each chromosomes in the nucleous of a diploid organisim has a partner that carriers the same gene. Such a pair of chromosomes is called homologous pair. Each chromosome in a pair may carry alternative forms of the same gene, these alternative forms are called alleles. If both alternative alleles are present in a particular cell nucleous, then the cell is heterozygous. If the nuclueous carries the same alele on both members of the homologous pair, then is homozygous. Letal alleles are alleles that cayse the death of the organism that carry them. Usually a result of mutation in genes that are essential to development. Crossing over ocur btw phorpase 1 and metaphase 1 and is the process where homologous chromosome pair up with each other and exchange different segments of their genetic material to form recombinant chromosomes. Albinism is caused by recessive allele, is a monohybrid inheritance. People with this do not produce melanine, this pigment normaly makes skin, the iris of the eye and hair a dark colour, sensitive to light. Sickle cell anaemia a homozygous has a disease. Codominance- Some genes have more than two aleles, both dominant. It results in a extra phenotype when both allels are present toguether .Mendelian inheritance- a type of biological inheritance that followes the law originally propose by Gregor Mendel. 1) law of dominance- some alleles are dominant while others are recessive, an organism with at least one dominant allele will display the effect of the domintant allele. 2)law of segregation- durind gamete formation, the alleles for each gene segregate from each other so that each gamete carries ony one allele for each gene. 3)law of independet assorpment- genes for different traits can segregate independently during the formation of gametes.