b13 Flashcards
gametes in plants
pollen and egg cells
gametes in animals
sperm and egg cells
why is there variation in sexual reproduction?
it is due to the mixing of gametes which leads to variety in offspring. gametes are formed by meiosis
what is asexual reprodution
it involves only one parent and no fusion of gametes. theres no mixing of genetic info which leads to identicle offsprings
what happens when a cell divides to form gametes?
cells in reproductive organs divide by meiosis. there are copies of the genetic information. the cell divides twice to form 4 gametes each with a single set of chromosomes which are all genetically different from each other.
what happens at fertilisation?
gametes join to restore the normal number of chromosomes. this cell then divides by mitosis. the number of cells increases. as the embryo develops, the cell differentiates.
what are the advantages of sexual reproduction?
it produces variation in offspring. if the environment changes, this variation gives a survival advantage by natural selection.
natural selection can be speeded up by humans in selective breeding to increase food population.
what are the advantages of asexual reproduction?
only one parent is needed. more time and energy efficient as theres no need to find a mate. much faster than sexual reproduction. many identicle offspring can be produced when conditions are favourable.
how do malarial parasites reproduce?
asexually in the human host, but sexually in the mosquito.
how do fungi reproduce?
asexually by spores but also sexually to give variation
how do plants reproduce
they produce seeds sexually, but also reproduce asexually by runners like strawberry plants, or bulb division like daffodils.
what is DNA
a polymer made up of two strands forming a double helix. the DNA is contained in structures called chromosomes.
what is a gene?
a small secion of DNA on a chromosome. each gene codes for a particular sequence of amino acids to make a specific protein.
what is a genome?
the genome of an organism is the entire genetic material of that organism. the whole human genome has been studied and this will have great importance for medicine in the future
what is the structure of DNA?
a polymer made from 4 different nucleotides. each nucleotide consists of a common sugar and phosphate group, with one of four different bases attached to the sugar ( T A G C)
DNA is a polymer made up of repeating nucleotide units.
what is the code for an amino acid?
a sequence of three bases. the order of the bases controls the order in which amino acids are assembled to produce a particular protein.
describe protein synthesis
proteins are synthesised on ribosomes, according to a template. carrier molecules bring specific amino acids to the growing protein chain in the correct order. when the protein chain is complete, it folds up to form a unique shape. this unique shape enables the proteins to do their job as enzymes, hormones or forming structures in the body like collagen.
what are mutations?
random changes that occur in the sequence of DNA bases in a gene or chromosome.
- they happen continuously
- mutations in a gene can sometimes lead to a change in the protein that the gene codes for.
- mutations can affect how genes are expressed.
allele
different versions of a particular gene
chromosome
a long, coiled molecule of DNA that carries genetic information in the form of genes
dominant
an allele that is always expressed, represented by a capital letter
gamete
sex cells with half the number of
usual chromosomes
gene
a section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein
heterozygous
when someone has two different alleles
homozygous
when someone has two identicle alleles
genotype
combination of alleles that control each characteristic
phenotype
an organism’s observable characteristics. due to interactions of the genotype and the environment
reccessive
an allele that is only expressed ub the absence of a dominant allele/ represented by a small letter.
what is cystic fibrosis?
a disorder of cell membranes that is caused by a recessive allele
what is polydactyly
having extra fingers or toes which is caused by a dominant allele
what are the arguments for embryo screening?
it can avoid suffering by stopping children from being born with genetic disorders
the treatment for disorders costs governments and taxpayers a lot of money
there are laws in place to stop embryo screening from being abused
what are the arguments against embryo screening?
it could imply that people with genetic disorders are undesirable which is not fair or true.
it is very expensive and therefore not available to all
sex chromosome for females
xx
sex chromosome for males
xy
