Evolution Of Sex #1 Flashcards
(79 cards)
1
Q
What is a gamete
A
Gametes are the reproductive cells used in sexual reproduction. Ie, the sperm or ovum. They contain a mix of alleles from parents due to independent assortment and recombination
2
Q
Diploid
A
Full set of chromosomes (46) ie, zygote
3
Q
Haploid
A
Half the number of chromosomes (23). Ie, sperm cell or ovum
4
Q
What is a zygote
A
Egg and sperm cell fused
5
Q
What are the two types of sexual reproduction based on the size and form of gametes.
A
Isogamy and anisogamy
6
Q
What is isogamy
A
Gametes are the same (equal partners in fusion)
- Fusion of gametes that are similar in size, shape and structure
- both gametes look similar and often motile
- no distinct male or female
Ie, algae, fungi and Protozoa
7
Q
What is anisogamy
A
Gametes are different one is small and mobile- sperm; one is large and nutrient rich- egg
- fusion of gametes that are different in size or form
- large non-motile egg/small motile sperm
- sexes are different
Ie, humans animals and most plants
8
Q
What are the 6 types of asexual reproduction and an example with each
A
- binary fission- bacteria, protists and some unicellular fungi
- budding- bakers yeast, hydra, anemone
- vegetative reproduction- plants
- spores- some fungi and algae
- fragmentation- lichens, annelids, sea stars and plants
- parthenogenesis- rotifers, insects, reptiles and amphibians
9
Q
What is binary fission
A
Single organism duplicates its DNA and divides into two identical daughter cells
10
Q
Explain the steps of binary fission
A
- DNA replication- single circular chromosome is copied
- Cell growth- the cell enlarges to prepare for division
- Chromosome segregation- DNA copies move to the opposite ends of the cell
- Cytokinesis- the cell membrane pinches in, dividing the cytoplasm
- Two identical cells- each daughter cell receives a complete copy of DNA
11
Q
What is Budding and key features
A
New organisms grow from small projections called buds on the surface of parents. The new organisms may remain attached or detach once mature
12
Q
Explain the steps of budding
A
- Cell or organism develops a small bud
- The bud grows while attached to the parent
- Nucleus divides (in unicellular organisms)
- Bud may separate or remain as a colony
13
Q
What is meiosis
A
- purpose= Sexual reproduction (gamete formation)
- 2 cell divisions
- 4 genetically different daughter cells
- haploid
- produces genetic variation
- occurs in germ cells (testes/ovaries)
14
Q
What is mitosis
A
- purpose= growth, repair, and sexual reproduction
- 1 number of divisions
- 2 identical daughter cells
- diploid
- no genetic variation
- occurs in somatic body cells
15
Q
Is asexual/sexual reproduction mitosis or meiosis
A
Mitosis= asexual reproduction
Meiosis= sexual reproduction
16
Q
What is sexual and asexual reproduction
A
sexual reproduction- the processess where two parent organisms produce offspring through the fusion of gametes (sperm and egg). ie, humans, animals, flowering plants and fungi
Asexual reproduction- the processess where a single parent produces offspring without gametes. Offspring are genetically identical to parent (clones). Ie, bacteria, yeast, planaria, mosses and ferns
17
Q
What is vegetative reproduction
A
Plants grow from parts like roots, stems or leaves of the parent plant without seeds or spores
18
Q
How is vegetative reproduction carried out
A
Either through natural or artificial methods
19
Q
What are the natural methods of vegetative reproduction
A
Runners (strawberry, grass)- horizontal stems grow above the ground and form new plants
Rhizomes (Ginger, bamboo)- underground stems that sprout new shoots
Tubers (potato’s)- swollen underground stems with buds (“eyes”)
Bulbs (onion, tulip)- underground storage leaves that grow into new plants
Corms (crocus, Gladiolus)- underground stem base that produces shoots
20
Q
What are spores
A
A tiny single celled reproductive structure that develops into a new organism without fertilization. They are most commonly found in fungi, mosses, ferns and some bacteria
21
Q
How are spores distributed
A
- lightweight and often dispersed by wind, water or animals
- Can survive harsh conditions due to protective outer walls
22
Q
What is the life cycle of spore producing organisms
A
- Sporophyte produces spores via meiosis
- Spores are released and grow into a gametophyte
- Gametophyte produces gametes—> fertilization —> new sporophyte
23
Q
Where are spores located in fungi, plants and bacteria
A
Fungi- sporangia (spore cases)
Plants- underside of leaves or capsules
Bacteria- endospores (survival structures)
24
Q
What is fragmentation
A
Where an organisms breaks into two or more fragments and each fragment grows into a new complete organism. Fragments must contain essential cells/ tissues to regenerate. It’s a form of regeneration. Ie, worms
25
What’s are the steps of fragmentation
1. Organism splits due to injury, natural causes or self division
2. Each fragment survives and begins to regenerate
3. Fragments grow into genetically identical individuals
26
What is parthenogenesis with example in nature
Egg develops into a new organism without being fertilized by a sperm. No male involvement and can be induced naturally or artificially.
Ie,
Fertilized eggs—> females (workers/queens)
Unfertilized eggs (parthenogenesis) —>males (drones)
27
What are the types of parthenogenesis
Obligate- species produce only by parthenogenesis= all individuals are females
Facultative- can produce with or without fertilization= offspring can arise either way
Haploid- offspring develop from unfertilized haploid eggs= often in male bees
Diploid- egg undergoes DNA duplication diploid offspring= females clones
28
Why is sex costly in comparison to asexual reproduction
- needs two separate sexes
- need time to find partners (or gamete)
- mating competition
- courtship (persuade into mating)
- need to produce gametes, most are wasted
- risk of disease
- own alleles are diluted 50% with those of partner
29
What is an allele
Different version of a gene found at the same place (locus) on a chromosome. They control the same trait but may cause different expressions of that trait.
Gene that controls eye colour. One allele might code for brown eyes and another allele might code for blue eyes
30
What is heterozygous and homozygous
Heterozygous- two different alleles (brown + blue)
Homozygous- two of the same alleles (blue + blue)
31
What is dominant and recessive
Dominant- expressed even if only one copy is present (eg, brown eyes)
Recessive- only expressed if two copies are present (eg, blue eyes)
32
What is the two fold cost of sex concept
- in sexual reproduction, only females produce offspring
- in asexual reproduction, every individual can reproduce
This means in asexual population can grow twice as fast because all individuals can reproduce, whereas in sexual population, only half (the females) contribute to population growth
33
What are the two main ‘costs’ of sexual reproduction
1. Cost of males
- males typically don’t directly produce offspring
- a sexual female passes on only 50% of her genes (shared with a man)
- in asexual reproduction, a female passes on 100% of her genes
2. Cost of recombination
- sex shuffles genes each generation, which might break up advantageous gene combinations
- asexual reproduction preserves successful gene combinations
34
Why does sex persist in the wild
- creates genetic variation
- Helps eliminate harmful mutations
- provides defence against parasites and diseases
35
How long has sex been around for and does it outcompete asexual reproduction?
It’s been around for about 1.2 billion years
- most life forms are sexual
- sex works show that sexual lineages outcompete asexual lineages in the long term
36
What are mealy bugs and where are they found
Small, sap sucking insects often considered pests. Found on Okinawa and Ishigaki islands in Japana
37
How are mealybugs related to how sex exists
- On Ishigaki island- mealybugs reproduce asexually (parthenogenesis)
- On Okinawa island- related mealybugs produce sexually (with males and females)
This allows scientists to compare advantages and disadvantages of sexual and asexual reproduction in similar environments
38
What are the differences in mealybugs reproduction on the different islands
Asexual mealybugs (Ishigaki)
- faster reproduction rate (no males)
- low genetic diversity
- lower adaptability (clones vulnerable to change)
- mutations accumulate
Sexual mealybugs (Okinawa)
- slower reproduction rate (only females reproduce)
- high genetic diversity
- higher adaptability (varied offspring better in changing environments)
- harmful mutations can be purged
39
What are the advantages of sex
1. leads to unique combinations of alleles
- alleles segregate independently into gametes (it only puts one allele from each gene into each gamete)
- fertilization combines alleles from different lineages
- crossing over shuffles alleles between chromosomes
2. Generates genetically diverse offspring
3. Eliminates costly mutations quickly
40
What is the difference between chromosomes, DNA, histones, genes and alleles. Also provide an example
Example:
- DNA is the material that holds all instructions
- A gene on chromosome 15 controls eye colour
- The allele you inherit from each parent (eg, brown or blue) determines what your eye colour will be
- the chromosome contains DNA which is made of segments of genes
Chromosomes- a long strand of DNA wrapped around proteins, containing many genes. Humans have 46 chromosomes (23 pairs)
DNA- the molecule that carries all genetic instructions. Its like the language of life
Histone- DNA wraps around histone proteins which form a structure called a nucleosome. These nucleosome are organized into structures called chromatin.
Gene- a segment of DNA that codes for a specific trait of protein
Allele- a variation of version of a gene. You have 2 alleles for each gene- one from each parent
41
What is Mullers ratchet
It describes how asexual populations (which reproduce by cloning) cant easily eliminate harmful mutations. Over time bad mutations build up and the overall fitness of the population declines
42
Why do mutations accumulate in asexual reproduction
- because offspring are genetically identical to parent
- there is no recombination to shuffle or eliminate mutations
- if the best individuals with the fewest mutations die by chance the population takes a permanent step down in fitness
43
Why does sex allow alleles to combine
1. Meiosis- creates gametes (sperm/egg) with shuffle genes
2. Fertilization- combines genes from two different individuals
These processes mix alleles from both parents, allowing beneficial alleles from different individuals to come together in a single offspring
Ie,
Individual A- beneficial allele for disease resistance
Individual B- beneficial allele for heat tolerance
Through asexual reproduction those traits stay separate. However in sexual reproduction the offspring inherit both alleles and overtime many individuals with multiple good traits can be produced or selected for
44
Asexual VS sexual reproduction
Asexual:
- requires less energy
- No costly non reproducing sex
- quicker
- offspring are clones of the parent
Sexual reproduction:
- requires more time and energy
- two fold cost of producing males
- offspring are genetically diverse
- mutations are more easily purged
- beneficial mutations can combine easily
45
What is sexual dimorphism
Refers to the physical differences between male and females of the same species beyond just the reproductive organs
46
Provide some examples of sexual dimorphism
- diamondback terrapin- females are much larger due to reproductive demands while males are smaller and more agile equipped for mating. Females= much larger, heavier and bulkier bodies, larger head and stronger jaws to help crush larger prey
- azorean bullfinch- show very little to no visible sexual dimorphism which is unusual for birds. Likely share parental duties, monogamous and show no strong sexual selection pressure for bright plumage or size difference
- pheasant- males evolve to impress and females to survive. Males= brighter colour plumage, longer/showy tails, red facial wattle markings, larger body size, more aggressive and territorial
- gorilla- males must fight competition and protect groups and females must prioritize reproduction and care. males= much larger, develop silverback (patch of grey on back to show maturity), larger chests and canines, display dominant and protective behaviour
- golden silk spider- females larger for reproduction and bigger webs and males smaller for stealth and speed. Females= very large bodies, striking gold colour, build large webs and have dominant behaviour in mating and web territory
47
What does monogamous mean
Only one mate at a time- either for a single breeding season or for life
48
What does strong sexual selection pressure mean
Intense evolutionary forces (bigger antlers, bright plumage and dancing, loud calls and displays) that shape traits in organisms based on their ability to attract mates or outcompete rivals for reproduction. Often leading to dramatic physical or behavioural differences
49
Natural selection and survival of the fittest
Natural selection- mechanism of evolution where individuals with traits better suited to their environment survive and reproduce more, passing on those traits (the process)
Survival of the fittest- individuals most “fit” for their environment are more likely to survive and reproduce (summarizes the results of natural selection)
50
What is the sex determination system
Sex determination system- how organisms sex is set, either by chromosomes, environment or reproductive method and varies widely across species
51
What are the man types of sex determination systems
Haplo-diploid- (bees, ants and wasps)
Males- haploid (unfertilized)
Females- diploid (fertilized)
Environmental- (turtles, crocodiles and clownfish)
Sex determined by temperature, location or social factors
Ie, spotted turtle (temperature dependent= egg temp 23-27 c mostly male. 30 c female —> hormone mediated)
XY- (humans, mammals and drosophila)
Males- XY
Females- XX
ZW- (birds, butterflies and snakes) ie, spotfin hatchetfish
Males- ZZ
Females- ZW
XO- (grasshoppers, some insects)
Males- XO
Females- XX
52
What does GSD and ESD stand for
GSD- genetic sex determination. Chromosomes or specific genes (humans, birds, insects)
ESD- environmental sex determination. Temperature or external cues (turtles, crocodiles and clownfish)
53
Give an example of a reproductive parasite
Wolbachia
54
What is wolbachia
type of bacteria that infects many arthropods (insects, spiders and crustaceans) and some nematodes (roundworms). One of most common reproductive parasites
- lives inside cells, especially reproductive tissue (is an endosymbionts)
- passed from mother to offspring through eggs (maternally inherited- transmission via host egg but not sperm)
- doesn’t infect humans, but manipulates reproduction in its host
55
What are intracellular parasites and endosymbionts
Intracellular parasites- lives inside host cells and harm the host to survive and reproduce.
(Can be virus, bacteria or Protozoa).
Ie, Plasmodium- causes malaria. HIV- infects T cells. Chlamydia- intracellular bacterium (STD).
Endosymbionts- live inside the host cells in a Mutualistic (or sometimes neutral) relationship
(Can be bacteria or algae in symbiosis with animals and plants)
Ie, mitochondria- once free living, now part of cells. Wolbachia- insects= reproductive manipulation. Zooxanthellae- corals= photosynthesis and energy
56
What is the effect (positive?) of wolbachia in arthropods
Cytoplasmic incompatibility- males cannot produce viable offspring with uninfected females. But infected females can mate with anyone
Viral resistance- wolbachia protects against disease
Increased egg production or longevity- infected females may be able to lay more eggs or live longer, further aiding in bacterial spread
Nutritional support- supply essential nutrients when the hosts diet is poor. Especially helpful in blood feeding insects with nutrients limited diets
Parthenogenesis induction- in some species wolbachia causes females to produce without males. Offspring are all female clones
Male killing- wolbachia kills male embryos early in development. Reducing competition for resources among surviving female siblings
Feminization- infected genetic males develop as functional females increasing the number of wolbachia transmitting individuals
57
What type of asexual reproduction is wolbachia
Trick question. It is not a type of asexual reproduction but instead a bacterium that can take on the form of types of asexual reproduction (parthenogenesis)
Ie, certain insects like wasps that have wolbachia can cause females to produce offspring without mating. All offspring are females.
58
What is feminization
The process where a genetic male develops female characteristics or becomes functionally female, either naturally, hormonally or due to infection (ie, wolbachia)
59
Give an example of infection induced sex determination
Armadillidium vulgare infected by wolbachia
60
Explain the infection induced sex determination between wolbachia and its host Armadillium vulgare
Normal sex determination of A. Vulgare (isopod crustacean with an androgenic gland)
- males (ZZ)
- females (ZW)
However when infected with wolbachia the genetic males (ZZ) can be feminized and develop as functional females.
61
How is Armadillium vulgare counteracting the feminization and what is it an example of
They have evolved genetic suppressors on the W chromosome and even on autosomes to counteract wolbachia’s feminizing effect.
Example of host parasite genetic arms race
62
Is wolbachia an endosymbionts or intracellular parasite
Endosymbionts
63
How can wolbachia feminize Armadillium vulgare
because:
- interferes with male development during embryogenesis
- blocks the expression of male specific genes, causing the host to follow the female developmental pathways
- degradation of androgenic gland
- populations become more female skewed and shifts the evolutionary pathway
64
What are hermaphrodites
Are organisms that have both male and female reproductive organs and can often perform both sexual roles- producing sperm and eggs
65
What are two examples of hermaphrodites
Clownfish (sequential)= all born male. Dominant individuals become female. Become one or the other at some point
Garden snail- (simultaneous)= have both male and female sex organs. Meaning it can function as both genders, engaging in complex mating behaviours to maximize reproductive success
66
What does sequential and simultaneous mean in terms of hermaphroditism
Simultaneous- all organisms have both male and female reproductive organs at the same time
Sequential- all organisms start life as one sex then changes to the other at some point
67
Explain the structure of ovum and sperm
Sperm:
- acrosome reaction
- acrosomal granule
- actin
- nucleus
- mitochondrial matrix
Ovum:
- egg cytoplasm
- cortical granule
- egg plasma
- perivitelline space
- cortical granule content
- fused plasma membrane
- Vitelline layer
- protein receptors
- jelly coat
68
Who is nuclear DNA and mitochondrial DNA inherited from
Nuclear DNA- is inherited from all ancestors (bi-parental- Mendelian inheritance)
Mitochondrial DNA- is inherited from a single lineage (uniparental- Non Mendelian inheritance)
69
What is mitochondrial DNA
Small circular DNA found inside the mitochondria and is essential for cellular energy production. Inherited from your mother (non Mendelian)
70
What is nuclear DNA
Found in the nucleus of eukaryotic cells and carries a vast majority of an organisms genetic information and is inherited from both parents (Mendelian inheritance)
71
Difference between sperm and ovum mitochondrial sizes
Ovum= 10^5 mitochondria (or order of magnitude more)
Sperm= <100 mitochondria
72
Why uni-parental inheritance over bi-parental inheritance
Biparental inheritance leads to
- cytoplasmic mixing (heteroplasmy)
- competition between mitochondria that are genetically different
- smaller genome gives more rapid replication and therefore competes more effectively
- but smaller genome may compromise ATP generation for the cell
73
Heteroplasmy
Cytoplasmic mixing- Condition in which a single cell or organism contains more than one type of mitochondrial DNA. Meaning there is a mix of normal and mutate mtDNA within the same cell
74
What is a genome
Genome is the complete set of genetic material in an organism. It includes all of the DNA, including:
- genes
- non coding DNA
- mitochondrial or chloroplast DNA
75
What is selective silencing
Processe where specific genes are turned off (silenced) while others remain active. This allows cells (or organisms) to control gene expression in a targeted way.
Ie,
- silencing foreign DNA
- turning off genes in unfavourable conditions
- regulating development of sexual reproduction
76
How does selective silencing relate to sex and reproduction
Controls which genes are turned off during gamete formation, fertilization or zygote development. Influencing who passes on traits, how sex is defined and which genes get expressed
77
Selective silencing and chlamydomonas Reinhardtii
Chlamydomonas reinhardtii:
- unicellular green algae
- Reproduces sexually and asexually
- has isogamous gametes
- reseatchers have discovered selective silencing in the context of sexual reproduction
1. During zygote formation- paternal chloroplasts genes are often selectively silenced or degraded so only the maternal chloroplasts DNA is inherited
2. This is an example of uniparental inheritance and may involve selective gene silencing mechanisms
78
What are the known mechanisms of sex determination
- environmental factors
- chromosome differences
- autosomal differences
79
Why is it thought that mtDNA isnt inherited biparentally
Because competition between different mtDNA haplotypes would lead to cell malfunction
