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Flashcards in B13 Reproduction Deck (46):

how do cells divide in asexual reproduction



how do gametes form



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



what are the male sex chromosomes



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



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'