Class Notes (839,116)
Canada (511,194)
Biology (6,826)
Biology 1001A (1,727)
Tom Haffie (1,170)

Bio LEcture 3

5 Pages

Course Code
Biology 1001A
Tom Haffie

This preview shows pages 1 and half of page 2. Sign up to view the full 5 pages of the document.
BIO1001 Jash Parikh 2012/11/05 Biology for Sciences I Lecture 16 Notes from Readings: Chapter 7  Relationship between sexual reproduction and genetic variation o Genes do not necessarily assort independently from each other if linked on same chromosome o Some sex-linked genes are localized to the X or Y chromosomes, which are not partitioned equally to females and males o Due to recombination, sections of chromosomes can exchange material thereby forming different linear arrays of nucleotides o As nucleotide sequences constitute genes, recombination can produce different combinations of genes along a chromosome o Millions of different kinds of gametes can be formed by recombination o Different proposals  Sex originated as a way of overcoming DNA damage by using recombinational DNA repair mechanisms  Any genetic variation created is an accidental by-product  The production of genetic variation is the primary reason for he persistence of sex  Removing deleterious mutations  More mutations accumulate with asexual than with sexual reproduction in the water flea  Sex is advantageous to organisms that exist in variable environments and that parasitic elements such as transposons and plasmids initiated or promoted sexual fusion as a mechanism to infect other cells  Sexual crossing in a population allows single individuals to incorporate different beneficial mutations from other members through mating and genetic recombination  Enable relatively rapid combinations of existing mutations  Additional genetic variation allowing a population to persist in a changing environment  Different modes of genetic sex determination o Penis fencing in flatworms  Hermaphrodites-consisting of both male and female parts  Hunt and fight for mates  Some have two penises giving a decided advantage o Temperature-Dependent Mechanisms  Sex of alligators and other reptiles are set during the embryonic development by the temperature at which the egg develops  High temp determines maleness, low temperature determine femaleness o Fish That Change Their Sex as Adults  Tropical reef fish change sex during lifetime in matters of hours  Switching without inhibiting the other sex o Compensatory Mechanisms in Chickens  Males have right and left testes of normal sizes BIO1001 Jash Parikh 2012/11/05  Females have left and right gonads but only the left one functions as an ovary, right being rudimentary  If functional ovary is removed, rudiment can develop into an ovary, testis, ovotestis, with features of both sexes o Fertilized Versus Unfertilized Eggs  Haplodiploidy  Honeybees: male; haploid, female; diploid  Only one female becomes a queen and lays eggs  All other females help raise the queen’s eggs and contribute to her reproductive success  Queen releases a hormone that supresses fertility in the workers  Female lays differently sexed eggs in response to the size of the wheat grain containing the larval host  Large; fertilized female egg, Small; unfertilized male egg  Different Modes of Environmental Sex Determination o Bonellia  Green spoon worm larvae that free swim and settle on sea bottom develop into females with a 10-20 cm long body and meter long proboscis  Larvae that land on proboscis metamorphose into tiny 1mm males that lack digestive organs producing nothing but sperm o Osedax  Tubeworm females lack digestive system but contain endosymbiotic bacteria thought to produce the enzymes responsible for digesting whale bones  Females are surrounded by non-feeding males  Larvae that settle on bone develop into females while larvae that settle on females become dwarf males with development arrested at larval stage o Painted Turtles  High temp incubation of eggs in painted turtle (recall reptile) make females o Social Fish  Loss of socially dominant males from a group is followed by conversion of the dominant female in the group into a male  Females become males when the surrounding fish in the group are relatively small o Parasitoid Wasps  Female parasitoid wasps deposit eggs that will develop into females into large host larvae and eggs developing into makes into small host larvae  Females grow large sizes in larger hosts therefore producing more eggs  Differentiate by size Why Sex?  Copulation? Recombination? Reproduction? Ge
More Less
Unlock Document

Only pages 1 and half of page 2 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.