MEDICAL BIOLOGY, ANATOMY, HUMAN PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

BIOLOGY

SECTION 1. BIOLOGICAL BASES OF HUMAN VITAL ACTIVITY

1.4. ONTOGENETIC LEVEL OF LIFE ORGANIZATION

1.4.1. Reproduction

Disorders of Meiosis

Normal meiosis results in The formation of Gametes with a standard haploid chromosome Complement (23). When chromosome segregation is impaired, the chromosome number in gametes changes (genomic Mutations). For instance, in non-disjunction of a single chromosome pair, one gamete will contain 24 Chromosomes, while the other will contain 22. When a gamete containing 23 chromosomes fuses during Fertilization with a gamete containing 24 or 22 chromosomes, the resulting Organism will have 47 chromosomes (trisomy) or 45 chromosomes (monosomy). Non-disjunction can occur during both meiosis I and meiosis II, affecting either autosomes or sex chromosomes. These meiotic errors result in germline mutations (p. 105). The causes include The impact of mutagenic agents and endogenous factors on Spermatogenesis and oogenesis. The frequency of meiotic disorders increases with maternal age (35 years and older). The consequences include spontaneous abortions and the birth of children with developmental anomalies, such as Heart defects, Nervous system disorders, cleft lip, cleft palate, and others. This correlation is particularly evident in Down syndrome (Table 1.5), which is chromosomal in origin (trisomy 21, translocation, mosaicism).

Class="center">Table 1.5.

Risk of giving birth to a child with Down syndrome for women of different age groups

(G.L. Lazyuk et al., 1991).