Sex Determination in Animals Flashcards
What does homogametic mean?
Organisms possessing two identical sex chromosomes
(e.g. XX in female humans or ZZ in male birds)
What does heterogametic mean?
Organisms possessing two different sex chromosomes
(e.g. XY in male humans and ZW in female birds)
What is the Lygaeus System?
Females: two X- chromosomes, homogametic (XX)
Male: single X chromosome and Y chromosome (XY), heterogametic
Most common, eg humans, rats, some reptiles- green iguana
What are some Human Abnormalities?
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)
What is the Protenor System?
Females: two X- chromosomes, homogametic (XX)
Male: single X chromosome, heterogametic (XO)
O is not a chromosome
eg. insects like Hemiptera, Orthoptera (grasshopper)
What is the Birds ZW-ZZ System?
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
What is the ZO-ZZ system?
Females: one Z- chromosome, heterogametic (ZO)
Male: two Z chromosomes, homogametic (ZZ)
O is not chromosome
eg. Butterflies, caddisflies (moths)
How does the environment determine the sex of an organism?
Hint: Marine Mollusk- common slipper limpet
- 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
How does the environment determine the sex of an organism?
Hint: Temperature
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)
If temperature effects the sexual phenotype of some reptiles, how would climate change effect these reptiles?
If there is a climate change then more of one sex would be produced over the other
How does Chromosome Balance Theory of Sex Determination (Genetic balance) determine the sex of an organism?
Hint: Drosophila melanogaster (fruit fly)
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)
What is the evidence for the Genetic Balance Theory in Drosophila melanogaster?
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)
What is a Gynandromorph?
an abnormal individual, especially an insect, having some male and some female characteristics
What are the characteristics of Intersex (Gynandromorphs) in Drosophila melanogaster?
- 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
What is the Transformer Gene in Drosophila melanogaster?
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