BIO2242 Lecture Notes - Lecture 17: Allosome, Dioecy, Hermaphrodite
Lecture 17 – Sexual Reproduction
What is Sexual Reproduction?
• A method of reproduction involving the fusion of haploid gametes
(fertilisation) to form a diploid zygote
• Two sexes: male and female
• Produce gametes and make available to the opposite sex
o Internal fertilisation
o External fertilisation
• Gametes
o Small, motile
o Large, non-motile
o Created through meiosis
• Segregation of parental chromosomes
o Recombination of homologous chromosomes
o Crossing over is optional: doesn’t occur in all species (fruitflies)
▪ Maternal chromosome on paternal
▪ Helps mix up genetic material
Sex Determination: Vertebrates
1. Genotypic sex-determination (GSD)
• Sex chromosomes (e.g. XX/ZY, ZZ/ZW)
• All birds and mammals, most fish, amphibians and reptiles
• All genetic groupings
2. Environmental sex-determination (ESD)
• Some aspect of environment influence sex of individual
o E.g. temperature, temperature dependent sex-determination
(TSD)
• Some fish and amphibians, common in reptiles
• Some species have both GSD and ESD
Sex Determination: Invertebrates
• Diverse range of sex determination
• Females: XX and ZW
• Males: XY, ZZ
• Based on diploidy level rather than chromosomes
Why Have Sexual Reproduction?
• Widespread in animals despite its numerous costs
• Recombination breaks up successful gene combinations
o Crossing over during meiosis
o But produces offspring with novel genotypes
o Genetic combination changes
Types of Sexual Reproduction
1. Gonochoristic (Dioecious)
• Separate male and female individuals
• Occurs in majority of animal phyla
2. Hermaphroditic
• Both male and female structures in the same individual
find more resources at oneclass.com
find more resources at oneclass.com
