Lesson 4: Non-Mendelian Genetics: Sex Determination and Sex-linked Traits

Question 1

Sex-linked Traits

Answer 1

Sex – linked traits are determined by alleles of genes that are
located on the X chromosome

The notation:

XA

X= X chromosome

A= allele of the gene

Sex – linked traits are unusual because they are only found
on the X –chromosome

The recessive phenotype of sex – linked traits is most often
observed in people that carry one X and one Y chromosome

Question 1

Sex Chromosomes

Answer 1

The 23rd pair of chromosomes

These chromosomes determine
genetic gender

Made up of combinations of X
and Y chromosomes

XX – genetically female

XY – genetically male
The X chromosome is much larger
than the Y chromosome and will
carry a larger amount of genetic
material and genes

The genetic information on the

Y chromosome is largely unknown

The Y chromosome contains the
genes for androgens which trigger
the development of male
reproductive organs and hormones

Question 2

Sex
Chromosome
Inheritance

Answer 2

Genetic males only have one X – chromosome and there is no
corresponding allele on the Y chromosome.

As a result, the allele present on the X – chromosome inherited
by the genetic male is expressed

Genetic females will inherit 2 X – chromosomes so the rules of
Dominance apply

Often genetic females will “carry” the recessive trait in the
heterozygous genotype.