Genetics - REPRODUCTION AND INHERITANCE Imagine you are entering an animal or plant cell Inside this cell you find membrane bound organelles one of

Genetics - REPRODUCTION AND INHERITANCE Imagine you are...

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REPRODUCTION AND INHERITANCE Imagine you are entering an animal or plant cell. Inside this cell you find membrane bound organelles one of which is the nucleus . The nucleus contains the genetic information in the form of DNA that determines all the traits of a particular organism. We may think of DNA as a genetic blueprint in the form of a code. In the nucleus DNA is attached to proteins (histones), forming long thread-like fibers called chromatin. Before cell division (mitosis and meiosis), chromatin coils up into thick structures called chromosomes. In turn, each chromosome is duplicated into two identical structures called sister chromatids joined together by a centromere (see Figure 1). Chromosomes are found together in pairs (homologous pairs). Each pair of homologous chromosomes contains the same genes that code for the same inherited traits or characteristics. The copies of a specific gene are also located on the same position (locus) in each chromosome. The two copies of any gene (one in each homologous chromosome) may exist in alternative forms that are called alleles (see Figure 2). All our body cells (except egg and sperm cells) carry 23 pairs of homologous chromosomes making a total of 46 chromosomes. These cells are referred to as diploid. However, sperm and egg cells carry only one copy of each chromosome and thus a total of 23 chromosomes. These cells are referred to as haploid. Question: What does haploid and diploid mean? Gene loci Fig. 1. A Duplicated Chromosome Genotype: PP aa Bb Homozygous Homozygous
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  • Winter '13
  • DavidGrueber
  • Genetics, Sex linkage, homologous chromosomes

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