2.3c Sex Determination Flashcards
1
Q
What is the sex of birds, mammals and some insects determined by?
A
the presence of sex chromosomes
2
Q
What determines the development of male characteristics in most mammals?
A
the SRY gene on the Y chromosome
3
Q
Explain heterogametic males
A
- they lack most of the corresponding homologous alleles on the shorter Y chromosome
- This can result in sex-linked patterns of inheritance as seen with carrier females (XBXb) and affected males (XbY)
4
Q
Explain X chromosome inactivation
A
- the process by which most of one X chromosome is inactivated
- in homogametic females on of the two X chromosomes present in each cell is randomly inactivated at an early stage of development
5
Q
What is the benefit of X chromosome inactivation?
A
- prevents a double dose of gene products, which could be harmful to cells
- carriers are less likely to be affected by any deleterious mutations on these X chromosomes
6
Q
Explain the effect of X chromosome inactivation being random
A
half of the cells in any tissue will have a working copy of the gene in question
7
Q
What are hermaphrodites?
A
- species that have functioning male and female reproductive organs in each individual
- they produce both male and female gametes and usually have a partner with which to exchange gametes
8
Q
What is the benefit of being a hermaphrodite?
A
if the chance of encountering a partner is an uncommon event, there is no requirement for that partner to be of the opposite sex
9
Q
Explain how, for some species, environmental rather than genetic factors determine sex and sex ratio
A
- environmental sex determination in reptiles is controlled by environmental temperature of egg incubation
- sex can change within individuals of some species as a result go size, competition or parasitic infection
- in some species the sex ratio of offspring can be adjusted in response to resource availability
