2.3 c) Sex Determination Flashcards
The sex of ___, ___ and some ___ is determined by ___ chromosomes.
birds, mammals, insects, sex
In most mammals, the ___ gene on the _ chromosome determines the development of ___ characteristics.
SRY, Y, male
Since males are ___ (XY), they lack most of the corresponding ___ ___ on the shorter Y chromosome.
heterogametic, homologous alleles
The fact that males are heterogametic (XY) is the reason behind ___-linked patterns of ___, as seen with ___ females and ___ males.
sex-linked, inheritance, carrier, affected
Explain carrier females if you please
Carrier females have X^B and X^b chromosomes. The B allele is dominant, and is a normal (non-diseased) allele. It takes precedence over the recessive, diseased b allele.
The possible females are X^B X^B (unaffected), X^B X^b (carrier) and X^b X^b affected
Explain affected males :)
Affected males have X^b and Y chromosomes. The b allele is diseased/affected, and it affects the male individual since there is no normal allele which is dominant over it. The Y chromosome cannot carry a copy of this gene
The possible males are X^B Y (unaffected) and X^b Y (affected)
Males have a greater chance of being affected by certain recessive conditions (such as… ) because they only need… whereas females need…
(colour blindness, haemophilia), one copy of the recessive allele, whereas females would need two.
*the recessive allele can only appear on X chromosomes
Females are ___ (XX).
One of the two X chromosomes are ___ ___ at an early stage of ___.
homogametic.
randomly deactivated, development
X chromosome deactivation is a process by which…
most of one X chromosome is deactivated
X chromosome inactivation prevents…
a double-dose of gene products, which can be harmful
Carriers of deleterious mutations are likely to be unaffected by the condition because…
Carriers are always (male/female).
the X chromosome that is inactivated in each cell is random, so only half of the cells in a tissue will be affected, and the other half will have a working copy of the gene (half b half B).
Female
Why can’t males be carriers of deleterious X chromosome mutations?
because they only have one X chromosome - so if they have it, they will be affected, and if they don’t they will be unaffected.
Carriers have it but are unaffected due to the presence of a dominant, normal allele on the other X chromosome
Many organisms (usually vertebrates) are ___.
hermaphroditic
What are hermaphrodites?
organisms that have functioning male and female reproductive organs (and produce both types of gamete)
Hermaphrodites produce both ___ and ___ g___, and usually have a ___ which which to exchange ___.
male, female gametes, partner, gametes
