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Flashcards in SB3 Genetics Deck (22)
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What is sexual reproduction?

Sexual reproduction is where genetic information from 2 organisms is combined to produce genetically different offspring.


Name the gametes involved in sexual reproduction in humans:

Sperm and egg cell


True or false:
Gametes contain half the number of chromosomes of normal cells. They are diploid.

Although gametes do contain 23 chromosomes, they are haploid not diploid. (Remember h=half=haploid)


At fertilisation, a zygote is produced. Is this haploid or diploid?

The zygote ends up with the full set of chromosomes. (23 from the egg and 23 from the sperm =46 chromosomes)


What is produced in Meiosis?

4 haploid daughter cells
Genetically different


Explain why the daughter cells in meiosis are not genetically identical

Each daughter has half the chromosomes from each parent so daughter cells have different combinations of chromosomes so they are all genetically different.


True or false:
Asexual reproduction is when cells divide by meiosis.

Asexual reproduction is when the cells divide by mitosis.
Sexual reproduction is when the cells divide by Meiosis.


Describe the process of meiosis

The cell duplicates it’s DNA.
In the first division, the chromosomes line up in pairs at the centre of the cell.
The pairs are pulled apart.
2 cells are produced which have a mixture of the parents’ chromosomes.
In the second division, chromosomes line up again and are pulled apart.
4 haploid daughter cells are produced.


State an advantage of sexual reproduction

It creates genetic variation within the population.


State an advantage of Asexual reproduction

• Not time consuming/ lots of offspring are produced very quickly.
• Only one parent is needed so there is no need for a mate.


State a disadvantage of sexual reproduction

• It is time consuming and needs more energy so organisms produce fewer offspring in their lifetime.
• 2 parents are needed which can be a problem if individuals are isolated


State a disadvantage of asexual reproduction

There is no genetic variation between offspring in the population.


What is the advantage of having genetic variation within a population?

If environmental conditions change it’s more likely that some of the individuals will have the characteristics to survive and then reproduce so the species will not become extinct.


Which DNA bases pair up according to complimentary base pairing?

A and T (Adenine and Thymine)
C and G (Cytosine and Guanine)


A DNA molecule is in the shape of:

A double helix


What type of bonds are the complimentary base pairs joined together by?

Weak hydrogen bonds


Where are the chromosomes of a cell found?

In the nucleus of a eukaryotic cell


What is a gene?

A section of DNA on a chromosome that codes for a particular protein.


The structure of DNA is made of nucleotides. What does this show?

DNA is a polymer.


Describe the process of DNA extraction.

Mash some strawberries and put them in a beaker containing a solution of detergent and salt.
Filter the mixture.
Gently add some ice cold alcohol to the filtered mixture.
The DNA will appear as a stringy white precipitate.
Take this out with a glass rod.


Why is a solution of detergent and salt used in DNA extraction?

Detergent = it breaks down the cell membrane to release the DNA
Salt = it makes the DNA stick together


Why does the DNA appear as a solid white precipitate and not dissolve in the cold alcohol?

DNA is not soluble in cold alcohol.