Topic 3 Full (copy)

Paper 1 (Understandings)

Gene

Heritable factor that consists of a length of DNA and influences a specific characteristic

Alleles

The variations of a gene

Locus

The position of a gene on a particular chromosome

Mutation

a change to the base sequence of a gene that can affect the structure and function of the protein it encodes

The genome

is the whole of the genetic information of an organism

Human Genome Project

Stores the entire base sequence of human genes

Genophore

singular chromosome consisting of a circular DNA molecule in prokaryotes

Plasmids

additional circular DNA in prokaryotes

Prokaryotic genetic material location

nucleoid

Eukaryotic genetic material

linear DNA molecules associated with histone proteins

Eukaryotic chromosome

multiple units that carry different genes

Organization of Eukaryotic chromosomes

Naked DNA, Nucleosome, Chromatosome, Solenoid, 30 nm fibre, Chromatic, Chromosome.

Homologous chromosomes

carry the same sequence of genes but not necessarily the same alleles

Diploid nuclei

pairs of homologous chromosomes (2n)

Haploid nuclei

one chromosome of each pair (n)

Karyograms

the number and types of chromosomes in a eukaryotic cell

Sex determination

by sex chromosomes (heterosomes)

Autosomes

chromosomes that do not determine sex

Meiosis summary

Before division = one diploid parent cell; Interphase = Homologous pair of replicated chromosomes; Meiosis I = Replicated pair of chromosomes separate; Meiosis II = Sister chromatids separate.

P-I

Chromosomes condense, nuclear membrane dissolves, homologous chromosomes for bivalents, crossing over occurs

M-I

Spindle fibres connect to bivalents at centromeres and align them

A-I

Spindle fibres contract, splitting bivalents and moving them to poles

T-I

Chromosomes decondense, nuclear membrane may reform, cytokinesis forms two haploid daughter cells

P-II

Chromosomes condense, centrosomes move to poles (perpendicular to before)

M-II

Spindle fibres attach to chromosomes at centromere and align them

A-II

Spindle fibres contract and separate the sister chromatids

T-II

Chromosomes decondense, nuclear membrane reforms, cytokenisis forms 4 haploid daughter cells

Random assortment

Orientation of pairs of homologous chromosomes prior to separation is random

Promotion of genetic variation

Crossing over, random assortment, fusion of gametes

Non-disjuction

chromosomes fail to separate, results in gametes with one extra or one missing chromosome

Chromosomes failing to separate happens during

A-I or A-II

Gregor Mendel

discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed

Mendel’s Laws of Genetics

Law of Segregation, Law of Independent Assortment, Principle of Dominance

Law of Segregation

When gametes form, alleles are separated so that each gamete carries only one allele for each gene

Law of Independent Assortment

The segregation of alleles for one gene occurs independently to that of any other gene (does not hold true for genes located on the same chromosome i.e. linked genes)

Principle of Dominance

Recessive alleles will be masked by dominant alleles (Not all genes show a complete dominance hierarchy – some genes show co-dominance or incomplete dominance)

Gametes

haploid sex cells formed by meiosis (sperm/ova)

Homozygous gene

maternal and paternal alleles are the same

Heterozygous gene

maternal and paternal alleles are different

Hemizygous

males only have one allele for each gamete

Genotype

genetic composition for a trait

Phenotype

observable characteristics of a trait

Complete dominance

the classical pattern whereby one allele is fully expressed over another

Co-Dominance

when pairs of alleles are expressed equally

Cystic fibrosis

autosomal recessive disorder, produces unusually thick and sticky mucus

Huntington’s Disease

autosomal dominant disorder, causes neurodegeneratioin

Sex linkage

when a gene is located on a sex chromosome

Mutagens

factors that induce mutations (Radioation, Chemicals, Biological Agents)

Carcinogens

mutagens that lead to the formation of cancer

PCR

Polymerase chain reaction, used in labs to amplify small fragments of DNA

Stages of PCR

Denaturation, Annealing, Elongation

PCR Denaturation

DNA is heated to separate it into 2 strands

PCR Annealing

DNA primers attach to 3’ ends

PCR Elongation

DNA polymerase binds to primer and copies the strand

Gel electrophoresis

used to separate and isolate proteins or fragments of DNA based on size/mass

DNA profiling

Technique by which individuals can be indentified/compared via their DNA

Genetic modification

transfer of genes between species

Transgenic organism

result of gene modification

Clones

groups of genetically identical organisms/group of cells derived from a single original parent cell (i.e asexual reproduction, identical twins)

Animal cloning methods

Binary Fission, Budding, Fragmentation, Parthenogenesis

Binary fission

parents organism divides equally in two, producing genetically identical daughter organisms (i.e Planaria/flatworms)

Budding

Cells split off parent organism, generating a smaller daughter organism that eventually separates (i.e yeasts)

Fragmentation

New organisms grow from a separated fragment of the parent organism (i.e starfish)

Parthenogenesis

Embryos are formed from unfertilised ova via diploid egg cells by the female (i.e frogs)

Artificial Cloning

early embryonic cella are pluripotent, if separated in a lab each group of cells will form cloned organisms (may occur naturally, i.e monozygotic twins)

Nucleosome

DNA complexed with eight histone proteins (octamer)

Chromatosome

Nucleosomes linked by an H1 histone

Solenoid

Coiled chromatosomes (~6 chromatosomes per turn)

30 nm Fibre

Condensed solenoid

Chromatin

Looped 30 nm fibres, which are compressed and folded around a protein scaffold

Chromosomes

Supercoiled chromatin (during cell division)