Genetics (IB)

State what it means if DNA is naked.

It is not associated with proteins.

Define plasmid.

Smaller extra loops of DNA.

Distinguish between chromosomes in eukaryotes and prokaryotes.

-chromosomes are linear in eukaryotes while they are circular in prokaryotes.
-they are associated with histone proteins in eukaryotes while in prokaryotes, the chromosomes are naked-they have no associated proteins.
-eukaryote chromosomes have no plasmid

Outline autoradiography with chromosomes.

-Cairns adapted technique to research chromosomes of E.coli and it was grown in a medium with radioactively labelled thymine.
-DNA became labelled instead of RNA.
-cells placed on membrane and digested cell walls allowing DNA to spill out over membrane.
-

Define chromatid.

Identical strands of chromosomes in a pair.

State the phase of mitosis at which chromosomes reach minimum length.

Metaphase.

Define genome.

Whole genetic info of an organism.

List genome sizes from smallest to largest among T2 phage, D. melanogaster, Homo sapiens, Paris japonica and E. coli.

T2 phage
E. coli
D. melanogaster
Homo sapiens
Paris japonica

Define homologous chromosome.

Chromosomes that have the same genes in the same sequence and they are not necessarily the same alleles.

Define allele.

Variations of a gene.

Define karyotype.

Number and type of chromosomes present in cell/organism.

Define karyogram.

Photograph/diagram in which chromosomes of an organism are shown in homologous pairs from increasing to decreasing length.

List organisms in decreasing chromosome number.

Homo sapiens
Pan troglodytes
Canis familiaris
Oryza sativa
Parascaris equorum

Outline the two common uses for karyograms in humans.

-deducing individual's sex: XX means they are female and XY means they are male.
-diagnosing conditions due to chromosomal abnormalities. Normal karyotypes have pair of each chromosome type including a pair of sex chromosomes. If there are more or less th

Define diploid.

When there are pairs of homologous chromosomes.

Define haploid.

When there is only one chromosome of each type.

State the pair of chromosomes that determines the sex of an individual.

23rd pair

State the chromosome number in a zygote in relation to a gamete.

2n.

Define meiosis.

Process in which there is the halving of the chromosome number and it allows a sexual life cycle with the fusion of gametes.

State when the pairs of chromosomes are separated to half the chromosome number.

Meiosis I

Outline the number of cells, number of chromosomes and chromatids per chromosome count in the stages of meiosis.

Number of cells:
Before meiosis: 1
After meiosis I: 2
After meiosis II: 4
Number of chromosomes:
Before meiosis: 2n
After meiosis I: n
After meiosis II: n
Chromatids per chromosome:
Before meiosis: 2
After meiosis I: 2
After meiosis II: 1

Outline the stages to meiosis.

Meiosis I:
Prophase I:
--> chromosomes pair up and each pair is homologous.
--> spindle microtubules grow from each pole to equator like mitosis.
--> nuclear membrane begins to disappear.
Metaphase I:
--> spindle microtubules from two poles attach to diff

List the two processes in meiosis that produce genetic variation and outline each one.

-random orientation of pairs of homologous chromosomes in metaphase I.
--> two possible orientations that determine which chromosome moves to each pole of the cell.
--> different combos of chromosomes are produced as orientation does not influence other p

State what promotes genetic variation.

At fertilization when alleles from two different parents are brought together in one new individual.

List the two ways that species that reproduce sexually can create genetic variation.

-meiosis
-random fusion of gametes

Outline non-disjunction.

-chromosomes do not separate and move to the same pole. Can happen in either anaphase I or anaphase II of meiosis.
-gametes on one side are too much or too few.
-gametes usually die with too little chromosomes but too much, it can survive.

Define trisomy.

When a zygote has three chromosome of one type instead of two.

State the relationship between chances of Down syndrome and age of parents.

Chances of Down syndrome (trisomy 21) increases with the age of the parent.

Outline two ways to obtain cells of an unborn child for chromosome testing.

Amniocentesis:
-involves injecting long needle to remove sample of amniotic fluid from amniotic sac surrounding fetus.
-the fetal cells in fluid are cultured for 2-4 weeks and then they are analyzed for chromosomal defects as well as other genetic disorde

State how Mendel deduced principles on which inheritance is based.

Crossing varieties of pea plants with different characteristics.

Outline how Mendel came up with the 3:1 ratio.

-when crossing two varieties of pea together he found that all offspring in F1 had the same characteristic as one of the parents.
-allowed F1 generation to self-fertilize which produced offspring in 3:1 ratio.
-parents are homozygous and F1 is heterozygou

Define genotype.

Alleles that an organism possesses.

Define phenotype.

An organism's characteristics.

Define segregation.

When two alleles of each gene separate into different haploid daughter nuclei during meiosis. Two alleles are on homologous chromosomes which move to opposite poles during segregation.

List two autosomal genetic diseases.

-Cystic fibrosis
-Huntington's disease

Outline Cystic fibrosis.

-caused by recessive allele of gene coding for chloride channel.
-usually neither parent has this disease, but both are carriers of recessive allele.
-does not affect phenotype if dominant allele is present.

Outline Huntington's disease.

-neurodegenerative disease which is dominant of gene coding for huntingtin.
-usually only develops during adulthood and they may have already passed it onto their children.

Define sex-linkage.

Association of a characteristic with an individual's sex since gene is located on a sex chromosome.

Why is sex-linkage always due to genes on the X chromosome?

Y chromosome has very few genes, but X chromosome is quite large and has important genes on it.

List two sex-linked disorders.

Hemophilia
Red-green colour blindness

What shows that hemophilia is sex-linked and not autosomal?

On a pedigree chart, it is evident that many males are affected by hemophilia. Mother can pass it onto her son and father could pass it onto his daughter.

Define codominant.

When two alleles have join effects on a heterozygous individual.

State when predicted ratios are accurate.

When there is a large number of offspring.

Define mutation.

Random changes in a gene's base sequence.

Define base substitution.

Replacement of one base in a gene with a different base.

Outline why mutations are important.

-they are a source of genetic variation needed for evolution to occur.
-most mutations are harmful, however.
-some even cause genetic disease and cancer.

Outline two mutagens that increase mutation rate.

High energy radiation-includes X-rays, short to medium wave UV, gamma rays and alpha particles from radioactive isotopes.
Mutagenic chemicals: nitrosamines in tobacco, mustard gas that was used as a chemical weapon and solvent benzene.

Define genetics.

The study of variation and inheritance.

Define gene.

A heritable factor that is made up of a length of DNA and it influences a specific characteristic.

List organisms in terms of number of genes from smallest to largest.

Homo sapiens
E.coli
Drosophilia melanogaster
Takifugu gambiae
Oryza sativa

Outline trends illustrated in terms of numbers of genes.

-bacteria have fewer genes than eukaryotes.
-some other animals have fewer genes than humans while some have more.
-plants may seem less complex than humans, but they have more genes.

Outline what is true about alleles.

-variations of the same gene.
-influences same characteristics and occupy same position on a type of chromosome.
-base sequences differ, but only by one or several bases.

State the commonest allele for the human gene in beta polypeptide and state the least common allele.

-Adenine (most common)
-Thymine (least common)

Outline sickle cell anemia.

-shows how base substitution can be significant.
-base substituted from A to T in triplet coding for sixth amino acid.
-HbA becomes HbS.
-one amino acid in polypeptide is altered since one codon in mRNA is different.
-glutamic acid is replaced by valine.

Outline the parts of a gene locus.

First number: number chromosome gene is on.
p: short arm
q: long arm
last number shows region of arm gene is in.

What happens to base sequences between two species over time?

They increase.

Outline the polymerase chain reaction.

-cycle of stages.
-millions of DNA copies can be produced in just a few hours.
-needed when there is only a small amount of DNA (e.g. in semen) when much larger amounts are needed.
-temperature increased to 73�C and this encourages Taq DNA polymerase to r

Define gel electrophoresis.

Method of separating mixtures of protein or fragments from DNA which are charged.

Outline gel electrophoresis.

-mixture placed on thin sheet of gel.
-acts like molecular sieve.
-electric field applied to gel by attaching electrodes to both ends.
-particles can be negatively or positively charged and they move towards one of the electrodes or the other.
-rate of mo

Outline the Human Genome Project.

-stimulates improvements in technology.
-improvements continued once project was underway and draft sequence was completed.
-allows genomes of other species to be sequenced at increasing rate and lower cost.

Define short tandem repeats.

Loci in chromosomes where there are much shorter sequences of bases (maybe four or five bases repeated many times).

Outline the use of STR alleles in DNA profiling.

-sample of DNA taken from person and it cannot be contaminated with DNA from other individuals or with another organism.
-DNA from selection of STR loci copied by PCR and DNA from between 11 and 13 loci copied in commonly used DNA profiling methods.
-copi

List what DNA profiling is used for.

-Forensic investigations
-Paternity investigations

Define genetic modification.

Transfer of genes from one species to another.

Outline genetic modification in terms of insulin.

-mRNA coding for insulin extracted from human pancreas cells that make insulin.
-DNA copiers of mRNA are made using enzyme reverse transcription.
-sticky ends made by adding extra G nucleotides to ends of the gene.
-plasmids are cut open using restriction

Outline benefits and harm of genetically modified crops.

Benefits:
-increased crop yields which creates more food for humans; less pest damage.
-less land needed for crop modification, so some could become areas for wildlife conservation.
-less use of insecticide sprays as they are expensive and can be harmful

Define cloning.

Process of creating an organism that is genetically identical to another organism.

State the simplest method for cloning.

Breaking up an embryo into more than one group of cells at an early age (when they are still undifferentiated) and each group of cells develops into genetically identical individuals. Drawback because at this stage characteristics of animal are unknown.

Define somatic-cell nuclear transfer.

Nucleus is removed from egg cell and replaced with nucleus from undifferentiated somatic.

Outline the cloning of adult animals using differentiated cells in terms of sheep.

-cells taken from udder of donor adult and cultured in lab for about six days.
-unfertilized egg taken from another sheep and nucleus is removed from egg.
-egg without nucleus fused with donor cell using pulse of electricity.
-embryo resulting from fusion

List two ways a plant can root when it is cut.

-in water
-inserted into solid medium