4 Genetics

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Gene

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a heritable factor that controls a specific characteristic, part of a chromosome, made of DNA

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genome

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the whole of the genetic information of an Organism

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chromosome

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a large DNA molecule consisting of about 1000 genes

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gene locus

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position of a gene on a chromosome

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allele

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a form of a gene, differing from other alleles of the gene by a few bases at most and occupying the same locus as the other alleles of that Gene.

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chromatids

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the two parts of the chromosome

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centromere

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connects the two chromatids of the chromosome

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gene mutation

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a change to the base sequence of a gene.

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base substitution

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gene mutation where one base in a gene is replaced by another base
- can result in disease such as sickle cell anemia

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consequence of gene mutation in the sickle cell disease

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red blood cells contain altered hemoglobin which may carry oxygen less efficiently but can give resistance to malaria

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diploid

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when the cell has two full set of chromosomes

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haploid

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when a cell contains only one full set of chromosomes

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homologous chromosomes

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have the same genes as each other, in the same sequence, but not necessarily the same alleles of thos Genes

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meiosis

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reduction division as the number of chromosomes in a cell can be resuced from diploid to haploid

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(Stages of Meoisis) Prophase I

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- chromosomes pair up
- nuclear membrane will soon break down
- spindle microtubules grow from each pole to the equator

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(Stages of Meoisis) Metaphase I

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- the pairs of chromosomes line up on the equator
- spindle microtubules from the two poles attach to different chromosomes in each pair, ensuring that one is pulled to one pole and the other to the other pole

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(Stages of Meoisis) Anaphase I

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- each chromosome still consists of two chromatids
- homologous chromosomes are pulled to opposite poles. This halves the chromosome number
- the cell membrane will soon be pulled inwards to divide the cell

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(Stages of Meoisis) Prophase II

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- New spindle microtubules grow from the poles to the equator
- the cell has divided to form two haploid cells which immediately divide again as meiosis involves two divisions

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(Stages of Meoisis) Anaphase II

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- the centromeres have divided making the chromatids into seperate chromosomes which move to opposite poles
- the cell membrane is pulles inwards again to divide the cell

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(Stages of Meoisis) Telophase II

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- each Nucleus now has half as many chromosomes as the nucleus of the parent cell
- nuclear membranes reformed
- both cells have divided again to form 4 haploid cells

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karyotype

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the number and appearance of the chromosomes in an organism

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2 ways how cells are obtained from the fetus for karyotyping

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1. amniocentesis
- sample of amniotic fluid is removed rom the amniotic sac around the fetus
2. Chorionic villus sampling
- cells are removed from fetal tissues in the placenta called chorionic villi

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what can be found out by karyotyping?

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gender, abnormalities

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non-disjunction

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non-separation of chromosomes

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the father of genetics

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Gregor Mendel

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Homozygous

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having two identical alleles of a gene

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Heterozygous

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having two different alleles of a gene

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Dominant allele

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an allele that has the same effect on the phenotype in a heterozygous individual

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recessive allele

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an allele that only has an effect on the phenotype in homozygous individuals

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sex chromosomes

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determine the gender of a child

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X chromosome

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relatively large and carries many genes

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Y chromosome

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much smaller carries inly a few genes

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If two X chromosomes are present ...

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the embryo develops into a girl

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If one X and one Y chromosome are present ...

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the embryo develops into a boy.

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when women reproduce they pass on ...

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one X chromosome in the egg.

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when men reproduce they pass on ...

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either one Y or one X chromosome in the sperm.

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sex linkage

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is the association of a characteristic with gender, because the gene controlling the characteristic is located on a sex chromosome.

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genetically modified organisms

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organisms that have had genes transferred to them

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Potential benefits of Bt maize (3)

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1. less pest damage and therefore higher crop Fields to help reduce food shortages
2. less land needed for crop production, so some couldbecome areas for wildlife conservation
3. less use of insecticide sprays, which are expensive and can be harmful to farm workers and to wildlife

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Possible harmful effects of Bt maize (3)

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1. humans and animals might be harmed by the bacterial DNA
2. insects that are not pests could be killed even if they do not feed on the maize
3. populations of wild plants might be changed

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Cloning

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producing identical copies of genes, cells or Organisms

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clone

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is a group of genetically identical organisms or a group of genetically identical cells derived from a single parent cell

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Therapeutic cloning

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when cloning is used to produce skin or other tissues needed to treat a patient

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reproductive cloning

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if an organim with the same characteristics is reproduced

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arguments for therapeutic cloning (3)

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1. save lifes and reduce sufferings
2. cells can be removed from embryos that have stopped developing, so would have died anyway
3. cells are removed at a stage when Embryos have no nerve cells and cannot feel pain

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arguments against therapeutic cloning (3)

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1. every human embryo is a potential human being, which should be given a chance of developing
2. more Embryos may be produced than are needed, so some may have to be killed
3. there is a danger of embryonic stem cells developing into tumour cells