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Flashcards · 4BI1 · Topic 3
Reproduction and inheritance flashcards
24 cards on Topic 3, subtopics a to b. Pick a subtopic or study them all.
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a Reproduction
- Sexual vs asexual reproduction
- Sexual: usually two parents, gametes fuse at fertilisation, offspring genetically different. Asexual: one parent, no gametes, mitosis, offspring genetically identical (clones).
- Fertilisation and zygote
- Fertilisation: the fusion of the nuclei of a male and a female gamete. The zygote is the single cell formed; it divides by mitosis to form an embryo.
- Pollination
- The transfer of pollen from an anther to a stigma.
- Insect-pollinated vs wind-pollinated flowers
- Insect: large, bright, scented petals; nectar; anthers and sticky stigma inside the flower; larger, sticky or spiky pollen. Wind: small or no petals; anthers outside on long filaments; large feathery stigma outside; lots of small, light, smooth pollen.
- After pollination: how is a seed formed, and what do the ovule and ovary become?
- A pollen tube grows down the style into the ovule; the male nucleus fuses with the female nucleus, forming a zygote, then an embryo. The ovule becomes the seed; the ovary becomes the fruit.
- Conditions needed for germination, and why
- Water: activates enzymes, the seed swells and the coat splits. Oxygen: for aerobic respiration to release energy. A suitable temperature: enzymes work at a useful rate. Light is not usually needed.
- Why does the dry mass of a germinating seed fall, then rise?
- It falls because stored food is broken down and respired, and there are no leaves yet to photosynthesise. It rises once the leaves photosynthesise faster than the seedling respires.
- Runners vs cuttings
- Runners (natural, e.g. strawberry): side stems along the soil grow roots and form new plants. Cuttings (artificial): cut below a node, remove lower leaves to reduce transpiration, use rooting powder. Both give clones of the parent.
- Functions of the oviduct, uterus and cervix
- Oviduct: cilia move the egg; site of fertilisation. Uterus: lining for implantation; muscular wall for birth. Cervix: ring of muscle that keeps the fetus in and widens at birth.
- Oestrogen vs progesterone in the menstrual cycle
- Both made in the ovary. Oestrogen repairs and thickens the uterus lining (about days 5–14). Progesterone (from the corpus luteum) maintains the lining (days 14–28); when it falls, menstruation follows.
- FSH and LH: where made and what they do
- Both from the pituitary gland. FSH makes an egg mature in a follicle and stimulates oestrogen production. An LH surge triggers ovulation (about day 14). Oestrogen inhibits FSH and stimulates LH; progesterone inhibits both. (Paper 2 only)
- What crosses the placenta, and what does amniotic fluid do?
- Mother → embryo: glucose, amino acids, fatty acids, minerals, vitamins, water, oxygen. Embryo → mother: carbon dioxide, urea. The bloods do not mix. Amniotic fluid cushions and supports the embryo against knocks.
b Inheritance
- Genome, gene and chromosome
- Genome: the entire DNA of an organism. Gene: a section of a DNA molecule that codes for a specific protein. Chromosome: a structure in the nucleus on which genes are located.
- Gene vs allele
- A gene codes for a protein; an allele is one version (an alternative form) of that gene.
- Genotype vs phenotype
- Genotype: the alleles an organism has (e.g. Hh). Phenotype: the characteristic shown (e.g. tall).
- Dominant, recessive, homozygous, heterozygous
- Dominant: expressed even with one copy. Recessive: expressed only with two copies (no dominant allele). Homozygous: two identical alleles (HH or hh). Heterozygous: two different alleles (Hh).
- DNA vs RNA
- DNA: two strands coiled into a double helix; bases A, T, C, G (A–T, C–G). RNA: one strand; bases A, U, C, G (U replaces T). (Paper 2 only)
- Protein synthesis: transcription and translation
- Transcription (nucleus): a complementary mRNA strand is made on one DNA strand. mRNA goes to a ribosome. Translation: the ribosome reads codons (three bases each); tRNA anticodons pair with them, bringing amino acids that are joined in order. (Paper 2 only)
- Codominance, and the ratio from two heterozygotes
- Both alleles in a heterozygote are expressed in the phenotype. A cross of two heterozygotes gives a 1 : 2 : 1 phenotype ratio. (Paper 2 only)
- Hh × Hh: offspring ratio, and probability of a recessive offspring
- Genotypes 1 HH : 2 Hh : 1 hh, so 3 dominant : 1 recessive (a ratio). Probability of a recessive offspring = 1/4 (0.25, 25%). Each fertilisation is independent.
- How can you find whether a dominant-phenotype organism is HH or Hh?
- Cross it with a homozygous recessive (hh). Any recessive offspring shows it is Hh. All dominant offspring in a large sample suggests HH.
- How is sex determined in humans?
- Females XX, males XY. All eggs carry X; half the sperm carry X and half Y, so the sperm decides the sex. Probability of a boy (or a girl) = 1/2 at every fertilisation.
- Mitosis vs meiosis
- Mitosis: 2 genetically identical diploid cells; for growth, repair, cloning and asexual reproduction. Meiosis: 4 genetically different haploid cells; makes gametes. Humans: diploid 46, haploid 23.
- Natural selection: the sequence of steps
- Variation (from mutation) → competition → the better-adapted survive → they reproduce → their alleles are passed on → the allele frequency increases over many generations. Example: antibiotic-resistant bacteria.