Brainteaser  Which way is the bus below traveling...toward the left or the right?

Sex linked traits and Pedigrees

_X_-Linked Traits Sex-linked traits are produced by genes only on the X chromosome. They can be Dominant or Recessive. A = dominant a = recessive What would be the genotypes of a male and female that have a Sex- linked Dominant trait and do not express the trait? Expresses Trait: Male - X A Y Female - X A X A or X A X a No Expression: Male - X a Y Female - X a X a What would be the genotypes of a male and female that have a Sex- linked Recessive trait and do not express the trait? Expresses Trait: Male - X a Y Female - X a X a No Expression: Male - X A Y Female - X A X A or X A X a (Carrier) Most Sex-linked traits are Recessive!

Red-green Color blindness X chromosome has a locus for colour vision with two alleles: –X N = Normal colour vision –X n = Red-green colour blindness Y chromosome does not have a colour vision locus. If a male receives the X n allele he will have impaired colour vision, whereas a female with X N X n will not.

Red-green color blindness Parental Phenotypes Carrier Female x Normal Male Genotypes X N X n X N Y Gametes Offspring 1 Genotypes Phenotypes Normal Female : Carrier Female : Normal Male : Colour blind Male 1 : 1 : 1 : 1 XNXN XnXn XNXN Y Female Gametes XNXN XnXn Male Gametes XNXN X N X N X n YX N YX n Y

Colorblindness Tests Test Name: Ishihara Test Colorblind sees: yellow square Normal color: yellow square & faint brown circle Colorblind sees: the number 17 Normal Color sees: the number 15

X-linked Disorders Examples: colorblindness, baldness, hemophilia *Occurs more often in MALES than females.

What is a Pedigree? def: a chart of the genetic history of a family over several generations. *It shows the patterns of inheritance in a family. *It’s used by a scientist or genetic counselor to study and predict patterns of inheritance.

How to Construct a Pedigree? A Pedigree is a chart showing the pattern of inheritance for a trait. (Family tree) Symbols and Rules: Male = Female = Affected = Unaffected = Carrier = Link parents together with a line and then make a vertical line to connect to offspring.

Constructing and Reading a pedigree a clear “CIRCLE” stands for a HEALTHY female a clear “SQUARE” stands for a HEALTHY male * a circle w/a line through, means that family member has deceased or died.

Constructing and Reading a pedigree a darkened in “CIRCLE” stands for a “AFFECTED” female a darkened “SQUARE” stands for a “AFFECTED” male *Affected means the person has the disorder. a HALF-darkened in “CIRCLE” stands for a “CARRIER” female. a HALF-darkened “SQUARE” stands for a “CARRIER” male. *CARRIER means the person has an allele for the disorder.

Constructing and Reading a pedigree *a vertical line means the married couple had” offspring, kids… a horizontal line between a male and female means the persons are married, “husband and wife”.

Constructing and Reading a pedigree *Roman Numerals (I, II, III) refers to the generations. *Arabic numbers refers to individuals. (1, 2, 3, 4, 5, …) I. III. II.

Reading the pedigree… How many generations are there? How many children did II-1 have? II-7? How are III-5 and III-2 related? Who is III-2 in reference to I-2? I. III. II. 7

Types of Pedigrees Is the pedigree autosomal or X-linked. Pedigrees can be: a.) autosomal *There is a 50/50 ratio between men and women of affected individuals. b.) X- linked *Most of the males in the pedigree are affected. Step One:

Autosomal Dominant Pedigree Draw a Pedigree showing a cross between Heterozygous parents that have 2 boys and 2 girls. (Show all possibilities) Genotypes of Affected and Unaffected: AA and Aa = Affected aa = Unaffected Aa AA aa

Autosomal Recessive Pedigree Draw a Pedigree showing a cross between Heterozygous parents that have 2 boys and 2 girls. (Show all possibilities) Genotypes of Affected and Unaffected: AA=Unaffected Aa=Carrier, Unaffected aa=Affected Aa AAaa

X-Linked Recessive Pedigree Draw a Pedigree showing a cross between a Red eyed Male fruit fly and a Carrier Female fruit fly which have 2 males and 2 females. (Show all possibilities) Red is dominant to white. Genotypes of Parents: Male = X R Y Female = X R X r XRYXRYXRXrXRXr XRYXRY XrYXrY XRXRXRXR XRXrXRXr

Is it Autosomal or X-Linked… Autosomal, equal numbers of males and females are affected I. III. II.

X-Linked Pedigree

X-Linked Recessive Disorders *Females w/one gene are carriers. *Females w/two genes are affected. In X-linked recessive disorders, when the mother is a carrier, each male child has a 50% chance of having the disorder. If the father has the disorder and is able to have children, boys won't be affected, because they receive only a Y chromosome from him. Girls receive his X chromosome and will be carriers.

Is it Dominant or Recessive… Dominant, only one parent has the disorder I. III. II.

Is it Dominant or Recessive… Recessive, neither parent has the disorder. Both are heterozygous I. III. II.

In Summary Function: to predict the chances of offspring having a genetic disorder. Steps: 1.) Determine if the disorder is autosomal or X-Linked 2.) Determine if the disorder is dominant or recessive.

Hemophilia is a recessive disorder (Xh) that is sex- linked and occurs on the X gene. Which offspring will likely develop hemophilia? A.offspring 2 B.offspring 4 C.offspring 1 and 2 D.offspring 3 and 4