genetics

the genetic constitution of an organism

the expression of the genotype and its interaction with the environment

variants of a particular gene

eye colour e.g. blue, green, brown

mutations in a gene that occur at different positions in the genes

chromosomes form pairs called homologous chromosomes

alleles at a specific locus can be homologous if they’re the same type of allele they are heterozygous if the alleles are different

there are 2 copies of a particular allele for the genotype as chromosomes form homologous pairs one copy is from each parent

an allele is dominant if it’s always expressed in the phenotype( of a heterozygous) so only one copy is needed for expression

an allele is recessive if it’s not expressed in the phenotype of a heterozygous so 2 copies have to present for expression

both alleles are equally dominant and equally expressed in the phenotype e.g. blood group AB

they can be used to predict the outcome of crossing two different genotypes e.g. Parental gentoype CC cc Gametes: C C c c

3: 1 dominant to recessive

e.gg. an unknown genotype is crossed with a homozygous recessive individual If all the offspring have a dominant phenotype, the unknown genotype is homozygous dominant as they must have inherited the homozygous allele from the unknown genotype if half of the offspring have recessive phenotype then the unknown genotype is heterozygous as some individuals have inherited the recessive allele form the unknown genotype

to work out the inheritance of 2 different genes together e.g. parental alleles: RRYY rryy R= round r= wrinkles Y = green y = yellow Gametes: RY RY ry ry

9: 3: 3: 1

autosomes are chromosomes that are not sex chromosomes

when there is 2 or more genes located on the same autosome, they are less likely to be separated during crossing over so they are inherited together this can impact the ratio of phenotypes e.g. the GB alleles and the gb alleles in the GgBb parent may have been linked. This means the GgBg parent produced mostly GB and gb gametes and makes the GbBg and ggbb genotypes more common in the offspring. This results in a higher proportion of the offspring would have their parent’s phenotypes, instead of the split even of phenotypes predicted

offspring are more likely to enable parental phenotype as the alleles are less likely to cross over during meiosis

when the gene is only on the X chromosome therefore, males are more likely to have recessive conditions e.g. hemophilia because they only require one copy of the sex-linked recessive allele for expression ( they have 1 X and 1 Y ) instead of 2 for females, they need to carry two (x and x) and when males have been x linked recessive condition, they have inherited it form their mother

it is the interaction between 2 genes where one gene masks the expression of the other gene in the phenotype

it is called the epistatic gene

the hypostatic gene

dominant or recessive