6. Inheritance notes
Using freesciencelessons
Sexual and asexual reproduction
- Human cells have 23 pairs of chromosomes in nucleus
- In mitosis one cell divides into 2 identical cells
- Gametes in humans are egg and sperm cells
- Gametes have half the number of chromosome , have 23 single chromosomes
- Gametes in plants are pollen and egg cells
- Gametes are made in meiosis, which are non identical
- So every egg and sperm cell are different
Sexual reproduction:
- Involves fusion of male and female gametes which is called fertilisation
- Variation in offspring is seen
- If environment changes variation allows some organisms to survive
- So sexual reproduction gives a species survival advantage by natural selection
- Greater chance of survival
- Humans can take advantage of this in selective breeding
Asexual reproduction
- Only 1 parent, less need for mate
- Doesn’t involve gametes
- No mix of genetic info and offspring are clones
- Meiosis doesn’t take place , only mitosis occurs
- Happens in bacteria, plants , some animals
- More efficient in time and energy= faster
- Useful when conditions are favourable
- Can produce many identical offspring rapidly
- Risk that all will die (extinction) if conditions change
Need to learn specific examples of organisms that reproduce sexually and asexually
- Malaria parasite:
- has part of its life cycle in human host and part of its lifecycle in mosquito vector
- In human host malaria parasite reproduced asexually
- In mosquito uses sexual reproduction
- Fungi:
- Produce spores for asexual reproduction
- Can reproduce sexually to have variation in offspring
- All flowering plants can reproduce sexually to produce seeds
, - for example strawberry plants
- However some plants can also reproduce asexually for example straweberry plant sends out
runners to develop new identical plant
- Daffodils:
- Reproduce asexually by bulb division
- Parent plant has underground bulb which produces buds
- Identical offspring
Meiosis and fertilisation
- Meiosis only takes place in reproductive organs
- In humans this is the testes in males and ovaries in females
- Stages of meiosis :
- First all chromosomes are copied
- Cells divide into 2
- Both cells divide again to form the gametes
- In gametes chromosomes are single not paired
- Meiosis has halves number of chromosomes
- 4 gametes from one cell which are genetically different
- Have different alleles
- Gametes from male and female fuse in sexual reproduction
- This is called fertilisation
- Cell’s 23 pairs (full number) are restored
- After fertilisation new fertilised cell divides by mitosis producing a clump of genetically identical
cells
- This is called embryo
- Cells differentiate into nerve and muscle cells for example, as the embryo develops
DNA and the genome
- Chromosomes contain DNA molecule
- DNA determines our inherent features
- 2 strands
- each strand is a polymer
- 2 strands wrap around each other to form a double helix
- Gene is small section of DNA on chromosome
- Proteins are made by joining amino acids
- Each gene encodes for a specific sequence of amino acids to make a specific protein
- Genome is entire genetic material of an organism
- Human genome has been studied
- Benefit of this:
- Search for genes that are linked to a disease , understand and treat inherited disorders such as
cystic fibrosis
Using freesciencelessons
Sexual and asexual reproduction
- Human cells have 23 pairs of chromosomes in nucleus
- In mitosis one cell divides into 2 identical cells
- Gametes in humans are egg and sperm cells
- Gametes have half the number of chromosome , have 23 single chromosomes
- Gametes in plants are pollen and egg cells
- Gametes are made in meiosis, which are non identical
- So every egg and sperm cell are different
Sexual reproduction:
- Involves fusion of male and female gametes which is called fertilisation
- Variation in offspring is seen
- If environment changes variation allows some organisms to survive
- So sexual reproduction gives a species survival advantage by natural selection
- Greater chance of survival
- Humans can take advantage of this in selective breeding
Asexual reproduction
- Only 1 parent, less need for mate
- Doesn’t involve gametes
- No mix of genetic info and offspring are clones
- Meiosis doesn’t take place , only mitosis occurs
- Happens in bacteria, plants , some animals
- More efficient in time and energy= faster
- Useful when conditions are favourable
- Can produce many identical offspring rapidly
- Risk that all will die (extinction) if conditions change
Need to learn specific examples of organisms that reproduce sexually and asexually
- Malaria parasite:
- has part of its life cycle in human host and part of its lifecycle in mosquito vector
- In human host malaria parasite reproduced asexually
- In mosquito uses sexual reproduction
- Fungi:
- Produce spores for asexual reproduction
- Can reproduce sexually to have variation in offspring
- All flowering plants can reproduce sexually to produce seeds
, - for example strawberry plants
- However some plants can also reproduce asexually for example straweberry plant sends out
runners to develop new identical plant
- Daffodils:
- Reproduce asexually by bulb division
- Parent plant has underground bulb which produces buds
- Identical offspring
Meiosis and fertilisation
- Meiosis only takes place in reproductive organs
- In humans this is the testes in males and ovaries in females
- Stages of meiosis :
- First all chromosomes are copied
- Cells divide into 2
- Both cells divide again to form the gametes
- In gametes chromosomes are single not paired
- Meiosis has halves number of chromosomes
- 4 gametes from one cell which are genetically different
- Have different alleles
- Gametes from male and female fuse in sexual reproduction
- This is called fertilisation
- Cell’s 23 pairs (full number) are restored
- After fertilisation new fertilised cell divides by mitosis producing a clump of genetically identical
cells
- This is called embryo
- Cells differentiate into nerve and muscle cells for example, as the embryo develops
DNA and the genome
- Chromosomes contain DNA molecule
- DNA determines our inherent features
- 2 strands
- each strand is a polymer
- 2 strands wrap around each other to form a double helix
- Gene is small section of DNA on chromosome
- Proteins are made by joining amino acids
- Each gene encodes for a specific sequence of amino acids to make a specific protein
- Genome is entire genetic material of an organism
- Human genome has been studied
- Benefit of this:
- Search for genes that are linked to a disease , understand and treat inherited disorders such as
cystic fibrosis
