6. Inheritance, Variation and Evolution (reproduction) Flashcards
What is sexual reproduction?
- a type of reproduction
- involves the production of gametes by meiosis
- a gamete from each parent fuses to form a zygote
- genetic information from each gamete is mixed so the resulting zygote is unique
What are gametes in animals?
sex cells (sperm and egg cells) with 23 chromosomes
What are the gametes for plants?
pollen and egg cells
What does haploid mean?
half the number of chromosomes
What is meiosis?
- A form of cell division involved in the formation of gametes in reproductive organs.
- The chromosome number is halved
- it involves two divisions
What must occur prior to meiosis?
Interphase - copies of genetic information are made during this process
What happens during the first stage of meiosis?
- Chromosome pairs line up along the cell equator
- The pair of chromosomes are separated and move to opposite poles of the cell
- The chromosome number is halved
What in the first stage of meiosis creates variation?
how the side to which each chromosome is pulled is random
What happens during the second stage of meiosis?
- Chromosomes line up along the cell equator
- The chromatids are separated and move to opposite poles of the cell
- Four unique haploid gametes are produced
Why is meiosis important for sexual reproduction? (2)
- it increases genetic variation
- it ensures that the zygote formed at fertilisation is diploid
Describe fertilisation and its resulting outcome
- gametes join together to restore the normal number of chromosomes and the new cell then divides by mitosis, which increases the number of cells
- as the embryo develops, cells differentiate
What is the advantage of sexual reproduction? (2)
- It creates genetic variation in offspring, increasing the probability of a species adapting to and surviving environmental changes
- natural selection can be speeded up by humans in selective breeding to increase food production
Describe the disadvantages of sexual reproduction? (2)
- two parents are required. so reproduction is difficult in endangered populations
- more time and energy is required so fewer offspring are produced
What is asexual reproduction?
- a type of reproduction
- involves mitosis only
- produces genetically indentical offsprings known as daughter cells
Describe the advantages of asexual reproduction? (3)
- only one parent is required
- lots of offsprings can be produced in a short amount of time, enabling the rapid colonisation of an area and reducing competition from other species
- requires less time and energy as do not need to mate
