Topic 11 pt 2: Sex Linked Inheritance Flashcards

1
Q

What did Thomas Hunt Morgan see in the F2 generation when crossing drosophila with red or white eyes

A

3:1 ratio (expected) BUT 1/4 white was all male

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2
Q

Thomas Hunt Morgan drosophila eye colour experiment

A

Crossed an X+X+ (red eyed) female with an XwY (white) male, got all red eyed offspring (dominant) in F1
Crossed the red eyed offspring (male x female) and got a 3:1 red:white ratio in F2, but all white eyed were males

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3
Q

Why did THM’s female flies always have red eyes

A

Because the gene controlling this trait is on the X chromosome, female has two X’s so is more likely to get at least one WT X

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4
Q

What is a reciprocal cross

A

Switching what sex has what trait

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5
Q

How can a reciprocal cross be used to determine if a trait is X linked

A

Switch what sex has what trait, if the ratios are not the same (one of the crosses has non-mendelian F1 and F2) then it is X linked

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6
Q

Where are the colour sensing cone-cells in our retinas located

A

Blue = pigment gene on chr 7
Green + red = pigment gene located together on the X chr

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7
Q

Red/green colourblindness allele has…

A

Both genes function (red and green) are knocked out

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8
Q

What allele is dominant in colour blindness

A

Wildtype, fully penetrant and haplosufficient

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9
Q

Things to note regarding colour blind crosses

A
  1. Male affected= normal mendelian ratios, female affected= 1:1 ratio
  2. Mother passes the mutant phenotype to their sons but not daughters (when crossed with normal male)
  3. fathers pass on mutant trait to the grandsons through carrier daughters
  4. female must have mutant allele from both parents to be affected
  5. male must receive mutant allele from mother
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10
Q

Y-linked traits characteristics

A

Very diff than X
Only in males
All sons of affected males are affected

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11
Q

What is dosage compensation

A

Mechanism used to balance or equalize amount of protein produced by sex chromsomes (since Y does not have same genes)

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12
Q

Why is dosage compensation required

A

Number of copies of a gene effects the amount of protein produced: autosomal to sex chromosome product will be imbalanced between sexes

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13
Q

What are Barr bodies? What is the lyon hypothesis

A

Barr bodies = highly condensed inactive X chr

Lyon hypothesis = Mary Lyon said one x-chr is deactivated in females, and that barr bodies are the deactivated chr

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14
Q

Which X chromosome is deactivated in females

A

Random, different in diff cells
50% of cells express one allele while 50% express the other

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15
Q

When does X chr deactivation occur

A

Early in development
Once inactivated remains inactive in that cell and its descendants

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16
Q

People with additional X chr will have..

A

additional barr bodies (normal phenotype bc extra X deactivated)

17
Q

Is X inactivation complete?

A

No, only 75% of genes are inactivated
15% escape inactivation
10% vary between individuals

18
Q

Slide 17

A

Calico cat (dosage compensation)

19
Q

Why is calico only in female cats

A

Different X chr deactivated
Orange patch = hair cells have black X chr inactivated
Black patch = opposite