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Summary Life sciences notes matric - genetics and genetic engineering
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- Life Sciences
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- 12
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GENETICS AND GENETIC ENGINEERINGWhat is genetics?
§ A branch of biology that studies heredity and variation in organisms
Heredity: passing on of traits from one generation to the next
WHO WAS THE FATHER OF GENETICS?
• Gregor Mendel: realized something was passed on from one generation to the next
They are genes which are a
part of DNA molecules in
chromosomes
GENES AND ALLELES:
o GENES:
§ Each chromatid is made of one, helical DNA molecule
§ Gene can be defined as a section of DNA (series of nucleotides/bases) that controls a
hereditary characteristic i.e. It is the basic unit of heredity in living organisms
§ Genes in humans = between 20 000 and 25 000
§ Nearly all somatic cells have exact copy of all the genes in that organism
§ Two of each kind (paternal and maternal) each cell contains two of each kind of gene
(before replication)
These versions
of a gene are
known as alleles
§ Gene pool is a set of all genes or genetic information, large gene pool = high genetic
diversity
HOW ACTIVE ARE GENES?
§ Although each cell contains a full complement of DNA, only genes that are
needed are activated and others are suppressed
§ Some genes play a role in early development of the embryo and are
inactive thereafter
, GENETICS AND GENETIC ENGINEERING
§ Some genes are active in many types of cells, making proteins for basic
functions = ‘housekeeping genes’
§ High proportion of genes are non-coding genes i.e. do not code for
proteins and occur in between the coding section, only 2% of our DNA
codes for proteins
o ALLELES:
§ Alleles are genes responsible for controlling different versions of a trait found in the
same locus on homologous chromosomes e.g. for the gene determining coat colour in
cattle
Allele: one of two or more forms of a NB!
gene
HOW ARE ALLELES REPRESENTED?
Alleles are represented by means of
letters CAPITAL LETTER= dominant
allele
LOWER CASE= recessive allele
HOW ARE ALLELES PASSED ON FROM PARENT TO OFFSPRING?
v Passed on from parents to offspring by way of chromosomes in the gametes
that are made by the process of meiosis in sex organs
Gamete: a reproductive cell/sex cell
TO SUM UP:
Normal body cells (somatic cells) are diploid (2n) as they have
• A pair of homologous chromosomes
• Two alleles which may be the same or different
Sex cells (gametes) are haploid (n) as they have
• One of a pair of homologous chromosomes
• One of each pair of alleles
WHAT HAPPENS TO THE GAMETES?
§ During fertilization a male gamete, with its alleles, fuses with a female
gamete, with its alleles to form a DIPLOID ZYGOTE
, GENETICS AND GENETIC ENGINEERING
§ This divides during mitosis to form an entire new organism made up of
cells made with the same set of chromosomes and alleles as in the zygote
GENOTYPES AND PHENOTYPES
Genotype: made up of all the genes an organism carries on its chromosomes which it
has inherited from its parents
Phenotype: is the physical appearance of an organism such as tallness or hair colour.
Partly programmed by genes, its genotype but also shaped by external factors such
as exercise, diet and environment
HOMOZYGOUS AND HETEROZYGOUS
Ø After fertilization, the zygote and all the cells that develop from it will
have two alleles for each gene, one from each parent
Ø These will be in the same locus on each chromosome of a homologous pair
If the pair of alleles at a locus are the SAME the organism =
HOMOZYGOUS for that particular trait
If the pair of alleles at a locus are DIFFERENT, the organism = HETEROZYGOUS (a hybrid)
DOMINANT AND RECESSIVE ALLELES:
In heterozygous pairing, one allele of a pair may be:
• Dominant- this trait is expressed in the offspring
• Recessive- this trait is suppressed in the presence of the dominant allele
and not expressed in the offspring
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