Name the major uses of the halogens.
Crossing Over can only happens When homologous chromosomes pair up loosely along their lengths When the chromosomes are not sisters and are still homologous When the segments are near the end of the chromosome Living Organisms are differentiated from their nonliving counterparts by their ability to reproduce themselves. Except viruses, but there’s lots of debate about whether they actually count as living organisms. Vocab for this Unit Traits; observable characteristics of things Heredity; the transmission of traits from generation to generation Variation; differences in appearance between parents and siblings Genetics; the study of variation of inherited traits Phenotype; the whole of an organism’s traits Asexual v Sexual Reproduction In Asexual reproduction, a single individual passes on 100% of its genes without the fusion of its gametes. Offspring are clones of their parents. A clone is a genetically identical individual with respect to its parent organism. Sexual reproduction involves genetically unique individuals from a pair of parent organisms. Children don’t inherit phenotypical traits; they inherit a collection of genes from their parents. Genes are the units of heredity, they’re a sequence of nucleotides that usually code for a protein but do occasionally code for structural RNA. Its location in the chromosome is called its locus. The Skinny on Chromosomes The term ‘ploidy’ refers to the number of sets of chromosomes in the cells. Most animals are diploid, maintaining two sets of chromosomes in their cells. Some animal cells are haploid, which means they only have one set of chromosomes in their cells. In a diploid cell, pairs of alike chromosomes are referred to as being homologous. That means chromosome one and the copy of chromosome one, not just any old pair of chromosomes that seem to share a resemblance. Chromosomes that are not alike are called non-homologous chromosomes, like chromosome one and chromosome eight. Sister chromatids are homologous. Humans have 23 pairs of chromosomes in their somatic cells. In each pair, one of the chromosomes comes from dad and one comes from mom. A karyotype is a map that shows all of the chromosomes in the middle of metaphase (because that’s when chromosomes are most compacted) in an ordered display. This is done to try to screen for possible deadly diseases and/or disorders. At sexual maturity, humans produce haploid gametes. Fertilization occurs when the sperm meets the egg, when the gametes fuse together. A fertilized egg is called a zygote, which has one set of chromosomes from each parent. Zygotes produce somatic cells via mitosis and develops (eventually) into an adult. The average human has about 30 to 50 trillion cells in their body. Meiosis In most animal cells, meiosis reduces the number of chromosome sets from diploid to haploid. Both mitosis and meiosis have to go through an S phase of chromosomal reproduction. Meiosis divides cellularly twice, in meiosis one and meiosis two DNA IS NOT REPLICATED BETWEEN MEIOSIS 1 AND MEIOSIS 2. DNA IS NOT REPLICATED BETWEEN MEIOSIS 1 AND MEIOSIS 2. Meiosis makes four haploid daughter cells, meaning each only has one set of chromosomes. Each meiosis only has four stages; Prophase One; includes mitosis’ prophase as well as prometaphase, because meiosis does not have prometaphase. IMPORTANT; PROPHASE ONE INVOLVES CROSSING OVER. IT IS THE ONLY ONE THAT DOES. Metaphase One is still when the chromosomes line up on the metaphase plate. In One, instead of individual pairs lining up, pairs of pairs line up. Anaphase One is still when the kinetochore tighten and pull the chromosomes to their respective sides, but in One it pulls pairs of chromosomes, instead of individuals like mitosis. Telophase/Cytokinesis is still exactly the same as it is in mitosis Prophase Two DOES NOT INVOLVE ANY DNA REPLICATION Metaphase Two only has pairs of chromosomes lining up on the metaphase plate Anaphase Two has only one lonely chromosome pulled away to its own side Cytokinesis/Telophase is still exactly the same as it is in mitosis The interphase microtubule skeleton is dissembled at the end of the G2 phase so that the spindle apparatus can be assembled.