Sex-linked Traits

Sex determination  Sex chromosomes – determines the sex of an individual YY XX  Males have X and Y  Two kinds of gametes  Female have two X’s  Only one type of gamete

□Autosomal Chromosomes □Sex Chromosomes

Which parents determines the sex of the offspring? XY male X Y XX Female X X It is the male that determines the sex of the offspring.

Sex Linked Traits  Traits controlled by genes located on sex chromosomes (X or Y)  Most are X-linked  The X chromosome is larger and has more genes  A Y has very few genes  Show inheritance pattern that differs for autosomal traits.  Autosome-any chromosome besides X and Y

X-linked Inheritance

 Males only have one copy of the X chromosome (hemizygous), plus a Y  Female have two X chromosomes, and may be homozygous or heterozygous for a trait  X-linked genes are never passed from father to son. The Y chromosome is the only sex chromosome that passes from father to son.

 Females with one copy of the normal gene and one copy of the mutated gene are called carriers. They don’t show the trait.  Males are never carriers – if they have a mutated gene on the X chromosome, it will be expressed

X-linked disorders  Recessive  Red-green color blindness  Hemophilia  Duchenne muscular dystrophy  Ichthyosis  Dominant  Hypertrichosis

Red-green color blindness  Can not distinguish red from green. Normal red-green Red-green colorblind

What a red-green colorblind person would see NormalRed-green colorblind

Hemophilia

Pedigree Charts I II III

Overview I.What is a pedigree? a. Definition b. Uses II. Constructing a pedigree a. Symbols b. Connecting the symbols III. Interpreting a pedigree

What is a Pedigree? □A pedigree is a chart of the genetic history of family over several generations. □Scientists or a genetic counselor would find out about your family history and make this chart to analyze.

Constructing a Pedigree Male Female

Connecting Pedigree Symbols □Married Couple □Siblings Examples of connected symbols:

Connecting Pedigree Symbols □Fraternal twins □Identical twins Examples of connected symbols:

Example  What does a pedigree chart look like?

Symbols in a Pedigree Chart □Affected □Carrier (autosomal or sex linked) □‘Normal’

Interpreting a Pedigree Chart 1.Determine if the pedigree chart shows an autosomal or X-linked/sex-linked disease. □If most of the males in the pedigree are affected the disorder is X-linked □If it is a 50/50 ratio between men and women the disorder is autosomal.

Example of Pedigree Charts □Is it Autosomal or X-linked?

Answer □Autosomal

Interpreting a Pedigree Chart 2.Determine whether the disorder is dominant or recessive. □If the disorder is dominant, one of the parents must have the disorder. □If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

Example of Pedigree Charts □Dominant or Recessive?

Answer □Dominant

Example of Pedigree Charts  Dominant or Recessive?

Answer  Recessive

Summary  Pedigrees are family trees that explain your genetic history.  Pedigrees are used to find out the probability of a child having a disorder in a particular family.  To begin to interpret a pedigree, determine if the disease or condition is autosomal or X-linked and dominant or recessive.

Pedigree Chart -Cystic Fibrosis

Hemophilia