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Understanding Sex Determination: Chromosomes, Genes, and Traits

This overview explores sex determination in humans, highlighting the roles of sex chromosomes (XX for females, XY for males) and the inheritance of sex-linked traits. It explains how the sex of offspring is determined by sperm cells and discusses the genetic differences between males and females. The SRY gene's role in testes development on the Y chromosome is addressed, along with the impact of X-linked recessive genes. The prevalence of sex-linked traits such as color blindness and hemophilia in males compared to females is also examined.

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Understanding Sex Determination: Chromosomes, Genes, and Traits

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  1. Sex Determination Of the 46 chromosomes, 2 are designated sex chromosomes 
(X & Y) the rest are designated autosomal.

  2. Sex Determining Chromosomes Female XX Male XY A punnett square shows that offspring will 
be 1/2 male, 1/2 female Since females are XX, every egg must contain an X chromosome. 
Since males are XY, a sperm cell will contain either an X chromosome 
of a Y chromosome. The sex of a fertilized egg is therefore determined 
by the sperm! (King Henry VIII & Ann Boleyn)

  3. Question Is everything on these chromosomes just for sex determination or is their 
other stuff on them? SRY gene development of testes Y chromosomes 
codes for 78 genes X chromosomes 
codes for 1500 genes

  4. Sex-linked Traits Men have an X and a Y combination of sex chromosomes, while women 
have two X's. Since only men inherit Y chromosomes, they are the only 
ones to inherit Y-linked traits. Men and women can get the X-linked ones since both inherit X chromosomes. If a gene is found only on the X chromosome and not the Y 
chromosome, it is said to be a sex-linked trait. The result is that 
females will have two copies of the sex-linked gene while males will 
only have one copy of this gene.

  5. If the gene is recessive, then males only need one such recessive gene 
to have a sex-linked trait rather than 2 recessive genes for traits that 
are not sex-linked. This is why males exhibit some traits more 
frequently than females. Examples of Sex-linked Traits Colour blindness Hemophilia Duchenne Muscular Dystrophy Male Pattern Baldness

  6. X Chromosome Recessive? Hemophilia NO Hemophilia Hemophilia Hemophilia Infrequent Mutuation? Who is more likely to have hemophilia, male or female?

  7. 1/7000 frequency of Xh 1/7000 X 1/7000 
= 1/49000000 This is why males exhibit some traits more frequently than females

  8. Sex linked Traits Worksheet Homework pg. 151 #8,9

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