Lecture 1

Learning outcomes

  1. Be familiar with the three general classes of genetic diseases

  • Chromosome disorders

    • Caused by excess or deficiency of all/part of a chromosome

    • ~50% of spontaneous abortions; 7 in 100 live births

  • Single-gene disorders

    • Due to mutation in 1 or both copies of a single gene

    • ~2% of the population

  • Multifactorial disorders with complex inheritance

    • Combined effect of multiple genetic defects, often influenced by environment

    • > 50% of the population

  1. Be able to describe the basic features of the nuclear genome (size, approximate number and kinds of genes and chromosomes)

  • 6.6 billion base pairs per diploid cell

  • 25,000 protein coding genes (mRNA)

  • 25,000 noncoding RNA genes

    • tRNAs, rRNAs, snoRNAs, snRNAs, lncRNAs,miRNAs —> Structural, catalytic, or regulatory roles

  • 23 pairs of homologous chromosomes

    • Autosomes: 1-22

    • Sex chromosomes x & y

  1. Be familiar with the human karyotype and terms used to describe chromosomal loci

  • G-banding (Giemsa staining) of metaphase chromosomes reveals banding patterns

    • Can reveal defects in the number or structure of chromosomes

  • Metacentric: centromere is located in the middle of chromosome

  • Submetacentric: slightly off centered

  • Acrocentric: centromere is toward 1 end of chromosome

  • Telocentric: centromere is located at the end of chromosome (rare)

  1. Be able to describe the relative abundance of single-copy and repetitive DNA sequences in the human genome

  • Genome contains equal percentages of single copy and repetitive DNA

    • Single-copy: unique sequence of DNA. includes most genes and regulatory elements. Less than 15% of the genome encodes proteins.

    • Repetitive DNA sequences: satellite DNA and dispersed elements

  • Satellite DNA: tandem repeats of relatively short (5-170 bp) sequences

    • Can span extremely large regions of the genome

    • Clustered in specific regions (centromeres, heterochromatin)

    • 10-15% of genome

  • Dispersed repeats: repetitive elements that are dispersed through the genome

    • Includes short- and long- interspersed nuclear elements (SINEs [Alu element] and LINEs)

    • 100s-1000s of bp in length

    • 30% of genome

    • Very important because many of these elements are transposons —> lead to mutations

  1. Be able to describe the basic features of the mitochondrial genome (size, approximate number and kinds of genes)

  • Mitochondrial DNA

    • Multiple circular DNA molecules ~16.6 kb

    • Some genetic diseases are caused by defects in the mitochondrial genome

  • Has 38 genes containing:

    • 14 protein coding genes

    • 2 ribosomal RNAs

    • 22 transfer RNAs

Key Terms

Chromosome

Single-gene disorder

Multifactorial disorder with complex inheritance

tRNA

rRNA

snoRNA

snRNA

lncRNA

miRNA

mRNA

Karyotype

G-banding

Autosome

Sex chromosome

Single-copy sequence

Repetitive DNA

Satellite DNA

Dispersed repeats

SINE

LINE

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