B13 Reproduction Flashcards
how do cells divide in asexual reproduction
mitosis
how do gametes form
meiosis
what is meiosis used for in plants
making egg and pollen cells
how do gametes introduce variation
each of the 4 gametes produced from 1 cell are different and contain random mixtures of the original chromosome which provides variation
what are advantages of asexual reproduction (2)
only one parent needed which is time and energy efficient
rapidly produces large numbers of identical offspring
what is an advantage of sexual reproduction
variation which gives a survival advantage if the environment changes
what is a disadvantage of asexual reproduction
no variation is a disadvantage if the environment changes as organism is unable to adapt
what is a disadvantage of sexual reproduction
takes time and energy to find a mate or spread gametes
slower than asexual reproduction
why do fungi reproduce sexully and asexually
they normally reproduce asexually when fungal spores go through mitosis but when conditions are not good eg dry, 2 hyphae from different fungi join and their nuclei fuse so the new hypha has 2 sets of chromosomes this then undergoes meiosis to make haploid spores each with only one set of chromosomes
how are flowers adapted for sexual reproduction
either adapted to attract animal pollinators or make it easy for their pollen to be carried by the wind and caught by another flower
how do malaria parasites reproduce
sexually in mosquitos and asexually in human host
what do genes code for
a particular sequence of amino acids to make a specific protein that make up different specialised cells that form tissues including the enzymes that control cell chemistry
what is DNA made up of
combinations of 4 different chemical bases (monomers)
what is the genome of an organism
the entire genetic material of that organism including all chromosomes and genetic material in the mitochondira
where does mitochondrial dna come from
inherited from the mother as it comes from the mitochondria in the egg
why are bacteria and virus genomes sequenced
helps to identify causes of disease very rapidly and choose the correct treatment
what is a gene
a small section of dna on a chromosome. Each gene codes for a articular sequence of amino acids to make a specic protein
what is a nucleotide
combination of a sugar, base and a phosphate
how do nucleotides help code for amino acids
nucleotides are grouped into threes and each set of 3 bases codes for a particular amino acid
dna in the nucleus controls protein synthesis but proteins are synthesised in the cytoplasm- explain this
genes in the dna produce a template for the protein which reflects the sequence of bases in the dna but is small enough to leave the nucleus through pores
template binds to the surface of a ribosome
the cytoplasm contains carrier molecules which are each attached to a specific amino acid
the carrier molecules attach to the template
amino acids are joined together to form a specific protein
carrier molecules keep bringing amino acids to add to the growing protein chain until the template is completed
what happens once the protein chain is completed
the molecule folds up to form a unique shape that will enable it to carry out its cell functions eg for an enzyme it will form the shape of the active site
what does the non coding part of dna do
involved in the switching on or off of genes or parts of genes
what does it mean when a gene is expressed
when it codes for a protein that is synthesised in the cell
what does variation in the non coding parts of dna cause
has an effect on how genes are expressed which affects phenotype (physical appearance)
what happens when there is a mutation in the coding DNA
protein formed is altered so slightly that apearance and function is not changed
what happens when there is a mutation in the non coding dna
can affect which genes are switched on and off which can have a big effect on the phenotype of the organism
what is an allele
different versions of the same gene. You have 2 allleles for each gene- one from each parent
define homozygote
an individual with 2 identical alleles for a characteristic eg BB or bb
define heterozygote
an individual with different alleles for a characteristic eg Bb
define genotype
what alleles the person has for that gene
define phenotype
what the individual looks like eg eye colour, dimples
what is a dominant allele
an allele that controls the characteristic when there is just one allele present
what is a recessive allele
an allele that must have 2 copies present to control the characteristic
what are the female sex chromosomes
XX
what are the male sex chromosomes
XY
what is an inherited disorder
result of a change in the bases or coding of genes and can be passed from parent to child
what is polydactyly
when a baby is born with extra fingers or toes
formed by a dominant allele so if you are heterozygous you have a 50% chance of passing it onto your child and if you are homozygous you have a 100% chance
what is huntingtons disease
a dominant genetic disorder
symptoms develop in middle ages
affects nervous system and can cause death
how is cystic fibrosis inherited
passed on by a recessive allele so both parents must be carriers
what is cystic fibrosis
disorder of cell membranes that affects movement of certain substances so mucus made by cells becomes very thick
lungs can become clogged and stop working properly
pancreas cannot make and secrete enzymes properly as tubes are blocked
causes infertility
what is the treatment for cystic fibrosis
no cure but physiotherapy and antibiotics used to help clear lungs of mucus and infection
enzymes are used to replace ones that pancreas can’t make
what is amniocentisis
carried out at 15-16 weeks of pregnancy involves taking some fluid from around the developing fetus which contain fetal cells and can then be used for embryonic genetic screening
what is chronic villus sampling of embryonic cells
done between 10-12 weeks of pregnancy by taking a small sample of tissue from the developing placenta- provides fetal cells to screen
what are the risks of embryonic screening
miscarriage
how is screening carried out
dna is separated from embryonic cell and tested
what are concerns about embryonic screening
can sometimes give a false positive or false negative
couple have to make the difficult decision of whether or not to terminate pregnancy
screening is expensive
could give a rise to ‘designer babies’
