Learning outcomes
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
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
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)
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
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