Biology 2016 JAMB Past Questions - Question 39: The crossing of individuals of the same species with different genetic characters is

Correct Answer

A

Explanation

A Crossing breeding or outbreeding is the mating of the same breed of organisms which are not closely related and thus are not genetically identical (with different genotypes). This results in the combination of two desirable traits of both parents while the recessive traits are masked. Inbreeding is the mating- of closely relatedindividuals to maintain certain desirable characteristics. Continued inbreedingresults in homozygosity. Polygenic inheritance or trait or quantitative inheritance is inheritance of trait controlled by two or more genes. Thus, one polygenic trait e.g. height in humans can have many genotypes and phenotypes. If the height of all the students in a class is measured, and the average height of this group is calculated, many students will be a little taller or shorter than the average while some will be very la!! or very short. Polygenic inheritance displays continuous variation. Non-disjunction Is the inability o? certain chromosome pairsto segregate during meiosis e.g. a pair of chromosomes number 21 in females refuse to segregate or separate resulting in the egg having 24 haploid number of chromosomes instead of normal 23haploid number of chromosomes. If a sperm with one chromosome 21, 3 zygote is formed which later -develops to form baby girt with, three chromosome -21 and a total o? 47 .hapioid chromosomes in each somatic or body cs!S instead of normal 46 n chromosomes. The child suffers from Down syndrome.