Topic 3 - Genetics Flashcards
What is sexual reproduction?
Where genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent.
What are the gametes in animals?
Sperm and egg cells
What are gametes?
Reproductive cells
How many chromosomes does a human cell nucleus contain?
46
What is the diploid number of chromosomes for a human?
46
What is the haploid number of chromosomes for a human cell nucleus?
23
What does diploid mean?
Has the full number of chromosomes, normal cells
What does haploid mean?
Contains half the full number of chromosomes of normal cells
Are gametes diploid or haploid?
Haploid
In sexual reproduction what do the father and mother produce?
Gametes
What happens in fertilisation in sexual reproduction?
A male gamete fuses with a female gamete to produce a fertilised egg
What is a fertilised egg also known as?
A zygote
Is a zygote diploid or haploid?
Diploid
How does a zygote develop into an embryo?
By undergoing cell division in the form of mitosis
Why does an embryo inherit characteristics from both parents?
Because it has received a mixture of chromosomes (and therefore genes) from the mother and father
In flowering plants where are the male gametes found?
In the pollen
In flowering plants where are the female gametes found?
In the ovaries at the bottom of the stigma
What is meiosis?
A type of cell division
How is meiosis different to mitosis?
Meiosis doesn’t produce identical cells
In humans where does meiosis occur?
Only in reproductive organs (ovaries and testes)
What happens before the cell starts to divide in meiosis?
The DNA is duplicated so there is enough for each new cell, one arm of each x-shaped chromosome (each chromatid) is an exact copy of the other
How many divisions are there in meiosis?
Two
What happens in the first division of meiosis?
•the chromosomes line up in pairs in the centre (on the equator) of the cell. One chromosome in each pair came from the organism’s mother and one from the father
- the pairs are then pulled apart by spindle fibres so each new cell only has one copy of each chromosome. Some of the mother’s chromosomes and some of the father’s chromosomes go into each new cell.
- each new cell will have a mixture of the mother’s and the father’s chromosomes.
Why is mixing the genes in the first cell division of meiosis important?
To create genetic variation in the offspring
What happens in the second cell division in meiosis?
- the second division is similar to mitosis
- the chromosomes line up again in the centre of the cell and the arms of the chromosomes are pulled apart
- four haploid daughter cells are produced, these are the gametes, the gametes are genetically different
What is the only way in which humans can reproduce?
Sexually
How do organisms pass on their genes?
By reproduction
What happens when cells reproduce asexually?
They divide by mitosis, resulting in two diploid daughter cells which are genetically identical to each other and the parent cell
What does sexual reproduction involve?
Meiosis and the production of genetically different haploid gametes which fuse to form a diploid cell at fertilisation
What are the advantages of asexual reproduction?
- asexual reproduction can produce lots of offspring very quickly because the reproductive cycle is so fast, this allows organisms to colonise a new area very rapidly
- only one parent is needed, meaning that organisms can reproduce whenever conditions are favourable without having to wait for a mate
•
What is the reproductive cycle?
The time it takes to produce independent offspring
What is an example of an organism reproducing quickly
and asexually?
Bacteria such as E.coli can divide every half an hour
What is an example of organisms reproducing asexually when the conditions are favourable and not having to wait for a mate?
Aphids reproducing asexually during summer when there is plenty of food
What is an advantage of sexual reproduction?
- creates genetic variation within the population, different individuals have different characteristics.
- This means that if the environmental conditions change, it’s more likely that at least some individuals in the population will have the characteristics to survive the change
- over time, this can lead to natural selection and evolution as species become better adapted to their new environment
What is a disadvantage of asexual reproduction?
- there’s no genetic variation between offspring in the population
- this means that if the environment changes and conditions become unfavourable, the whole population may be affected
What is Black Sigatoka?
A disease that affects banana plants
What is an example of how a lack of genetic variation is a disadvantage of asexual reproduction?
Bananas reproduce asexually so if there is an outbreak of disease (Black Sigatoka) it’s likely that all the banana plants in the population will be affected as none of the bananas are resistant to it
What are some disadvantages of sexual reproduction?
- sexual reproduction takes more time and energy than asexual reproduction so organisms produce fewer offspring in their lifetime, organisms need to find and attract mates
- two parents are needed for sexual reproduction, this can be an issue if individuals are isolated
What is an example of the disadvantage that sexual reproduction takes time?
Male bowerbirds build structures out of twigs and then dance to impress females
What is an example of the disadvantage that sexual reproduction requires two parents?
Polar bears often live alone so male polar bears may have to walk up to 100 miles to find a mate
What are DNA strands?
Polymers made up of lots of repeating units called nucleotides
What does each nucleotide in a DNA stand consist of?
One sugar molecule, one phosphate molecule and one ‘base’
What do the sugar and phosphate molecules in the nucleotides form for the DNA strands?
A ‘backbone’, the sugar and phosphate molecules alternate
One of how many bases joins to each sugar in a DNA strand?
One of four bases
What are the four potential bases in DNA strands?
A, T, C and G
What does the base A stand for?
Adenine
What does the base T stand for?
Thymine
What does the base C stand for?
Cytosine
What does the base G stand for?
Guanine
What is the structure of a DNA molecule?
Two strands coiled together in the shape of a double helix, each base links to a base on the opposite strand in the helix
What base does A pair with?
T
What base does T pair with?
A
What base does C pair with?
G
What base does G pair with?
C
What are the pairings of bases called?
Complementary base pairs
What are the complementary base pairs joined together with?
Weak hydrogen bonds
What are chromosomes?
Long, coiled up molecule of DNA
Where are chromosomes found?
In the nucleus of eukaryotic cells
What is a gene?
A section of DNA on a chromosome that codes for a particular protein
What makes up an organism’s genome?
All of an organism’s DNA (including the non-coding regions)
Describe the practical to extract DNA from strawberries.
1) mash some strawberries and then put them in a beaker containing a solution of detergent and salt. Mix well
2) filter the mixture to remove the froth and the big insoluble parts of the cell
3) gently add some ice-cold alcohol to the filtered mixture
4) the DNA will start to come out of the solution due to it being insoluble in cold alcohol
5) the DNA will appear as a stringy white precipitate that can be carefully removed from the solution with a glass rod
Why is detergent used when extracting DNA from strawberries?
To break down the cell/nuclear membranes to release the DNA
Why is salt used when extracting DNA from strawberries?
To make the DNA stick together
Who were the people awarded a Nobel Prize for their work in determining the structure of DNA in 1962?
Crick, Watson, and Wilkins
What do DNA molecules contain that determines which proteins are built?
A genetic code
What do proteins (made by a genetic code) do?
Determine how all the cells in the body function
What does DNA control?
The production of proteins (protein synthesis) in a cell
What is protein synthesis?
The production of proteins
What are proteins made up of?
Chains of amino acids, each protein has its own particular number and order of amino acids
Why does each protein have a different function?
The amino acid chains fold up to give each protein a different, specific shape which means that each protein can have a different function, this is why enzymes have active sites with a specific shape and so only catalyse a specific reaction
Why do enzymes have active sites with a specific shape and only catalyse a specific reaction?
Because the amino acid chains in proteins fold up to give each protein a different, specific shape, meaning that each protein can have a different function
What decides the order of amino acids in a protein?
The order of the bases in a gene
What is a base triplet?
Each amino acid is coded for by a sequence of three bases in a gene
What is a code based on base triplets?
A triplet code
How are amino acids joined together to make proteins?
Following the order of the bases in the gene: if one base triplet in DNA is “T C G” for example and the other base triplet next to this is “T G G” the cell will read the genetic code to match the amino acid to the base triplet (so the amino acids would be “T C G” and “T G G”) to put the amino acids together.