3. reproduction and inheritance Flashcards
done
where is oestrogen produced?
in the ovary
what is the role of oestrogen?
- stimulates the uterus to develop a lining (causes uterus lining to thicken)
- post ovulation, inhibits FSH and LH production
where is progesterone produced?
in the ovary
what is the role of progesterone?
- maintains and thickens the lining of the uterus
- inhibits FSH and LH production
- if fertilisation doesn’t occur, levels drop and menstruation occurs
where is FSH produced?
pituitary gland
what is the role of FSH
- causes eggs to mature in ovaries
- stimulates follicles in the ovaries to secrete oestrogen
where is LH produced?
pituitary gland
what is the role of LH?
- stimulates ovulation (release of egg from ovary to oviduct)
number of parent organisms in asexual reproduction and sexual reproduction
A- 1, S- 2
What type of cell division is required to produce offspring in asexual and sexual reproduction?
A- mitosis
S- meiosis (to produce gametes), mitosis after fertilisation
what level of genetic similarity between offspring is in asexual and sexual reproduction?
A- genetically identical to each other and to the parent
S- genetically unique and different from both parents
what sources of genetic variation in offspring is in asexual and sexual reproduction?
A- only one source (mutation)
S- three sources-
- contribution of 50% if their DNA from each of the 2 parents
- production of gametes by meiosis (resulting in new combinations of alleles on the chromosomes)
- random assortment of chromosomes into gametes during meiosis
what number of offspring is usually produced and what is the time taken to produce the offspring in asexual and sexual reproduction?
A- relatively large numbers, fast
S- limited numbers, slow
what is an allele
- variation of the same gene
- having them give rise to differences in inherited characteristics and variation within species
what is a gene
a short length of DNA that codes for a specific protein
what is a dominant allele
an allele that is always expressed, even if only one copy is present
what is a recessive allele
can only be expressed if two copies are present (if there is no dominant allele)
what does homozygous mean
two alleles of a gene that are the same- e.g. YY and yy
what does heterozygous mean
two alleles of a gene that are different- e.g. Yy
what is a genotype
the combination of alleles that control each characteristic
what is a phenotype
the observable characteristics of an organism (seen just by looking- e.g. eye colour, or found through testing- e.g. blood type)
what chromosomes do males and females carry
males = XY
females = XX
how are petals adapted for pollination in an insect pollinated flower
large and brightly coloured to attract insects
how is the scent and nectar adapted for pollination in an insect pollinated flower
produced to encourage insects to visit the flower and push past the stamen to get to the nectar
how is the anthers adapted for pollination in an insect pollinated flower
held on stiff filaments within the flower so that they brush against the insects
how is the stigma adapted for pollination in an insect pollinated flower
sticky stigmas within the flowers to catch pollen grains when insects brush past
how are petals adapted for pollination in a wind pollinated flower
small and dull, often green or brown in colour
how is scent and nectar adapted for pollination in a wind pollinated flower
not produced
how is anthers adapted for pollination in a wind pollinated flower
held on long filaments outside the flower to release pollen grains easily into the wind
how is the stigma adapted for pollination in a wind pollinated flower
feathery stigmas outside the flower catch airborne pollen grains
how can plants reproduce asexually by natural methods
grow runners (side branches), which grow sideways out of the parent plant and once they touch the soil they grow roots and become independent
how can plants reproduce by artificial methods
by taking cuttings (where a section of the parent plant with a new bud is cut off and then replanted)
what is the role of the placenta
to enable exchange of substances between the mothers blood and that of the fetus- these include oxygen and nutrients (e.g. glucose, amino acids, and mineral ions) and take away carbon dioxide and urea
how is the placenta adapted
has a large surface area and a thin wall for efficient diffusion of nutrients
contains lots of capillaries and the blood vessels are separate from the mother and fetus (don’t mix)
also contains villi
what is amniotic fluid
-surrounds the developing embryo in the uterus
-contained within the amniotic membrane (also known as the amniotic sac)
-protects the embryo by cushioning it from bumps when the mother moves around
what is a genome
the entire DNA of an organism
what is a gene
a section of a molecule of DNA that codes for a specific protein
name some examples of proteins
- enzymes
- hormones (like insulin, glucagon and ADH)
- haemoglobin
- antibodies
- structural proteins (like collagen found in skin cells)
how many chromosomes does an ordinary human body contain
- 23 pairs, or 46 in total
- diploid number, so often shown as 2n
- one chromosome from a pair is inherited from each parent
- each pair is called a homologous pair
what does each gene in the genome code for
a particular sequence of amino acids, which form different types of proteins
what do genes control
our characteristics, as they code for proteins
where are genes found
in specific locations on the chromosomes- these locations were identified in the human genome project
what does DNA stand for
deoxyribonucleic acid
where is DNA found
in the nucleus
describe a DNA molecule:
- a polymer made up of two strands coiled around to make a double helix
- the strands form to make a sugar phosphate backbone with bases (A,T,G,C) which are bonded together by complementary base pairing
what are the names of the bases in DNA
A= adenine
T= thymine
G= guanine
C= cytosine
what do the bases in DNA pair with
bonded together by complementary base pairing
A (adenine) pairs with T (thymine)
G (guanine) pairs with C (cytosine)
what does RNA stand for
ribonucleic acid
what is RNA made up of
is a polynucleotide, so made up of many nucleotides linked together in a long chain
what bases does RNA contain
A (adenine), G (guanine), C (cytosine) and U (uracil)
is RNA double or single stranded?
single
(DNA is double though)
what are examples of RNA molecules
- messenger RNA (mRNA)- transcript copy of a gene that encodes a specific polypeptide
- transfer RNA (tRNA)- involved in protein synthesis
- ribosomal RNA (rRNA)- forms part of a ribosome
differences between DNA and RNA?
DNA-
- double stranded
- deoxyribose sugar
- contains bases A, T, G, C
- longer
RNA-
- single stranded
- ribose sugar
- contains bases A, U, G, C
- shorter
what do the bases in RNA pair with
- REMEMBER IT CONTAINS URACIL INSTEAD OF THYMINE
- so, A-U, G-C
what are the two stages of protein synthesis
transcription and translation
describes what happens at transcription in protein synthesis
- happens in the nucleus, transcribes DNA to make a complementary copy of mRNA
- uses 2 enzymes (DNA Helicase and RNA Polymerase)
what does DNA Helicase do in protein synthesis (transcription)
unzips the DNA molecule, breaking the hydrogen bonds between the bases
what does RNA Polymerase do in protein synthesis (transcription)
RNA nucleotides form a new complementary copy using this enzyme to form the new mRNA molecule
describe what happens at translation in protein synthesis
- mRNA arrives at ribosomes
- the mRNA has codons
- ribosome moves along mRNA strand
- tRNA brings amino acids to ribosome
- the anticodons on tRNA binds with the complementary codons on mRNA
- this produces an amino acid chain
what is translation in protein synthesis
- happens after transcription
- translates mRNA into a protein
- this RNA code leaves the nucleus and goes to a ribosome
- each 3 bases (codon) on the RNA translate to amino acid
what is the difference between transcription and translation in protein synthesis
TRANSCRIPTION:
- occurs in the nucleus
- uses DNA to make RNA
- DNA unzips
- makes mRNA
TRANSLATION:
- takes place at the ribosomes
- involves mRNA and tRNA
- anticodons bind to codons
- produces amino acid chain
what is codominance
when both alleles within a genotype are expressed in the phenotype
what is an example of codominance
inheritance of blood group
what are most characteristics a result of
multiple genes interacting, rather than a single gene
what is polygenic
when characteristics are controlled by more than one gene
why is polygenic inheritance difficult to show using genetic diagrams
because of the wide range of combinations- e.g. eye colour
what are polygenic characteristics
- have phenotypes that can show a wide range of combinations of features
- the inheritance of these polygenic characteristics is called polygenic inheritance
what is monohybrid inheritance
- the inheritance of characteristics that are controlled by a single gene
- can be determines using a punnet square
what does a punnet square diagram show
- the possible combinations of alleles that could be produced in the offspring
- remember the dominant allele is shown using a capital letter and the recessive is same letter but lowercase
what are family pedigree diagrams usually used for
- to trace the pattern of inheritance of a specific characteristic (usually a disease) through generations of a family
- can be used to work out the probability that someone will inherit the genetic disorder
what is the sex of a person determined by
an entire chromosome pair
what sex chromosome pair do females have
XX
what sex chromosome pair do males have
XY
what is a mutation
- rare, random changes that occur in the sequence of DNA bases in a gene or chromosome
- can be inherited
- they occur continuously
what can a change in the DNA affect
the phenotype of an individual as it alters the sequence of amino acids in a protein
what are the three main ways that the sequence of DNA can be changed
- INSERTION of a new base into the DNA sequence
- DELETION of a base within the DNA sequence
- SUBSTITUTION of a base within the DNA sequence
what effect does the insertion mutation of a base have on the DNA sequence
- changes the amino acid that would have been coded for
- has a knock on effect (changes the codon)
what effect does the deletion mutation of a base have on the DNA sequence
- changes the amino acid that would have been coded for
- has a knock on effect (changes the codon)
what does the substitution mutation of a base have on the DNA sequence
- only changes the amino acid for the codon
- will NOT have a knock on effect
what are the effects of mutations
- most mutations do not alter the protein, or only alter it slightly so that its appearance or function is not changed
- therefore, there is no effect on the phenotype
what can the incidence of mutations be increased by
- the exposure to gamma rats, x-rays and UV rays (all types of ionising radiation which can damage bonds and cause changes in base sequences)
- chemical mutagens (e.g. tar in tobacco
what can increased rates of mutations cause
can cause cells to become cancerous
what is Darwin’s theory of evolution by natural selection
- individuals in a species show variation that is caused by differences in genes
- individuals with characteristics that are advantageous in their environment have a higher chance of survival (known as ‘survival of the fittest’)
- surviving individuals are more likely to reproduce and so are more likely to pass on their advantageous alleles
- over many generations this characteristic is more common in the population
what are the main steps of natural selection
- variation (random mutation gives rise to a resistant allele)
- increased survival (individuals with the resistance allele are more likely to survive)
- increased reproduction (the resistance allele is passed on)
- increased allele frequency (the resistance allele becomes more common in the population)
examiner tip: any description of how antibiotic resistance occurs must include the main steps of what?
natural selection
how does antibiotic resistance increase in bacterial populations?
- a random mutation can give rise to a new bacterial allele that codes for antibiotic resistance
- when the bacterial population is exposed to an antibiotic any individuals without the resistance allele die, while those with the resistance allele survive
- the surviving bacteria are more likely to reproduce, passing on their resistance alleles to offspring
- over generations, the frequency of the resistance allele increases eventually resulting in an antibiotic resistant strain of bacteria
how can antibiotic resistance make bacterial infections more difficult to control
- as once a bacterial population has developed resistance to a particular antibiotic, it can only be treated with the application of a different antibiotic; in some cases several are needed
what is fertilisation
- the fusion of a male and a female gamete to produce a zygote
- the zygote then divides by mitosis to develop into an embryo
what are gametes
- sex cells produced by meiosis
- is the sperm and ovum in animals, and pollen nucleus and oven in plants
how many chromosomes do gametes contain
half the number of chromosomes compared to normal body cells (23 in human gametes)
what adaptations do gametes have to improve the chances of successful fertilisation and embryo development?
- sperm cells have a tail to propel them towards the egg, and mitochondria to provide energy for this movement
- egg cells have energy stores within the cytoplasm to support early embryo development
how many chromosomes does a human zygote contain
46 (23 pairs)
describe the process of fertilisation in plants
- after successful pollination a pollen tube forms to deliver the male nucleus to the egg cell (ovum) in the ovary
- the pollen tube grows down the style towards the ovary
- the pollen grain travels down the pollen tube
- fertilisation occurs when the pollen nucleus and the ovum nucleus fuse together to form a zygote
describe the process of seed and fruit formation in plants
- after fertilisation the ovule develops into a seed
- the parts of the flower surrounding the ovule develop into a fruit, which contains the seeds
- fruits provide a mechanism for seed dispersal
what is the difference between pollination and fertilisation
pollination - pollen landing on the stigma of a flower
fertilisation - fusion of the male and female nuclei
what are the conditions needed for seed germination
- water- swells the seed, breaks the seed coat, and activates enzymes for growth
- oxygen- for aerobic respiration to provide energy
- warmth- for optimum enzyme activity
what is germination
- the beginning of seed growth (the seed contains a zygote that develops into the embryo)
- during germination, the embryo grows into a seedling
what are cotyledons
- surround the embryo, storing food for the seedling during germination
- some plants have one, others have two
- they provide energy until the plant can photosynthesize
what does water absorption to the seed coat in germination
splits the seed coat (testa), allowing the plumule (first emerging shoot) and radicle (first emerging root) to emerge
what are the key components of the male reproductive system
- prostate gland
- sperm duct
- urethra
- testis
- scrotum
- penis
what is the prostate gland
- part of the male reproductive system
- produces fluid called semen that provides sperm cells with nutrients
what is the sperm duct
- part of the male reproductive system
- sperm passes through this to be mixed with fluids produced by the glands before being passed into the urethra for ejaculation
what is the urethra
- part of the male reproductive system
- tube that runs down the centre of the penis that can carry urine or semen- a ring of muscle prevents them from mixing
what is the testis
- part of the male reproductive system
- contained in a bag of skin (scrotum) and produces sperm (male gamete) and testosterone (hormone)
what is the scrotum
- part of the male reproductive system
- sac supporting the testes outside the body to ensure sperm are kept at a temperature slightly lower than body temperature
what are the key components of the female reproductive system
- oviducts
- ovaries
- uterus
- cervix
- vagina
what are the oviducts
- part of the female reproductive system
- connects ovary to the uterus
- lined with ciliated cells to push released ovum
- fertilisation occurs here
what are the ovaries
- part of the female reproductive system
- contains ova (female gametes) that mature and develop when hormones are released
what is the uterus
- part of the female reproductive system
- muscular bag with soft lining where fertilised egg (zygote) implants to develop into foetus
what is the cervix
- part of the female reproductive system
- ring of muscle at the lower end of the uterus to keep the developing foetus in place during pregnancy
what is the vagina
- part of the female reproductive system
- muscular tube leading to inside of woman’s body, where male’s penis enters and sperm are deposited during intercourse
what are secondary sexual characteristics
- the changes that occur during puberty
- development is controlled by release of hormones oestrogen (females) and testosterone (males)
what are the secondary sexual characteristics in females from the effects of oestrogen
- development of breasts
- body hair grows
- menstrual cycle begins
- hips get wider
what are the secondary sexual characteristics in males from the effects of testosterone
- growth of penis and testes
- growth of facial and body hair
- muscles develop
- voice breaks
- testes start to produce sperm
what are some secondary sexual characteristics that occur in both males and females
- growth of sexual organs
- growth of body hair
- emotional changes
what is the nucleus of a cell
contains chromosomes on which genes are located
what does division of a diploid cell by mitosis produce
two cells that contain identical sets of chromosomes
when does mitosis occur
during growth, repair, cloning and asexual reproduction
what is a diploid cell
- cell that contains two complete sets of chromosomes (2n)
- these chromosomes contain the DNA necessary for protein synthesis and cell function
- nearly all cells in the human body are diploid with 23 pairs (46) chromosomes in their nucleus
what is a haploid cell
- cell that contains one complete set of chromosomes (n)
- have half the number of chromosomes compared to diploid cells (23 total in nucleus)
- called gametes
what is mitosis
type of cell division that produces two genetically identical diploid daughter cells
what is meiosis
type of cell division that produces four genetically different haploid sex cells or gametes
what does division of a cell by meiosis produce
four cells, each with half the number of chromosomes, which results in the formation of genetically different haploid gametes
what are the differences between mitosis and meiosis
MITOSIS
- two cells produced (daughter cells)
- daughter cells are diploid
- daughter cells are genetically identical to eachother and the parent cell
- one cell division
MEIOSIS
- four cells produced (daughter cells)
- daughter cells are haploid
- daughter cells are genetically different to eachother and the parent cell
- two cell divisions occur
what does meiosis create
- genetic variation between the gametes produced by an individual
- this means each gamete carries different alleles
what does random fertilisation create
genetic variation of offspring
what are some examples of genetic variation in humans
- blood group
- eye colour
- gender
- ability to roll tongue
- whether ear lobes are free or fixed
what is variation
differences between individuals of the same species
what can variation be caused by
- differences in genes brought about by random fertilisation of gametes
- environmental factors
- combination of both
what are environmental factors that can cause variation
climate, diet, accidents, culture and lifestyle
what is discontinuous variation
- distinct differences for a characteristic - e.g. blood groups, biological sex
- usually caused by genetic variation alone
what is continuous features
- when characteristics can vary over a range of quantitative values - e.g. height in humans, beak length in birds
- varied because of a combination of genetic and environmental causes
