Variation & Sexual Reproduction Flashcards
What is sexual reproduction?
The process of producing new living organisms by combining genetic information from 2 individuals of different types/sexes
Costs of sexual reproduction
Males are unable to produce offspring (only females can)
Only half of each parents genome is passed onto offspring, disrupting successful parental genomes
Benefit of sexual reproduction
Increase in genetic variation in the population (benefit outweighs the costs)
Genetic variation provides…
Raw material required for adaption, therefore gives sexually reproducing organisms a better chance of survival under changing selection pressures
The Red Queen hypothesis can explain …
Persistence of sexual reproduction as the co-evolutionary interactions between parasites and hosts may select for sexually reproducing hosts
What leads to greater fitness?
Hosts better able to resist to tolerate parasitism
Parasites better able to feed, reproduce and find new hosts
How does genetic variability (as a result of reproducing sexually) affect offspring?
Reduces the chances that all will be susceptible to infection by parasites
What is asexual reproduction?
Costs of asexual reproduction
Genetic variation of population is low
Benefit of asexual reproduction
Offspring can be reproduced more often and in larger numbers
Why can asexual reproduction be a successful reproduction strategy?
Whole genomes are passed on from parent to offspring
Just one parent can…
Produce daughter cells and establish a colony of virtually unlimited size over time
Maintaining the genome of the parent is an advantage particularly in…
Very narrow, stable niches or when re-colonising disturbed habitats
What is parthenogenesis?
Reproduction from a female gamete without fertilisation
Parthenogenesis is more common in…
Cooler climates as this is disadvantageous to parasites
Regions of low parasite density and diversity
Example of asexual reproduction in eukaryotes
Vegetative cloning in plants and parthenogenesis in lower plants and animals
Asexually reproducing populations are not able to…
Adapt easily to changes in their environment but mutations can occur that provide some degree of variation and enable some natural selection and evolution to occur
Asexually reproducing organisms often have mechanisms for…
Horizontal gene transfer between individuals to increase variation
What is meiosis?
The division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte
What are 2 chromosome in a pair known as?
Homologous chromosomes
All body cells are…
Diploid- 2 chromosomes, 1 set each from male and female parent
Gametes are…
Haploid- 1 set of chromosomes
Homologous chromosomes have the same…
Size, centromere position, sequence of genes at the same loci
Fertilisation occurs when…
Haploid nuclei of 2 gametes fuse together to form a diploid nucleus
What does combining haploid gametes of 2 different individuals result in?
New combination of alleles in offspring which increases variation
What is independent assortment?
When each pair of homologous chromosomes is positioned independently of other pairs, irrespective of their maternal or paternal origin
What happens during meiosis II?
Each of the 2 cells produced in meiosis I undergoes a further division during which the sister chromatids of each chromosome are separated, producing a total of 4 haploid cells
What is the sex of birds, mammals and some insects determined by?
Presence of sex chromosomes
In live-bearing mammals females have… while males have…
Homologous pair of chromosomes (XX)
One X and a smaller Y (XY)
What are the genetic factors that determine sex?
Sex chromosomes
Sex-linked inheritance
Inactivation
What does homogametic mean?
Females produce all gametes with the same combination of chromosomes
What does heterogametic mean?
Males produce gametes with 2 possible combinations of chromosomes
What is the default setting for human embryonic development?
To become female
What determines the development of male characteristics in most mammals?
SRY gene on Y chromosome (sex determining region of Y chromosome)
Sex and sex ratio can also be determined by…
Environmental factors
Example of environmental factor
Environmental sex determination in reptiles is controlled by environmental temperature of egg incubation
Sex can change within individuals of some species as a result of…
Size
Competition
Parasitic infection
How is the sex ratio of offspring adjusted in some species?
In response to resource availability
Sex-linked inheritance…
Heterogametic males lack most of the corresponding homologous chromosomes on the shorter Y chromosome
What is inactivation?
In homogametic females one of the two X chromosomes is randomly inactivated at an early stage of development
What does inactivation prevent?
Double dose of gene products which could be harmful to cells e.g. production of harmful protein
Inactivation is a…
Random process as half of the cells in any given tissue will have a working copy of that gene (other is inactive)
Carriers are less likely to…
Be affected by any deleterious mutations on these X chromosomes
What are hermaphrodites?
Species that have functioning male and female reproductive organs in each individual
Benefit of having functioning male and female reproductive organs
If chance of encountering a partner is an uncommon event, there is no requirement for that partner to be of the opposite sex
