from chromosomes to genomes

chapter. 6: genomes, genes and alleles; chromosomes

DNA

deoxyribonucleic acid, contains genetic information, common to all species

DNA structure

macromolecule in form of double polymer, 2 long strands of nucleotides wound together in a double helix

nucleotide structure

5 carbon (pentose) deoxyribose sugar, negatively charged phosphate sugar, nitrogenous base

nucleotide bonds

sugar molecule bonds to phosphate group of next nucleotide in strand, nitrogenous base is hydrogen bonded with corresponding nitrogenous base

Complementary Base Pairing

nitrogenous base pairing, adenine bonds with thymine, cytosine bonds with guanine

Genes

sections of DNA/ sequence of nucleotides that code for a specific protein

Alleles

alternative forms of genes, have same gene locus on chromosome but different nitrogenous base sequences

allele origin

two alleles for each gene in an organism, one from each parent

genome

sum of all DNA, measured in number of nucleotide bases in haploid set of chromosomes

genomics

study of genomes

Human genome

mapped in 2003 by human genome project, 20,000 to 25,000 genes in human

bioinformatics

science of analysing biological data using advanced computing techniques

chromosomes

one DNA molecule, found in nucleus, made of tightly coiled DNA

histones

proteins that DNA wraps around to become a chromosome

heredity

study of inheritance; how genes pass from one generation to next

karyotype

photograph of chromosomes, arranged in homologous pairs from largest to smallest, show size, centromere location and banding patterns

homologous

chromosomes with similar size and shape, but potentially different base sequences

autosome

first 22 pairs, homologous, code for physical characteristics

sex chromosome

code for sex and some other traits, match in females(XX), don’t match in males(XY)

haploid

represented by n, amount of chromosomes in gametes, 23 in humans, half of chromosomes in somatic cells

diploid

number of chromosomes in somatic cells, represented by 2n

gene locus

particular position of a gene along length of chromosome, homologous chromosomes have same gene loci

linked genes

genes on the same chromosome, tend to be inherited together

sex determination

sperm gametes determine sex of offspring

sex-linked

genes on sex chromosomes, far more genes on X, meaning sex linked conditions often come from the X chromosome

aneuploidy

addition or loss of one chromosome in a cell

polyploidy

extra sets of homologous chromosomes(4n, 6n), common in plants and some amphibians, does not always result in disease, lethal in humans

non-disjunction

incorrect separation of homologous chromosomes during meiosis, causes aneuploidy

trisomy

one extra chromosome e.g down syndrome, klinefelter syndrome

monosomy

one less chromosome e.g turner syndrome

meiosis

cell division that produces gametes, creates genetically unique offspring

meiosis location

gonads (ovaries, testes) in animals, anther and ovary in plants

Meiosis I

reduction division, homologous pairs seperate

Interphase I

chromosomes replicate, normal cell processes

Prophase I

centrioles move to opposite poles, spindle forms, homologous pairs synapse

Synapsis

the joining of homologous chromosomes together during prophase I, pair is called a bivalent

Crossing over

exchange of genetic information between synapsed chromosomes, occurs at chiasmata

Metaphase I

synapsed homologous chromosomes move to spindle equator

Anaphase I

homologous chromosomes seperate and move to opposite poles

telophase I

new nucleus forms with one chromosome from each homologous pair, spindle breaks down

Meiosis II

chromatids from each chromosome seperate, similar to mitosis

Interphase II

brief, no dna replication

prophase II

chromosomes re-condense, new spindles form, no synapsis or crossing over

Metaphase II

chromosomes align along equator

Anaphase II

sister chromatids seperate to opposite poles

telophase II

four haploid cells produced, spindle disappears, nuclear envelopes form, cytokinesis

independent assortment

homologous chromosomes line up independently of each other during meiosis I, meaning assortment of alleles in resulting gametes is random

monoploidy

fully functional organisms with only one copy of each chromosome, produced by parthenogenesis (no fertilisation). common in males of colony insects e.g bees

prokaryote chromosomes

DNA found in cytosol, usually as a single circular chromosome, can be condensed, said to be haploid

plasmids

small rings of DNA in prokaryotes, replicate independently

chloroplast DNA

single circular chromosomes (similar to prokaryotes), contains roughly 100 genes coding for proteins needed in photosyntheis

mitochondrial DNA

similar to chloroplast DNA, codes for some proteins needed to make up mitochondria, comes only from the mother (sperm has no mtDNA)

endosymbiosis

theory explaining eukaryotic cell evolution, mitochondria evolved from aerobic bacteria and chloroplasts evolved from cyanobacteria, both of which were engulfed by an ancestral host cell