Heredity Study Notes

Heredity Explain how meiosis results in the transmission of chromosomes from one generation to the next. Meiosis is a process that ensures the formation of haploid gamete cells in sexually reproducing diploid organisms— a. Meiosis results in daughter cells with half the number of chromosomes of the parent cell. b. Meiosis involves two rounds of a sequential series of steps (meiosis I and meiosis II). Describe similarities and/ or differences between the phases and outcomes of mitosis and meiosis. • Mitosis and meiosis are similar in the way chromosomes segregate but differ in the number of cells produced and the genetic content of the daughter cells. Explain how the process of meiosis generates genetic diversity. • • • Separation of the homologous chromosomes in meiosis I ensures that each gamete receives a haploid (1n) set of chromosomes that comprises both maternal and paternal chromosomes. During meiosis I, homologous chromatids exchange genetic material via a process called “crossing over” (recombination), which increases genetic diversity among the resultant gametes. Sexual reproduction in eukaryotes involving gamete formation—including crossing over, the random assortment of chromosomes during meiosis, and subsequent fertilization of gametes—serves to increase variation. The diagram above illustrates which of the following processes? 1. 2. 3. 4. 5. Crossing-over Base pair substitution Duplication Deletion Posttranscriptional processing A spermatocyte produces the following four sperm cells. These cells are the result of nondisjunction during which of the following phases? 1. 2. 3. 4. 5. Interphase (G1 or G2) Interphase (S) Mitosis Meiosis I Meiosis II If 2n = 48 for a particular cell, then the chromosome number in each cell after meiosis would be 1. 2. 3. 4. 5. 96 48 24 12 6 The events listed below generally take place during meiosis. I. II. III. IV. Synapsis occurs. Crossing-over is completed. Condensation of chromosomes begins. Separation of homologous chromosomes begins. Which of the following is the correct sequence of these events? a) b) c) d) e) I, II, III, IV II, I, III, IV III, I, II, IV III, IV, II, I IV, II, III, I Explain how shared, conserved, fundamental processes and features support the concept of common ancestry for all organisms. 1. DNA and RNA are carriers of genetic information; you should know this one by now. 2. Ribosomes are found in all forms of life. Yes, this too. 3. Major features of the genetic code are shared by all modern living systems. 4. Core metabolic pathways are conserved across all currently recognized domains. Explain the inheritance of genes and traits as described by Mendel’s laws. 1. Mendel’s laws of segregation and independent assortment can be applied to genes that are on different chromosomes. 2. Fertilization involves the fusion of two haploid gametes, restoring the diploid number of chromosomes and increasing genetic variation in populations by creating new combinations of alleles in the zygote— a) Rules of probability can be applied to analyze passage of single-gene traits from parent to offspring. b) The pattern of inheritance (monohybrid, dihybrid, sex-linked, and genetically linked genes) can often be predicted from data, including pedigree, that give the parent genotype/phenotype and the offspring genotypes/phenotypes. Assume that genes A and B are not linked. If the probability of allele A in a gamete is 1/2 and the probability of allele B in a gamete is 1/2, then the probability that both A and B are in the same gamete is 1. 2. 3. 4. 5. 1/2 x 1/2 1/2 + 1/2 (1/2) / (1/2) √(1/2) [that’s square root] |1/2 — 1/2|[that’s absolute value] In the pedigree above, circles represent females, squares represent males, and shaded figures represent individuals expressing a specific trait. The expression of this trait is most likely due to which of the following? 1. 2. 3. 4. 5. Allosome/sex-linked dominant inheritance Allosome/sex-linked recessive inheritance Autosomal dominant inheritance Autosomal recessive inheritance A codominant relationship of a single pair of alleles Explain deviations from Mendel’s model of the inheritance of traits. 1. Patterns of inheritance of many traits do not follow ratios predicted by Mendel’s laws and can be identified by quantitative analysis, where observed phenotypic ratios statistically differ from the predicted ratios— a. Genes that are adjacent and close to one another on the same chromosome may appear to be genetically linked; the probability that genetically linked genes will segregate as a unit can be used to calculate the map distance between them. 2. Some traits are determined by genes on sex chromosomes and are known as sex-linked traits. The pattern of inheritance of sex-linked traits can often be predicted from data, including pedigree, indicating the parent genotype/phenotype and the offspring genotypes/phenotypes. 3. Many traits are the product of multiple genes and/or physiological processes acting in combination; these traits therefore do not segregate in Mendelian patterns. 4. Some traits result from non-nuclear inheritance— a. Chloroplasts and mitochondria are randomly assorted to gametes and daughter cells; thus, traits determined by chloroplast and mitochondrial DNA do not follow simple Mendelian rules. b. In animals, mitochondria are transmitted by the egg and not by sperm; as such, traits determined by the mitochondrial DNA are maternally inherited. c. In plants, mitochondria and chloroplasts are transmitted in the ovule and not in the pollen; as such, mitochondria-determined and chloroplast-determined traits are maternally inherited. A series of crosses is performed with fruit flies (Drosophila melanogaster) to examine inheritance of the genes vestigial (vg) and cinnabar (cn). The recessive vg allele causes small, malformed wings called vestigial wings. The recessive cn allele causes bright-red eyes called cinnabar eyes. In the first cross, a female with wild-type wings and eyes is mated with a male with vestigial wings and cinnabar eyes. All the F1 individuals have wild-type wings and eyes. In the second cross, female F1 flies are mated with males with vestigial wings and cinnabar eyes. The phenotypes of 500 F2 individuals are shown in the table. Which of the following is the most likely explanation of the results? 1. 2. 3. 4. The two genes are located on two different chromosomes. The two genes are sex-linked. The two genes are located on mitochondrial DNA. The two genes are linked on an autosome. Eye pigment in a particular strain of fly is determined by two genes. An autosomal gene that controls the color of the pigments in the eye has two alleles: a dominant allele (R) that results in red eyes and a recessive allele (r) that results in sepia eyes. A sex-linked gene that controls the expression of the colored pigments also has two alleles: a dominant allele (T) that allows for expression of the colored pigments and a recessive allele (t) that does not allow for expression of the colored pigments. Individuals without a T allele have white eyes regardless of the alleles of other eye-color genes. Which of the following represents a cross between a white-eyed female and a red-eyed male? 1. 2. 3. 4. TtXRXR × ttXrY TtXrXr × ttXRY RRXTXT × RrXTY RrXtXt × RrXTY Gregor Mendel’s pioneering genetic experiments with pea plants occurred before the discovery of the structure and function of chromosomes. Which of the following observations about inheritance in pea plants could be explained only after the discovery that genes may be linked on a chromosome? 1. Pea color and pea shape display independent inheritance patterns. 2. Offspring of a given cross show all possible combinations of traits in equal proportions. 3. Most offspring of a given cross have a combination of traits that is identical to that of either one parent or the other. 4. Recessive phenotypes can skip a generation, showing up only in the parental and F2 generations. In sheep, eye color is controlled by a single gene with two alleles. When a homozygous browneyed sheep is crossed with a homozygous green-eyed sheep, blue-eyed offspring are produced. If the blue-eyed sheep are mated with each other, what percent of their offspring will most likely have brown eyes? 1. 2. 3. 4. 5. 0% 25% 50% 75% 100% Explain how the same genotype can result in multiple phenotypes under different environmental conditions. Environmental factors influence gene expression and can lead to phenotypic plasticity. Phenotypic plasticity occurs when individuals with the same genotype exhibit different phenotypes in different environments Explain how chromosomal inheritance generates genetic variation in sexual reproduction. 1. Segregation, independent assortment of chromosomes, and fertilization result in genetic variation in populations. 2. The chromosomal basis of inheritance provides an understanding of the pattern of transmission of genes from parent to offspring. 3. Certain human genetic conditions can be attributed to the inheritance of a single affected or mutated allele or specific chromosomal changes, such as nondisjunction.