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BIO 335 Genetics > Exam 3 > Flashcards

Exam 3 Flashcards

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1
Q

What is heterogamy?

A

True male/female

  • gametes differ (sperm/egg)
  • XX and XY (or ZZ and ZY)
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2
Q

Can genes necessary for survival be on the Y chromosome?

A

No

Genes on Y chromosome are accessory genes
- such as to make sperm etc

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3
Q

If the Y chromosome contains accessory genes only, then what type of chromosome is the X chromosome?

A

X is a normal chromosome

  • everyone needs it to be alive
  • carries genes necessary for survival
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4
Q

What is isogamy?

A

no true male/female

- gametes from each mating time are identical

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5
Q

What is the difference between homogametic sex and heterogametic sex?

A

Homogametic sex: 2 like chromosomes (XX)

Heterogametic sex: 2 unlike chromosomes (XY)

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6
Q

What kind of sex determination system do bees have?

A

Haplo-Diplo system

Females: Diploid (fertilized eggs)

Males: Haploid (unfertilized eggs)
- produce sperm through mitosis

No sex chromosomes

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7
Q

What is genic balance?

A

Sex determined by ratio of copies of X’s to copies of autosomes

Typical female: 2 copies of X’s & 2 sets of autosomes
- ratio = 1:1 (1.0)
Typical male: 1 copy of X & 2 copies of autosomes
- ratio = 1:2 (0.5)

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8
Q

According to genic balance, if a female accidentally had a XXY genetic makeup what would be the result?

A

The female would be normal and fertile because the ratio is still 2 copies of X & 2 copies of autosomes
- ratio still 1.0 so normal female

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9
Q

According to genic balance, if the ratio of X’s to autosomes is different that 1.0 or 0.5 what occurs?

A

sterile,reduced viability or intersex

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10
Q

Which animal’s gender is determined by genic balance?

A

drosophilia (fruit flies

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11
Q

In simplest terms, how is sex determined in humans?

A

Presence of Y = male

Absence of Y = female

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12
Q

What is the significant of the Y chromosome for male development?

A

One Gene on the Y chromosome needed for development of undifferentiated gonadal tissue into testes

Testes produces testosterone early and causes cascade in development of genitalia

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13
Q

What is the male gene on the Y chromosome?

A

SRY gene is the sex determining region of the Y chromosome

Master regulatory gene for sex determination

produces protein that is transcription factror

  • this transcription factor binds DNA and turns transcription of male genes on
  • testes development->testosterone->male characteristics

No SRY = female cascade

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14
Q

How can a person with the SRY gene develop as a female?

A

If you have 2 copies of the DAX-1 gene then it deletes the SRY gene
- default is female cascade

Regular is 1 copy of DAX-1
- normal male development`

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15
Q

To develop internal male genitalia what hormone is required? To develop external male genitalia what hormone is required?

A

Testosterone will develop internal male genitalia

Dihydrotestosterone will develop external male genitalia

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16
Q

What is the basic overview of human sexual determination?

A

Begin undifferentiated embryo

SRY gene triggers development of testes
- absence of SRY gene = development of ovaries (default)

Testes release Testosterone

  • development of internal male genitalia
  • dihydrotestosterone needed to develop external genitalia

Ovaries release estrogen
- development of internal genitalia+ external genitalia

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17
Q

What are the three genes that we covered that affect phenotypic sex? (changes in sexual development)

These are all mendellian (single gene)

A
  1. Androgen insensitivity
  2. Guevodoces
  3. Congenital adrenal hyperplasia
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18
Q

What is androgen insensitivity syndrome?

A

Have an XY chromosome

  • genetically males
  • phenotypically normal females
No menstruation (typically discovered at puberty)
 - No cervix or uterus but undeveloped testes

Cause: gene that codes for androgen receptor protein not functioning = no testosterone gets into cells = no differentiation into male (like not even there)

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19
Q

Do ppl w/ androgen insensitivity syndrome (AIS) have the SRY gene?

A

Yes. They have testes that produce testosterone but no functional receptors on cells so it doesn’t get in the cells

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20
Q

What kind of allele is AIS? What are the possible genotypes?

A

Sex linked Recessive

X^A X^A = Normal Female
X^A X^a = Female Carrier
X^A Y = Male
X^a Y = AIS Female

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21
Q

What is guevodoces?

A

Born w/ ambiguous genitalia

  • at puberty definite masculinity occurs
  • become 100% functional men

Cause:

  • autosomal recessive alleles affect testosterone metabolism
  • gene that produces enzyme that converts testosterone to dihydrotestosterone (DHT) not functioning
  • no conversion of testosterone to DHT so no development of external male genitalia
  • huge surge in testosterone at puberty overrides need for DHT and develops external male genitalia
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22
Q

What enzyme converts testosterone to dihydrotestosterone?

A

5a- reductase

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23
Q

What is congenital adrenal hyperplasia?

A

Masculinization of females
Males w/ it aren’t feminized but have other complications

Defect in enzyme that converts precursor molecules in to cortisol

  • Autosomal recessive (homozygous dominant or heterozygous = able to make cortisol)
  • precursor molecules are converted to testosterone instead of cortisol
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24
Q

Do sex chromosomes follow diploid model?

A

No

Diploidy is having 2 copies of homologous chromosomes
- X & Y are not homologous (don’t carry same genes)

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25
Q

What is hemizygous?

A

Males are hemizygous for whatever trait you’re looking at

  • 1 copy of X chromosome (w/ trait) 1 copy of Y
  • the sex linked trait will be on X chromosome
  • so male can be aY or AY for trait

Females can be homozygous or heterozygous

  • AA, Aa, aa
  • just like autosomal traits
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26
Q

What is sex linkage?

A

trait on the X chromosome

Male will have the trait or not
- know male genotype from his phenotype

Females can be carriers so you don’t know genotype from phenotype

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27
Q

What is the difference between reciprocal crosses and test crosses?

A

Test crosses are used to determine genotype of parent
- offspring x homozygous recessive

Reciprocal crosses are used to determine if a trait is sex linked
- you’ll get different results from crosses if sex linked than if autosomal

28
Q

How can you determine if a trait is sex linked?

A

reciprocal crosses

if you get males of one phenotype and females of another then the likely explanation is that the trait is sex linked

rr x RY can show that this trait is sex linked

 R    Y r    Rr   rY    Red female and White male

RR x rY doesn’t necessarily show trait is sex linked (do both) b/c its just like autosomal trait (cross Homozygous Dominant x recessive)

  r    Y R    Rr   RY   Red female and Red male
29
Q

For drosophilia eyes, what tare the results of this cross?

Rr x RY

A

R Y
R RR RY
r Rr rY

For sex linked traits keep sexes separate

  • so 2:1:1 ratio
  • 2 red females, 1 red male, 1 white male
  • 3 phenotypic classes so 2 degrees of freedom
30
Q

For drosophilia eyes, what tare the results of this cross?

Rr x rY

A

r Y
R Rr RY
r rr rY

1: 1:1:1 ratio
- 1 red female, 1 white female, 1 red male, 1 white male
- 3 degrees of freedom

31
Q

What kinds of traits show up in males more than females?

A

Sex linked recessive traits

32
Q

What are the possible genotypes for hemophilia? How is it normally passed on?

A

Females

  • HH: normal, non carrier
  • Hh: normal, carrier
  • hh: hemophiliac

Male

  • HY: normal
  • hY: hemophiliac

Normally passed from carrier mother to son

33
Q

How does a female get a sex linked recessive trait?

A

The father MUST have the trait and the mother must either have it or be a carrier

That’s why a sex linked recessive trait usually shows up in males more often

If father has the trait then the daughter will at least be a carrier (has to get his X chromosome)

34
Q

Does the father have to have the trait in order for a son to receive a sex linked recessive trait like hemophilia?

A

No

 H      Y H  HH    HY h   Hh     hY

hemophiliac son

35
Q

Can a sex linked trait be passed from father to son?

A

No, father is passing on his Y chromosome to his son

- not his X chromosome

36
Q

If you’re looking at a pedigree, how can you rule out sex linkage?

A

If you see a girl with the trait but her dad doesn’t have it then the trait must be autosomal

37
Q

For hemophilia you cross a carrier mom and normal father.

  • What is the chance the offspring has hemophilia?
  • What is the chance you have a girl with hemophilia?
  • What is the chance you have a boy with hemophilia?
A

H Y
H HH HY
h Hh hY

1/4 chance offspring has hemophilia
0% chance girl w/ hemophilia
1/2 chance boy w/ hemophilia

38
Q

Do traits skip generations?

A

They appear to skip generations when passed to carrier daughters
- can reappear next generation from carrier mom

39
Q

What are X linked dominants and Y linked traits?

A

X linked dominants tend to be more prevalent in females
- opposite of sex linked recessive traits which show up more in males

Y linked traits only occur in males
- passed from father to each son

40
Q

What is Dosage Compensation and X Inactivation?

A

Same thing.

Natures way of being fair

  • females can be homozygous or heterozygous
  • men can only be hemizygous

Females don’t have twice the number of active X-linked genes as males

  • mechanism so that one of the X chromosomes inactivates (condenses) and becomes a barr body
  • if someone has more that 1 X chromosome then the extra X condenses into barr body
41
Q

How many barr bodies does a female have? How many does a male have?

A

Female has 1 barr body

Male has 0 barr bodies

42
Q

Is the barr body completely inactive? How do you know?

A

It is partially active

know this because in ppl who have an extra X chromosome that turns into barr body there is health issues

function best w/ just one copy of genes on X chromosome

43
Q

What are some dosage compensation and X inactivation anomalies?

A

XO - Turner syndrome
- female w/ no Barr body

XXX - female
- 2 barr bodies

XXY - Klinefelter syndrome
- male w/ 1 barr body

44
Q

What is the Lyon hypothesis? What impact does this have on homo and heterozygotes?

A

Which X inactivates to become a Barr body is random

  • occurs early in embryonic development
  • all descendents of that cell (mitotic copies) have same X chromosome inactivated

Homozygotes have no impact

  • AA -> AO or OA
  • aa -> aO or Oa
  • same no matter which inactivates

Heterozygotes

  • Aa -> AO or Oa
  • end up w/ patches of cells w/ 1 X inactivated and others patches w/ the other X inactivated
45
Q

What is mosaicism?

A

patches of cells w/ different phenotypes

heterozygote female has the different alleles inactivate during embryonic development and then replicate

46
Q

What is genic interaction?

A

interactions between more than 1 gene to determine phenotype

47
Q

How does dominance influence allelic actions?

A

The dominant allele will USUALLY code for production of a functional protein
- eg. P => purple pigment (mendels pea plant example)

The recessive allele does not code for a functional protein
- eg. p => no pigment

hemophilia - dominant allele gives you clotting factor and the recessive allele gives you nothing

48
Q

If you have two alleles and its not a simple case of one working (dominant) and the other not (recessive), what occurs?

A

Incomplete dominance: phenotype is visible

Co-Dominance: detect phenotype any way other than visiually

Both alleles code for different but FUNCTIONAL protein
- heterozygote shows phenotype different from either homozygote

49
Q

If carnations are incomplete dominance, R codes for red pigment and W codes for white pigment, what would RW be? Could you continuously produce this color offspring through crosses?

A

RW = Red+White = Pink flower

Can’t continuously produce pink flowers b/c

  R      W R   RR     RW W  RW    WW

1/2 are pink, 1/4 are red and 1/4 are white 1:2:1 ratio

50
Q

What is a way to tell the difference between incomplete and co-dominance other than visual/non-visual?

A

If heterozygote shows a BLEND then alleles are incompletely dominant

If heterozygote shows BOTH then alleles are co-dominant

Bothe alleles are functioning!

51
Q

What impact does having multiple alleles (greater than 2) have?

A

The individual person can only have 2 alleles at most for a gene at a particular locus (at most heterozygous)

However, multiple alleles is a population level phenomenon
- there may be 3 or more alleles in the population

52
Q

If you have 3 alleles in the population, A B C, how many genotypes can you have?

A

6 genotypes

  • 3x2x1
  • AA BB CC AB AC BC
53
Q

For ABO Blood grouping, is this co-dominance or incomplete dominance?

A

These 3 alleles have Co-dominance and a dominant recessive relationship

  • A is co-dominant to B but both are dominant to O
  • O is non-functional (doesn’t code for surface antigens)
  • since O is not making anything it’s recessive
54
Q

Somebody has an AO genotype (ABO Blood grouping) what will their blood type be? What would be the results of the following cross AB x AO?

A

AO genotype = Type A blood

 A     O A  AA   AO   B   AB   BO

1: 2:1 ratio
- 2 Type A, 1 type AB, 1 type B

55
Q

C^+ is agouti, C^ch is chinchilla (dark grey), C^h is himalayan (white w/ black tips), C^a is albino

C^+ is dominant to all others
C^ch is incompletely dominant to C^h and C^a
C^h is dominant to C^a

C^+ and anything else => ?
C^ch C^ch  => ?
C^ch C^a => ?
C^ch C^h => ?
C^h C^h or C^h C^a => ?
C^a C^a => ?
A

C^+ and anything else => agouti

C^ch C^ch => Chinchilla

C^ch C^a => Light Grey Blend

C^ch C^h => Light Grey blend w/ dark tips

C^h C^h or C^h C^a => Himalayan

C^a C^a => Albino

Many Genotypes (24) but only 6 Phenotypes

56
Q

What are lethal alleles?

A

Alleles that have an unrelated secondary effect causing death

  • tend to be RECESSIVE and don’t code for a protein necessary to live
  • dominant to one allele but lethal recessively
57
Q

When Cuenot was breeding his yellow haired mice, why didn’t he ever produce true breeding (homozygous) yellow mice?

A

Every time he would breed yellow mice he would see a 2:1 ratio (1/3 would be agouti)

He realized when he backcrossed the yellow’s w/ agouti that the yellow’s were heterozygotes
- so he should have seen a 3:1 ratio when crossing 2 yelllow mice

The yellow allele is recessive lethal (but dominant to agouti)
- 1/4 of the mice were dying as embryos b/c lethal allele

Yellow (A^Y A^+) X Yellow (A^Y A^+)
A^Y A^+
A^Y A^y A^y A^y A^+
A^+ A^y A^+ A^+A^+

The A^y A^y were dying off embryonically and the surviving were either heterozygote yellow or agouti

58
Q

What is achondroplasia?

A

Form of short limbed dwarfism
- mutation in gene that codes for growth factor receptor protein = can’t take up protein needed to grow long bones

Dominant but recessive lethal allele

  • Homozygous = lethal
  • Heterozygous = healthy but dwarf phenotypically
59
Q

What are the results of 2 individuals w/ achondroplasia?

Dwarf (a^A a^+) X Dwarf (a^A a^+)

A

a^A a^+
a^A a^A a^A a^A a^+
a^+ a^+ a^A a^+ a^+

1/4 die as embryo (a^A a^A)
2:1 Ratio Dwarf to normal

60
Q

What are genic interactions w/ multiple alles?

A

Two or more genes acting on one trait

  • gives you novel phenotypes
  • eg AB = Blue, Ab = pink, ab = black, aB = Red
  • epistasis: one gene can mask another gene
61
Q

Crossed a Red eyed X White eyed fruit flies (drosophilia).

P: Red Eyed X White Eyed

F1: Red Eyed
- Cross Red Eyed X Red Eyed

F2: 9 Red Eyed, 3 Brown Eyed, 3 Scarlet Eyed, 1 White Eye

What is going on?

A

You would have expected to get a 3:1 ratio of Red Eyed to White Eyed

What we got is a Dihybrid ratio (9:3:3:1) indicating that there is a genic interaction of 2 or more genes acting on single trait to give you novel phenotypes (scarlet and brown colors came out of nowhere)

62
Q

How are the new eye colors created in drosophilia?

A

Genic interaction of multiple genes acting on single trait (eye color) yielding novel phenotypes

S allele controls production of brown pigment
B allele control production of Scarlet pigment
- 2 independent pathways to make an enzyme that converts a compound into the colored pigment

CPD Y => Enzyme S => Brown
CPDX => Enzyme B => Scarlet

Brown Pigment + Scarlet Pigment => Red Pigment
 - can have allele that doesn't create any enzyme = white
63
Q

With incomplete or co-dominance what is the maximum number of phenotypes you can have with a monohybrid?

A

Monohybrid max is 3 phenotypes (AA, Ab, bb)
- 1 locus

Dihybrid max is 4 phenotypes (A_B_, A_bb, aaB_, aabb)
- 2 loci

64
Q

What is epistasis?

A

One gene masks a second gene

Each gene codes for an enzyme critical in a step in a linear metabolic pathway

Any gene that acts earlier in a pathway will be epistatic
- it will mask the genes that come later in the pathway

Get weird ratios

65
Q

What does the following tell you about what is going on?

B = Agouti   A = non-albino
b = Black     a = albino

A_B_ = agouti
A_bb = black
aa_ _ = albino

A

This shows that if your have the albino alleles (homozygous recessive) then you can’t be agouti or black
- this means albino comes earlier in the linear pathway

If you the Agouti and non-albino alleles then you become agouti
- must be at the end of the pathway

If you have non-albino allele but not agouti allele then you end up black
- in the middle

Colorless precursor =(enzyme A)=> Black pigment
=(enzyme B)=> Agouti pigment

BIO 335 Genetics (4 decks)

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