Genetics Flashcards
What are gametes?
Reproductive cells: sperm and egg cells.
Why are gametes haploid?
Because they contain half the amount of chromosomes of normal cells.
What happens at fertilisation?
A male gamete fuses with a female gamete to produce a fertilised egg, also known as a zygote.
Why is a zygote diploid?
It contains a full set of chromosomes.
How is Meiosis different to Mitosis?
It’s different because it doesn’t produce identical cells.
What happens in Meiosis?
- Cell duplicates DNA, one arm of each X-shaped chromosome is an exact copy of the other.
- In the first division, the chromosomes line up in pairs in the centre of the cell. One chromosome in each pair came from mother/father.
- The pair are then pulled apart, so each cell only has one copy of each chromosome, some of mother some of father.
- Mixing genes creates genetic variation
- In the second division, the chromosome line up again in the centre. The arms are pulled apart, You get four haploid daughter cells - these are gametes, each gamete only has a single set amount of chromosomes. The gametes are genetically different.
What is asexual reproduction?
They divide by mitosis - this results in two diploid daughter cells, which are identical to each other and the parent cell.
What is sexual reproduction?
This involves meiosis and the production of genetically different haploid gametes, which fuse during fertilisation.
What are the advantages of asexual reproduction?
- Can produce a lot of offspring quickly
- Only one parent is needed
What are the disadvantages of asexual reproduction?
- No genetic variation
- If conditions are unfavourable then whole population may be affected
What are the advantages of sexual reproduction?
- Creates genetic variation
- If conditions change, some of population with survive
- Leads to evolution
What are the disadvantages of sexual reproduction?
- It takes more time than asexual reproduction
- Two parents need - this is a problem if individuals are isolated.
DNA stands are made up of repeating units called what?
Nucleotides.
What does a nucleotide consist of?
One sugar molecule, one phosphate molecule and one `base’.
The sugar and phosphate molecules form a what?
Backbone.
What are the four bases?
Adenine, thymine, cytosine and guanine. (A, T, C, G).
What is the structure of a DNA molecule?
It has two strands coiled together in the shape of a double helix.
What are the complementary base pairs?
A and T, C and G.
The complementary base pairs are joined together by what?
Weak hydrogen bonds.
What is a chromosome?
A long, coiled up molecule of DNA. They are 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 a genome?
All of an organism’s DNA.
How do you extract DNA from fruit cells?
- Mash strawberries and then put in beaker containing solution of detergent and salt.
- The detergent breaks down the cell membranes to release the DNA.
- The salt will make the DNA stick together.
- Filter the mixture.
- Add some ice-cold alcohol to the filtered mixture.
- The DNA will start to come out of solution as it’s not soluble in cold alcohol. It will appear as stringy white precipitate that can be fished out with a glass rod.
DNA controls the production of what?
Proteins (protein synthesis).
Proteins are made up of chains of molecules called what?
Amino acids.
What is a base triplet?
Each amino acids is coded for by a sequence of three bases in the gene.
Proteins are made in two stages, what are they?
Transcription and translation.
What is transcription?
- RNA polymerase binds to region of non-coding DNA in front of a gene
- The two strands unzip and the RNA polymerase moves along one of the strands of the DNA
- It uses the coding DNA in the gene as a template to make the mRNA. Base pairing between the DNA and RNA ensures that the mRNA is complementary to the gene
- Once made the mRNA molecule moves out of the nucleus and joins with a ribosome.
What is translation?
- Amino acids are brought to the ribosome by another RNA molecule called transfer RNA (tRNA).
- The order in which the amino acids are brought to the ribosome matches the order of the base triplets in mRNA. Base triplets in mRNA are also known as codons.
- Part of the tRNA’s structure is called and anticodon - it is complementary to the codon for the amino acid. The pairing of the codon and anticodon makes sure that the amino acids are brought to the ribosome in the correct order.
- The amino acids are joined together by the ribosome. This makes polypeptide (protein).
What is a mutation?
It is a rare, random change to an organism’s DNA base sequence that can be inherited.
If a mutation happens in a gene, it produces what?
A genetic variant.
How can a genetic variant affect the phenotype of an organism?
It may code for a different sequence of amino acids, which may change the shape of the final protein and so it’s activity. The activity of an enzyme might increase/decrease/stop which could affect the characteristics of an organism.
What did Mendel’s pea plant experiment show?
- Characteristics in plants are determined by hereditary units
- These units are passed on to offspring unchanged from both parents, one unit from each
- These units can be dominant or recessive
What is an allele?
Alleles are different forms of a gene.
What does heterozygous mean?
Individuals who are heterozygous for a certain gene carry two different alleles.
What does homozygous mean?
Individuals who are homozygous for a certain gene carry two copies of the same allele.
What is monohybrid inheritance?
The inheritance of a single characteristic.
What genetic diagrams can be used to show monohybrid inheritance?
Monohybrid cross, Punnett square and Family pedigrees.
What chromosomes do males have?
XY.
What chromosomes do females have?
XX.
How are sex-linked disorders inherited?
They are inherited as sex-linked disorders are located on a sex chromosome.
What are the four blood types?
A, B, O and AB.
How can you have an AB blood type?
This is because A and B are co-dominant with each other - this means one allele isn’t dominant over the other.
Why is blood type O rare?
Blood type O is a recessive allele so you need two of them to be present.
What is genetic variation?
Different characteristics as a result of mutation and sexual reproduction.
What is environmental variation?
Different characteristics caused by an organism’s environment (acquired characteristics).
Both genetic and environmental variations lead to what?
Differences in phenotype.
What is the Human Genome Project?
The big idea was to find every single human gene.
What are the medical applications of the HGP?
- Prediction and prevention of disease
- Testing and treatment of inherited disorders
- New and better medicines
