Lecture 6, Reproduction and chromosome transmission

Lecture 6, Reproduction and chromosome transmission -...

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Unformatted text preview: Lecture 6 (Chapter 3) REPRODUCTION AND CHROMOSOME TRANSMISSION INTRODUCTION In this chapter we will survey reproduction at the level of chromosomes (cellular level) rather than at the molecular level Chromosomes are large enough to be visible by light microscopy This examination provides us with insights to understand the inheritance patterns of traits 3-2 The field of genetics involves the microscopic examination of chromosomes and their behavior A cytogeneticist typically examines the chromosomal composition of a particular cell or organism This allows the detection of individuals with abnormal chromosome number or structure This also provides a way to distinguish between two closely-related species Cytogenetics Figure 3.2 In a cytogenetics laboratory, the microscopes are equipped with a camera Microscopic images can now be scanned into a computer There, the chromosomes in the images can be organized in a standard way, usually from largest to smallest A karyotype is the photographic representation of the chromosomes within a cell Refer to Figure 3.2 Cytogenetics Eukaryotic Chromosomes Are Inherited in Sets Most eukaryotic species are diploid Have two complete sets of chromosomes For example Humans 46 total chromosomes (23 per set) Dogs 78 total chromosomes (39 per set) Fruit fly 8 total chromosomes (4 per set) Eukaryotic Chromosomes Are Inherited in Sets Members of a pair of chromosomes are called homologues The two homologues form a homologous pair The two chromosomes in a homologous pair Are nearly identical in size Have the same banding pattern and centromere location Have the same genes But not necessarily the same alleles Eukaryotic Chromosomes Are Inherited in Sets The DNA sequences on homologous chromosomes are also very similar There is usually less than 1% difference between homologues (on average, about 0.1%) Nevertheless, these slight differences in DNA sequence provide the allelic differences in genes Eye color gene Blue allele vs brown allele Eukaryotic Chromosomes Are Inherited in Sets The sex chromosomes (X and Y) are not strictly homologous, though they behave as homologues during meiosis They differ in size and genetic composition They do have short regions of homology, especially at the tips Figure 3.3 considers two homologous chromosomes labeled with 3 different genes 3-17 The physical loc ation of a gene on a chromosome is called its locus . Figure 3.3 One purpose of cell division is asexual reproduction This is the means by which some unicellular organisms produce the next generation of the organism Examples Bacteria Amoeba Yeast Saccharomyces cerevisiae (Baker’s yeas 3.2 CELLULAR DIVISION A second purpose for asexual reproduction is to produce multi-celled organisms and to enable these organisms to grow and repair damaged tissue Plants, animals and certain fungi are derived...
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This note was uploaded on 10/18/2010 for the course BIOLOGY 111 taught by Professor Shay during the Spring '10 term at CCAD.

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Lecture 6, Reproduction and chromosome transmission -...

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