describe the differences between asexual and asexual reproduction
sexual - involves the fusion of a male and a femalegamete (fertilisation), mixing of genetic information, variation in the offspring
asexual - onlyone parent, does not involve gametes, no mixing of genetic information, all off springs are identical, clones
describe how meiosis halves the number of chromosomes in gametes
meiosis only takes place in reproductive organs
23 chromosomes pairs are copied
divided into 2
divide one more time, chromosomes are single not paired
meiosis forms four gametes
describe how fertilisation restores the full number of chromosomes
gametes from male and female joins (fertilisation) the full number is restored as each gamete contains singlechromosomes, however when joint they form a full 23 pair chromosomes
describe the structure of DNA
chromosomes contain DNA, which determine our inherited features.
two strands
each strand is a polymer
double helix
DNA is found in chromosomes and gene is a small section of DNA in a chromosome
each gene encodes for a specific sequence of amino acids to make a specific protein
human genome
help us understand and treat inherited disorders
trace human migration patterns
help search for genes that are linked to a disease
alleles
versions of a gene
genotype
tells us the alleles present
homozygous
two copies of the same allele
phenotype
tells us the characteristics caused by the person's allele
heterozygous
two differentalleles
dominant allele
will show even if there is only one copy present
recessive alleles
will only show in the phenotype if two recessive alleles are present
cystic fibrosis
disorder of cell membrane
carrier - if they have one normal cell membrane allele and one defective cell membrane allele
polydactyly
extra fingers or toes
caused by dominant allele
cannot be a carrier
embryo screening - embryos are tested to see if they have alleles for inherited disorder, if not are implanted into woman
discuss the issues around embryo screening
expensive
large numbers of embryos are created but only a small number are implanted so sme healthy embryos are destroyed
produce offsprings with desirable feature in the future, unethical
inheritance of sex
22pairs contains genes which only determine inherited characteristics