Patterns of Inheritance Revision Notes
Genetic Variation
Phenotype and Genotype
-the phenotype of an organism (visible characteristics) are influenced by the genotype of the organism (genetic makeup) and the environment
-genotypes can be described in 2 ways
Homozygous – two identical alleles (homozygous dominant = 2 dominant alleles / homozygous recessive = 2 recessive alleles)
Heterozygous – two different alleles for a characteristic (dominant allele will be expressed)
Genetic Factors
-gene mutations, chromosome mutations and sexual reproduction cause variation
Gene Mutations
-mutagens increase the rate of mutation
Physical Agents – radiation (UV light, X-rays and Gamma rays)
Chemical Agents – free radicals
Biological Agents – viruses, bacteria
-also occur during gamete formation
Persistent – transmitted through many generations without change
Random – not directed by need on the part of an organism where they occur
Chromosome Mutations
-may occur during meiosis
Deletion – a section of chromosome breaks off and is lost within a cell
Duplication – sections of chromosome are duplicated
Translocation – a section of one chromosome breaks off and joins a non-homologous chromosome
Inversion – a section of chromosome breaks off, is reversed, and re-joins the chromosome
Non-disjunction – chromosomes/chromatids fail to separate causing a gamete to have 1 extra chromosome (Down’s Syndrome occurs
when there are 3 chromosome 21s)
Aneuploidy – the chromosome number is not exact multiple of the haploid number for that organism
Polyploidy – diploid gamete is fertilises by a haploid gamete the zygote will be triploid
Sexual Reproduction
-meiosis produces genetically different gametes as they only have one chromosome of each homologues pair
-genetic variation occurs when random gametes fuse randomly
-variation may result from
Crossing over (allele swapping) in prophase 1
Independent assortment in metaphase/anaphase 1
Independent assortment in metaphase/anaphase 2
Environmental Factors
-some variation is caused by the environment and not passed on through genes
-environment can also interact with genes to cause variation
Variation Caused by the Environment
Speaking with a regional accent
Losing a limb/digit
Scar due to injury/operation
Environment Caused by the Environment Interacting with Genes
-environment may prevent the expression of genes
o Chlorotic Plants
-where the plants leaves are yellow/pale due to chlorophyll not being produced
Not enough light – plants will turn off chlorophyll production to conserve resources
Mineral deficiencies – lack of Mg2+ prevents chlorophyll formation
Virus infection – viruses may inhibit the production of chlorophyll
o Animal Body Mass
-determined by both genetic and environmental factors
Environmental obese – eating a poor diet and lack of exercise causes obesity
Genetically obese – mutation on chromosome 7 causes fat deposit of the body to be altered, becoming obese
Genetic Variation
Phenotype and Genotype
-the phenotype of an organism (visible characteristics) are influenced by the genotype of the organism (genetic makeup) and the environment
-genotypes can be described in 2 ways
Homozygous – two identical alleles (homozygous dominant = 2 dominant alleles / homozygous recessive = 2 recessive alleles)
Heterozygous – two different alleles for a characteristic (dominant allele will be expressed)
Genetic Factors
-gene mutations, chromosome mutations and sexual reproduction cause variation
Gene Mutations
-mutagens increase the rate of mutation
Physical Agents – radiation (UV light, X-rays and Gamma rays)
Chemical Agents – free radicals
Biological Agents – viruses, bacteria
-also occur during gamete formation
Persistent – transmitted through many generations without change
Random – not directed by need on the part of an organism where they occur
Chromosome Mutations
-may occur during meiosis
Deletion – a section of chromosome breaks off and is lost within a cell
Duplication – sections of chromosome are duplicated
Translocation – a section of one chromosome breaks off and joins a non-homologous chromosome
Inversion – a section of chromosome breaks off, is reversed, and re-joins the chromosome
Non-disjunction – chromosomes/chromatids fail to separate causing a gamete to have 1 extra chromosome (Down’s Syndrome occurs
when there are 3 chromosome 21s)
Aneuploidy – the chromosome number is not exact multiple of the haploid number for that organism
Polyploidy – diploid gamete is fertilises by a haploid gamete the zygote will be triploid
Sexual Reproduction
-meiosis produces genetically different gametes as they only have one chromosome of each homologues pair
-genetic variation occurs when random gametes fuse randomly
-variation may result from
Crossing over (allele swapping) in prophase 1
Independent assortment in metaphase/anaphase 1
Independent assortment in metaphase/anaphase 2
Environmental Factors
-some variation is caused by the environment and not passed on through genes
-environment can also interact with genes to cause variation
Variation Caused by the Environment
Speaking with a regional accent
Losing a limb/digit
Scar due to injury/operation
Environment Caused by the Environment Interacting with Genes
-environment may prevent the expression of genes
o Chlorotic Plants
-where the plants leaves are yellow/pale due to chlorophyll not being produced
Not enough light – plants will turn off chlorophyll production to conserve resources
Mineral deficiencies – lack of Mg2+ prevents chlorophyll formation
Virus infection – viruses may inhibit the production of chlorophyll
o Animal Body Mass
-determined by both genetic and environmental factors
Environmental obese – eating a poor diet and lack of exercise causes obesity
Genetically obese – mutation on chromosome 7 causes fat deposit of the body to be altered, becoming obese
