Class Notes (806,890)
Canada (492,505)
Biology (6,676)
Biology 1001A (1,723)
Tom Haffie (1,166)
Lecture 14

Biology 1001A - Lecture 14.docx

6 Pages
Unlock Document

Western University
Biology 1001A
Tom Haffie

Biology 1001A Lecture 14 &15: Evolutionary Forces and Sexual Selection Sex ≠ Reproduction  Everything doesn’t reproduce sexually, some reproduce ASEXUALLY  First living things reproduced asexually  Bacteria (picture) is reproducing (binary fission) but it is NOT engaging in sexual recombination o The duplicated bacterium will be genetically identical to the parent  Plants are simultaneously engaging in sexual reproduction (flowers are transfer pollen) and asexually (sending out vegetative runners, which sprout in the ground and grow into a clone of the parent)  Some fish, such as the Guppy, reproduce parthenogenetically. A form of asexual reproduction in females where the growth of embryos occur without fertilization by a male.  Many things reproduce asexually, we can have reproduction without sex (sexual recombination) Sexual Organisms can be Dioecious  Organisms can be sexual in many ways  In humans, and many other vertebrates, are called dioecious. o Dioecious: Individual is male OR female …. Or Monoecious  Simultaneously Monoecious: Have both functional eggs and sperm (hermaphrodite). They can mate with each other.  Sequentially Monoecious: Can start off with one gender and can change into another later in life. I.e. Born as female, by certain age or body size, can develop into a male (clownfish). Sex-advantage Model of Sex Change  In some species, Males have relatively little to gain by body size in order to gain reproductive success  The relationship is MORE IMPORTANT for FEMALES. They have more to gain from body size, since a bigger female can lay MORE eggs, where as males can produce sperm with little cost.  In the clownfish example, the fish would be born as males first, and after reaching a certain body size or age, the functions of males and females cross (Protandry: male reproductive organs come to maturity), they should change genders, and start reproducing as females  Sometimes this can be the opposite. Females can have little to gain form body size and males have more to gain. They are born as females and at female maturity (Protogyny), they should change genders and start reproducing as males. Why reproduce Sexually?  Well, many reasons NOT to o Finding, attracting, competing for mates takes a LONG time o Increased chances of acquiring Sexually Transmitted Diseases (STDs) o Cost of meiosis  Transmitting ONLY half of genome, while asexual reproduction results in transmitting ALL of genomes (clone) o Cost of males  Females are the ones ONLY capable of giving birth. Only females ultimately produce new offspring.  In diagram below, 2 females. One reproduce sexually, the other asexually, both producing 4 offspring each. Asexual lineage takes over in the number of offspring. Sexual lineage has to invest time into finding a male.  Asexual (clonal) females should quickly outcompete sexual females, unless sex improves offspring quality So why do so many species do it?  Multi-cellular organisms majority reproduce sexually, require copulation  Asexual reproduction still requires courtship or copulation (new from evolution) Sex  New combinations of alleles  Sex generates new combinations of alleles, genetically different from one another, due to recombination among non-homologous chromatids, independent segregation of chromosomes, into the gametes, ne combination of alleles. Mutational explanations for sex  Over time, asexual populations accumulate harmful mutations  If you are in an asexual population, and reproduced clonally, over time, the average number of mutations is going to increase  Sex continually recreates genotypes with fewer (or more) harmful mutations (fitter genes)  Ruby in the Rubbish Hypothesis Ecological Explanations for Sex  The Lottery Principle: Sex in Constant versus Changeable Environments o In a constant environment, any female at reproductive age is probably very adapted to the environment, and can clone herself, and clone will be adapted to same conditions o In an environment that is changing, a female would do better to produce offspring that are genetically diverse (Sexually), offspring will be adapted to the unpredictable environmental conditions.  Parasites place Negative Frequency-Dependant selection on host genotypes o Parasites tend to infect the most common genotypes in a population, since it’s the most ‘profitable’ prey.  Sex (producing diversity of offspring genotypes) favoured in parasite-rich environments (Red Queen Hypothesis) o You have to continue to
More Less

Related notes for Biology 1001A

Log In


Don't have an account?

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.