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Genes Evo & Dev Y1 > GED L12 Notes > Flashcards

GED L12 Notes Flashcards

1
Q

Give an example of genetic sex determination

A

Eg. Birds & bees

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2
Q

Give an example of environmental sex determination

A

Eg. Turtles & alligators -> Egg temperature

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3
Q

What are autosomes?

A

• Autosomes:

Non-sex chromosomes

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4
Q

What are pseudosutosomal regions?

A 
•	Pseudoautosomal regions:
-	PAR1 & PAR2 
-	Shared between X & Y chromosomes 
	~30 genes -> Humans
-	Required -> X-Y pairing -> male meiosis
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5
Q

Characteristocs of human chromosomes?

A 
•	Human chromosomes
-	Male specific region -> Y chromosome (MSY)
>>80 genes
>> ~60Mb
-	X – specific region 
>> >1000 genes
>> ~160Mb
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6
Q

Which of the sexes is homogametic?

A

 Females

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7
Q

Which of the sexes is heterogametic?

A

Males

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8
Q

What is Aneuploidy?

A

 • Aneuploidy:
When an individual has incorrect number of chromosomes
 Provides evidence Y chromosome confers maleness
 XO individuals -> Female
-> One chromosome
 XXY individuals -> Male
-> Even though male has 2 X chromosomes, presence of single section of Y chromosome determined -> male.

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9
Q

What determines the male sex?

A

• Only one gene of Y chromosome required to determine males

 SRY (Sex-determining Region on the Y)

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10
Q

What is sex reversal?

A

• Sex reversal:
 Translocation of SRY -> X chromosome
»Found -> Rare XX males

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11
Q

What is a result of a mutation in the SRY gene?

A

 XY females

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12
Q

Describe how gender is conferred in the SRY gene

A

• Confer of gender in SRY gene:
- DNA binding protein (transcription factor)
 Regulate expression -> genes -> testis formation

  • Week 4:
    Genital redge (Somatic cells)
  • Week 6:
    Indifferent gonad (Germ & somatic cells)
  • Week 8:
    SRY expression -> Testis formation
    >Females -> no SRY expression -> Ovary formation.
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13
Q

Describe chromosomal sex determination in birds / the sex system of birds.

A

 Chromosomal sex determination:
- ZX system:
 Males -> ZZ
 Females -> ZW

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14
Q

Describe what a gynandroorph is

A 
	Gyandromorph:
-	Cells -> Right side -> Body 
>>Female sex chromosome set (ZW)
-	Cells -> Left side -> Body 
>>Male sex chromosome set (ZZ)
-	Example of Cell-autonomous sex identity (CASI)
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15
Q

Give an example of cell -autonomous sex identity

A 
	Gyandromorph:
-	Cells -> Right side -> Body 
>>Female sex chromosome set (ZW)
-	Cells -> Left side -> Body 
>>Male sex chromosome set (ZZ)
-	Example of Cell-autonomous sex identity (CASI)
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16
Q

Describe the evolution of sex chromosomes in birds and why it differs from mammals

A 
•	Evolution -> Sex chromosomes:
-	Mammalian & bird sex chromosomes evolved -> different autosomes
-	Birds -> ZW system:
	Males -> ZZ
	Females -> ZW
17
Q

Describe sex-linked inheritance using a reciprocal cross

A 
•	Sex-linked inheritance:
-	Reciprocal crosses -> same results 
	- Yellow F x Green M
>> 100% Yellow F1
- Offspring cross
>> 3 yellow : 1 green 
	- Green F x Yellow M
>> 100% Yellow F1
- Offspring cross
>> 3 yellow : 1 green
18
Q

What is a reciprocal cross (inheritance)

A

• Sex-linked inheritance:

- Reciprocal crosses -> same results

19
Q

Describe the discovery of the white mutant in Drosophilia

A
  • White mutant -> Drosophila:
     Thomas Hunt Morgan -> Spontaneous mutant fly -> white eyes.
     Reciprocal crosses with white mutant flies
    » No identical Mendelian phenotypic ratios
    1. White Male x Red Female
    » F1 -> 100% red eyes
    &raquo_space;Red dominant
    2. F1 Female x F1 Male
    » 3 Red : 1 White
    » All white eyed flies -> male.
    » Red eyed flies -> 2 females : 1 Male
    3. White male x F1 Female
    » 1 red Male : 1 red Female : 1 white Male : 1 white Female
    4. White Female x F1 Male -» Reciprocal cross
    » Red Females & White Males

 Parallel genetic data -> cytological observations -> chromosomes of Drosophila.
» Drosophilla -> 4 pairs chromosomes
-» 3 homomorphic pairs
> similar in size of chromosomes in chromosomal pair
-» 1 heteromorphic pair
> different sizes of chromosomes in chromosomal pair
» Females -> All eggs -> one X chromosome
» Males -> Sperm -> 50% -> X & 50% -> Y
Hypothesis:
White gene on X chromosome
1. X+X+ x XWY
Red Female x White Male

F1: &raquo_space; X+XW & X+Y
Red Females & Red Males
-> 100% red offspring

  1. F1 Female x F1 Male

> > X+X+ x X+Y x X+XW x XWY

3 Red : 1 White
All white -> Male
Red flies -> 2 Female : 1 Male

20
Q

Give an example of inheritance which did not demonstrate mendelian phenoty[ic ratios

A
  • White mutant -> Drosophila:
     Thomas Hunt Morgan -> Spontaneous mutant fly -> white eyes.
     Reciprocal crosses with white mutant flies
    » No identical Mendelian phenotypic ratios
    1. White Male x Red Female
    » F1 -> 100% red eyes
    &raquo_space;Red dominant
    2. F1 Female x F1 Male
    » 3 Red : 1 White
    » All white eyed flies -> male.
    » Red eyed flies -> 2 females : 1 Male
    3. White male x F1 Female
    » 1 red Male : 1 red Female : 1 white Male : 1 white Female
    4. White Female x F1 Male -» Reciprocal cross
    » Red Females & White Males

 Parallel genetic data -> cytological observations -> chromosomes of Drosophila.
» Drosophilla -> 4 pairs chromosomes
-» 3 homomorphic pairs
> similar in size of chromosomes in chromosomal pair
-» 1 heteromorphic pair
> different sizes of chromosomes in chromosomal pair
» Females -> All eggs -> one X chromosome
» Males -> Sperm -> 50% -> X & 50% -> Y

21
Q

Why is it thought the white mutant of Drosophilia doesn’t demonstrate Mendelian phenotypic ratios?
Outline the genetic crosses behind this theory

A

 Parallel genetic data -> cytological observations -> chromosomes of Drosophila.
» Drosophilla -> 4 pairs chromosomes
-» 3 homomorphic pairs
> similar in size of chromosomes in chromosomal pair
-» 1 heteromorphic pair
> different sizes of chromosomes in chromosomal pair
» Females -> All eggs -> one X chromosome
» Males -> Sperm -> 50% -> X & 50% -> Y
Hypothesis:
White gene on X chromosome
1. X+X+ x XWY
Red Female x White Male

F1: &raquo_space; X+XW & X+Y
Red Females & Red Males
-> 100% red offspring

  1. F1 Female x F1 Male

> > X+X+ x X+Y x X+XW x XWY

3 Red : 1 White
All white -> Male
Red flies -> 2 Female : 1 Male

22
Q

Describe characetristics of sex-linked inheritance.

A

• Sex-linked inheritance:
- Involves genes located -> X chromosome
» (X-linkage)
- Y-linked genes -> male-specific functions (spermatogenesis)
» Only small % -> sex linkage
- Most genes -> X
» Unrelated to sex determination / sex function
» Expressed in males & femalws
- Males
» Hemizygous for genes -> X chromosome

23
Q

What does sex-linked inheritance involve?

A
  • Involves genes located -> X chromosome

|&raquo_space; (X-linkage)

24
Q

What is a characteristic of Y-linked genes in genetic inheritance

A
  • Y-linked genes -> male-specific functions (spermatogenesis)
    » Only small % -> sex linkage
25
Q

Describe characteristics of the X chromosome in genetic linkage

A
  • Most genes -> X
    » Unrelated to sex determination / sex function
    » Expressed in males & females
26
Q

Name the relationship between males and the X chromosome

A
  • Males

|&raquo_space; Hemizygous for genes -> X chromosome

27
Q

What are characteristics of x-linked traits in humans

A 
•	X-linked traits -> Humans
-	Nearly all -> recessive
-	More common in males (hemizygous) than females
-	~300 known X-linked disease genes 
~10% total disease genes
28
Q

What are characteristics of x-linked traits in humans. Include examples.

A

• X-linked traits -> Humans
- Nearly all -> recessive
- More common in males (hemizygous) than females
- ~300 known X-linked disease genes
~10% total disease genes
Eg.
- Haemophilia A (Factor XIII)
- Haemophilia B (Factor IX)
- Duchenne muscular dystrophy
- Red-green colour vision deficiency -> (~8% males)
» 1/12 men & 1/200 women -> colour vision deficiency

29
Q

Describe red-green colour deficiency

A

• Red-green colour deficiency:
- Red-green colour vision deficiency -> (~8% males)
» 1/12 men & 1/200 women -> colour vision deficiency
- Human red (L) & green (M) visual opsin genes -> adjacent -> X.
 L & M opsin genes -> high sequence similarity -> recent gene duplication
 3 aa residues specify -> spectral sensitivity -> opsins
 Most common form deficiency (deuteranomaly) -> recombination -> L & M genes
» λmax -> hybrid M-L opsin -> closer to that of M opsin

30
Q

Describe X chromosome activation in mammals

A
  • X chromosome activation -> mammals:
     Females -> 2 x X chromosomes
    »Double the gene dosage -> X-linked genes compared -> males
     1 of X chromosomes in each female cell -> inactivated
    ->Dosage compensation.
    »Becomes highly condensed
    ->No expression -> genes
    -> Cytologically visible -> interphase as -> Barr body.
     Inactivation -> starts early -> development
    »Random -> effects either X chromosome
    »Persists -> all subsequent mitotic cell divisions
    Therefore female mammals -> mosaics
    &raquo_space;Example -> epigenetic control -> gene expression.
31
Q

Describe X chromosome activation in female mammals

A
  • X chromosome activation -> mammals:
     Females -> 2 x X chromosomes
    »Double the gene dosage -> X-linked genes compared -> males
     1 of X chromosomes in each female cell -> inactivated
    ->Dosage compensation.
    »Becomes highly condensed
    ->No expression -> genes
    -> Cytologically visible -> interphase as -> Barr body.
32
Q

Why are female mammals classed as mosaics?

A

 Inactivation -> starts early -> development
»Random -> effects either X chromosome
»Persists -> all subsequent mitotic cell divisions
Therefore female mammals -> mosaics
&raquo_space;Example -> epigenetic control -> gene expression.

33
Q

Describe the effects of gene inactivation in tortoiseshell cats

A 
•	Tortoiseshell Cats:
	Female -> Heterozygous -> O (Orange) & o (black) alleles -> X chromosome
>>In some patches:
->> O inactivated --> black fur
      >>Other patches:
->> o inactivated -> orange fur

 Can have male tortoiseshell if more than one X chromosome
Eg. XXY male

34
Q

Describe expression of genes in individuals with multiple X chromosomes.

A

• Individuals -> multiple X chromsomes
Eg. XX females, XXY males, XXX females
»Each cell -> expresses only 1 X chromosome
Other X chromosomes -> Barr bodies

35
Q

How can X chromosome inactivation occur in males?

A

• X chromosome inactivation can occur -> males -> more than one X chromosome

Genes Evo & Dev Y1 (23 decks)

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