Mod 5 Heredity Flashcards
What is sexual reproduction?
Fusion of two gametes to form a zygote
What are the advantages of sexual reproduction?
- Fertilisation is less risky and young are more likely to survive
- Unfavourable genetic variations can be eliminated from the population
- Creates genetic variation which can increase adaptations
- Populations are better suited to adapting to environmental changes
- Improves long term evolutionary potential of populations
What are the disadvantages of sexual reproduction?
- Requires more energy
- Makes organisms more vulnerable to predators
- Fewer offpsring produced
- Slower reproductive rate - fewer organisms are produced over a longer period of time
- Potential for sexually transmitted diseases throughout the population
Describe the process of fertilisation
The meeting of two gametes
Each species has a certain number of chromosomes arranged in homologous pairs within their body (humans have 46 & 23 pairs)
Diploid is when cells have 46 chromomes and is used to describe somatic cells
Haploid is when they only have 23 chromosomes and are used for gametes
When two gametes meet, the zygote becomes diploid
What are hormones?
Chemical substances that act as messengers within the body, co-ordinating functions
What are sex hormones?
Hormones that affect the growth or functioning of reproductive organs or the development of secondary sex characteristics
What is the role of the pituitary gland?
Secrete stimulate or inhibit other endocrine glands, regulating the release of their hormones for growth, metabolism and reproduction
Growth, metabolism and reproduction
What is the main hormone in Spermatogenesis?
And additional hormones?
Testosterone but LH, FSH and oestrogen are also present in low amounts
What is spermatogenesis?
Developement of sperm cells within the male reproductive system
What parts of the body does spermatogenesis involve?
Hypthalamus, Leydig Cells and Sertoli Cells in the testes & Pituitary Gland
What is the role of the Hypothalamus in Spermatogenesis?
Produces GnRH which initiates pituitary gland to produce LH and FSH which stimulates Sertoli Cells to facilitate sperm production
GnRH -> Pituitary -> LH & FSH -> Sertoli Cells -> Sperm
What is the role of Sertoli Cells in Spermatogenesis?
Facilitates sperm production and produces inhibin once the sperm count has been reached
What is the role of Inhibin in Spermatogenesis?
Protein secreted by Sertoli Cells to the Pituitary Gland to decrease the production of FSH only
What is the role of Leydig Cells in Spermatogenesis?
Decrease the levels of testosterone which helps the pituitary gland stop producing LH and FSH
Explain the structure of sperm
Consists of head, neck, tail and middle piece & acrosome
Explain the role of the acrosome in reproduction
Acrosome contains digestive enzymes that break down the zona pellucida and assist in sperm penetration
plain
What is the role of the middle piece of the sperm?
Contains mitochondria which helps with movement
Explain the follicular phase
Day 1-14
- FH starts maturation of follicle
- Cells lining follicle secrete oestrogen which promotes production of LH
- Oestrogen peaks at Day 12 which causes peak in LH which triggers ovulation
What is the role of the fimbriae?
Small finger like projections on the outside of the ovaries that assist in moving the ovum to the fallopian tubes
Explain the luteal phase
Day 15-28
- LH causes corpus lutem (burst follicle) to build up lutein which turns it yellow
- Corpus luteum secretes progesterone which thickens endometrium for ovum to attach to
- Corpus luteum breaks down once placenta has formed or fertilisation does not occur
How does the corpus luteum know if fertilisation has occured?
Upon fertilisation, the hormone called HcG is released which signals that fertilisation has been successful and the corpus luteum produces progesterone for three months until the placenta takes over
What happens to the corpus luteum if implantation does not occur?
The corpus luteum degrades once the chemical trigger from the HCG is absent. The corpus luteum decreases the production of progesterone. The decrease in progesterone signals to the reproductive system that implantation was not successful and endometrial lining and egg sheds
What is the role of progesterone?
Thickens the endometrium and stimulates glands in the endometrium to release nutrients for the early embryo
What is the role of oestrogen?
- Helps an ovum mature and burst from it’s follicle during ovulation
- Maintains thickness of endometrium
What is the role of LH in the ovarian cycle?
Rises quickly which triggers ovulation to occur
What is the role of FSH in the Ovarian Cycle?
Starts the maturation of a follicle
What is the role of progesterone during pregnancy and birth?
- Stimulates secretion of mucus by the cells lining the endometrium
- Suppresses uterine activity
- Reduces mothers response to foecal antigens
- Prevents lactation during pregnancy
- Strenghthens muscles of pelvic walls to prepare for labour
How long after a failed implantation does it take for the corpus luteum to degrade & what is the name of the new cell?
8-10 days after ovulation, forms the corpus albicans
Viviparous
Fertilised egg develops within the mother’s body and is born fully alive
What type of organisms generally use asexual reproduction?
Simple
What type of organisms generally use sexual reproduction?
Complex
What type of reproduction is mitosis
Add a brief description on waht mitosis is
Asexual identical cell replication
Seen in worms & single celled yeast organisms
What is budding and is it sexual or asexual?
Asexual - New organism is developed from a small part of the parent’s body
Hydra and yeast
What is parthenogenesis and is it sexual or asexual?
Asexual - Embryo develops directly from egg without fertilisation and young are produced as genetic clones of their mother
Bees and wasps
What is fragmentation and is it sexual or asexual?
Asexual - In multicellular organisms, the body of the organism breaks into two or more parts which regernates the missing pieces to form a complete individual
Marine worms
Fertilisation
Sexual - when a sperm fuses with a ovum to create a zygote
What is asexual reproduction?
One parent produces offspring with genetic makeup that is identical to the parent
What are the advantages of asexual reproduction?
- Efficient form of reproduction
- Less time and energy required to produce the offspring
- Population sizes can rapidly increase in correct environments
- No need for sexual partner
- Offspring are identical to their mother so they’re genetically suited to their environment
What are the disadvantages of asexual reproduction?
- Rapid population growth can lead to overcrowding and competition for resources
- Lack of genetic variation can cause death of the entire population if a disease or pathogen enters the environment
What are hermaphrodites and what are the advanatges and disadvantages of hermaphroditism?
Advantages: Beneficial in oragnisms with low populatinod densities where finding a mate is difficult
Disadvantages: Low genetic variation and more energy required for organism to grow two sets of reproductive systems
What is internal fertilisation?
When the Gamete is deposited inside the moist reproductive tract of the female
What are the advantages of internal fertilisation?
- Fewer gametes are required for sufficient number of offspring
- More control of mate choice → quicker natural selection which improves overall health of population over time
- Organisms aren’t limited to aquatic/moist environments
- Higher chance of fertilisation
- Organisms aren’t at risk of external environmental factors like temperature, infection and predation
What are the disadvantages of internal fertilisation?
- Requires more energy and generally produces less offspring
- Requires mating behaviours and finding a mate
- Generally takes longer for birth
What is external fertilisation?
Both gametes are released outside of the body and fertilised in the environment
What are the advantages of external fertilisation?
- Little no parental care
- Dispersal of gametes means little to no compeition for food and environment –> rapid population recovery
- Low energy
What are the disadvantages of external fertilisation?
- More gametes must be produced in order to ensure some offspring survive
- Vulnerable to predation, infection etc
- Can’t choose which gametes to fertilise with - often won’t posses favourable traits
- Possibility that gametes don’t meet and fertilise
Compare internal and external fertilisation
Gametes:
- Internal: large number of male produced and small number of female
- External: large number of male and female gametes produced
- Similarities: both require ovum and sperm
Fusion:
- Internal: occurs in moist reproductive tract of female
- External: occurs in external environment
- Similarities: both require close proximity and wet environment to prevent dehydration of gamete
Environment for Zygote:
- Internal: develops inside mothers body until birth where temperature is controlled and there is a lower chance of zygote loss
- External: external wet environment where they are vulnerable to predation, infection etc
- Similarities: zygote needs watery environment to develop
What is the role of the anther in plants?
Produces pollen
What is the role of the filament in plants?
Stalk that hols up the anther
What are the male parts of a flower called?
Stamen
What is the role of the ovary in plants?
Where ovules are produced for fertilisation
What is the role of the Style in plants?
Connects the stigma to the ovary
What is the role of the sigma in plants?
Sticky surface in which pollen is collected
What are the two types of sexual reproduction in plants?
- Self Pollination
- Cross Pollination
Describe the process of sexual reproduction in plants
- Pollen is produced in the anther
- When pollen touches the stigma they become trapped to it’s sticky surface
- The Pollen’s Tube Cell creates a pathway for the Generative Cell to travel down the style and into the ovary
- The Generative Cell divides into two sperm cells which fertilise the two polar nuclei and the egg inside the ovule
- The fertilised polar nuclei form the endosperm which provides nutrients to the zygote & the fertilised egg becomes the zygote
- After fertilisation the ovule matures into a seed which contains the zygote and the endosperm and is then dispersed to germinate –> the ovary is replaced by a fruit to nourish and protect the seed and make it attractive for germinators
- Once the seed has germinated, the zygote develops into an embryo and a new plant forms
What is self pollination?
When a plant is fertilised by its own pollen
What are the advantages of self pollination?
- Plant doesn’t need to waste energy on attracting features like flowers
- Consistent reproduction as plants don’t need to rely on external agents like wind and insects
- Independence from pollinators: Plants don’t require help from pollinators to reproduce and can survive in areas with little animals or if there is an event that reduces the population of pollinators
What are the advantages of seed dispersal?
- Reduces overcrowding and competition for nutrients
- Increases continuity of species in case of an environmental threat in one area like fire/flood
What are the disavantages of seed dispersal in plants?
- Loss of seeds if they are deposited in an area not suitable for growth
- Inability to escape deteriorating environments
- Predation before the seed germinates
What are the disadvantages of self-pollination?
- Less immunity of the plant due to little genetic variation
- New plant varieties cannot be created
What is cross pollination?
When the pollen of one plant fertilises another plant of the same species
What are the advantages of cross pollination?
- Healthier children
- More seeds that are successful
- Greater genetic diversity
What are the disadvantages of cross pollination?
- More energy for attracting features like petals etc
- Pollinators are always required and can endanger the plant in case of unavailability
- Lots of wasted pollen as it requires a lot of pollen as they have to travel long distances and the stigma is very small
Coral Spawning
- Shed millions of gametes into the sea that are released when the coral reproductive cycle is synced –> through envrironmental indicators like temperature,tides etc
- Gametes meet in the ocean and fertilise
- When one coral colony starts to spawn pheromones released alongside the gametes trigger nearby coral to spawn which results in coordinated spawning over a large area
Asexual Reproduction
The Splash Tera
- Two fish leap outside the water and hang to a clinging leaf
- Female lays eggs on the leaf and the process happens multiple times
- Daddy Fish drops down into the water and splashes the eggs with water until they hatch –> force of the water causes them to hatch
Asexual Reproduction
Kangaroos
- Mother produces up to three young at a time
- One in pouch attached to nipple
- One out of pouch still drinking milk
- One fertilised ovum
- Milk production lasts longer so the kangaroo undergoes embryonic diapause to delay development of zygote until oldest doesn’t need any more milk
- In drought periods kangaroos stop reproducing until rain comes and triggers a hormonal response
Compare Self Pollination & Cross Pollination
Genetic Diversity:
- Self Pollination: Low genetic diversity as offspring is genetically similar to the parent plant
- Cross Pollination: Higher genetic diversity as offspring has genes from both parents
Pollination agents:
- Self Pollination:Most often don’t require any as the pollen is transferred within the same plant
- Cross Pollination:Relies on abiotic or biotic agents to carry pollen from one plant to another
Energy required:
- Self Pollination:Less energy required as attracting features like petals are not required
- Cross Pollination:More energy required to attract pollinators to look or scent
What are the types of asexual reproduction in plants?
- Vegetative Porpogation (Cuttings)
- Runners
- Rhizomes
- Suckers
- Tubers
- Bulbs
Why is asexual reproduction preferred in plants over sexual reproduction?
In most cases
The organism is already perfectly suited to the environment and reproduction occurs much quicker
Runners
Special stem called runner grows horizontal to the plant and have nodes where buds are formed which grow into new plants
- Nodes are formed at intervals along the runner whcih form roots and shoots when it touches the ground
- Stolon breaks away completely once the plant has matured, leaving a new plant
