Chapter 13: Meiosis and Sexual Life Cycles 1) Genes are the units of heredity, and are made up of segments of DNA. 2) In asexual reproduction, one parent produces genetically identical offspring my mitosis. In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents. 3) Humans have somatic cells, which are any cell other than a gamete, have 23 pairs of chromosomes. A karyotype is an ordered display of the paired of chromosomes from a cell. The 2 chromosomes in each pair are called homologous chromosomes or homologs.
The sex chromosomes are X and Y. Human females have a homologous pair of X chromosomes (XX). Human males have one X and Y chromosome. The 22 pairs of chromosomes that do not determine sex are called autosomes. Each pair of homologous chromosomes includes one chromosome from each parent. The 46 chromosomes in a human somatic cell are two sets of 23 one from the mother and one from the father. A diploid cell (2n) has two sets of chromosomes. For humans the diploid number is 46 (2n=46). 4) Meiosis is the production of gametes that result in one set of chromosomes in each amete.
Gametes fuse to form a diploid zygote that divides by mitosis and develop into a multicellular organism. 5) Mitosis and meiosis are alike in the respect that go through most of the same phases, and are used for reproduction purposes. However, meiosis results in sexual reproduction, in order to create multicellular organisms, occurring in only animals, humans, fungi, and plants, whereas mitosis occurs in all organisms. Mitosis only goes through one division, has the same number of chromosomes, and creates only two diploid cells.
Meiosis undergoes two divisions, he creation of four haploid cells, and half reduces the chromosomes. 6) 7) In the first cell division (meiosis l), homologous chromosomes separate. Meiosis I results in two haploid daughter cells with replicated chromosomes; it sis called the reductional division. In the second cell division (meiosis II), sister chromatids separate. Meiosis II results in four haploid daughter cells with unreplicated chromosomes, it is called the equational division. Meiosis I is preceded by interphase, in which chromosomes are replicated to form sister chromatids.
The ister chromatids are genetically identical and Joined at the centromere. The single centrosome replicates, forming two centrosomes. 8) The three mechanisms that contribute to genetic variation are independent assortment of chromosomes, crossing over, and random fertilization. In independent assortment, each pair of chromosomes sort maternal and paternal homologues into daughter cells independently of the other pairs. Crossing over produces recombinant chromosomes, which combine genes inherited from each parent. Random fertilization adds genetic variation because any sperm can fuse with any ovum. ) Natural selection results in the accumulation of genetic variations favored by the environment. Sexual reproduction contributes to the genetic variation in a population, which originates from mutations. 1) Mendel chose to track only those characters that varied in an either-or manner. He also used varieties that were true breeding. In a typical experiment, Mendel mated two contrasting, true breeding varieties, a process called hybridization. Mendel discovered a ratio of about three to one. What Mendel called a “heritable factor” is what we now call a gene. ) Genes are units of heredity, and are made up of egment of DNA. The alternative versions of a gene are called alleles. A trait is the feature of an organism. 3) P generations are the parental generation, that a true breeding. The F generations are the hybrids between the parents. 4) A monohybrid cross when there is only one trait being tested, whereas a dihybrid cross there are two traits being crossed. 5) The law of segregation states that two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes. ) Dominant alleles determine the organism’s appearance, and the ecessive allele has no noticeable effect on appearance. Two identical alleles are homozygous, while two different alleles are heterozygous. Genotype is the genetic makeup while phenotype is the physical appearance. 7) If P (purple) is dominant and p (white) is recessive and are crossed then there will be a three to one ratio of purple to white. You can determine that if there are three purple flowers that there has to be three dominate PS, the second allele can vary to be recessive or dominant. ) We can apply the multiplication and addition rules to predict the outcome of crosses nvolving multiple characters. A dihybrid cross is equivalent to two or more independent crosses involving multiple monohybrid crosses occurring simultaneously. 9) Many heritable characters are not determined by only one gene with two alleles. 10) Complete dominance occurs when phenotypes of the heterozygotes and dominant homozygote are identical. In incomplete dominance, the phenotype of Fl hybrids is somewhere between the phenotypes of the two parental varieties.
In codominance two dominant alleles affect the phenotype in separate, distinguishable ways. 11) The four phenotypes of the ABO blood group in humans re determined by three alleles for the enzyme (l) that attaches A or B carbohydrates to red blood cells: IA, 1B, and i. The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme coded 1B allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither. 12) Pleiotropy is when the genes have multiple phenotypic effects. In epistasis, agene at one locus alters the phenotypic expression of a gene at a second locus.
Polygenic inheritance is the additive effect of two or more genes on a single phenotype. 13) An organism’s phenotype includes its hysical appearance, internal anatomy, physiology, and behavior. An organism’s phenotype reflects its overall genotype and unique environment history. 14) A pedigree is a family tree that describes the interrelationships of parents and children across generations. allele. Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal. 16) The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes.
Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small ntestine. Sickle-cell disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells. Symptoms include physical weakness, pain, organ damages, and even paralysis. 17) Dominantly inherited disorders occur when some disorders are caused by dominant alleles instead of recessive ones, these alleles are rare and arise from mutations. 18) Multifactorial disorders are genetically and environmentally linked. 19) In amniocentesis, the liquid that bathes the fetus is removed and tested.
Chapter 15: The Chromosomal Basis of Inheritance ) We credit Morgan with the discovery of specific gene with a specific chromosome. Morgan used wild type flies and bred them with mutant flies to finds the crosses between the two. 2) Linked genes are genes located on the same chromosome that tend to be inherited together. 3) Offspring with nonparental phenotypes are called recombinant types, and are achieved through breeding. 4) A genetic map is an ordered list of the genetic loci along a particular chromosome, which shows the crossing over rate. A linkage map is a genetic map of a chromosome based on recombination frequencies. Sex linked disorders, are ones where the disorder is attached to the X chromosome and is rarely attached to the Y chromosome. An example would be hemophilia. 6) In nondisjunction, pairs of homologous chromosomes do not separate normally during meiosis II, which can cause aneuploidy; offspring with this condition have an abnormal number of a particular chromosome. 7) Breakage of a chromosome can lead to four types of changes in chromosome structure. Deletion removes a chromosomal segment. Duplication repeats a segment. Inversion reverses a segment within some chromosome.