Sex Determination

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