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Summary Genetics and Inheritance- Matric NSC Grade 12
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A complete summary of genetics and inheritance, with diagrams and definitions. Everything that is required to know for NSC Grade 12 Life Science.
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Genetics and inheritanceChromatin and chromosomes
Mention of Mendel as the father of genetics: • Chromosomes are made up of genes- a gene is part
• Gregor Mendel was an Austrian Monk who of the DNA in a chromosome that contains the code
studied and taught natural science and math's for protein synthesis
• He performed experiments on pea plants in his • Chromosomes are found in the nucleus of every
free time to study the inheritance of living cell ( can be called somatic cells which = body
characteristics from on generation to the next cells)
• He was only recognized 20 years after his death • A chromosome= DNA strand + histones (proteins)
• Mendel is regarded as the father of genetics Explain the process step by step of how 1 single
Why pea plants? chromosome develops into 2 identical chromosomes
• They are self-pollinating known as chromatids
• Easy to artificially cross in order to pollinate • These strands of DNA are wrapped around a histone
flowers to produce hybrids (by cutting off the and is collectively know as the chromatin network
anther) and then performed cross pollination (that is when meiosis is not taking)
himself using his own pollen of choice. He then • After Meiosis 1 occurs the chromatin network
“painted” ripe pollen onto a stigma with a small condenses, thus the strands of DNA are shorter and
brush and could thus control the cross thickened becoming visible as a single chromosome
What experiments did he conduct- by looking at pea • Before Meiosis 1 can occur, DNA replication needs
plants? to occur to ensure that both daughter cells formed
• He worked with purebred pea plants i.e. self- during Mitosis are correct having identical genetic
pollinated pea offspring parents information to the original mother cell
• Investigated the inheritance of characteristics • As a result of the DNA replication the single
with contrasting traits e.g. height of plant (tall or stranded chromosome consists of 2 identical units of
dwarf), color of seeds (yellow or green), seed chromosomes known as chromatids. Which are
shape (round or wrinkled) joined by a centromere
• Crossbred purebred plants with only one set of Explain why the number of chromosome are are always
contrasting traits. Called monohybrid cross even numbers?
• Crossbred purebred plants with 2 sets of • In organisms that reproduce sexually the number of
contrasting traits called dihybrid crosses chromosomes is always an even number because it
consist of 2 sets of chromosomes= diploid
chromosomes.
Mendel's conclusions of his investigations
• One chromosome of the pair comes from the
• At the of monohybrid cross of purebred plants mother and the other one chromosome of the pair
Mendel found offspring had only of the parents' comes from the father (these pairs of chromosomes
traits are known as homologous pairs of chromosomes).
• If these plants fertilized themselves offspring had Allele
either one or the other trait having a ratio of 3:1
• Each alleles carries a slightly different genetic code
• Mendel called purebred parents the P1 (Parental) about the same characteristic
generation their offspring the F1 (First filial) • Only 2 alleles for each gene are carried on the
generation and the next generation the F2 homologous pairs of chromosomes. One from eh
(Second filial) generation mother and one from the father
Analysis of results:
Each pair of genes carry the genetic code for the same
• Pairs of factors in cells that control each trait or characteristic
characteristic such as height
• If the factors for a characteristic are different one
dominates the other one (which is the recessive Definitions:
• Homologous pairs of chromosomes: Identical genes on
allele)
each of the two chromosomes. Each pair of genes
occupies the same locus on the chromosomes
Definition • Gene: The section found on a DNA strand that carries the
• Chromosome: A linear collection of genes genetic code to make a strand of RNA that will make up a
• Allele: Different copies of the same gene carrying protein. The sequence of codons that will designate the
different information about the same characteristic order of AA making up a protein.
, Genetics and inheritance
Homologous pairs and heterogenous pairs of
chromosomes Meiosis and the separation of alleles
• Homologous pairs of chromosomes: Alleles • During Meiosis, Somatic cells: homologous
of a gene are the same chromosome occur in pairs (that carry pairs
of alleles to to control hereditary
• Heterogenous pairs of chromosomes: Alleles
of a gene are different characteristics) separate from each other.
Thys 2 alleles for every gene making it
diploid
• Thus each gamete that is produced receives
only 1 allele of a gene pair
Mendel's law of segregation:
• When sex cells that are produced by parents
only one allele of a pair of alleles found in
the parent cells is found in each sex cell.
Genotype and phenotype
Phenotype: the observable characteristic (physical
appearance) of an organisms, as determined by its
genotype as well as its environment
Genotype: The genetic composition of an individual
Multiple Alleles:
• When a gene has more than 2 possible alleles to
control a hereditary characteristic
• However only 2 alleles can occur in a somatic cell
at a time
• A human characteristic that is controlled by more
than 2 possible alleles is-Blood groups
• The more alleles that control a specific
characteristic the more possible gene
combinations there are and the greater the Definitions:
diversity of phenotypes • Polygenic characteristics
Definition of polygenic: A hereditary
Mendel’s law of dominance: characteristic that is controlled by more than
States that if the 2 alleles are different only the one gene pair at different loci. These genes can
dominant allele will be expressed also have multiple alleles.
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