Inheritance

• The genome is the total genetic makeup of an organism
• A gene is a section of DNA on a chromosome coding for a polypeptide
• A locus is the position of a gene on a chromosome
• A recessive allele is only expressed on a homozygous recessive gene
• A dominant allele is always expressed
• Codominant alleles are equally expressed
• Homozygous means containing the same two alleles on a gene
• Heterozygous means containing two different pairs of alleles on a gene
• Dihybrid inheritance is where two separate genes are acquired
• Genetic linkage is where two genes are found on the same chromosome and inherited together
• An autosome is not a sex chromosome
• Sex linkage is where a gene is carried on the X or Y chromosome
• F1 is the first homozygous offsprings generation
• Monohybrid inheritance is where a single gene is inherited and is based on Mendel
• Mendel concluded that a characteristic can be carried across a generation and not be expressed and that dominant alleles mask recessive alleles
• A genetic cross needs the parental phenotypes and genotypes with the possible allele combinations or gametes shown, the phenotypes, genotypes of the offspring must be shown as well as the ratio
• Exact ratios of genotypes in offspring vary in reality due to random fertilisation, the ratios will become closer in larger sample sizes
• The Y chromosome is smaller so carries less genes than the X chromosome, in males, recessive alleles on the X chromosome are expressed as there is no pair
• In dihybrid inheritance, genes are carried on separate chromosomes
• The chi squared test can be done to test if there is a significant difference between observed and expected frequencies
• Autosomal linkage results can differ from expected ratios due to recombinant chromosomes from crossing over
• The further apart the 2 linked genes on a chromosome are, the higher the chance of crossing over
• Epistasis is where the expression of one gene prevents the expression of another
• Pedigree analysis is where genome trees are used to determine probability of inheritance
• Evidence for a non sex linked chromosome would occur when the father is not affected as she would need to obtain the recessive allele from her father to be affected
• Evidence for a sex linked disorder would occur when a father and mother are unaffected but their male offspring are affected due to the mother carrying a recessive allele
• The hardy weinberg equation can be applied in a stable and large gene pool with no mutations, mating must be random with no immigration, this provides constant allele frequency
• p + q = 1 is used to calculate allele frequency
• p^2 + 2pq + q^2 = 1 is used to calculate genotype percentages
• P is often the dominant allele whilst Q represents the recessive allele