Sexual / Asexual reproduction + DNA Flashcards
(44 cards)
How many pairs of chromosomes in the nucleus of human cells
Human cells contain 23 pairs of chromosomes in the nucleus
Normal human cells contain chromosomes that are in pairs
Difference between mitosis and meiosis
meiosis leads to non-identical cells being formed while mitosis leads to identical cells being formed.
(every sperm cell and every egg cell are different)
Type of cells where the chromosomes are not paired
These cells are called gametes
The chromosomes are single not paired
How many chromosomes do human gametes contain
Human sperm and egg cells contain 23 single chromosomes
What is sexual reproduction
Sexual reproduction involves the joining (fusion) of male and female gametes. This process is called fertilisation
Examples of male and female gametes in plants and animals
- sperm and egg cells in animals
- pollen and egg cells in flowering plants.
Features of sexual reproduction
Sexual reproduction involves the joining (fusion) of male and female gametes. This process is called fertilisation
In sexual reproduction there is mixing of genetic information (the offspring receives genetic information from both the male and female parents) which leads to variety in the offspring
(as every gamete is different)
because every gamete is different this means we can variation in the offspring
What does the formation of gametes involve
How are gametes made
The formation of gametes involves a type of cell division called meiosis.
Features of asexual reproduction
Asexual reproduction involves only one parent (aphid is the only parent of the offspring) and no fusion of gametes.
Asexual reproduction does not involve gametes
(because there is only one parent) There is no mixing of genetic information
This leads to genetically identical offspring (these offspring are called clones).
(offspring are genetically identical to the parent)
Asexual reproduction only involves mitosis
_________________________________________
because Asexual reproduction does not involve gametes, meiosis does not take place
Where does meiosis only take place
Meiosis only takes place in reproductive organs
Reproductive organs in males and females
Humans
Male - testes
Females - ovaries
describe how meiosis halves the number of
chromosomes in gametes
(a cell in human reproductive organ - contains 23 chromosome pairs)
In the first stage of meiosis, all of the chromosomes are copied
The cell now divides into two
Both of these cells now divide one more time, forming the gametes
In the gametes, the chromosomes are now single, not paired.
Meiosis has halved the number of chromosomes
(in the cell we started with, the chromosomes where in pairs, however in the gametes, the chromosomes are now single - in other words, Meiosis has halved the number of chromosomes
)
How many gametes does meiosis produce from one cell.
Describe the gametes.
Meiosis produces four gametes from one original cell.
Each of these four gametes are genetically different from each other
Each gamete has different alleles
What does meiosis do to the number of chromosomes
Meiosis has halved the number of chromosomes
What does meiosis produce
Meiosis produces gametes
describe how fertilisation restores the full number of
chromosomes.
Gametes join at fertilisation to restore the normal number of chromosomes.
In sexual reproduction, these gametes (from male and female) join together. This is called fertilisation
After fertilisation, the cell now has the full number of chromosomes.
In fertilisation, the full number of chromosomes is restored
how many chromosomes
human sperm cell
human egg cell
fertilised egg
human sperm cell - 23 single chromosomes
human egg cell - 23 single chromosmes
fertilised egg - 23 chromosome pairs - 46 chromosomes
sperm cell \____fertilisation________—> fertilised egg
egg cell /
What happens after fertilisation
The new cell divides by mitosis. The number of cells
increases. As the embryo develops cells differentiate.
The new cell divides by mitosis (the number of cells increasing), producing a group of identical cells. This is called an embryo. As the embryo develops cells differentiate, forming different cell types.
Advantages of sexual reproduction
Advantages of sexual reproduction:
* produces variation in the offspring
* if the environment changes, this variation gives a species a survival advantage by natural selection
(if environment changes e.g. becomes colder then this variation means that some of the offspring may survive
- sexual reproduction gives a species a greater chance of survival if conditions become challenging)
- natural selection can be sped up by humans in selective breeding to increase food production.
(means population can adapt to changing conditions - allows for evolution (process by which species change over time) to take place - most favourable traits are most likely to be passed on)
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. (asexual reproduction allows an organism to produce many genetically identical offspring rapidly)
Disadvantages of asexual reproduction
Asexual reproduction is very risky
Because all the offspring are genetically identical (clones), there isnt any genetic variation, therefore there is a risk they could all die if conditions become unfavourable
Less chance of adapting to new conditions
Disadvantages of sexual reproduction
It takes energy to find a mate. E.g. flowering plants spend energy making flowers full of nectar to bribe insects to spread their pollen (male gametes) to other plants. This is costly to the plant
organisms which reproduce by both methods depending on the circumstances.
Malarial parasites reproduce asexually in the human host, but sexually in the mosquito.
- Many fungi reproduce asexually by spores but also reproduce sexually to give variation in their offspring.
- Many (all flowering) plants can reproduce sexual to produce seeds , but also reproduce asexually by runners such as strawberry plants (where the runner touches the soil, it can develop into a new plant, genetically identical to the parent) , or bulb division such as daffodils (the parent plant has an underground bulb which produces buds. These buds eventually form new offspring plants. The offspring are genetically identical to the parent)
where are chromosomes found
Chromosomes are found in the nucleus of cells
