Sex Determination in Animals Flashcards

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1
Q

What does homogametic mean?

A

Organisms possessing two identical sex chromosomes
(e.g. XX in female humans or ZZ in male birds)

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2
Q

What does heterogametic mean?

A

Organisms possessing two different sex chromosomes
(e.g. XY in male humans and ZW in female birds)

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3
Q

What is the Lygaeus System?

A

Females: two X- chromosomes, homogametic (XX)
Male: single X chromosome and Y chromosome (XY), heterogametic

Most common, eg humans, rats, some reptiles- green iguana

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4
Q

What are some Human Abnormalities?

A

Normal Humans
XX- female
XY- male
Males’ Y chromosomes have the sex-determining region Y (SRY) gene which is Holandric (Y-linked) and codes for testis-determining factor (maleness)

Human Abnormalities
XX- male (SRY gene located on the top homologous region of the X chromosome)
XY- female (the SRY gene was mutated or missing on the y chromosome)

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5
Q

What is the Protenor System?

A

Females: two X- chromosomes, homogametic (XX)
Male: single X chromosome, heterogametic (XO)
O is not a chromosome

eg. insects like Hemiptera, Orthoptera (grasshopper)

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6
Q

What is the Birds ZW-ZZ System?

A

Females: one Z- chromosome and one W chromosome, heterogametic (ZW)
Male: two Z chromosomes, homogametic (ZZ)

eg. Birds, moths, some isopods, some amphibians and some fishes

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7
Q

What is the ZO-ZZ system?

A

Females: one Z- chromosome, heterogametic (ZO)
Male: two Z chromosomes, homogametic (ZZ)
O is not chromosome

eg. Butterflies, caddisflies (moths)

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8
Q

How does the environment determine the sex of an organism?
Hint: Marine Mollusk- common slipper limpet

A
  • Lives in stacks- one on top of the other
  • First to settle on a solid unoccupied substrate develops into a female
  • Those that settle on top become the males and serve as mates for females
  • After a while the males turn into females and attract more male larvae on top of them
  • This is referred to as sequential hermaphroditism- each animal can be both male and female, although not at the same time
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9
Q

How does the environment determine the sex of an organism?
Hint: Temperature

A

For some reptiles temperature during embryonic development determines sexual phenotype
- Turtles: warm temperatures produce females; cool temperatures produce males
- Alligators: warm temperatures produce males (>34 degrees C); cool temperatures produce females (<30 degrees C)

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10
Q

If temperature effects the sexual phenotype of some reptiles, how would climate change effect these reptiles?

A

If there is a climate change then more of one sex would be produced over the other

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11
Q

How does Chromosome Balance Theory of Sex Determination (Genetic balance) determine the sex of an organism?
Hint: Drosophila melanogaster (fruit fly)

A

Sex is determined by the balance between sex chromosomes and autosomal complement of chromosomes… How?

Lets say that ‘A’ represents a haploid set of autosomal chromosomes
X/A ratio = 1 or higher = female
X/A ratio = 0.5 or lower = male
X/A = >0.5-<1.0 = intersex

Female genome- AAXX
Male genome- AAXY *(Y chromosome is involves in male fertility but not in the determination of sex)

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12
Q

What is the evidence for the Genetic Balance Theory in Drosophila melanogaster?

A

Bridges (1922) observed that Drosophila occasionally produces a triploid due to non- disjunction

Abnormal Normal
AAXY x AAXX AAXY x AAXX
/ \ / / \ /
AX AY AAXX AX AY AX
AAAXXX AAAXXY AAXX AAXY
X/A=1 X/A=0.66 X/A=1 X/A=1

AAXY x AAAXXX
/ \ / \
AX AY AAX AXX
AAAXX AAXXX AAAXY AAXXY
X/A=0.6 =1.5 =0.33 =1
intersex superfemale supermale female
(infertile (fertile male)
male)

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13
Q

What is a Gynandromorph?

A

an abnormal individual, especially an insect, having some male and some female characteristics

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14
Q

What are the characteristics of Intersex (Gynandromorphs) in Drosophila melanogaster?

A
  • Have male and female organs
  • Highly influenced by the environment (temperature)
    - high T- more female
    - low T- more male
  • Modifying factors also influence - more male or female
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15
Q

What is the Transformer Gene in Drosophila melanogaster?

A

Superimposed on the genetic balance system is another level of control of the determination of sex
-transformer gene (autosomal gene)

This gene in the homozygous recessive state (tra.tra) converts a diploid female into a sterile male
tra.tra
AAXX ————–> Sterile Male
Tra.___
AAXX ————–> Female

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16
Q

What is Haplo-diploidy sex determination?
Hint: Bees

A

a sex-determination system in which males develop from unfertilized eggs and are haploid, and females develop from fertilized eggs and are diploid
Autosomes are involved- the number of autosomal complements determine sex

eg. Hymenopteran insects such as bees, wasps, ants
In Bees- eggs ———————-> haploid males (A)
l Parthenogenesis
l (arrhenotoky)
————————–> diploid females (AA)
/ \ (quality of food)
Queen Female worker
*The queen controls sex ratio

17
Q

What is Haplo-diploidy complimentary gene method sex determination?
Hint: Wasps

A

In Wasps- eggs ———————-> haploid males (A)
l Parthenogenesis
l (arrhenotoky)
————————–> diploid male worker
l Homozygous (infertile-no meiosis)
l gene ‘S’
————————–> diploid female worker
Heterozygous gene ‘S’

18
Q

What is Haplo-diploidy complimentary gene method sex determination?
Hint: Alleles in Wasps

A

The ‘S’ gene has 9 multiple alleles
Homozygous states
S^aS^a, S^bS^b, S^cS^c, S^dS^d…. S^iS^i =2N worker male

Heterozygous states
S^aS^b, S^aS^c, S^aS^d etc. =2N worker females

*There are more heterozygous combinations than homozygous and hence more worker females than worker males

19
Q

What is the genic sex determination in Fungi?

A

Lower plants such as Chlamydomonas and fungi
- one or a few autosomal genes control sex.

e.g. Chlamydomonas - ‘A’ = + mating type
= - mating type
e.g. Basidiomycete fungi – two genes, A & B
AB – mating type-1
Ab – mating type-2
aB - mating type-3
ab – mating type-4
*males and females look similar