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What is a gene?

A heritable factor that is one length of DNA. It influences characteristics.


What is a chromosome?

Many genes


What is the specific position that a gene occupies on a chromosome?

The locus


What are alleles?

Various forms of genes


How many alleles can occupy each locus?



How many copies of each chromosome do animals and plants have, and what does this mean?

Animals and plants have 2 copies of each chromosome, which means that they can have 2 different alleles for the same gene.


What are differences between alleles?

They differ by only one or a few bases


What is genetic mutations?

Where new alleles are formed through random changes, most significantly through base substitution.


What do mutations in cells that develop into gametes cause?

Genetic disease


What is the cause of sickle cell anaemia?

- It is caused by a change to the base sequence of mRNA transcribed and therefore a change to the polypeptide sequence in haemoglobin. mRNA produces has GUG instead of GAG and produces valine, not glutamic acid.

- it is a change to the gene Hb. Most humans have allele Hb4.

- base mutation covered 6th colon of gene GAG to GTG, forming a new allele.

- offspring inherits it if it occurs in the cell of ovary or testes that develop into gametes.


What is sickle cell anaemia?

A genetic disease that causes haemoglobin molecules to stick together in tissues with low oxygen concentration. Red blood cells change into a sickle shape and can become trapped in the capillaries, with a risk of stroke and blood flow reduction. In a high oxygen concentration, cells return to a normal shape, so they change with circulation. Th life of red blood cells is reduced to 4 days minimum.


What is a genome?

The whole of the genetic information of an organism, the entire base sequence of each of its DNA molecules.


What does the human genome consist of?

46 molecules, the same number as it’s chromosomes


What does a plant genome consist of?

DNA molecules of chromosomes in their nucleus, mitochondria and chloroplasts


What is the human genome project?

- the entire base sequence of human genes
- began in 1989, published in 2003.


What did the human genome project show?

- it helps us predict protein coding genes (23,000 in genome)
- showed us that most of the genome is not transcribed, and that there is junk DNA, repetitive sequences
- that humans majoritively share the same base sequences, but single nucleotide polymorphisms create human diversity.


What are the characteristics of bacterial chromosomes?

- circular DNA
- not associated with proteins
- single copy of each gene in 1 chromosome
- 2 identical copies are present briefly after replication, ready for cell division


What are plasmids?

- small extra DNA molecules containing a few genes, not those for basic life processes
- they are not always replicated at the same time as chromosomes or at the same rate, so there may be multiple copies of plasmids that have not been through cell division
- they cross species barrier, so the plasmid is absorbed by cells of other species


How is DNA measured using auto radiography?

- cells are grown for 2 generations in a culture containing trusted thymidine, which is linked to deoxyribose, used by ecoli to make nucleotides.
- trusted thymine = tritium, radioactive isotope of carbon, radioactively labelled DNA produced by replication of E. coli cells.
- placed on dialysis machine- cell walls digested using lysozyme.
- they are burst to release DNA on surface- photographic emulsion is applied to the surface of the membrane and it is left in the dark for 2 months to allow tritium to decay
- it indicates the position of DNA


What are eukaryote chromosomes?

- linear DNA molecules associated with histoine
- composed of DNA and protein, DNA wound around histoines


What are haploid nuclei?

- one chromosome of each pair
- gametes- 1 allele


What are diploid nuclei?

-full pairs of homologous chromosomes
- prevents harmful recessive diseases affecting all with allele


Why can we not interbreed with other species?

Because we cannot interbreed with a different number of chromosomes


What are properties of the X chromosome?

Large, centromere near centre, contains genes vital to both sexes so is present in both.


What are the properties of the Y chromosomes?

Small, centromere near the end, contains less gene, dome the same as x, some only for men. SRY and TFD is a gene on Y that initiates development of male features


What do karyograms show?

- shows chromosomes as homologous pairs, decreasing in length


How do karyograms work?

- chromosomes are stained in metaphase to give the clearest image
- the dividing cell is placed on a microscope slide, a cover slip is placed over, the cell is burst and the chromosomes spread across the slide and a micrograph is taken


How can we identify Down syndrome?

A karyotype shows chromosome abnormalities. A sample can be taken from foetal cells. If 3 copies of chromosome 21 are present, child has Down syndrome.


How is Down syndrome caused?

Non disjunction (failure to separate chromosomes during formation of gametes) in chromosome 21


What are the effects of Down syndrome?

Causes hearing, heart, vision, growth and mental issues