Reproduction and Inheritance Flashcards
what is the role of oestrogen in the menstrual cycle
inhibits FSH production (stops another egg being matured)
stimulates LH production
thickens uterus lining
what is the role of progesterone in the menstrual cycle
inhibits FSH and LH (stops further egg being matured and released)
maintains the thickness of the uterus lining
what is the role of LH in the menstrual cycle
ovulation - follicle on ovary releases mature egg in oviduct
remnant of follicle on ovary becomes corpus luteum
what is the role of FSH in the menstrual cycle
follicle develops and egg matures
maturing follicle releases oestrogen
what is LH
luteinising hormone
what is FSH
follicle-stimulating hormone
when is oestrogen released
levels rise from day 1 to peak just before day 14
The peak in oestrogen occurs just before the egg is released
when is progesterone released
stays low from day 1 – 14 and starts to rise once ovulation has occurred
difference between asexual and sexual reproduction
AS only needs 1 parent organim whereas S needs 2
AS uses mitosis whereas S uses meiosis
AS produces genetically identical offspring whereas S produces genetically unique offspring
AS is usually a quick process whereas S takes much longer
what is fertilisation
fusion of a male and female gamete to produce a zygote that undergoes cell division and developes into an embryo
structure and function of wind pollinated flowers
For wind-pollinated flowers, the process of pollination is more random than it is for insect-pollinated flowers
When ripe, the anthers open and shed their pollen into the open air
The pollen is then either blown by the wind or carried by air currents until it (by chance) lands on the stigma of a plant of the same species, resulting in pollination
petals - small and dull, often green or brown in colour ( as the plant does not need to attract insects)
Scent and nectar - absent as theres no need to waste energy producing these as there is no need to attract insects
number of pollen grains - large amounts as most do not get to another flower to the more produced the higher chance that successfull pollination happens
pollen grains - smooth, small and light so they are easily blown by the wind
anthers - outside the flower, swinging loose on long filaments to release pollen easily
stigma - outside the flower, feathery to catch drifting pollen grains
structure and function of insect pollinated flowers
Insects often visit these flowers to collect nectar (a sugary substance produced by insect-pollinated flowers and the base of their petals, which provides the insects with energy)
As an insect enters the flowers in search of nectar, it often brushes against the anthers, which deposit sticky pollen onto the insect’s body
When the insect visits another flower, it may brush against the stigma of this second flower and in the process, may deposit some of the pollen from the first flower, resulting in pollination
petals - large and brightly coloured to attract insects
scent and nector - present as it entices insects to visit the flower and push past the stamen to get nectar
number of pollon grains - moderate as insects transfer pollon grains efficiently with a high chance of successful pollination
pollen grains - larger, sticky, and or spiky to attach to insects to be carried away
anthers - inside the flower, stiff and firmly attached to brush against insects
stigma - inside flower, sticky so pollen grains stick to it when an insect brushes past
fertilisation in plants
In plants, the ovary contains one or more ovules
The ovules are the structures that eventually develop into seeds
Each ovule contains an ovum
An ovum is an egg cell that contains the female nucleus that a male pollen nucleus can fuse with
In plants, fertilisation occurs when the pollen grain nucleus fuses with the ovum nucleus
The growth of the pollen tube
Unlike the male gametes in animals (sperm), the pollen grain has no ‘tail’ to swim to the ovary of the flower
Instead, in order to reach the ovum nucleus, the pollen grain grows a pollen tube
This only happens if the pollen grain has landed on the right kind of stigma (i.e. of the same species as the flower the pollen came from)
The nucleus inside the pollen grain moves down the tube as the tube grows down the style towards the ovary (which contains the ovule that, in turn, contains the ovum)
Once the nucleus of the pollen grain and the nucleus of the ovum have fused (joined together), that particular ovule has been fertilised and a zygote has been formed
The zygote will then start to divide (it is the structure that eventually develops into an embryo plant)
After fertilisation, the ovule (that contains the zygote) develops into the seed
The wall of the ovule develops into the seed coat, known as the testa
The parts of the flower surrounding the ovule (mainly the ovary walls) develop into the fruit, which contains the seeds
3.5 practical: investigate the conditions needed for seed germination
Set up 4 test tubes, with each containing 10 cress seeds on cotton wool
Label the test tubes A, B, C and D
For test tube A, leave the cotton wool dry
For test tube B, add enough water to the cotton wool so that it becomes moist
For test tube C, add enough water to cover the cotton wool and seeds, then carefully add a layer of oil on top of the water
For test tube D, add enough water to the cotton wool so that it becomes moist
Leave tubes A, B and C at room temperature or incubated at a specific temperature (e.g. 20°C)
Place tube D in a fridge (approximately 4°C)
Leave all tubes for a set period of time (e.g. 3 - 5 days)
Ensure the cotton wool in tubes B and D remains moist throughout this time by adding more drops of water if required
Compare the results and see which tube has the greatest number of germinated seeds
The test tubes are set up so that each of the factors required for germination (water, oxygen and warmth) can be tested, by selectively removing each in turn
In test tube A, water is removed
Test tube B is the control tube, where all factors are present
In test tube C, oxygen is removed (oxygen cannot pass through the oil and water layers on top of the seeds)
In test tube D, warmth is removed
As germination cannot occur if the conditions are not right (i.e. if even one of the three factors required is absent), it would be expected that only the seeds in the control tube will germinate
how do germinating seeds grow
When the seed germinates, this embryo begins to grow into the young seedling
Structures known as cotyledons surround the embryo
Some plants have one cotyledon, whereas others have two
The cotyledons contain food reserves that supply the young seedling with food (and, therefore, energy for growth) when the seed starts to germinate
The cotyledons fulfil this role until the young plant grows its own leaves and becomes capable of making its own food via photosynthesis
Once water has entered the seed, the seed coat (testa) splits
This leads to the production of the plumule (the first emerging shoot) and radicle (the first emerging root)
The cotyledon provides carbohydrate stores which are broken down to provide glucose for respn. This continues until the plant has sprouted leaves and starts photosynthesising
how can plants reproduce asexully
plants can reproduce asexually by natural and artificial methods
natural
some plants grow side branches, known as runners, that have small plantlets at their ends
Runners are horizontal stems that grow sideways out of the parent plant
Once they touch the soil, these plantlets will grow roots and the new plantlets will grow and become independent from the parent plant as a genetically identical plant
artificial
A simple method to clone plants (mainly used by gardeners) is by taking cuttings
This is an artificial method of asexual reproduction
The method for taking cuttings is as follows:
Gardeners take cuttings from good parent plants (i.e. those that are healthiest and best-looking)
A section of the parent plant with a new bud is cut off
This cutting can either be placed into water until new roots grow or can sometimes be placed directly into soil
Sometimes, the stem of the cutting may first be dipped into ‘rooting powder’, which contains plant growth regulators (rooting hormones) that encourage new root growth
These cuttings are then planted and eventually grow into adult plants that are genetically identical to the original plant
Plants cloned by taking cuttings can be produced cheaply and quickly
structure and function of the male reproductive system
prostate gland - produces fluid called semen that provide sperm cells with nutrients
sperm duct - sperm passes through the sperm duct to be mixed with fluids produced by the glands before being passed into the urethra for ejaculation
urethra - tube running down the center of the penis that can carry out urine or semen, a ring of muscle in the urethra stops urine and semen from mixing
testis - contained in a bag of skin (scrotum) and produces sperm and testosterone
scotum - sac supporting the testes outside the body to ensure sperm are kept at the temperature slightly lower than body temperature
penis - passes urine out of the body from the bladder and allows semen to pass into the vagina of a women during sex
structure and function of the female reproductive system
oviduct - connects the ovary to the uterus and is lined with ciliated cells to push the released ovum down it. fertilisation occurs here
ovary - contains ova which will mature and develop when hormones are released
uterus - muscular bag with a soft lining where the fertilised egg will be implanted to develop into a foetus
cervix - a ring of muscle at the lower end of the uterus to keep the developing foetus in place during pregnancy
vagina - muscular tube that leads to the inside of the womans body, where the males penis will enter during sex and where sperm are deposited
what is the role of the placenta in the nutrition of the developing embryo
the placenta allows:
- Nutrients (i.e. glucose, amino acids and salts) and oxygen to move from the mother to the embryo
- Metabolic wastes - carbon dioxide and urea - to move from the embryo to the mother
These materials pass from one to the other by diffusion
how is the developing embryo is protected by amniotic fluid
During pregnancy a membrane called the amnion encloses the developing embryo. The amnion secretes a fluid called amniotic fluid, which protects the developing embryo against jolts and bumps (mechanical shocks), drying out, and temperature fluctuations (due to waters high specific heat capacity)
what is the role of oestrogen in the development of secondary sexual characteristics
Secondary sexual characteristics are the changes that occur during puberty as children become adolescents
breasts develope
body hair grows
menstrual cycle begins
hips get wider
what is the role of testosterone in the development of secondary sexual characteristics
growth of penis and testes
growth of facial and body hair
muscles develope
voice breaks
testes start to produce sperm
what is a genome
an entire section of DNA of an organism
what is a gene
a section of a molecule of DNA that codes for a specific protein
what does the nucleus contain
Contains chromosomes on which genes are located
structure of a DNA molecule
DNA (deoxyribonucleic acid) is a polymer made up of 2 strands coiled around each other to make a double helix where the strands are linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G)
structure of a RNA molecule
RNA (ribonucleic acid) is made of a single polynucleotide strand and contains the nitrogenous bases: adenine, guanine, cytosine and Uracil
it is made of many nucleotides linked together in a long chain
how do genes exist as alleles
Alleles are variations of the same gene
As we have two copies of each chromosome, we have two copies of each gene and therefore two alleles for each gene
One of the alleles is inherited from the mother and the other from the father
This means that the alleles do not have to ‘say’ the same thing
For example, an individual has two copies of the gene for eye colour but one allele could code for brown eyes and one allele could code for blue eyes
what does dominant mean
a dominant allele is always expressed even if only one copy is present
what does recessive mean
a recessive allele is only expressed if 2 copies are present (so no dominant)
what does homozygous mean
when both alleles of a gene is are the same
what does heterozygous mean
when the 2 alleles of the gene are different
what does phenotype mean
the observable characteristics of an organism (hair colour)
what does genotype mean
the combination of alleles that control each characteristic
what does codominance mean
when both alleles within a genotype are expressed in the phenotype of an individual
eg a red petal flower with a white petal flower becomes a pink petal flower
polygenic inheritance
Characteristics that are controlled by more than one gene
most phenotypic features are a result of polygenic inheritance
how is the sex of a person controlled
by one pair of chromosomes, XX in a female and XY in a male
when does mitosis occur
during growth, repair, cloning and asexual reproduction
what is the diploid and haploid number of chromosomes in a human
diploid = 46 ( diploid is when each cell has 2 copies of each chromosome)
haploid = 23
what can variation be in a species
genetic, enviromental or a combo of the 2
what is mutation
a rare, random change in genetic material that can be inherited
what does mitosis (of a diploid cell) produce
2 cells containing identical sets of chromosomes
process of mitosis
DNA is duplicated
nuclear membrane breaks down
chromosomes line up along the centre of the cell
chromotids are pulled to each end of the cell
the cell divides
2 genetically identical daughter cells are produced
what does meiosis produce
four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes
process of meiosis
DNA is duplicated
nuclear membrane breaks down
chromosomes line up along the centre of the cell in pairs
sections of DNA are swapped between chromosome pairs
chromosome pairs seperate, moving to the opposite ends of the cell
the cell divides
the chromosomes line up along the centre
the chromosomes are pulled apart to opposite ends of the cell (like in mitosis)
four haploid daughter cells will be produced
how does random fertilisation produce genetic variation of offspring
Meiosis creates genetic variation between the gametes produced by an individual
This means each gamete carries substantially different alleles
During fertilization, any male gamete can fuse with any female gamete to form a zygote
This random fusion of gametes at fertilization creates genetic variation between zygotes as each will have a unique combination of alleles
Transcription
occurs in the nucleus of the cell and it is where a copy of a section of DNA is made
order:
part of the DNA molecule unwinds when the hydrogen bonds between the complementary base pairs break
the template strand of the gene which codes for the protein which is being copied is now exposed
Free mRNA (messanger RNA) nucleotides that are present bind to the exposed nucleotides (bases) on the template strand using the base pair rule
The mRNA nucleotides join together to form a single strand of mRNA
the mRNA leaves the nucleus via a pore
the new strand of mRNA is now a complimentary copy of the orginal DNA (opposite bases)
Translation
occurs in the cytoplasm of the cell and produces a chain of amino acids which form a protein
order:
once the mRNA has left the nucleus it attaches to a ribosome
in the cytoplasm, there are free molecules of tRNA (transfer RNA) which have an unpaired base on one end (anticodon) an a corresponding amino acid on the other
the anticodon on each tRNA pairs with a complementary codon on the mRNA and brings the amino acid with it
other tRNA connect to other parts of the mRNA and a peptide bond is formed between the neighboring amino acids
this continues until a ‘stop’ codon on the mRNA is reached as this signals for the translation to stop as the amino acid is complete
the amino acid chain is then folded and modified into the final protein molecule
order of protein synthesis
transcription
mRNA attaches to a ribosome
translation
how does a change in the DNA affect the phenotype
as the DNA base pairs determine the sequence and type of amino acids which make up a protein, if the pairs change, then there will be different amino acids or they will be arranged in a different order which will result in a different protein being made
substitution mutation
where one letter swaps to another eg. A to C
option 1: codes for the same amino acid so there is no affect
option 2: codes for a different amino acid but it is far away from the active site so there is no affect
option 3: codes for a different amino acid which is near the active site which prevents the substrate binding - negative mutation
option 4: codes for a stop codon which will mean the protein isn’t made at all - very negative
addition mutation
adds in a letter which then causes a frame shift which is very bad as all the amino acids change as the triplets are now different making completely different protein
stop codon may also be created in the wrong place also causing wrong protein.
deletion mutation
adds in a letter which then causes a frame shift which is very bad as all the amino acids change as the triplets are now different making completely different protein
stop codon may also be created in the wrong place also causing wrong protein.
do most genetic mutations effect the phenotype
no as most of them either don’t change the amino acid or the change occurs far away from the active site so the function of the protein does not change therefore no effect on the phenotype.
rarely the new DNA will change the allele and create a new one which may be good or bad however either way this will change the phenotype
what factors can increase the chance of mutations
mutations happen spontaneously and continuously but can be increased in some ways
Exposure to:
gamma rays, x-rays and ultraviolet rays (all types of ionising radiation that can damage bonds and cause changes in base sequences)
Chemical mutagens (chemicals in tobacco such as tar)
increased rates of mutation can cause cells to become cancerous
Darwins theory of evolution by natural selection
evolutionary change has occurred, and that natural selection has driven this change
how does natural selection allow more species to survive
individuals in a species naturally show variation caused by different genes
individuals with characteristics which are advantageous to their environment are more likely to survive (eg a snail with a white shell in a snowy environment)
individuals which survive for longer are more likely to reproduce and so more likely to pass on their advantageous alleles
over many generations the characteristics become more common as they are passed on more and more
how can antibiotic resistance increase bacterial populations
a random mutation can give rise to a new bacterial allele what codes for antibiotic resistance
when the bacterial population is exposed to an antibiotic, any individuals without resistance allele die so only ones with the resistance allele survive.
The surviving bacteria are more likely to reproduce, passing on their resistance alleles to offspring
over several generations the frequency of the resistance allele increases eventually resulting in a antibiotic resistant strain
this makes it much harder to kill bacteria with only one anti biotic meaning several need to be used which make bacterial infections more more difficult to control
