Mod 5 Heredity Flashcards
What are the advantages and disadvantages of external fertilisation in animals?
Advantages
* produces a larger number of offsprings
* The gametes released can drift - easy to find mates
* higher genetic diversity due to a larger mixing of genes within a group
Disadvantanges
* success rate very low
* large quantity of gametes is wasted and left unfertilized
* Chances of fertilization are diminished by environmental hazards and predators
* dessication of zygote or gametes
What are the advantages and disadvantages of internal fertilisation in animals?
Advantages
* Fertilized egg is protected from predators and harsh environments
* higher probability of fertilisation
* paternal care increases chance of survival for embryo
Disadvantanges
* less offspring produced
* takes up lots of energy and time from female before birth and parents after birth
How do plants reproduce asexually?
Vegetative propapagtion or self-fertilisation
Describe vegetative propagation
- Runners e.g. strawberries - stems grow along surface & give rise to new plants
- Rhizomes e.g. ginger - stems grow underground & give rise to leaves and roots
- Suckers e.g. mint, banana plant - roots that can give rise to a new plant
- Tubers e.g. potatoes - swollen roots store nutrients & can grow a new plant
- Bulb e.g. tulips - short swollen underground stems store nutrients & can grow new bulbs
Describe fertilisation in plants
- Pollination - transfer of pollen from anther to stigma
- One sperm cell in pollen grain creates pollen tube from stigma to ovary
- The two sperm cells travel down the pollen tube into an ovule
- Double fertilisation - One sperm cell fertilises the egg. The other sperm cell combines with two polar nuclei to form endosperm that provides nourishment for the zygote
- The ovule matures into a seed containing the fertilised egg (diploid) and endosperm
- The zygote develops into an embryo, which will grow into a new plant by mitosis after the seed germinates
How do plants sexually reproduce?
Pollination & Fertilisation
How do fungi reproduce asexually?
Budding or spores
How do fungi reproduce sexually?
Producing spores by meiosis, they temporarily fuse to another fungi to create a diploid structure
Describe the process of budding
- one organism splits into two or more smaller organisms
- e.g. yeast (unicellular fungus) or hydra (symbiotic animal & algae)
- Bud begins to form on the side of the cell
- Nuclear division (mitosis) provides each cell with a genetically identical nucleus
- when bud is nearly as large as parent, cytokinesis occurs
- the daughter cell is smaller than the parent cell
Describe asexual reproduction by spores
- haploid spores are produced by mitosis
- spore lands on substrate and germinates
- mycellium developed by mitosis
Describe sexual reproduction by spores
- rare fusion of mycellium
- two fungi temporarily fuse to create a diploid structure (zygote)
- this structure produces haploid spores by meiosis
Describe the process of binary fission in bacteria
- DNA replicates - NO MITOSIS
- one copy moves to opposite end of cell
- cell elongates
- cleavage furrow begins to form
- cytokinesis occurs
- two new cells are idential in genetic material and size
Describe the process of binary fission in protists
- Mitosis occurs
- Cytokinesis occurs
How can protists reproduce?
binary fission and budding (asexual)
they can also reproduce sexually but we didn’t learn about that
What are advantages and disadvantages of asexual reproduction?
Advantages:
* no male needed - saves energy in searching & courtship
* rapid reproductive cycle - large numbers of offspring are reproduced very quickly (when conditions are favourable)
Disadvantages:
* little to no genetic variation - genetic clones
* disease/unfavourable conditions could affect whole population
* some methods produce offspring close together - competition for food & space
* species may only be suitable for one habitat
What are advantages and disadvantages of sexual reproduction?
Advantages:
* increased genetic diversity
* species can adapt to new environment due to variation - giving them a survival advantage
* a disease is less likely to affect whole population
Disadvantages:
* courtship is costly - time and energy needed to find a mate
* not possible for isolated individual to mate
Compare internal and external fertilisation
Similarities:
* involve fusion of haploid gametes - ovum and sperm
* sperm is motile
* produce lots of sperm
* sexual reproduction
* produce a diploid zygote
Differences:
* Internal - few eggs produced, external - thousands of eggs produced
* internal - energy used in maternal care, external - energy used in producing eggs
* internal - usually maternal care, external - usually no maternal/paternal care
What does HCG do?
keeps the corpus luetum alive
What does progesterone do?
maintains thickness of uterine lining - vascularisation
What does oestrogen do?
helps uterus grow, thickens uterine lining, helps foetus develop
What does relaxin do?
inhibits uterus contraction to prevent premature birth
What does prolactin do?
enlarges mammary glands to produce breast milk
What does oxytocin do?
- stimulates contractions of uterine muscle & lactation
- promotes future interaction between mother and child, decreases fear and stress levels
- helps mother to bond with baby after birth - reinforced by skin-to-skin contact
- creates positive feedback loop during contractions
What is a hormone?
chemical messenger (protein) released by glands that travels via blood to target organs
What is a positive feedback loop?
stimulatory effect
What is a negative feedback loop?
inhibitory effect
What does GnRH do?
triggers pituitary to release FSH and LH
What does FSH do?
- stimulates follicle growth
- stimulates oestrogen secretion from developing follicles
What does LH do?
- surge causes ovulation
- results in formation of corpus luteum
What protein structure has ɑ-helixes or β-pleated sheets?
secondary
What protein structure has ɑ-helixes and β-pleated sheets?
tertiary
Describe the stages of meiosis
Diploid cell:
1. Interphase - cell grows, DNA replicates, cell grows again
2. Prophase I - crossing over, chromosomes find homologous pairs, centrosomes move to opposite ends of cell and spindles begin to form, nucleus breaks down
3. Metaphase I - nucleus disappears, chromosomes line up in homologus pairs along middle of cell, spindle fibres help with this
4. Anaphase I - spindle fibres pull homologous pairs apart
5. Telophase I - cleavage furrow, nuclear membrane re-forms
6. Cytokinesis I - cell membrane divides and reforms
7. Prophase II - no crossing over, centrosomes replicate, centrosomes move to opposite ends of cell, nucleus breaks down
8. Metaphase II - chromosomes line up along middle of cell, no homologous pairs, nucleus disappears
9. Anaphase II - sister chromatids pulled apart by spindle fibres
10. Telophase II - cleavage furrow, nucleus re-forms
Haploid:
11. Cytokinesis II - cell membrane divides and reforms to form 4 haploid gametes
Describe mitosis
- Interphase - cell grows, DNA replicates, cell grows again
- Prophase - centrosomes move to opposite ends of cell and spindles begin to form, nucleus breaks down
- Metaphase - nucleus disappears, chromosomes line up in single file along middle of cell, spindle fibres help with this
- Anaphase - spindle fibres pull sister chromatids apart
- Telophase - cleavage furrow, nuclear membrane re-forms
- Cytokinesis - cell membrane divides and reforms, 2 diploid cells
Describe DNA Replication
Initiation
* DS DNA unwinds
* Helicase ‘unzips’ DS DNA by breaking hydrogen bonds between BPs
* creates a replication fork as each strand acts as a template for replication
Elongation
* DNA Polymerase adds free floating nucleotides by complementary base pairing
* Lagging strand is synthesised in opposite direction to the action of Helicase
* Leading strand is synthesised in the same direction to the action of Helicase - continuous synthesis
* BOTH STRANDS HAVE A LEADING AND LAGGING STRAND
* All strands synthesised 5’-3’
* Ligase joins adjacent Okazaki fragments (by recreating phosphodiester bonds)
Termination
* Semi-conservative replication has occured (half parental strand half newly synthesised)
SS = Single stranded
BP = base pair
DS = Double stranded
Compare the DNA in Eukaryotes and Prokaryotes
Similarities:
* Double helical structure
* A, C, T, G
* A-T, C-G
* Code for proteins
* Have extranuclear DNA
Differences:
* Prokaryote - circular, Eukaryote - Linear
* Prokaryote - no histone, Eukaryote - folded around histone
* Prokaryote - smaller genome, Eukaryote - Larger genome
* Prokaryote - less folded, Eukaryote - highly folded
* Prokaryote - nucleoid region, Eukaryote - nuclear membrane
* Prokaryote - RNA has only exons, Eukarytoe - RNA has introns and exons
* Prokaryote - Extranuclear DNA in plasmids, Eukaruote - extranuclear DNA in mitochondria
* Prokaryote - transcription & translation happen simultaneously, Eukaryote - transcription & translation happen separately
What is a purine base?
- Adenine and Guanine
- double ring
What is a pyrimidine base?
- Cytosine and Thymine
- Single ring
Describe the process of transcription
- DS DNA unwinds
- Helicase ‘unzips’ DS DNA by breaking hydrogen bonds between BPs
- creates a replication fork
- one strand is used as template for RNA
- RNA polymerase adds free floating nucleotides to template (A, C, U, G) by complementary base pairing
- synthesised 5’-3’
- Introns are spliced
- mature mRNA exits nucleus and enters cytoplasm (ribosome)
Describe the process of translation
- mature mRNA enters ribosome
- ribosome reads mRNA in triplet codons
- tRNA bonds to codon by complementary base pairing of anticodon site
- tRNA places amino acid in polypeptide chain
- tRNA detaches
What protein structure contains a chain of amino acids?
primary
What protein structure contains multiple folded polypeptide chains?
quaternary
What are the types of RNA in eukaryotic cells?
RNA
* SS molecule of nucleotides
* ribose sugar
* A, C, U, G
mRNA
* messenger RNA
* SS complementary to DNA sequence of template strand
* each triplet codon codes for specific amino acid
* transfers genetic code from nucleus to ribosome in cytoplasm
tRNA
* transfer RNA
* clover-lead shaped, short segment of RNA
* carries a specific amino acid on one end, determined by the anticodon at the other
rRNA
* ribosomal RNA
* forms ribosome subunits
What is incomplete dominance?
- dominant allele is not completely dominant over recessive allele
- blend of recessive and dominant allele
- e.g. pink flower colour coming from red and white flower
What is co-dominance?
- both alleles are expressed separately
- e.g. roan cows - brown and white spots on coat
How does X-linked recessive inheritance work?
- if X chromosmoe has a recessive gene, the male will be affected as there is no corresponding dominant gene to cancel it out
- these recessive traits disproportionately affect males
- passed from female → male → female
- male cannot pass to male as they would only pass on their Y chromosome (does not have allele)
What does sex-linkage refer to?
- traits carried on sex chromosomes (X or Y)
- Hemizygous chromosomes - there is no corresponding locus on Y chromosome for traits on X chromosome
How can a pedigree indicate autosomal inheritance?
- Can be passed from only male parent → male or only female parent → female
- If dominant X-linked, two unaffected parents cannot have an affected child & two affected parents can only have unaffected son
- If recessive X-linked, two unaffected parents can only have an affected son & two affected parents cannot have an unaffected child
How can a pedigree indicate a dominant allele?
- two affected recessive parents cannot have an unaffected offspring - must be dominant AND heterozygous parents
- 100% incidence of affected daughters from father suggests X-linked dominance - dominant affected father & recessive unaffected mother will produce all affected daughters and no affected sons (daughters must inherit dominant X from father and will be affected)
How can a pedigree chart indicate a recessive allele?
- if dominant, two unaffected parents cannot have an affected offspring - must be recessive autosomal, parents must be heterozygous
- 100% incidence of affected sons from an affected mother suggests X-linked recessive - dominant unaffected father & recessive affected mother will produce all unaffected daughters and all affected sons (sons will not get dominance from father as they have to get the Y)
How can a pedigree chart indicate an X-linked allele?
male → female → male → female pattern suggests X-linked but cannot be confirmed
