2.3 variation and sexual reproduction Flashcards
what environmental factors, other than temperature, can be used to determine the sex of an organism?
size, parasitic infection, competition
where is TSD most prevalent?
in reptiles
what is TSD?
where the temperature experienced during the incubation period of the embryo determines its sex
what is the main benefit of being a hermaphrodite?
their mate does not have to be of the opposite sex if they are struggling to find one
do hermaphrodites have partners to exchange gametes with
yes usually
what is a hermaphrodite?
a species that has both male and female reproductive organs, so can produce both types of gametes
what does x inactivation leave
only one active x chromosome in each cell of the female embryo
what does x inactivation mean for carriers?
they are less likes to be affected by deleterious mutations on the x chromosomes
what are two qualities of x inactivation
random in each cell
irreversible
what does x-inactivation prevent
female from presenting double the quantity of x linked gene products which could be harmful to cells
what happens during x inactivation
during embryonic development of every female, most of one of the two X chromosomes in each cell inactivates
what does heterogametic mean
females produce gametes with two possible combinations of chromosomes
what does homogametic mean
females produce gametes with the same combination of chromosomes
a male has a recessive allele on one X chromosome…
which has no copy to mask its effects
a female has a recessive allele on one X chromosome…
which can be masked by a dominant allele on the other X
what is the root cause of the pattern of inheritance called sex linkage?
the Y chromosome lacks many genes found on its homologous x chromosome
why are x and y homologous?
they pair up during meiosis I
what determines the development of male traits in most mammals?
the SRY gene on the Y chromosome
what do sex chromosomes do?
determine whether an individual is male or female
what are the four things we must remember about meiosis II?
single chromosomes line up at the equator
spindles contract and chromatids move to opposite poles
cytokinesis occurs
4 non-identical haploid gametes
what does a greater distance between linked genes mean?
there is a greater chances of crossing over, resulting in greater frequency of allele recombination
what are linked genes?
genes on the same chromosome
what are linked genes?
genes on the same chromosome
what does independent assortment result in?
the production of gametes with varying combinations of maternal and paternal chromosomes
how does meiosis I end?
cytokinesis occurs and two daughter cells are formed
what happens fourth in meiosis I?
spindles contract and each homologous partner moves to opposite poles of the cell
what is independent assortment?
homologous chromosomes line up at the equator independent of maternal and paternal origin
what does crossing over result in?
recombination of alleles as info is shared between linked genes
what happens third in meiosis I?
homologous chromosomes line up at the equator and independent assortment occurs
what happens second in meiosis I?
chiasmata form at points of contact between non-sister chromatids and crossing over occurs
what begins meiosis I?
chromosomes condense and homologous chromosomes pair up
does meiosis occur in asexual reproduction?
no
what are two examples of cells that undergo horizontal gene transfer?
bacteria and yeast cells (prokaryotes)
what does horizontal gene transfer allow for?
gene transfer between individuals = increased variation and faster evolutionary change
in which organisms can horizontal gene transfer occur?
asexually reproducing organisms
what allows for natural selection and evolution to take place in asexually reproducing populations?
mutations can sometimes occur that allow for small degrees of variation
where is parthenogenesis more common?
cooler climates with low parasite density
what is parthenogenesis?
reproduction from a
female gamete without fertilisation.
what are examples of asexual reproduction in eukaryotes include?
vegetative cloning in plants
parthenogenesis in lower plants and animals
asexual reproduction involves one parent producing daughter cells - what does this allow?
an unlimited colony to be produced over time
when can asexual reproduction be a particularly successful reproductive strategy?
in narrow, stable niches
recolonising disturbed habitats
why does sexual reproduction remain the main reproductive method used?
the benefit of increased genetic variation outweighs the costs
why is genetic variation vital?
provides the raw material required for adaptation
reduces the chance of parasitic infection
what is the cost of asexual reproduction?
no variation
what is the benefit of sexual reproduction?
variation = fundamental to evolution
what are the costs of sexual reproduction?
males are unable to produce offspring
only half of each parent’s genome is passed on
disrupts successful genomes
what are the benefits of asexual reproduction?
time-efficient
less energy required
only 1 parent required
increased number of offspring regularly
what is asexual reproduction?
a mode of reproduction by which offspring arise from a single organism and inherit the genes from that parent only
what are 2 problems arising from heterogametic males and homogametic females
males and females will have different inheritance patterns
female has a potential double dose effect from the 2 copies of the non-homologous section
what is sexual reproduction?
the production of new living organisms by combining genetic information from individuals of different types
