Unit 2.3c Flashcards
What determines whether an individual is male or female?
Sex chromosomes
In humans animals, what are the two sex chromosomes?
X and Y
Pair them up:
Female
Male
Heterogametic
Homogametic
Female = Homogametic
Male = Heterogametic
What kind of chromosomes do females have?
They have two homologous X chromosomes
What kind of chromosomes do males have?
They have an X and a Y chromosome
On the Y chromosome, which gene determines the development of male characteristics?
The SRY gene found on the short arm
What do you heterogametic males lack?
They lack most of the homologous alleles on the shorter Y chromosome
Can males be sex linked pattern carriers?
No because the Y chromosome does not hold the genes necessary
What are sex linked genes?
They are genes that can be found on the X chromosome, but have no homologous allele on the Y-chromosome
In males, where do you sex linked gene show and why?
They show in the males phenotype as there a no genes on the Y chromosome to counteract them
What are three sex linked disorders?
- Duchenne muscular dystrophy
- Characterised by progressive weakening of muscles and loss of coordination - Haemophilia.
- Defined by lack of protein involved in blood clotting - Red/green colour blindness
Are males or females more likely to have a sex linked characteristic?
Males as they only require one recessive gene, females need two
Who do males inherit sex linked characteristics from?
Their mothers
What is a phenotype?
The physical appearance caused by the alleles in the genes
What is a genotype?
An organisms genetic information
What happens to one of the homogametic females X chromosomes?
It is inactivated at an early stage
Why in females is one of the X chromosomes inactivated?
To prevent a double dose of gene products (proteins) which could be potentially harmful to cells
Are carriers more or less likely to be affected by deleterious mutations on the X chromosomes?
Carriers are less likely to be cells deleterious. Mutations as the X chromosome inactivation is done at random only half the cells in any tissue will have a working copy of the gene with the deleterious allele
What is sexual dimorphism?
It’s one of the different sexes present different characteristics, i.e. peacocks
What does it mean when an organism is a hermaphrodite?
It has both male and female reproductive structures
What are the two different types of hermaphrodites?
Simultaneous and sequential
What does it mean if an organism is a simultaneous hermaphrodite?
It has both male and female reproductive structures at the same time
Some can self-fertilise like banana slugs and others have mechanisms to avoid doing this, and must meet another individual to reproduce like earthworms
What does it mean if an organism is a sequential hermaphrodite?
The organism is born one sex, but can change to another sex at some point throughout it’s life.
This usually happens if reproductive success is likely to be much greater by being the other sex.
It’s common in jellyfish and gastropods.
Do you hermaphrodites produce both male and female gametes?
Yes but there is usually another partner who also exchanges gametes.
Do you hermaphrodites have to meet the opposite sex to sexually reproduce?
No, if the chance of encountering a partner is uncommon, the partner can be of the same sex.
What can determines sex and sex ratios?
(5 examples)
Environmental factors, such as:
Size
Competition
Parasitic infection
Temperature
Resource availability
What is sex change influence by?
The balance of androgen and oestrogen hormones in a group
What are two examples of sex changes?
Clownfish
- Small groups with a large, dominant female, a large male and small males. If female is removed largest male becomes female.
Bluehead wrasse
- One male in group of females, if male removed largest female grows twice its size and changes coloration and behaviour to become a male
How does temperature-dependent sex determination work?
The embryos sex is determined during a temperature sensitive period of egg incubation
What species does temperature-dependent sex determination usually occur in?
Reptiles, birds and fish
At what temperature is do tortoises, terrapins and turtles, produce males and females?
Males = cool
Females = warm
At what temperature do lizards and alligators produce males and females?
Males = warm
Females = cool
What temperature do crocodiles and snapping turtles produce males and females?
Males = intermediate
Females = cool and warm
