Topic 3: Genetics Flashcards
What is sexual reproduction?
When genetic information from two organisms is combined to produce offspring which are genetically different to either parent
What are the steps of sexual reproduction?
- Parents produce haploid gametes (reproductive cells)
- Gametes fuse at fertilisation
- A diploid zygote is produced
- The zygote divides by mitosis and becomes an embryo
What are chromosomes?
Long molecules of DNA that normally come in pairs
What does haploid mean?
Contains half the number of chromosomes of normal cells
What does diploid mean?
Contains a full set of chromosomes
What is meiosis?
Type of cell division that produces four haploid daughter cells
Meiosis v Mitosis: uses
Meiosis - creating sex cells
Mitosis - growth and repair
Meiosis v Mitosis: type of reproduction
Meiosis - sexual
Mitosis - asexual
Meiosis v Mitosis: number of cells created
Meiosis - 4 cells
Mitosis - 2 cells
Meiosis v Mitosis: number of chromosomes in the cells produced
Meiosis - 23 chromosomes (haploid)
Mitosis - 46 chromosomes (diploid)
Meiosis v Mitosis: the created cells’s genetics
Meiosis - cells are genetically different
Mitosis - cells are genetically identical
What does asexual reproduction mean?
When a single parent produces genetically identical offspring e.g. mitosis
Advantages of asexual reproduction?
Fast compared to sexual reproduction
Only one parent needed - no energy wasted finding a mate
Disadvantages of asexual reproduction?
No genetic variation between offspring - whole population can be affected by unfavourable conditions
Advantages of sexual reproduction?
Variation in offspring - increased chance that some individuals in the species may survive a change in environment leading to evolution or natural selection
Disadvantages of sexual reproduction?
Need to find a mate - takes time and energy
Hard for isolated individuals
What is the structure of DNA?
A polymer made of two strands coiled into a double helix
What are the parts of a DNA strand?
Sugar-phosphate backbone
Phosphate
Sugar
The above are part of a nucleotide - the monomers that make up DNA
What are the complimentary base pairs?
A T
G C
What are complimentary bonds held together with?
Weak hydrogen bonds
Practical: how to extract DNA from fruit?
- Mash the fruit - to break down cell wall
- Add detergent, salt and proteases - detergent breaks down the cell membrane to release DNA, salt makes DNA stick together and proteases prevents the enzymes breaking down DNA
- Filter - to filter large and insoluble clumps of fruit and get rid of them
- Pour ice cold ethanol over the solution - precipitates DNA and makes it visible
What is a genome?
All an organisms DNA
What is a gene?
A small section of DNA found on a chromosome that codes for a particular protein
What are the processes in protein synthesis?
Transcription then translation
Where does transcription take place?
In the nucleus
What is the process of transcription?
- DNA strands unwinds because of helicase, then the RNA polymerase will bind with DNA as they have complimentary base pairs
- Base paring between DNA and RNA makes a complimentary mRNA strand
- The mRNA moves out of the nucleus and binds to the ribosome
What is the difference between RNA and DNA?
RNA - single stranded & there are difference base pairs (A pairs with U and C pairs with G)
DNA - double stranded & the base pairs are different (A pairs with T and C pairs with G)
Where does translation take place?
In the cytoplasm/ribosomes
What are the steps of translation?
- mRNA leaves the nucleus and goes to the ribosome where they bind together
- tRNA brings amino acids to the ribosome
- Anticodons on the tRNA are complimentary to codons on the mRNA and they bind together
- Amino acids are therefore joined in the correct order
- The ribosome join the amino acids together making a polypeptide - which folds up to make the protein
What is a mutation?
A random change to the base sequence of DNA
What did Mendel study?
How characteristics in plants are passed on from one generation to the next
What did Mendel find out when he bred a tall pea plant and a dwarf pea plant?
That a tall pea plant when bred with a dwarf pea plant made all tall pea plant offspring
What were Mendels conclusions?
- Hereditary units determine characteristics
- Units are passed on to offspring unchanged
- The units can be dominant or recessive
How did Mendel’s findings help other discoveries?
Scientists learnt about chromosomes
‘Units’ were named genes
Structure of DNA was able to be determined
What is an allele?
A version of a gene
What does dominant mean?
An allele that is always expressed
What does recessive mean?
An allele that is only expressed when two copies are present
What does homozygous mean?
When both of an organisms alleles for a trait are the same
E.g. bb or BB
What does heterozygous mean?
When an organisms alleles for a trait are different
E.g. Bb
What is a genotype?
An organisms combination of alleles
What is a phenotype?
The characteristics an organism has
What does a punnet square show?
- The gametes’ genotypes of both parents (female and male)
- The offspring’s genotypes
What can a punnet square represent?
The likelihood the offspring will have a certain characteristic, blood group or what it’s sex will be
What do family pedigrees have?
- A key showing males & females specifically: those that are affected by the disease, those that are carriers, those that are unaffected
- Horizontal lines link the parents
- Vertical lines connect parents to offspring
What is a family pedigree similar to?
Family tree
What can family pedigree represent?
The likelihood the offspring will have the disease and what it’s sex will be
What’s a sex linked disorder?
When the allele that codes for a disorder is located on a sex chromosome
What can sex linked disorders of parents and how it’ll affect offspring be represented on?
Punnet square
How is a sex linked disorder shown?
E.g. X^N X^n
E.g. X^n X^n
E.g. X^N X^N
How is a genotype shown where one chromosome is affected not the other?
E.g. X^n Y
Unaffected chromosome stays the same
What are the different alleles for the different blood type?
I^O
I^A
I^B
Which of the blood type alleles are codominant?
I^A
I^B
What are the 4 blood groups?
O
A
B
AB
What blood type allele is recessive?
I^O
What can blood groups of parents and how it’ll affect offspring be represented on?
Punnet square
What is variation?
Differences in the characteristics of organisms
Where does genetic variation come from?
- Sexual reproduction - since offspring made aren’t identical
- Mutations
What affect do mutations have on phenotypes?
It depends
What happens in environmental variation?
Differences in the conditions in which organisms develop cause variation - they get acquired characteristics
E.g. leaf colour
What happens in genetic and environmental variation?
For most characteristics, variation is caused by both genetics and the environment
E.g. plant height
What has the human genome project done?
Worked out the complete human genome
What has the human genome project helped do?
- Predict and prevent diseases - knowing which gene leads to what disease can help doctors tailor advice and treatments
- Test and treat inherited disorders - people can be tested early and we can develop better treatments
- Develop new and better medicines - drugs can be tailored to individuals and there is potential for more effective treatments with fewer side effects
What is the negative of the human genome project?
Could lead to some people to being more stressed & more discrimination by employers and insurers
