Genetics and Genetic Engineering
Genetics
A branch of biology that studies heredity and variation in organisms
Heredity: passing on of traits/characteristics from one generation to the next
Gregor Mendel
- Father of genetics : Austrian monk
- First major breakthrough in heredity by investigating the transfer of traits
- Discovery: ‘something’ (we know they are genes but he called them factors) is passed on through
offspring which are unique yet the same
- Published his work but not recognised until after he died and was accepted as Darwin’s theory was
Genes and Alleles
Genes
Chromatid: one, helical DNA molecule
DNA molecule: series of genes
Gene: section of DNA that controls a hereditary trait (the base unit of heredity)
- Each chromosome has between 100s & 1000s of genes. Total around 20k-25k
- Nearly all somatic cells w nuclei have an exact copy
- Each cell has two of each kind of gene before replication (maternal & paternal) AKA alleles
- Gene pool: set of all genes or genetic info in a population.
- Large: high genetic diversity and more chances of survival
- Small: low genetic diversity and more chances of extinction
Gene Activity
- Cells have a full complement of DNA but only useful ones for specific proteins are activated
- Some play a role only in development of embryo and are then inactive
- Housekeeping genes: active genes that make proteins
- Non-coding genes: 98% and occur between coding sections
Alleles
Genes responsible for controlling different versions of a trait found in the same locus on a homologous
chromosome
One of two or more forms of a gene
Representation: capital letter for dominant alleles, lower case for recessive alleles
, How alleles are passed on
By way of chromosomes in gametes that are made during meiosis
Summary
Somatic cells are diploid (2n) as they have:
- A pair of homologous chromosomes
- Two alleles which may be the same or different
Sex cells are haplloid (n) as they have:
- One pair of homologous chromosomes
- One of each pair of alleles
Gametes
Fertilisation: male and female gamete fuse each with their alleles to form diploid zygote
Divides by mitosis to form a new organism made up of cells with the same set of chromosomes and alleles as
zygote
Genotypes and Phenotypes
Genotype: made up of all the genes an organism carries on its chromosomes which are inherited
Phenotype: the physical appearance of an organism, partly programmed by genes but also by external factors
Homozygous and Heterozygous
A zygote will have 2 alleles for each gene (one from each parent) on the same locus of each chromosome of a
homologous pair
- Homozygous: pair of alleles at locus are the same
- Heterozygous: pair of alleles at locus are different
Dominant and recessive alleles
Dominant: trait that is expressed in the offspring
Recessive: trait that is suppressed in the presence of a dominant allele
There will be 3 genotypes yet 2 phenotypes because:
- If there is a dominant alleles the homozygous organism will have the same phenotype as the
heterozygous
- The recessive will only be expressed as the phenotype when there is no dominant allele present
(homozygous)
Genetics
A branch of biology that studies heredity and variation in organisms
Heredity: passing on of traits/characteristics from one generation to the next
Gregor Mendel
- Father of genetics : Austrian monk
- First major breakthrough in heredity by investigating the transfer of traits
- Discovery: ‘something’ (we know they are genes but he called them factors) is passed on through
offspring which are unique yet the same
- Published his work but not recognised until after he died and was accepted as Darwin’s theory was
Genes and Alleles
Genes
Chromatid: one, helical DNA molecule
DNA molecule: series of genes
Gene: section of DNA that controls a hereditary trait (the base unit of heredity)
- Each chromosome has between 100s & 1000s of genes. Total around 20k-25k
- Nearly all somatic cells w nuclei have an exact copy
- Each cell has two of each kind of gene before replication (maternal & paternal) AKA alleles
- Gene pool: set of all genes or genetic info in a population.
- Large: high genetic diversity and more chances of survival
- Small: low genetic diversity and more chances of extinction
Gene Activity
- Cells have a full complement of DNA but only useful ones for specific proteins are activated
- Some play a role only in development of embryo and are then inactive
- Housekeeping genes: active genes that make proteins
- Non-coding genes: 98% and occur between coding sections
Alleles
Genes responsible for controlling different versions of a trait found in the same locus on a homologous
chromosome
One of two or more forms of a gene
Representation: capital letter for dominant alleles, lower case for recessive alleles
, How alleles are passed on
By way of chromosomes in gametes that are made during meiosis
Summary
Somatic cells are diploid (2n) as they have:
- A pair of homologous chromosomes
- Two alleles which may be the same or different
Sex cells are haplloid (n) as they have:
- One pair of homologous chromosomes
- One of each pair of alleles
Gametes
Fertilisation: male and female gamete fuse each with their alleles to form diploid zygote
Divides by mitosis to form a new organism made up of cells with the same set of chromosomes and alleles as
zygote
Genotypes and Phenotypes
Genotype: made up of all the genes an organism carries on its chromosomes which are inherited
Phenotype: the physical appearance of an organism, partly programmed by genes but also by external factors
Homozygous and Heterozygous
A zygote will have 2 alleles for each gene (one from each parent) on the same locus of each chromosome of a
homologous pair
- Homozygous: pair of alleles at locus are the same
- Heterozygous: pair of alleles at locus are different
Dominant and recessive alleles
Dominant: trait that is expressed in the offspring
Recessive: trait that is suppressed in the presence of a dominant allele
There will be 3 genotypes yet 2 phenotypes because:
- If there is a dominant alleles the homozygous organism will have the same phenotype as the
heterozygous
- The recessive will only be expressed as the phenotype when there is no dominant allele present
(homozygous)
