ch6- from chromosomes to genes Flashcards
DNA
- a molecule which carries heritable information from one generation to the next.
- packed into units called chromosomes
- the DNA is tightly wound around proteins called histones. (they are positive, stick to wall well)
nucleotides
- repeated units formed on DNA
- four types: thymine, guanine, cytosine, adenine.
- A-T- with 2 hydrogen bonds
- G-C- with 3 hydrogen bonds
- makes them complementary
Covalent bonds
- strong
- join the phosphates and sugars while nitrogen-containing bases are joined by hydrogen bonds (weak)
nucleotide structure
alternating phosphates and deoxyribose sugars form the sides of the ladder, with the bases forming the rungs.
gene
a section of DNA which carries coded information for making a protein or an RNA molecule
alleles
different versions of a gene
- for some genes only 1 version exists so all individuals will be the same but other genes have multiple alleles and this results in differences between individuals
meiosis
- the process of forming haploid cells
- most haploid cells are gametes (egg and sperm cells)
- replication of DNA, then 2 sets of cell division so that the daughter cell contains only one member of each homologous pair and one sex chromosome.
chromatids
single stranded chromosome that is copied to become two identical strands.
genome
-the genome of an organism is all of its DNA, both coding and non-coding, in a haploid cell.
proteome
all of the protein in a cell
genomics and proteomics together
result in the development of therapies for people based on their own particular genetics.
karyotype
a picture of the chromosomes of an organism where the chromosomes have been paired up and arranged in order of size.
autosomes
all of the chromosomes except the sex chromosomes which are X and Y in humans and most mammals.
sex chromosomes
carries the gene that determines the sex of the individual
eukaryotic chromosomes
-linear and consist of multiple chromosomes (humans have 46)
- organized with histone proteins
- enclosed within nucleus
prokaryotic chromosomes
- single and circular
- without histones which is attached to the inside of the plasma membrane.
- contain one or more plasmids
meiosis- prior to cell division
single stranded chromosomes are copied to become two identical strands (chromatids)
meiosis- stages
- prophase 1
-synapsis
-crossing over - metaphase 1
- anaphase 1
- telophase 1
- prophase 11
- metaphase 11
- anaphase 11
- telophase 11
meiosis- prophase 1 (crossing over)
- the two close chromatids wrap around each other.
- contact point is called chiasmata
- the chromosomes at the chiasmata can break and swap pieces in a process called crossing over.
- increase in gamete variation
meiosis- anaphase 1
- spindles retract towards the poles of the cell causing the homologous pairs to separate to either side.
meiosis- prophase 1 (synapsis)
- ## DNA condenses and chromosomes appear
meiosis- metaphase 1
- breakdown of nuclear membrane is completed
- spindle fibers attach to centromeres of the chromosomes
- the homologous pairs move to the equator of the spindle which is fully formed
meiosis- prophase 11
- new spindle forms
- DNA condenses, chromosomes appear (double stranded)
- the 2 daughter cells are haploid
meiosis- telophase 1
- chromosomes unwind
- spindle breaks down
- nuclear membranes form around chromosomes
-cytokinesis occurs (the division of the cytoplasm) - results in 2 haploid cells
meiosis- metaphase 11
- the chromosomes line up in single file across the equator of the cell
- spindle is connected to the centromere of the chromosome
meiosis- telophase 11
- new nuclear membranes form around each bundle of cells
- spindle breaks down
- chromosomes unwind and disappear
- new nucleoli form (RNA)
- four separate cells
meiosis- anaphase 11
- spindle fibres contract and pull sister chromatids apart
role of crossing over
Crossing over produces new combinations of alleles on each chromosome, increasing genetic variation among offspring.
role of independent assortment
- how one pair of chromosomes, and hence alleles, separates is independent of how a different pair of different chromosomes separate.
- all combinations are possible
when non-disjunction occurs
meiosis I- homologous chromosomes fail to separate, leading to gametes with either an extra chromosomes or missing a chromosomes
meiosis II- sister chromatids fail to separate, resulting in similar errors with chromosomes numbers in the gametes.
non-disjunction
- chromosomes fail to separate properly
- results in cells with an abnormal number of chromosomes
- an error in cell division
chromosomal errors
- duplication - one segment repeated during crossing over
- deletion - chromosome way be lost during cell division
- inversion - DNA is read backwards
- translocation - attached to non-homologous chromosome
