Biology #3 Genetics CHROMS & MEIOSIS

What is the difference between eukaryotic DNA and prokaryotic DNA? (4)

Euk is linear, prok is circular. Euk is associated with histone proteins, prok is naked (not associated with histones). Prok have plasmids, euk does not. Euk contains 2+ different chromosomes (23 pairs in humans), but prok only have 1 type.

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Outline autoradiography (as used by Cairns using E.Coli bacteria) in research into chromosomes

Grow cells for 2 gens in radioactively labelled thymine. Place on dialysis memb: walls digested by lysosome: DNA spills onto memb. Photo film applied to surface & left in dark. Radioactive atoms decay, react w film & leave dark grain, showing chroms

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What is a genome?

The whole of the genetic information of an organism/ the total amount of DNA in 1 set of chromosomes in a species.

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Define karyogram

A photo/ diagram showing homolgous pairs of chromosomes in an organism in decreasing length

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Define karyotype

The number and type of chromosomes present in a cell

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What are homologous chromosomes?

A pair of chromosomes: 1 maternal, 1 paternal. Have the same genes in the same sequence, but not necessarily the same alleles.

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What are 2 common uses of karyograms in humans?

Deducing the sex of an individual, diagnosing conditions due to chromosome abnormalities (i.e. downs syndrome = 3 copies of chrom 21)

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What is the difference between diploid and haploid cells?

Haploid= 1 set of DNA, e.g. in gametes (23 chroms in humans). Diploid= 2 (full) set of DNA, i.e. somatic cells (46 chroms in humans).

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What is meiosis?

Cell division to produce gametes (diploid cell divides into 4 haploid cells)

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Outline the stages of meiosis?

P1: homologous chroms pair up. M1: nuclear memb breaks down, chrom pairs line up at equator. A1: homologous chroms are pulled to opp poles by spindle microtubules. P2: memb pinches @ equator. A2: sister chroms pulled to opp poles. T2: nucleus reforms

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Why is genetic variation important for a species?

Allows them to adapt to changing environment & makes them viable

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How is genetic variation promoted during meiosis? (2 ways)

1. Random orientation of chroms during M1 (2 possible orientations: determines which chrom moves to which pole). 2. Crossing over (recombination) during P1: parts of non-sister chroms exchanged. Produces chroms with new combinations of alleles

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What is non-disjunction?

Chromosomes that should have separated & moved to opposite poles but have not & instead move to the same pole. i.e. trisomy 21= downs syndrome

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What are the 2 ways that a foetus can have chromosome testing?

1. amniocentesis (amniotic fluid from sac around foetus contains cells from foetus) 2. chorionic villus sampling (cells from foetal tissues themselves in the placenta, called chorionic villi). Both require use of hypodermic needle through abdomen

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What does genotype and phenotype mean?

Genotype: the alleles possessed by an organism (i.e. Bb) Phenotype: the characteristics of an organism (i.e. brown eyes)

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What are autosomal genetic diseases?

Gene for a specific genetic disease on a non-sex chromosome

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What is sex-linkage?

When the gene controlling a specific characteristic (i.e. genetic disease) is located only on a sex chromosome (mostly on X chromosome)

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Give an example of a recessive and dominant genetic disease

Recessive: cystic fibrosis. Dominant: huntington's

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What is co-dominance?

Neither allele is recessive (i.e. for blood groups), so both are given upper case letters. On a heterozygous individual, both affect the phenotype.

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What are the 3 'multiple' alleles for blood groups (and therefore the 4 possible blood groups)?

IA, IB, i ... A, B, AB, O (aka the ABO system)

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What is a mutation?

A random change to the base sequence of a gene, producing a new allele

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What are 2 types of mutagens?

High energy radiation (X-rays, short/medium UV rays, alpha particles from radioactive isotopes) and mutagenic chemicals (nitrosamines in tobacco, mustard gas)

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What 2 major incidents caused increased deaths due to leukaemia and other cancers?

The nuclear accident at Chernobyl, Ukraine. The nuclear bombing of Hiroshima, Japan.

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Define genetics

The study of variation and inheritance

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Define gene

A section of DNA that codes for a polypeptide chain (protein) which influences a specific characteristic (phenotype)

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What is an allele?

A different form of a gene that has almost the same base sequence but differs on a small number of bases

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What is the cause for sickle cell anaemia?

Adenine in gene for haemoglobin replaced by thymine. Happens through base substitution. Causes red blood cells containing altered haemoglobin to become sickle-shaped.

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Why is sickle cell anaemia both good and bad?

Carries oxygen less efficiently BUT can give resistance to malaria. A heterozygous form of this gene may be beneficial?

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Define locus

The particular position of a gene on a pair of homologous chromosomes

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Outline how gel electrophoresis works

Is a method of separating charged proteins or fragments of DNA. Mixture placed on thin sheet of gel acting as molecular sieve. Immersed in conducting fluid. Electric fluid applied. Particles/ DNA move to electrodes (small molecules faster than large)

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Why is DNA profiling/ fingerprinting used? (2)

For paternity testing and for forensic investigations

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What are short tandem repeats (STRs) in chromosomes?

Loci containing short sequences of 3, 4 or 5 bases that are repeated many times.

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What are the processes involved in DNA profiling?

1. obtain sample of uncontaminated DNA from person/ suspect. 2.DNA from between 11-13 loci of short tandem repeats (STRs) copied by PCR. 3. copies of STR alleles are separated by gel electrophoresis

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What are the different components that are used in genetic transfer/ modification via plasmids?

restriction endonuclease: enzyme that cuts DNA at specific places. DNA ligase: enzyme that makes sugar-phosphate bonds to link nucleotides together & form continuous strand. recombinant plasmid: the plasmid with the desired gene

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Outline how genes are transferred via plasmids

Extract coding for specific gene (i.e. insulin) & make DNA copies. Make sticky ends to DNA and plasmid ends (cut using restriction endonuclease) & seal complementary ends with DNA ligase. Insert into host (e.g. E.Coli & culture to produce insulin)

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What is the name of the bacterial protein used in corn/maize & toxic to insects?

Bt toxin

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What are benefits of genetically modified crops? (3)

higher crop yield -- more food. less land needed. less insecticide sprayed (save money & less harm to natural wildlife)

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What are possible harmful effects of genetically modified crops? (3)

insects (i.e. monarch butterfly) are affected even though they do not feed on maize. transferred gene might spread to other plants via cross-pollination. insects/ pests may develop resistance.

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What is a clone?

A group of genetically identical organisms denied from a single original parent cell/ organism

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Outline how an animal might be cloned artificially

somatic cell of donor adult cultured in lab. remove nucleus of unfertilised egg from another adult. fuse nucleus with somatic cell w electricity pulse/ heat. after cells have begun to multiply, transfer embryo to uterus of a surrogate mother.

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Biology #3 Genetics CHROMS & MEIOSIS

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