B13 Reproduction Flashcards
compare asexual and sexual reproduction
asexual
- cells divide by mitosis,
- offspring is genetically identical to (a clone of) parent: no variation,
sexual
- cells divide by meiosis to form gametes,
- gametes fuse to form a zygote,
- offspring inherits genetic information and characteristics from both parents: variation.
in which part of the body are gametes produced in animals?
e.g. for humans?
in the sex organs
e.g. testes and ovaries.
what are the animal
and the plant
gametes?
humans:
- female: egg cells,
- male: sperm
plants:
- female: egg cells,
- male: pollen.
describe the process of meiosis of a cell
- cell copies its genetic information, so that there are now 4 (rather than 2) sets of each chromosome which each forms a pair of chromatids,
- cell divides twice in quick succession to form four gametes, each with one set of chromosomes.
how many chromosomes does a human body cell have?
so how many chromosomes does a human gamete have?
46 (in 23 pairs)
gamete has 23
advantages + disadvantages of asexual reproduction
asexual
advantages
- time + energy efficient: one parent so no need to find a mate or spread gametes,
- no variation in offspring, can produce large amount of clones which can be useful e.g. in agriculture.
disadvantage
- introduces no variation: if there is an unfavourable change in the environment, no organisms of the species can survive.
advantages + disadvantages of sexual reproduction
asexual
advantage
- variation in offspring, higher chance of some surviving if there is a change in the environment, natural selection,
disadvantages
- time + energy inefficient: two parents so it takes energy and time to find a mate or spread gametes.
describe how malarial parasites reproduce
- asexually in human liver and blood cells,
- when mosquito takes blood meal, the drop in temperature triggers sexual reproduction in parasites in the red blood cells,
- for 20 mins, sexual forms burst from the blood cells and meet to form zygotes with 2 sets of chromosomes,
- zygotes undergo meiosis to produce new asexual parasites to infect a new human host.
what are chromosomes made of?
DNA
what are genes?
sections of DNA which store genetic information
each gene codes for…
each gene codes for a specific sequence of amino acids that forms a particular protein
what is the genome of an organism?
the sum of all the organism’s genetic material
why is studying the human genome important?
- helps us PREDICT and thus prevent the growth of DISEASES through lifestyle changes (since some genes are linked to certain diseases),
- helps us understand human evolution and history,
- helps us understand inherited disorders and how to overcome them.
what is a nucleotide?
what do they make up?
- nucleotide: the combination of a phosphate and a sugar, which is attached to a base (A, T, C or G),
- repeating nucleotide units make up the DNA polymer.
which bases always link up with each other in a DNA molecule?
A and T
G and C
(remember: AT Gemma Collins)
why are the links of bases together important for the functioning of a DNA molecule?
- they hold the structure of the DNA double helix together,
- they help the information from genes on DNA be translated into proteins in the cell.
describe the process of protein synthesis
- gene produces a template which reflects the order of bases given by DNA and is small enough to leave nucleus through pores in the nuclear membrane,
- template leaves nucleus and binds to surface of a ribosome,
- carrier molecules from cytoplasm attached to amino acids repeatedly bring and attach them to the template in the given order,
- until template is complete and a complete amino acid is formed,
- amino acids join together into proteins which are shaped for a specific function.
why does changing the order of bases in the DNA affect the protein that is formed during protein synthesis?
- changed order of bases in DNA means a different template is formed,
- meaning it gives a different order of amino acids which will produce a different protein being produced by a gene.
what is a mutation?
a change in an existing gene that results in a new gene
what is an allele?
a form of a gene which codes for a particular protein and combine with each other to determine an offspring’s characteristics.
how can a mutation affect the protein formed by a gene?
- most of the time only alter a protein’s appearance or function very slightly or not at all,
- sometimes a mutation can affect the shape of a protein which affects its function negatively (e.g. enzyme no longer binding to substrate) or positively (e.g. producing a more efficient enzyme).
what is a homozygote
and a heterozygote?
homozygote: has two identical alleles for a characteristic,
heterozygote: has two different alleles for a characteristic.
what is a genotype + example?
the alleles present in an individual regarding a particular characteristic,
e.g. Bb, bb.
what is polydactyly?
what kind of allele is it caused by?
an inherited disorder which causes extra toes or fingers,
caused by a dominant allele.
what is cystic fibrosis?
what kind of allele is it caused by?
an inherited cell membrane disorder that affects the function of certain organs,
caused by a recessive allele (so is a recessive phenotype).
if an offspring inherits a disorder caused by a recessive allele
what can be said about the alleles of its parents?
its parents must both carry the recessive allele
human female pair of chromosomes
human male pair of chromosomes
female: XX
male: XY
what chromosome does
an egg cell
a sperm cell
contain?
- every egg cell contains an X chromosome,
- half of all sperm cells contain an X,
half contain a Y.
who is a ‘carrier’?
somebody who carries a recessive allele for a disorder but exhibits no symptoms of it.
compare the two ways (non IVF) of screening an embryo or fetus
1) amniocentesis:
- carried out at 15-16 weeks of pregnancy,
- screen fetal cells from the fluid around the developing fetus,
- risk of miscarriage,
2) chorionic villus sampling:
-carried out at 10-12 weeks of pregnancy,
- screen fetal cells from tissue of developing
placenta,
- risk of miscarriage.
5 arguments against embryo screening
- risk of miscarriage; could miscarry a healthy fetus,
- can give false negative/positive,
- ethical debate about terminating pregnancies,
- economic: screening is expensive,
- social: could give rise to ‘designer babies’.
