Paper 1 - Topic 3, Genetics Flashcards
What type of cells does sexual reproduction produce
Genetically different cells
What is produced in sexual reproduction
Gametes, sperm and egg cells
What do gametes contain
Half the number of chromosomes of normal cells - haploid cells
What happens at fertilisation
A male gamete fuses with a female gamete to produce a fertilised egg
What is a fertilised egg called
A zygote
How does a zygote develop into an embryo
Cell division by mitosis
How many chromosomes does a human cell contain
46
Where are the male gametes found in flowers
The pollen
Where are the female gametes found in flowers
In the ovaries at the bottom of a stigma
How is meiosis different to mitosis
Meiosis produces genetically different cells, meiosis only happens in the reproductive organs
Describe division 1 of meiosis
- It duplicates its DNA, one arm of each X-chromosome is an exact copy of the other arm
- The chromosomes then line up in centre of cell, one chromosome in each pair came from the mother and one from the father
- The pairs are pulled apart so each new cell has one copy of each chromosome, some of the mothers and father’s chromosomes in each new cell
- Each new cell has mixture of mothers and fathers chromosomes, mixing up genes creates genetic variation in offspring
Describe division 2 in meiosis
- The chromosomes line up again in centre of cell, the arms of the chromosomes are pulled apart
- You then get four haploid daughter cells, these are gametes, each gamete has a single set of chromosomes, the gametes are genetically different
What happens if something reproduces asexually
- divide by mitosis
- results in two diploid daughter cells
- they are genetically identical to each other and the parent
What happens if something reproduces sexually
- meiosis
- produces genetically different haploid gametes which fuse to form a diploid cell at fertilisation
What are the advantages of asexual reproduction
- can produce lots of offspring very quickly because the reproductive cycle is so quick
- only one parent is needed - organisms can reproduce whenever conditions are favourable without having to wait for a mate
What are disadvantages of asexual reproduction
- no genetic variation so if environment changes and conditions become unfavourable, whole population may be affected
What are the advantages of sexual reproduction
- creates genetic variation within population so individuals have different characteristics and if environment changes its more likely some individuals will survive the change
What are the disadvantages of sexual reproduction
- takes more time and energy, so less offspring are created in an organisms lifetime (need to attract mates which takes time and energy
- two parents are need so if individuals are isolated it can be a problem
What do nucleotides consist of
A sugar, a phosphate and one base
What does the sugar and phosphate create
The backbone
What are DNA strands
Polymers made up of lots of repeating units called nucleotides
What are the four bases called
Adenine
Thymine
Cytosine
Guanine
What are the complementary base pairs joined together by
Weak hydrogen bonds
Where are chromosomes 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
How do you extract DNA from fruit cells
- Mash strawberries and put in beaker containing a solution of detergent and salt and mix
- Filter mixture to get the froth and big insoluble cells out
- Add ice cold alcohol to filtered mixture
- DNA will start to come out solution as not soluble in cold alcohol, appears as stringy white precipitate
What will the detergent salt solution do in the DNA extraction from fruit cells experiment
Detergent: break down the cell membranes to release DNA
Salt: make DNA stick together
What are proteins made up of
Amino acids
What do the order of bases in a gene determine
The order of amino acids in a protein
How is each amino acid coded
By a sequence of three bases in a gene
What is a mutation
A rare ,random change to an organisms DNA base sequence that can be inherited
What happens if a mutation happens in a gene
Produces a genetic variant
Where are proteins made
In the cell cytoplasm by ribosomes
What is mRNA
Messenger RNA, a polymer of nucleotides which is short and single stranded and uses Uracil instead of Thymine
What is RNA polymerase
The enzyme involved in joining together RNA nucleotides to make mRNA
How does transcription work
- RNA polymerase binds to a region of non-coding DNA in front of a gene
- The two DNA strands unzip and the RNA polymerase moves along one of the strands of 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 moves out of the nucleus and joins with a ribosome
How does translation work
- Amino acids are brought to ribosomes by another RNA molecule called transfer RNA (tRNA)
- The order in which amino acids are brought to ribosomes matches the order of base triplets in the mRNA (base triplets called codons)
- Part of the tRNA structure in an anticodon which is complementary to the codon for the amino acid, the paring of the codon and anti-codon make sure amino acids are brought to ribosome in correct order
- The amino acids are joined together by ribosome which makes polypeptide
