AH Bio 2.3

what are the 3 disadvantages of sexual reproduction?

- half of the population are unable to produce offspring
- each parent is only able to pass on half their genetic material rather than the full 100%
- there can be disruption of successful parental genomes

qhat are the 2 benefits of sexual reproduction?

increase in genetic variation in the population because of the mixing of parental genomes
- genetic variation providing raw material required for adaption, giving sexually reproducing organisms a better
chance of survival under changing selection pressures

what could the red queen hypothesis help to explain in terms of sexual reproduction?

the persistence of sexual reproduction despite its disadvantages

what happens in terms of parasitism if the hosts reproduce sexually?

the genetic variation in their offspring reduces their chances that all of them will be susceptible to infection by parasites

what means that parasites have a greater fitness?

they have greater virulence, are better able to feed and find new hosts

what happens if parasites reproduce sexually?

the genetic variation in their offspring increases their chance of some of the offspring having improved ability to exploit their hosts

what does asexual reproduction involve?

the production of genetically identical offspring by a single parent

when is asexual reproduction very successful and rapid?

in narrow or stable niches or when recolonising disturbed habitats

what is a benefit of asexual reproduction?

only one parent is needed and can establish a colony of virtually unlimited size over time

what is an example of asexual reproduction in plants?

vegetative cloning

what is parthenogenesis?

the reproduction from a female gamete without fertilisation

where is parthenogenesis more common?

cooler climates

how does variation come about in asexually reproducing organisms?

mutations

what can organisms that principally use asexual reproduction often have mechanisms for?

horizontal gene transfer

how can prokaryotes use horizontal gene transfer?

transfer of plasmids

what does horizontal gene transfer result in?

faster evolutionary change

what is meiosis?

the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte

how do chromosomes typically appear in diploid cells?

as homologous pairs

what are homologous chromosomes

chromosomes of the same size, same centromere position and with the same sequence of genes

what happens during meiosis one?

homologous pairs separate

what does a chiasmata do?

forms at points of contact between the non-sister chromatids of a homologous pair and sections of DNA are exchanged

what are linked genes?

those on the same chromosome

what can crossing over result in?

new combinations of the alleles of these genes

what does crossing over of DNA produce?

genetically different recombinant chromosomes

what are the 4 stages of meiosis?

prophase, metaphase, anaphase, teolphase

what happens during metaphase?

spindle fibres attach to homologous pairs and line them up at the equator of the nucleus

what is independant assortment?

when each pair of homologous chromosomes are positioned independently of the other pairs, irrespective of their maternal and paternal origin

what happens during anaphase?

the chromosomes of each homologous pair are separated and move towards opposite poles

what happens during telophase?

the chromosomes reach the poles and the nuclear membrane often reforms

what is cytokinesis?

division of the cytoplasm

what is produced after meiosis I?

2 diploid cells

what is produced after meiosis II?

4 haploid cells

what happens during meiosis II?

the sister chromatids of each chromosome are separated

what is the sex of birds, mammals and some insects determined by?

the presence of sex chromosomes

what sex chromosomes do females have?

XX

what sex chromosomes do males have?

XY

why are females homogametic?

all their eggs contain an X chromosome

why are males heterogametic?

50% of the sperm have an X chromosome and 50% have a T chromosome

what gene that is carried on the Y chromosome determines the development of male characteristics?

SRY

How does the SRY gene determine development of male characteristics?

by encoding and expressing a protein called testes-determining factor

what are sex-linked patterns of inheritence?

when carrier females (XBXb) pass on recessive deleterious sex-linked alleles to give affected males (XbY)

what happens to one of the X chromosomes in homogametic females at an early stage of development?

it is randomly inactivated

what does X chromosome inacivation prevent?

possible production of a double dose of gene products which could be harmful to cells

what are 3 environmental things that could determine the sex ratio of a species

size, competition, parasitic infection

what can the sex ratio of offspring sometimes be adjusted in response to in some species?

resource availability

what is environmental sex determination in reptiles controlled by?

environmental temperature of egg incubation

what are hermaphrodites?

species that have functioning male and female reproductive organs in each individual

what do hermaphrodites produce?

both male and female gametes

what is a benefit for hermaphrodites?

they can reproduce with any other individual and does not need to find a partner of the opposite sex