Complex Inheritance Definitions Autosomes paired chromosomes present in both males and females all chromosomes except the X and Y chromosomes Sex Chromosomes Paired chromosomes that differ between males and females XX in females YY in males Y Chromosome one of two sex chromosomes in humans The presence of a Y chromosome signals the male developmental pathway during fetal development X Chromosome one of the two sex chromosomes in humans X Linked Trait a phenotype determined by an allele of an X chromosome Incomplete Dominance a form of inheritance in which heterozygotes have a phenotype that is intermediate between homozygous dominant and homozygous recessive Codominance a form of inheritance in which both alleles contribute equally to the phenotype Polygenetic Trait a trait whose phenotype is determined by the interaction among alleles of more than one gene Multifactorial Inheritance an interaction between genes and the environment that contributes to a phenotype or trait Aneuploidy an abnormal number of one or more chromosomes either extra or missing copies Nondisjunction Failure of chromosomes to separate accurately during cell division nondisjunction in meiosis leads to aneuploid gametes Trisomy 21 carrying an extra copy of chromosome 21 also known as Down syndrome Amniocentesis a procedure that removes fluid surrounding the fetus to obtain and analyze fetal cells to diagnose genetic disorders Karyotype the chromosomal makeup of cells Karyotype analysis can be used to detect trisomy 21 prenatally
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