CHAPTER 14 Heredity transmission of traits from one generation to the next Variation demonstrated by the differences in appearance that offspring show from parents and siblings Genetics study of heredity and variation Genes units of heredity made of dna segments passed to next generation via reproductive cells gonads called gametes sperm and eggs Genes specific location along a chromosome is called the LOCUS Ploidy of chromosome sets in nucleus o Diploid or 2n 2 sets of chromosomes o Humans have 2 sets of 23 chromosomes in their SOMATIC CELLS Have 22 pair of autosomes and 1 pair of sex chromosome Haploid or n 1 set of chromosomes Meiosis cell division that produces haploid cells from a cell that was originally diploid o Has similarities to mitiosis but several crucial difference o Required for sexual reproduction Asexual reproduction single individual passes all of its genes to its offspring without fusion of gametes some euk And plants o Make clones via mitotic division Sexual reproduction 2 parents give rise to offspring with unique combos of genes o Via a fertilization event 2 haploid gametes unite to create a diploid cell called a ZYGOTE o Requires meiosis and fertilization o Meiosis reduces the number of chromos In the gametes to one half the diploid o Fertilization restores the diploid number After fertilization mitosis for development Life cycle o Stages in reproductive history of an organism Includes haploid n and diploid 2n states Time spent in n or 2n varies Haploid or diploid cells can divide by mitosis Only DIPLOID cells can undergo MEIOSIS o Different forms of sexual life cycles They differ largely in how prevalent the haploid stage is IN MAMMALS ONLY GAMETES ARE HAPLOID Diploid multicellular organism o Plants and some algea alternation of generation differ from haploid multicellular organism GAMETOPHYTE and diploid multicellular organism SPOROPHYTE Spores are haploid o Haploid unicellular or multicellular organism no diploid multicellular organism but only diploid zygote MOST FUNGI and some protists Karyotype of human somatic cell o Pair of homologous replicated chromosomes a pair of chromosomes one mom one dad with same length centromere position and genetic content Chromosomes are o Sister chromatids of one duplicated chromosome o Connected at the centromere o 2 nonsister chromatids in a homologous pair Meiosis reduces chromosomes to the haploid number by performing 2 rounds of chromosome division without an intervening round of DNA synthesis and chromosome doubling o Meiosis 1 homologous chromosomes separate haploid cells with replicated chromosomes Prophase 1 diploid cells with replicated chromosomes CROSSING OVER create synaptonemal complex place where it was crossed is the chiasmata Metaphase 1 line up in the middle independent assortment Anaphase 1 homologous chromosomes separate Telophase 1 and cytokinesis haploid cells with replicated chromosomes o Meiosis 2 sister chromatids separate Haploid cells with unreplicated chromosomes Prophase 2 no chromosome replication between 1 and 2 All same things happen just WITH TWO CELLS AT A TIME ending with haploid cells with unreplicated chromosomes 4 ending cells Somatic cells 2 sets of chromosomes Gametes half as many chromosomes as somatic cells o A T C G DNA molecules packaged into chromosomes o Gregor Mendel o Simple system pea plants o True breeding plants o Study one characteristic at a time o Use quantitative analysis determine patterns o Law of independent assortment based on two characters A dihybrid cross btwn f1 dihybrids can determine whether two characters are transmitted to offspring as a package or independently Mendels pea characters segregated in the f2 generation INDEPENDENTLY OF EACHOTHER Each pair of alleles segregates independently of each other pair of alleles during gamete formation This law APPLIES ONLY TO GENES ON DIFFERENT NON HOMOLOGOUS CHROMOSOMES OR THOSE FAR APART ON THE SAME CHROMOSOME Genes located near eachother may be inherited together o CHANCE THAT AN EVENT WILL HAVE A PARTICULAR OUTCOME P of times an event occurs total number of possible outcomes Product rule Probablility that two or more independent events will occur is equal to the product of their individual probabilities Prob of event one prob of event two probability that they will both happen at the same time Sum rule Probability that one of twoor more MUTUALLY EXCLUSIVE outcomes will occur is the sum of the probabilities of the possible outcomes In a cross between two heterozygous pea plants we may want to know the probability of a particular offspring being a homozygote Prob of event 1 prob of event 2
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