Summary
Summary Grade 12 IEB Life Science: DNA - Genetic Engineering
- Course
- Grade 12 Life Sciences
- Institution
- Clifton School, Durban, KwaZulu Natal
Life Science IEB Genetic Engineering notes Grade 12
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GeneticsWhat is genetics?
- A branch of biology in which heredity and variation of organisms are studied
- It is used to explain the differences and similarities between parents and their
offspring.
- Gregor Mendel (the Father of Genetics) was responsible for investigating the
transfer of characteristics from one generation to the next - his work was
published in 1866, and his findings were gradually accepted over time - many
biologists use his work for the grounding of their own studies
- Mendel used to call genes ‘factors’ (they are a part of DNA molecules in
chromosomes.)
- Each chromatid is made up of one, helical DNA molecule - each DNA molecule
is made up of a series of genes
- A gene is a section of DNA that is responsible for control a specific
characteristic. Each chromosome has between 100 and 1000 genes (the total in
humans is between 20 and 25 thousand genes)
- All somatic cells contain the exact copy of all genes in that organism (expect
mature red blood cells - they have no nucleus and thus no DNA).
- There are 2 of each chromosome (1 paternal and 1 maternal), each contain 2 of
each kind of gene. These different versions of genes are known as alleles.
- The gene pool is a set of genes or genetic information in a population of sexually
reproducing organisms. If there is a large gene pool, then there is large genetic
variety and thus higher genetic diversity and an increased chance of survival.
How active are genes?
- Each cell contains a full copy of all DNA, however only the genes that are
required each cell are activated - therefore, different genes are activated in
different cells, resulting in specific proteins giving each cell type a particular
characteristic
- Genes that play a role in early development of an embryo are inactivated after
they are no longer needed. There are genes that are active in most cells - the
housekeeping genes - they make protein needed for basic functions.
- 98% of genes are non-coding and do not code for proteins.
Hox genes: the master control genes that determine the way in which a body
develops after conception.
Human Epigenome Project: the study that aims to document what activates and
deactivates genes.
Epigenome: The control of genes
Alleles
, - The genes that are responsible for controlling different versions of a trait found
at the same locus on homologous chromosomes.
- They are represented by means of a letter, in which the dominant trait is drawn
with a capital letter, and the recessive trait with a lower case letter
- Alleles are passed on from parents to offspring by means of chromosomes in
the gametes that are made by the process of meiosis.
Body/somatic cells = diploid = 2n:
— Have a pair of homologous chromosomes
— 2 alleles (may be the same or different)
Sex cells/Gametes = haploid = n:
— Have a pair of homologous chromosomes
— 1 pair of alleles
- During fertilisations males gamete and its allele forms with a female gamete and
it’s allele, forming a diploid zygote, carrying chromosomes inherited from both
it’s parents
- This divides by mitosis, forming a new organism that carries the same set of
chromosomes and alleles as the zygote
- A genotype is made up of all genes that an organism carries on it’s
chromosomes which it inherited from it’s parents
- The phenotype is the physical appearance of an organism which is partly
programmed by genes, but also shaped by external factors (diet, exercise,
environment). The dominant trait is usually the phenotype.
- The zygote has 2 alleles per gene, found at the same locus on each
chromosome of a homologous pair
- If these alleles are the same, the organism is homozygous for that trait
- If they are different, they are heterozygous. If pairing is heterozygous, the
dominant trait is that which is shown phenotypically, where as the recessive is
suppressed and not expressed in offspring.
Mendel’s experiment
- He took pure-breeding pea plants, testing over 28 000 of the to analyse 7 pairs
of characteristics (eg. height, pod shape, pod colour ect.)
- He was trying to discover what happened to the alternative trait forms
- He transferred pollen of pure breeding tall pea plants and short pea plants,
collecting and sewing seeds. F1 generation grew into tall plants and were
allowed to self pollenate, creating F2 generation. He found that 3/4 were tall,
and 1/4 was short
Complete dominance
- This is a characteristic that is fully expressed in the phenotype of a
heterozygous organism is the dominant allele
- When dominant and recessive are shown, only dominant is portrayed.
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