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Home »  Biology »  Genetics

Pedigree and Sex Determination

Topic Review on "Title":

Sex chromosome
Sex chromosomes are those specialized for determining sex phenotype of an organism, males and females have different chromosomes.  In contrary, autosomal chromosomes are not sex-determining, males and females share same autosomes. 

Sex determination systems
Sex determination can be caused by genetics or by environment.  There are three genetic sex determination systems: XX-XY, XX-XO and ZW-ZZ.  In some insects, sex can be determined by chromosome numbers, for example, honey bees, 2N individuals are females and 1N are males.  In plants, there is no particular sex chromosome, and sex is determined by genes scattered within the whole genome. 

Inheritance of sex-linked traits
Inheritance of sex-linked traits exhibit special patterns.  The inheritance for X-linked recessive trait exhibit crisscross pattern, meaning the recessive trait from male individual will not show in next generation, but will show on the third generation males.  When X chromosome nondisjunction occurs during gamete formation, the sex chromosome may change and cause recessive trait show up where it is not expected, it also cause aneuploidy. 

Aneuploidy
Aneuploidy includes nullisomy, monosomy, trisomy and tetrasomy.  When this occurs on sex chromosomes, it may cause serious genetic disorder.  For exaple, the Klinefelter's Syndrome is caused by extra X chromosome(s).

Human sex-linked traits
The x-linked recessive traits show crisscross inheritance pattern.  An example is hemophilia in royal family of England.  X-linked dominant traits occur in both male and female, no skipping generation, for example, vitamin D-resistant rickets.  Y-linked traits only occur in males and pass from father to son.  All these inheritance patterns follow Mendelian genetics rules.

Twin Studies
Twin studies are more usefull in determining which factor plays more important role in development of individuals,  genetics or environment. 


Rapid Study Kit for "Title":
Flash Movie Flash Game Flash Card
Core Concept Tutorial Problem Solving Drill Review Cheat Sheet

"Title" Tutorial Summary :
Sex chromosomes are those specialized for determining sex phenotype of an organism.   There are three genetic sex determination systems: XX-XY, XX-XO and ZW-ZZ.  The inheritance for X-linked recessive trait exhibit crisscross pattern (skip a generation), and occur mainly in males.  X-linked dominant traits occur in both males and female, they do not skip generation. Y-linked traits only occur in males and pass from father to son.

Tutorial Features:
  • External concept map to describe the importance of sex determination in biological science
  • Internal concept map to reveal the relationships among the content within this tutorial
  • Detailed Prunette square to explain sex inheritance ratios
  • Case-study of X-linked traits in Drosophila
  • Detailed explanation on chromosome nondisjunction
  • The hemophila pedigree of royal family from England. 

"Title" Topic List:

Introduction

  • Monoecious and diecious
  • Sex and autosomal chromosome

Sex determination systems

  • XX-XO system
  • XX-XY system
  • ZW-ZZ system
  • Haplodiploid
  • Other sex determination

Inheritance of sex-linked traits

  • Inheritance of X-linked traits
  • Non-disjunction of chromosomes
  • Aneuploidy, monoploidy and euploidy
  • Phenotype of aneuploidy

Human sex-linked traits

  • X-linked recessive traits
  • X-linked dominant traits
  • Y-linked traits

Twin Studies

  • Dizygotic and monozygotic twins
  • Concordance

See all 24 lessons in Genetics, including concept tutorials, problem drills and cheat sheets:
Teach Yourself Genetics Visually in 24 Hours

Home »  Biology »  Genetics
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