Module 6.2 The Human Genome Flashcards
Human Genome
features (6)
- 3.05 billion bases
- linear nuclear genome
- circular mitochondrial genome
- average gene size = 27,000 bp
- 19,969 protein coding genes
- 43,525 non coding genes (inconclusive)
histones
- proteins high in lysine and arginine residues
- act as spools that DNA winds around to create nucleosomes
nucleosome
- structure = segment of DNA wound around eight histone proteins
- fundamental subunit of chromatin
heterochromatin
- densely packed chromatin found in the nucleus of eukaryotic cells
- doesn’t enable DNA and RNA polymerases to access DNA which prevents DNA replication and transcription
euchromatin
lightly packed chromatin that allows the DNA to be replicated and transcribed in eukaryotic cells
chromatin
unraveled, condensed structure of DNA, packaged by histones in nucleus
chromosomes
features
- thread like structures located inside nucleus of cells
- single enormously long linear DNA molecule associated with proteins that fold and pack fine DNA thread into more compact structure
- 22 pairs of autosomes and one pair of sex chromosomes (X & Y) = 46 chromosomes
homologous chromosomes
- maternal and paternal chromosomes of a pair
- sex chromosomes are non-homologous (maternal X, paternal Y)
linear chromosome
Specialized nucleotide sequences
3
- replication origin (many)
- centromere (one)
- telomere (two)
replication origin
- location where duplication of DNA begins
- many origins of replication to ensure that entire chromosome can be replicated rapidly
centromere
- holds duplicated chromosomes together until ready to be moved apart
- consists of large arrays of repetitive DNA
- tightly packed heterochromatin region
telomere
- at ends of chromosomes
- repeated telomere DNA sequences + adjoining region = structures that mark end of chromosome and protect ends from being recognized by cell as broken DNA molecules
- tightly packed heterechromatin region
haplotype
features (3)
- aka haploid genotype
- group of alleles in an organism that are inherited together from a single parent
- can be all chromosomes from one parent or a minor part of a chromosome
gene
- segment of DNA that contains the instructions making a particular protein or RNA
- contains regulatory DNA sequences, exons, and introns
exon
protein-coding sequence in gene
intron
- intervening non-coding sequences
- removed by splicing to create mature RNA
genes
regulatory sequences
- responsible for ensuring that gene is expressed at proper level and time and at right location
- spread out over tens of thousands of nucleotide sequences in humans
LINE / SINE
- Long / Short Interspersed Nuclear Element
- retrotransposable elements, that invade new genomic sites using RNA intermediates
- account for >34% of human genome
transposons
types (4) + feature
- LINEs
- SINEs
- retroviral-like elements
- DNA-only transposon ‘fossils’
multiplied in genome by replicating themselves and inserting new copies in different positions
simple sequence repeats
nucleotide sequences <14 base pairs that repeat for long stretches
segmental duplications
large blocks of genome 1,000-200,000 bp long that are present at two or more locations in genome
human genome
repeated sequences
3
54% of genome
1. transposons
2. simple sequence repeats
3. segmental duplications
human genome
unique sequences
2
- genes (>50%)
- regulatory DNA
Telomere to Telomere Consortium
- reported complete sequence of female genome in 2022
- published human Y chromosome from HG 002 genome that corrects multiple errors in HG 38 Y chromosome and added over 30 million bp of sequence to reference
- potentially 0.3% errors
Telomere to Telomere Consortium
CHM 13
special cell line almost completely homozygous for all chromosomes
Human genome
Difficult sequencing areas
- centromeres and telomeres (heterochromatin)
- AT/GC rich regions
- palindromic sequences
- hairpin structures
