T6 reproduction Flashcards
what is sexual reproduction
involves the production of gametes by meiosis
a gamete from each parent fuses to form a zygote
genetic information from each gamete is mixed so the resulting zygote is unique
what are gametes
sex cells (sperm and egg cells in animals, pollen and egg cells in flowering plants)
haploid (half the number of chromosomes)
what is meiosis
form of cell division involved in the formation of gametes in reproductive organs
chromosome number is halved
involves 2 divisions
what must occur prior to meiosis
interphase - copies of genetic information are made during this process
what happens during the first stage of meiosis
chromosome pairs line up along the cell equator
pair of chromosomes are separated and move to opposite poles of the cell
chromosome number is halved
what happens during the second stage of meiosis
chromosomes line up along the cell equator
chromatids are separated and move to opposite poles of the cell
four unique haploid gametes are produced
why is meiosis important for sexual reproduction
increases genetic variation
ensures that the zygote formed at fertilisation is diploid
describe fertilisation and its resulting outcome
gametes join together to restore the normal number of chromosomes and the new cell then divides by mitosis
as the embryo develops, cells differentiate
advantage of sexual reproduction
creates genetic variation in offspring, increasing chances of species adapting and surviving environmental changes
natural selection can be speeded up by humans in selective breeding to increase food production
disadvantages of sexual reproduction
two parents required making reproduction difficult in endangered populations or in species which have solitary lifestyles
more time and energy is required so fewer offspring are produced
what is asexual reproduction
involves mitosis only
produces genetically identical offspring known as daughter cells
advantages of asexual reproduction
1 parent required
lots of offspring produced quickly, enabling rapid colonisation of an area and reducing competition from other species
requires less energy and time as don’t need mate
disadvantage of asexual reproduction
no genetic variation reducing the chances of a species being able to adapt to environmental change
describe the circumstances in which malarial parasites reproduce sexually and asexually
sexual in mosquito
asexual in human host
describe the circumstances in which fungi and plants reproduce sexually and asexually
a - spores, seeds
s - to give variation, runner or bulb division
what is DNA
double-stranded polymer of nucleotides would to form a double helix
genetic material of the cell found in its nucleus
define genome
entire genetic material of an organism
why is understanding the human genome important
important for development of medicine
searching for genes linked to disease
understanding and treating inherited disorders
tracing human migration patterns from the past
what is a chromosome
long, coiled molecule of DNA that carries genetic information in the form of genes
define gene
small section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein
what are the monomers of DNA
nucleotides
what are DNA nucleotides made of
common sugar
phosphate group
A T C G
full names of the four bases in nucleotides
adenine
thymine
cytosine
guanine
describe how nucleotides interact to form a molecule of DNA
sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand
base connected to each sugar
complementary base pairs joined by weak hydrogen bonds
explain how a gene codes for a protein
sequence of three bases in a gene forms a triplet
each triplet codes for an amino acid
order of amino acids determines the structure and function of protein formed
why is the folding of amino acids important in proteins such as enzymes
determines the shape of the active site which must be highly specific to the shape of its substrate
what is protein synthesis
formation of a protein from a gene
two stages of protein synthesis
transcription
translation
what does transcription involve
formation of mRNA from a DNA template
outline transcription
DNA double helix unwinds
RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand
RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand
mRNA formation complete, mRNA detaches and leaves the nucleus
what does translation involve
ribosome joins amino acids in a specific order dictated by mRNA to form a protein
outline translation
mRNA attaches to a ribosome
ribosome reads the mRNA bases in triplets
Each triplet codes for 1 amino acid which is brought to the ribosome by a tRNA molecule (carrier molecule)
polypeptide chain is formed from the sequence of amino acids which join together
what is a mutation
random change in the base sequence of DNA which results mostly in no change to the protein coded for, or genetic variants of the protein
occur continuously
describe the effect of a gene mutation in coding DNA
if a mutation changes the amino acid sequence, protein structure and function may change (enzyme may no longer fits its substrate binding site or a structural protein may lost its strength)
if a mutation doesn’t change amino acid sequence, there is no effect on protein structure or function
what is non-coding DNA
DNA which doesn’t code for a protein but instead controls gene expression
describe the effect of a gene mutation in non-coding DNA
gene expression may be altered, affecting protein production and the resulting phenotype
what are alleles
different versions of the same gene
what is a dominant allele
version of a gene where only 1 copy is needed for it to be expressed
what is a recessive allele
version of a gene where 2 copies are needed for it to be expressed
what is meant when an organism is homozygous
when an organism has 2 copies of the same allele
what is meant when an organism is heterozygous
when an organism has 2 different versions of the same gene
what is the genotype
gene present for a trait
what is the phenotype
visible characteristic
problem with single gene crosses
most characteristics are controlled by multiple alleles rather than just one
what is an inherited disorder
disorder caused by the inheritance of certain alleles
how are embryos screened for inherited disorders
During IVF, one cell is removed and tested for disorder-causing alleles
if the cell doesn’t have any indicator alleles, then the originating embryo is implanted into the uterus
what are the ethical issues concerning embryo screening
could lead to beliefs in society that being disabled or having a disorder is less human or associated with inferiority
destruction of embryos with inherited disorders is seen by some as murder as these would go on to become humans
could be viewed as part of concept of designer babies as it may be for the parents convenience or wishes rather than child’s wellbeing
what are the economic issues concerning embryo screening
costs of hospital treatment and medication will need to be considered if it is known that a child will have an inherited disorder and financial support explored if necessary
social issues concerning embryo screening
social care for children with IH may need to be considered if parents are unable to provide care
if an embryo is found to have an IH and is terminated, this can prevent a child and its parents from potential suffering in the future due to the disorder
what is gene therapy
insertion of a normal allele into the cells of a person with an IH to functionally replace the faulty allele
ethical concerns surrounding gene therapy
going against and playing God
introduced genes could enter sex cells and so be passed to future generations
sex chromosomes
M: XY
F: XX
why does the inheritance of a Y chromosome mean that an embryo develops into a male
testes development in an embryo is stimulated by a gene present on the Y chromosome
what is a sex-linked characteristic
characteristic that is coded for by an allele found on a sex chromosome
why are men more likely to show the phenotype for a recessive sex-linked trait than women
many genes are found on X chromosome that have no counterpart on the Y chromosome
women (XX) have 2 alleles for each sex-linked gene whereas men (XY) often only have 1 allele
only 1 recessive allele is required to produce the recessive phenotype in males
why are the majority of genes found on the X chromosome rather than the Y chromosome
X chromosome is bigger than Y so more genes are carried on it
