Biology - Genetics & Genetic Engineering

Gametes

haploid cells that are capable of fusion

Fertilisation

the union of two gametes to form a single cell called a zygote

Alleles

are different (or alternative) forms of the same gene

Locus

the position of a gene on a chromosome

Dominant

the allele that prevents the recessive allele from being expressed

Recessive

the allele is prevented from being expressed by a dominant allele

Genotype

the genetic make-up of an organism

i.e. the genes that are present

Phenotype

the physical make-up, or appearance, of an organism

Progeny

refers to the offspring that are produced

Homozygous

means that two alleles are identical

Heterozygous

means that two alleles are different

Punnett Square

a grid used to show the ratio of the genotypes of the progeny in a genetic cross

Incomplete Dominance

neither allele is dominant or recessive with respect to the other

→ both alleles are equally expressed in the heterozygous genotype to produce an intermediate phenotype

Pedigree

a diagram showing the genetic history of a group of related individuals

XX

individual is female

XY

individual is male

Gregor Mendel

known as the father of genetics

Law of Segregation

states that:

• inherited characteristics are controlled by pairs of alleles

• alleles segregate from each other at gamete formation, with only one member of the pair being found in each gamete

Monohybrid Cross

involves the study of a single characteristic

Dihybrid Cross

involves the study of two characteristics

Law of Independent Assortment

states that:

• when gametes are formed…

• either of a pair of alleles…

• is equally likely…

• to combine with either of another pair of alleles

Linkage

means that genes are located on the same chromosome

Sex Linkage

means that a characteristic is controlled by a gene on a sex (or X) chromosome

Examples of Sex Linked Characteristics

• colour blindness

• haemophilia

Recessive Phenotype

is more common in males than females, in sex-linked traits

Non Nuclear DNA

• found in chloroplasts and mitochondria

• passed on only from the female

• allows organelles to reproduce independently of the cell

Genetic Engineering

the artificial manipulation or alteration of genes

Recombinant DNA

the name give to altered DNA, as it recombines after a small section of DNA is inserted into it

Substances used in Genetic Engineering

• source of DNA

• cloning vector

• restriction enzymes

• DNA ligase

Source of DNA

taken from on organism to be placed into the DNA of a second organism

Cloning Vector

a special kind of DNA that can accept foreign DNA and replicate itself and the foreign DNA

e.g. bacterial plasmid

Restriction Enzymes

enzymes that cut DNA at specific places

DNA Ligase

enzyme that is used to stick DNA molecules from different source together

Genetic Engineering Process

1. isolation

2. cutting

3. ligation

4. transformation

5. cloning

6. expression

Isolation

the removal of the chromosome (containing the target gene) from the human cell and the plasmid DNA from the bacterium

Cutting

a restriction enzyme cuts the chromosome and plasmids

Ligation

the joining of two sections of DNA to form a single strand

Transformation

the uptake of DNA into a cell

Cloning

the production of identical copies of the bacterium (containing the target gene)

Expression

the formation of the product by the organism with the recombinant DNA

Weed Killer Resistant Crops

application of genetic engineering in plants

Emphysema

application of genetic engineering in sheep, protein inserted into sheep DNA to help treat this condition

Insulin

application of genetic engineering in microorganisms, made by bacteria and injected into humans to treat diabetes