett Square a. A diagram used to determine probabilities of offspring having particular genotypes, given the genotypes of the parents. b. Reginald C. Punnett, devised this. c. Matches up the possible parental gametes and shows the likelihood that particular parental alleles will combine. VI. Carrier a. An individual who is heterozygous for a particular gene of interest, and therefore can pass on the recessing allele without showing any of its effects. b. That the offspring will carry the recessive allele. i. But will not have the disease because the allele’s effect is masked by the dominant allele. VII.Not all recessive alleles cause disease. a. Physical traits are the result of inheriting two recessive alleles of a gene. TABLE 11.1 INHERITED GENETIC CONDITIONS IN HUMANS b. Recessive trait i. Albinism 1. Lack of pigment in skin, hair, and eyes. ii. Cystic fibrosis 1. Excess mucus in lungs, digestive tract, and liver. 2. Increased susceptibility to infectious. iii. Sickle cell disease 1. Sickled red blood cells. 2. Damage to tissue. iv. Tay-Sachs disease 1. Lipid accumulation in brain cells. 2. Mental deficiency, blindness, and death in childhood. c. Dominant trait i. Huntington disease 1. Mental deterioration and uncontrollable movements. 2. Onset at middle age. ii. Freckles 1. Pigmented spots on skin. 2. Particularly on face and arms. iii. Polydactyly 1. More than five digits on hands or feet. iv. Dimples 1. Indentations in the skin of the cheeks. v. Chin cleft 1. Indentation in chin. 4 CHAPTER 11 SUMMARY I. Genes, which code for proteins, are the units of inheritance, physically passed down from parents to offspring. II. An organism’s physical traits constitute its phenotype. a. Its genes constitute its genotype. b. A person’s genotype cant always be determined from his or her phenotype. III. Humans are diploid organisms. a. Meaning they have two copies of each chromosome in their cells. b. Because chromosomes come in pairs, we have two copies of nearly ever gene in our body cells. c. These copies can be the same or different from each other. IV. Different versions of the same gene are called alleles. a. Alleles arise from mutations that change the nucleotide sequence of a gene. V. Alleles may be dominant or recessive. a. Dominant alleles can mask the effects of recessive alleles. i. Can be hidden. VI. Many traits result from carrying two recessive alleles. a. Others result from carrying one dominant allele. VII.Meiosis is a type of cell division that produces genetically distinct sperm and egg. VIII. Homologous chromosomes recombine and assort independently during meiosis to generate genetically diverse sperm and eggs. a. No two sperm or egg cells produced by the same person will be exactly alike. IX. Haploid gametes fuse randomly during fertilization. a. Generating genetically unique diploid zygotes. X. A Punnett square can help predict a child’s genotype and phenotype when the pattern of inheritance is known. a. Dominant or recessive. 5
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