Biology II Exam 2 1 9 18 2015 Lecture 10 Chapter 13 Sections 1 3 Cell Division Meiosis and genetic variation A Inheritance How do organisms produce their offspring that are similar but distinct from themselves or how do sexual reproduction and inheritance interact Not all organisms have sex Some undergo asexual reproduction to produce organisms o For example Cloning and Asexual Reproduction occurs in some plants Trees such as the poplar or aspen send up new stems from their roots In time an entire patch of trees forms just from part of a clone of the original tree Another example would be that of Dandelions o However asexual reproduction is not restricted to plants nor do all plants take part in this For example squash contain female and male flowers that reproduce sexually While there is a species of lizards that reproduce asexually pathogenic Due to genetics in humans we are not identical but have family resemblance As stated in previous chapters Mitosis generally produces two identical daughter cells from one cell that gets copied during the S phase Now to bring in the process that produces the gametes egg and sperm Meiosis produces daughter cells that contain a subset of Parent cells genes formation of gametes o Gonads testes ovary the organs that produce gametes o Zygote fertilized egg Biology II Exam 2 2 The number of chromosomes in a cell doesn t tell you much about the organism Some species have few big chromosomes other have lots of small chromosomes o Humans have n 23 pairs and 2n 46 chromosomes Difference between Homologous chromosomes and sister chromatids o Homologous chromosomes genetically similar but not necessarily identical o Sister chromatids of same chromosome are genetically identical o result of S phase of cell cycle Meiosis produces haploid cells o Occurs in the gonads o Producing haploid cells is necessary for sexual life cycles so the chromosomes will not double each time of reproduction Chapter 13 Questions 1 What process do cells undergo to make gametes eggs and sperm Meiosis 2 What are organs that produce gametes Gonads Which are the testes and ovaries 3 What is asexual reproduction its offspring without the fusion of gametes 4 What is sexual reproduction inherited from the two parents 5 What are gametes Occurs when a single individual is the sole parent and passes copies of all its genes to Occurs when two parents give rise to offspring that have unique combinations of genes Biology II Exam 2 3 The reproductive cells that are the vehicles that transmit genes from one generation to the next 6 What are homologous chromosomes They are the two chromosomes of a pair that have the same length centromere and staining pattern Both chromosomes of each pair carry genes controlling the same 7 Dandelions are example of an asexual reproductive organism or a sexual reproductive inherited characters organism Explain Dandelions are asexual organisms through parthenogenesis This is where their offspring are produced identically as the parent from the parents ovules The ovules develop into seeds after they are blown off 8 How many chromosomes do humans have 46 chromosomes 23 pairs of chromosomes 9 Where does Meiosis occur Inside the gonads 10 What is the difference between homologous chromosomes and sister chromatids Sister chromatids are genetically the same they are identical copies of one another created just for cell division while homologous chromosomes contain the same gene loci but consists of two non identical copies of a chromosome one from each parent 11 What is a zygote A zygote is a fertilized egg 12 What is a clone Biology II Exam 2 4 The cells of an individual plant or animal are clones because they descend from a single fertilized cell and are genetically identical to the parent 13 What is a spore A spore is a haploid cell produced during Meiosis in the sporophyte that doesn t fuse with another cell but divides mitotically generating a multicellular haploid stage 14 Define a sister chromatid Are two identical strands joined by a common centromere 15 How is Meiosis different from Mitosis Meiosis produces 4 new haploid cells and involves the exchange of genetic material from homologous chromosomes Mitosis produces 2 diploid cells and involves sister chromatids 16 Why is it important to produce haploid cells every generation 17 What are sister chromatids Producing haploid gametes by meiosis keeps the chromosome number from doubling in Sister chromatids are duplicated copies of a single chromosome that are attached to each other by the centromere and are identical 18 What is a haploid cell A haploid cell is a cell with a single set of chromosomes Humans have 23 chromosomes in their haploid cells 19 What is a diploid cell chromosomes in each diploid cell It is a cell that contains two homologous pairs of chromosomes Humans have 46 Biology II Exam 2 5 20 What number and types of chromosomes are found in a human somatic cell 44 autosomes 22 pairs of autosomes and 2 sex chromosomes either two X chromosomes in females or an X and a Y chromosome in males 21 When does synapsis occur It occurs during meiosis during prophase I but not during mitosis 9 21 2015 Lecture 11 Chapter 13 3 and 13 4 Review of Mitosis o Interphase is broken into G1 S and G2 and takes up the majority of the cell cycle and then the Mitotic phase occurs that is broken down into Mitosis and Cytokinesis o During Mitosis each cell of the two produced is genetically identical to itself and to its parent cell How much genetic info is in each cell o Mitosis G1 2n diploid G2 2n doubled diploid copied M 2n o Meiosis G1 2n G2 2n doubled Me I haploid n still doubled o Meiosis G1 n not doubled single copy go through 2 rounds of division There are 4 stages of Meiosis prophase metaphase anaphase telophase o Prophase I Each chromosome pairs with its homolog aligned gene and crossing over occurs Then homologous chromosome pairs pair up making 4 chromatids When the set of 4 sister chromatids line up they are called tetrad o Metaphase I pairs of homologous chromosome line up on the metaphase plate Both chromatids of one homolog are attached to kinetochore microtubules Biology II Exam 2 6 from one pole those of the other homolog are attached to microtubles from the o Anaphase I homologous pairs separate and move toward opposite poles opposite pole guided by the spindle apparatus o Telophase I Now each half of the cell has a complete haploid set of duplicated chromosomes that is composed of two sister chromatids
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