_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, …) 321456 1 1 2 2 345 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? 32145 61 1 2 2 345 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. 3 214 5 6 1 1 2 23 4 3 I. III. II.
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. 3 214 5 6 1 1 2 23 4 3 I. III. II.
Is it Dominant or Recessive… Recessive, neither parent has the disorder. Both are heterozygous. 3 214 5 6 1 1 2 23 4 3 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