Unit 2 - Topic 3 - Variation and Sexual Reproduction - Section C - Sex Determination Flashcards
How can the sex of birds, mammals and some insects be determined
By the presence of sex chromosomes
In most mammals what gene on which chromosome determines the development of male characteristics
The SRY gene on the Y chromosome
What do heterogametic males lack most of and what can this result in
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)
In homogametic females what happens at an early stage of development
One of the two X chromosomes present in each cell is randomly inactivated
What is X chromosome inactivation
A process by which most of one X chromosome is inactivated
What does X chromosome inactivation prevent
A double dose of gene products, which could be harmful to cells
Who are going to be less likely affect by any deleterious mutations on X chromosomes
Carriers
What does the random X-chromosome inactivation cause
Half of the cells in any tissue will have a working copy of the gene in question
What are hermaphrodites
Species that have functioning male and female reproductive organs in each individual
What do hermaphrodites have
They produce both male and female gametes and usually have a partner with which to exchange gametes
What are the benefits of hermaphrodites
That if the chance of encountering a partner is an uncommon event, there is no requirement for that partner to be of the opposite sex
For other species what determines the sex and sex ratio
Environmental rather than genetic factors
What is environmental sex determination in reptiles controlled by
Environmental temperature of egg incubation.
What can result in sex change within individuals of some species
Size, competition, or parasitic infection
In some species the sex ratio of offspring can
be adjusted in response to what
Resources availability
