Topic 3 - Genetics Flashcards
What does sexual reproduction produce?
Genetically different cells
What is sexual reproduction?
Where genetic information from two organisms is combined to produce offspring which are genetically different
What happpens in fertilisation?
A male gamete fuses with a female gamete and forms a zygote
What happens to the zygote?
It undergoes cell division and develops into an embryo
Why does the embyro inherit characteristics from both parents?
It has recieved a mixture of chromosomes froom mum and dad
How is meiosis different to mitosis?
Meisosis only happens in the reproductive organs and doesn’t produce identical cells
What does meiosis produce?
Non-identical cells
What happens in the first division of meiosis?
DNA is duplicated
The chromosomes line up and the pairs are pulled apart and put into the new cells
What type of cell division does the zygote undergo?
Mitosis
What happens in the second division of meiosis?
The chromosomes line up again and the chromatids are pulled apart
You get four haploid daughter cells that are genetically different
What are the arms of the chromosomes called?
Chromatids
Why is it important genes are mixed up?
To introduce genetic variation
The haploid gamete of a plant species has 12 chromosomes
Two of these gametes fuse to make a zygote
How many chromosomes will there be in the zygote?
24
How does meiosis introduce genetic variation?
The products of meiosis are all genetically different, as some of the mothers chromosomes and some of the fathers go into different cells
How do asexual organisms reproduce?
Mitosis
How do sexual organisms reproduce?
Meisois and the production of genetically different haploid gametes which fuse to form a diploid cell
What are the advantages of asexual reproduction
Lots of offspring can be made quickly
Only one parent is needed
Whats the advantage of lot of offspring being made quickly?
An area can be colonised very rapidly
Whats the advantage of only needing one parent?
The organisms can produce when conditions are favourable
Whats the disadvantages of asexual reproduction
No genetic variation
Whats the disadvantages of having no genetic variation?
If there is an environment change, the whole population may be affected
Strawberry plants produce asexually
Discuss the advantages and disadvantages of this form of reproduction
There will be no genetic variation therefore if there is an environment change the whole population may be affected
However, there will be lots of offspring that can be made extremely quickly reducing the chance of extinction and also allowed an area to be colonised extremely quickly
Only one parent is needed therefore the parent can reproduce when conditions are more favourable without having to mate
What does each nucleotide consist of?
A sugar
A phosphate group
One base
What do the sugar and phosphate groups form?
A ‘backbone’ to the DNA strands
What are the four different bases in DNA?
A, T, C, G
What can DNA be described as?
Two strands of Nucleotides, that consist of a Sugar and Phosphate group with one of the four different bases attached to the sugar, coiled to form a double helix
The strands are linked by a series of complementary base pairs joined together by weak hydrogen bonds
How are the strands linked in DNA?
By a series of complementary base pairs joined together by weak hydrogen bonds
What are the complementary base pairs?
A and T
C and G
What are the complementary base pairs joined together by?
Weak hydrogen bonds
What are chromosomes?
Long, coiled up molecules of DNA
What is a gene?
A section of DNA on a chromosome that codes for a particular protein
What is a genome?
All of an organism’s DNA
How do you extract DNA from fruit cells?
Mash strawberries and put them in a beaker with detergent and salt
FIlter the mixture to get the froth and big, insoluble bits of cell out
Add some ice-cold ethanol
What does the detergent do?
Break down the cell membranes to release the DNA
What does the salt do?
Make the DNA clump together
Why is ice-cold ethanol added?
The DNA is not soluble in cold ethanol
What is formed after you extract DNA from fruit cells
A stringy white precipitate
Which DNA bases pair up according to complementary base pairing?
A and T
C and G
Why is it useful to use salt when extracting DNA?
It clumps the DNA together which makes it much easier to see and will allow it to interact with the ice-cold ethanol easier
How are proteins made?
By reading the code in DNA
What are proteins made of?
Chains of molecules called amino acids
What do the amino acid chains do?
Fold up to give each protein a different, specific shape
Why do proteins have different functions?
The amino acids fold to give a different and specific shape
What do the non-coding regions of DNA do?
Nothing but some may still be involved in protein synthesis
What is a mutation?
A rare, random change to an organisms DNA base sequence
How does a mutation affect the organism?
The variant may code for a different sequence of amino acids which may change the shape of the final protein and so its activity
Explain how a gene can code for a particular protein?
The order of bases in a gene determines the order of the amino acids
Each gene contains a different order of bases, which the gene can code for a particular protein
Explain how a genetic variant can result in a protein with a very low activity?
A genetic variant could alter the sequence of amino acids coded for by a gene which could affect the shape of the protein, decreasing its activity
What are the two stages of protein synthesis?
Transcription and Translation
What happens in the transcription of proteins?
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 the DNA
It uses the coding DNA in the gene as a template to make the mRNA
What is RNA polymerase?
An enzyme involved in joining together RNA nucleotides to make mRNA
Why can’t DNA move out of the cell nucleus?
It is too large
What is mRNA
Messsenger RNA which is a polymer of nucleotides expect it’s shorter and only a single strand
What happens in the translation of proteins?
Amino acids are brought to the ribosome by tRNA
The order of the amino acids matches the mRNA and joins together to make a polypeptide
What are base triplets in mRNA called?
Codons
What is an anticodon?
Complementary to the codon for the amino acid
Why does non-coding DNA affect the binding of RNA polymerase?
RNA polymerase must bind to a non-coding DNA
If a mutation happens in this region it could affect the ability of RNA (easier or harder)
How does the ability to bind to the non-coding DNA affect protein synthesis?
How much mRNA is transcribed and therefore how much is produced
The potential phenotype of the orgaism (depending on the function of the protein)
Describe how a gene is transcribed to form mRNA?
RNA polymerase binds to a noncoding region of the DNA and the two DNA strands unzip and the RNA polymerase moves along one of the strands to the coding region in which it copies the gene as a template using complementary base pairs
What did Mendel do for his first experiment?
He bred a tall pea plant with a small pea plant, the offspring were all tall pea plants
He then bred the offspring together where he found a 3:1 of tall:dwarf plants
What did Mendel show through his experiment?
The height characteristic in pea plants were determined by separately inherited units passed on from each parent
Suggest why the importance of Mendel’s work wasn’t realised straight away?
Scientists then didnt have the background knowledge to understand his findings
What is a homozygous?
An organism that has two alleles for a particular gene that are the same
What is a heterozygous?
An organism that has two different alleles for a particular gene
What is the genotype?
The specific alleles the organism has
What is the phenotype?
The characteritic the genotype represents
What sex chromosomes do males have?
XY
What sex chromosomes do females have?
XX
What does sex determination depend on in humans?
The sperm (male)
What chromosomes do eggs always possess?
X
When is a characteristic sex-linked?
If the allele that codes for it is located on a sex chromosome
Give examples of sex-linked disorders?
Colour blindness
Haemophillia
Haemophillia is caused by a recessive allele located on the X chromosome. A couple are having a baby
The mother is a carrier of haemophillia
The father does not have the disorder
What is the probability the son will have haemophillia?
25%
Haemophillia is caused by a recessive allele located on the X chromosome. A couple are having a baby
The mother is a carrier of haemophillia
The father does not have the disorder
What is the probability the daughter will have haemophillia?
0%
How many blood types do humans have?
O, A, B and AB
What blood genes are codominant?
IA and IB
Why are IA and IB codominant?
One allele isn’t dominant over the other one (there is no recessive)
Both genotypes when together show both phenotypes
Explain how a mother with A and a father with B can have a child with O?
Both parents may have O as a recessive, therefore, although unlikely, both gametes that produce the zygote may have O as the gene so the offspring will have O blood
What types of variation are possible?
Genetic and environmental
How is genetic variation caused?
By organisms having different alleles which can lead to differences in phenotype
How does sexual reproduction lead to variation?
Sexual reproduction offers many different combinations of offspring due to meisosis producing 4 genetically different gametes
How does the environment affect variation?
Organisms will acquire characteristics to combat environmental changes
What is most variation often involved with?
A mix of genetic and environmental factors
Give an example of a mix of genetic and environmental factors?
A plants max height is determined by its genes, however, how far it actually grows depends on the environment
What are neutral mutations?
Mutations that show no phenotype (effect) on an organism
