The Biology Coach: AH Bio, Topic 2, Key Area 3c

Sexual dimorphism

Differences in physical characteristics between males and females of the same species.

Low sexual dimorphism

When the male and female of the species look very similar, e.g. swans

High sexual dimorphism

When the male and female of the species look very different, e.g. peacock

Unisexual

Being male OR female

Simultaneous hermaphrodite

Organisms with both male and female reproductive organs, e.g. slugs

Sequential hermaphrodites

Organisms exist as one sex but may change to the other at some point during their life, e.g. some fish.

Sex chromosomes

XX (female) or XY (male) - determines the sex of birds, mammals and some insects.

SRY gene

Present on the Y chromosome and determines the development of male characteristics

Homogametic

Possessing 2 of the same sex chromosomes, i.e. XX

Heterogametic

Possessing different sex chromosomes, i.e. XY

X chromosome inactivation

The random switching off of one X chromosome in each cell to prevent a double-dose of gene products in females.

Social and environmental cues that influence sex

parasitic infection, size, competition and temperature.