2. Members of a family show many similarities in appearance, but are not identical (except in the case of identical twins). Why do offspring inherit certain characteristics from their parents, but not others? Unit 1 – Understanding Biological Inheritance
7. Mendel's Contribution The story of Gregor Mendel and his work provides a fascinating glimpse into the nature of science. Mendel was born in 1822 and as a young man attended the University of Vienna. There he studied chemistry, biology and physics, but left before graduating, probably for health reasons. He entered the Augustinian monastery in Brno, and with the support of the abbot, began his investigation of the inheritance of certain traits in pea plants ( Pisum sativum ). His choice of pea plants as the experimental subject was excellent as peas grow and reproduce quickly, their mating can be controlled, and the plants have a number of distinct traits that are readily observed. Over the course of the next eight years, Mendel conducted experiments and maintained detailed records of his results. His university training led him to design simple experiments that permitted him to observe the inheritance of one trait at a time. His use of mathematics allowed him to formulate conclusions based on his results. These conclusions are known as Mendel’s Laws or Principles.
67. nucleolus centromere 2n = 4 DNA replication 2n = 4 synapsis sister chromatids Meiosis I Homologous pairs separate. n = 2 n = 2
68. nucleolus centromere 2n = 4 DNA replication 2n = 4 synapsis sister chromatids n = 2 n = 2 Meiosis II Sister chromatids separate, becoming daughter chromosomes. Meiosis I Homologous pairs separate. n = 2 n = 2
69.
70.
71.
72. Homologous pairs align at the metaphase plate. Metaphase I DNA Replication Homologous chromosomes separate, pulled to opposite poles by centromeric spindle fibers. Anaphase I Daughter cells have one chromosome from each homologous pair. Telophase I Homologous chromosomes pair during synapsis. Prophase I Meiosis I 2n = 4 Chromosomes still consist of two chromatids. Interkinesis n = 2
75. Homologous pairs align at the metaphase plate. Metaphase I DNA Replication Homologous chromosomes pair during synapsis. Prophase I Meiosis I 2n = 4
76. Homologous pairs align at the metaphase plate. Metaphase I DNA Replication Homologous chromosomes separate, pulled to opposite poles by centromeric spindle fibers. Anaphase I Homologous chromosomes pair during synapsis. Prophase I Meiosis I 2n = 4
77. Homologous pairs align at the metaphase plate. Metaphase I DNA Replication Homologous chromosomes separate, pulled to opposite poles by centromeric spindle fibers. Anaphase I Daughter cells have one chromosome from each homologous pair. Telophase I Homologous chromosomes pair during synapsis. Prophase I Meiosis I 2n = 4
78. Homologous pairs align at the metaphase plate. Metaphase I DNA Replication Homologous chromosomes separate, pulled to opposite poles by centromeric spindle fibers. Anaphase I Daughter cells have one chromosome from each homologous pair. Telophase I Homologous chromosomes pair during synapsis. Prophase I Meiosis I 2n = 4 Chromosomes still consist of two chromatids. Interkinesis n = 2
79.
80. Metaphase II Chromosomes align at the metaphase plate. Anaphase II Daughter chromosomes move toward the poles. Telophase II Spindle disappears, nuclei form, and cytokinesis takes place. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2 Daughter Cells Meiosis results in four haploid daughter cells. n = 2 n = 2
81. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2
82. Metaphase II Chromosomes align at the metaphase plate. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2
83. Metaphase II Chromosomes align at the metaphase plate. Anaphase II Daughter chromosomes move toward the poles. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2
84. Metaphase II Chromosomes align at the metaphase plate. Anaphase II Daughter chromosomes move toward the poles. Telophase II Spindle disappears, nuclei form, and cytokinesis takes place. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2
85. Metaphase II Chromosomes align at the metaphase plate. Anaphase II Daughter chromosomes move toward the poles. Telophase II Spindle disappears, nuclei form, and cytokinesis takes place. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2 Daughter Cells Meiosis results in four haploid daughter cells. n = 2 n = 2
if a female carrier and a normal male give birth to a daughter, she has a 1 in 2 chance of being a carrier of the trait (like her mother). If the child is a son, he has a 1 in 2 chance of being affected by the trait (for example, colorblindness). If a female carrier and an affected male give birth to a daughter, she will either be affected or be a carrier. If the child is a son, he will either be affected or be entirely free of the gene. See the following Punnett squares (The letters X and Y represent their respective normal chromosomes; X underlined represents the colorblindness allele).
if a female carrier and a normal male give birth to a daughter, she has a 1 in 2 chance of being a carrier of the trait (like her mother). If the child is a son, he has a 1 in 2 chance of being affected by the trait (for example, colorblindness). If a female carrier and an affected male give birth to a daughter, she will either be affected or be a carrier. If the child is a son, he will either be affected or be entirely free of the gene. See the following Punnett squares (The letters X and Y represent their respective normal chromosomes; X underlined represents the colorblindness allele).
