brainteaser which way is the bus below traveling...toward the left or the right?
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_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 - XA Y Female - XA XA or XA Xa
• No Expression: Male - Xa Y Female - Xa Xa
• 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 - Xa Y Female - Xa Xa
• No Expression: Male - XA Y Female - XA XA or XA Xa (Carrier)
• Most Sex-linked traits are Recessive!
Red-green Color blindness
• X chromosome has a locus for colour vision with two alleles:– XN = Normal colour vision– Xn = Red-green colour blindness
• Y chromosome does not have a colour vision locus.
• If a male receives the Xn allele he will have impaired colour vision, whereas a female with XNXn will not.
Red-green color blindnessParental
Phenotypes Carrier Female x Normal MaleGenotypes XNXn XNYGametes
Offspring 1Genotypes
Phenotypes Normal Female : Carrier Female : Normal Male : Colour blind Male 1 : 1 : 1 : 1
XN Xn XN Y
Female Gametes
XN Xn
Male Gametes
XN XN XN XN Xn
Y XN Y Xn 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, …)
321 4 5 6
1
1
2
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?
321 4 5
61
1
2
2
3 4 5
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 Aa AAaa
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 Aa
Aa 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 = XR Y Female = XR Xr
XRY XRXr
XRY XrY XRXR XRXr
Is it Autosomal or X-Linked…
Autosomal, equal numbers of males and females are affected.
3
21 4
5 61
1
2
2 3
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, whenthe mother is a carrier, each malechild has a 50% chance of having the disorder.
If the father has the disorder and isable to have children, boys won't beaffected, because they receive only a Ychromosome from him.
Girls receive his X chromosome andwill be carriers.
Is it Dominant or Recessive…
Dominant, only one parent has the disorder.
3
21 4
5 61
1
2
2 3
4
3
I.
III.
II.
Is it Dominant or Recessive…
Recessive, neither parent has the disorder. Both are heterozygous.
3
21 4
5 61
1
2
2 3
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-Linked2.) Determine if the disorder is dominant or recessive.
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