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Summary Inheritence, Variation and Evolution
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After fertilization, you get a zygote. This is a fertilized egg. There are 23 chromosomes in an egg andsperm and 46 chromosomes in a zygote. Human bodies cell contain 23 pairs of chromosomes while
human gametes contain 23 single chromosomes.
Sexual reproduction is where the baby gets genes from both parents. They inherit different features
from both parents. Females produce half of the sex cell (gametes) while men produce the other half.
A sperm and egg fuse together to make the off spring, known as fertilization.
Asexual reproduction is when a cell split and divides to produces the off spring. The off spring get all
their genes from one parent. The off springs are clones of the parent.
A disadvantage of asexual reproduction is that if one plant get a disease all their off springs will too,
which can lead to a wipe out of that species. This is an advantage of sexual reproduction because if
one species get it, their off springs are unlikely to get it as they are different.
DNA is arranged in structures called chromosome inside the cell’s nucleus.
A gene is a small section on a chromosome. Each gene codes for a particular sequence of
amino acids, to make a specific protein.
In a human body cells are usually found in pairs. Each cell has 23 pairs of chromosomes.
The genome of an organism is defined as the genetic material of that organism.
Genetic variation are characteristics which have been inherited from parents, while environmental
variation are characteristics caused by the difference in places where the organism lie and grow and
the conditions in these places.
Mitosis is the types of cell division that leads to growth and repair (46 chromosome). It leads to
identical cells (clones) being formed. While, meiosis leads to non-identical cells being formed. Cells
in the reproductive organs divide by meiosis to form gametes. The main features of meiosis are:
The chromosomes are copied
The cells divide twice, forming 4 gametes
Meiosis Mitosis
Genetic mixing happens New cells have the same number of
Gamete production occurs chromosomes as parents
New cells show variation Happens in skin cells
Two division occur Two new cells are formed as a result
Identical cells ae formed
Homologous Chromosomes- in all living thing, characteristics are passed on in the chromosome that
off spring inherit from parents.
Like many species of animals and plants, humans are diploid, meaning that most of their
chromosomes come in matched sets known as homologous pairs. The chromosomes in a matching
pairs contain the same types of genes that code for the characteristics.
Different versions of a gene, that code for different versions of a characteristic, are called alleles.
Letters are used to represent different alleles: a dominant allele is always a capital letter (B) and a
recessive allele is always the corresponding small letter (b).
The allele pair for each characteristic is called a genotype
The physical expression of an allele pair Is the phenotype
, Homozygous when two allele are the same (BB or bb)
Heterozygous when two allele are different (Bb)
These instructions are found in the nucleus of the cells. The instructions for each characteristic is
called a gene.
Cystic Fibrosis is an inherited disorder that affects the cell membranes, causing the production of
thick and sticky mucus. It is caused by a recessive allele. This means that it must be inherited from
both parents. Symptoms:
A persistent cough that produces thick mucus or phlegm
Shortness of breath, especially when exercising
Polydactyly is an inherited condition in which a person has extra fingers or toes. It is caused by a
dominant allele. This means that it can be passed on by just one parent, if they have the disorder.
Born with one extra finger or toe. The extra digit may be a small, raised bump or a piece of
skin that looks like a small finger or toe that isn’t fully formed. Treatment: remove extra digit
Genetic engineering is process which involves modifying the genome of an organism by introducing
a gene from another organism to give a desired characteristic. Scientists can now, more or less,
transfer genes from any organism, including plants, animals, bacteria or viruses.
Genetically Engineered Plants- genetic engineering has transformed crop production. Genes from
many organisms, often not even plants, are cut out of their chromosomes and inserted into the cells
of crop plants. Such crop plants and other organisms are genetically modified, GM crops or GM
organisms (GMOs). Plants have been engineered to be resistant to disease, and to increase yields
such as producing bigger, better fruit. Several types of crop plants have been produces that are
resistant to diseases caused by viruses.
An herbicide is a chemical which kills plants (also called a weed-killer). If a crop plant is resistant to
herbicide, the farmer can spray herbicide to kill all other plants in the field without affecting the
crop. Plants resistant to insect attack have been modified to produce their own pesticide.
In genetic engineering, genes from the chromosomes of humans and other organisms are cut out of
the DNA using enzymes. The genes are then transferred to the cells of the organism to be genetically
modified.
Genetic engineering is now used to produce ‘human insulin’ from genetically modified bacteria. It is
cheaper, safer and more ethically acceptable than using specially bred pigs which had to be killed.
The genetic engineering technique:
Enzymes are used to remove the required gene, or genes, from the organism that carries the
gene(s).
The gene is transferred, using a vector, to the organism that is to be modified. The vector is
often a plasmid.
The gene is inserted and sealed into the plasmid DNA using another enzyme.
The gene is a small section gene is a small section of a DNA on a chromosome. Some characteristics
like hair or eye colour are controlled by a single gene. Each gene may have different forms called
alleles. Each allele codes for a different protein.
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