LV Cell division IGNORE FOR NOW Flashcards
Name the two types of reproduction
- Asexual reproduction
- Sexual reproduction
Define asexual reproduction
- Asexual reproduction involves only one parent and no fusion of gametes
- There is no mixing of genetic information
- This leads to genetically identical offspring (clones)
- Only mitosis is involved
Define sexual reproduction
- Reproduction that involves two parents
- It involves the mixing of genetic information
- This leads to variety in the offspring
- The formation of gametes involves meiosis
- It involves the fusing of gametes
State the 2 types of gametes that are involved in sexual reproduction in animals
- sperm
- ova (egg cells)
State the 2 types of gametes that are involved in sexual reproduction in flowering plants
- pollen
- ova (egg cells)
Give 3 advantages of sexual reproduction
- Produces variation in the offspring
- If the environment changes variation gives a survival advantage by natural selection
- Natural selection can be sped up by humans in selective breeding to increase food production
Give 4 advantages of asexual reproduction
- Only one parent needed
- More time and energy efficient as do not need to find a mate
- Faster than sexual reproduction
- Many identical offspring can be produced when conditions are favourable
Name 3 organisms that reproduce by both asexual and sexual reproduction depending on the circumstances
- Malarial parasites
- Fungi
- Plants e.g. strawberry plants
State how malarial parasites demonstrate both sexual and asexual reproduction
Malarial parasites reproduce asexually in the human host, but sexually in the mosquito
State how fungi demonstrate both sexual and asexual reproduction
- Many fungi reproduce asexually by spores
- They also reproduce sexually by spores to give variation
Remember: fungal spores can be produced asexually and sexually
Explain why it is an advantage for fungi to be able to produce spores asexually and sexually
- When conditions are favourable the fungi can produce spores asexually to make many identical spores in a short period of time
- When conditions are unfavourable fungi can produce spores sexually to make genetically different spores to increase the chances of surviving the environmental conditions
State how some plants demonstrate both sexual and asexual reproduction
- Flowering plants produce seeds sexually
- They also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils
State the type of cell division involved in asexual reproduction
Mitosis
State the type of cell division involved in sexual reproduction
Meiosis
Which type of reproduction involves the production of haploid gametes
Meiosis
State the term that describes the fusing of two gametes to form a zygote
Fertilisation
How many chromosomes are found in a gamete?
- Half the full number i.e. haploid (n)
- For human cells this is 23
How many chromosomes are found in a somatic (body) cell?
- A full set of chromosomes i.e. diploid (2n)
- For human cells this is 46
Explain why sexual reproduction causes greater genetic variation in the offspring
- Sexual reproduction involves the fusing of two gametes
- Each gamete contains genetic material from each parent
- The zygote will have half the DNA from the mother and half from the father
- This mixture of genetic information produces variation
State the 4 advantages of sexual reproduction
- It increases genetic variation
- Genetic variation increases the chances of survival of the species if there is a change in the environment
- Genetic variation will mean some individuals will be better adapted to the environment and therefore more likely to survive and breed and pass the successful alleles on to the next generation (called natural selection)
- Scientists can use selective breeding to speed up natural selection
State the 5 advantages of asexual reproduction
- Only one parent is required (so there is no need to find a mate)
- This means asexual reproduction uses less energy (no energy used in finding a mate, producing gametes)
- It is also faster (as no time is used in finding a mate)
- Many genetically identical offspring can be produced when conditions are favourable
- It maintains genetic stability by producing genetically identical cells
Explain the importance of producing haploid gametes
- Gametes must contain half the chromosomes number so that when 2 gametes fuse during fertilisation the chromosome number is restored
- If the gametes had a full set of chromosomes (2n) then the chromosome number would double at each generation
How many daughter cells are produced in mitosis?
2
How many daughter cells are produced in meiosis?
4
State the 3 main stages of mitosis
- Copies of the genetic information are made
- The cell divides once to form two daughter cells, each with a full set of chromosomes(2n)
- All gametes are genetically identical to each other.
State the 3 main stages of meiosis
- Copies of the genetic information are made
- The cell divides twice to form four gametes, each with a single set of chromosomes
- All gametes are genetically different from each other
State where meiosis occurs
In the reproductive organs
- testes
- ovaries
State the type of cell division that occurs in an embryo to form a fetus
Mitosis
How does the cell number change as the embryo forms a fetus?
The number of cells increases The number of cells doubles after each division
As the embryo develops the cells become specialised. Name this process.
Differentiation
Put these structures in order of increasing complexity: Gamete Organism Fetus Embryo Zygote
Gamete → zygote → embryo → fetus → organism
Give an example of asexual reproduction in plants
- Runners e.g. strawberry plants
- Bulbs e.g. daffodils
How many pairs of chromosomes are found in a somatic (body) cell?
23
Please note the questions asked you for the number of PAIRS
What is the name for the pair of chromosomes that determines the gender of the individual?
Sex chromosomes
What 2 sex chromosomes are found in all somatic (body) cells of a female human?
XX
What 2 sex chromosomes are found in all somatic (body) cells of a male human?
XY
What percentage of female ova will carry an X chromosome?
100%
What percentage of male sperm will carry an X chromosome?
50%
What percentage of male sperm will carry a Y chromosome?
50%
State gamete will determine the sex of a human at fertilisation. Explain your answer.
- Male
- If the ovum is fertilised by a sperm carrying an X chromosome the individual will be female.
- If the ovum is fertilised by a sperm carrying a Y chromosome the individual will be male.
State the genotype of a human male
XY
State the genotype of a human female
XX
