Genetics Flashcards
Where is DNA found in humans?
in chromosomes in the nucleus of cells
What do chromosomes contain?
1000s of genes
Why are chromosomes found in pairs?
one is maternal and the other is paternal
How many pairs of chromosomes do humans have?
23
What is DNA made of?
A polymer of nucleotides
What does each nucleotide contain?
a phosphate, a sugar and 1 of 4 bases
What are the four bases?
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
What codes for proteins?
The sequence of bases
What type of structure is the double stranded DNA molecule found in?
Double helix structure
What is the human genome?
The entire genetic material of a human
How many genes are present in the human genome?
30,000
Why is knowledge of the human genome important?
- to search for genes linked to diseases
- to understand and treat hereditary disorders
- to trace human migration
What does each gene code for?
A protein
How many bases of DNA strand code for 1 of the 20 amino acids in a protein?
3
What does the sequence of the base determine?
The sequence of the amino acids
Is the double stranded structure stable or unstable?
Stable
Why does DNA have two strands?
One strand of DNA codes for genes, the other is complementary to it to give it strength
What are the pairs of bases in genes?
A binds with T
C binds with G
What are loacted either sides of genes?
Control regions which tell the body how often a gene needs to be expressed (used)
Describe the process of protein synthesis:
- An enzyme will make a copy of the gene in a molecule called mRNA (messenger) which travels out the nucleus to a ribosome in the cytoplasm.
- Here, each triplet (three bases), is paried with a tRNA(transfer) molecule with a specific amino acid attached.
- The amino acids are joined together in a specific sequence to form a protein chain
- This chain will fold in a specific way to make a protein with a specific shape e.g. enzyme
What is a DNA mutation?
Any change to the base sequence in DNA
What are the possible affects of a DNA mutation?
- The amino acid sequence can be changed and the function of the protein can be thus affected e.g. changing the shape of an enzyme’s active site
- The regulation of the gene can be affected, making it switch on more or less often than required
When do mutations occur?
Randomly during cell division
What factors increase the rate of mutations?
Radiation and carcinogens
What is the function of the cell cycle?
To control the replication of organelles and DNA so that cell division can occur
Describe the basic cell cycle:
- Growth 1: replication of organelles
- Synthesis: DNA replication
- Growth 2: Replication of organelles and cell growth
- Nuclear division: mitosis/meiosis
Describe the stages of mitosis:
- DNA becomes visible in the nucleus
- Nucleus disappears and chromosomes pair up
- chromosomes line up down the middle of the cell
- spindle fibres connect to the chromosomes
- spindle fibres pull the chromosomes apart
- nucleii form around the separated chromosomes
- cell divides into two identical cells
What is the product of mitosis?
2 daughter cells that are identical to the parent cell are formed which are diploid
What does diploid mean?
They have 2 copies of each chromosome (ie. 23 pairs)
What is mitosis used for?
growth, repair and asexual reproduction
What is the product of meiosis?
4 non-identical haploid gametes
Describe the stages of meiosis:
- The DNA in the cell replicates
- The nucleus disappears and the chromosomes pair up together
- The chromosomes line up in pairs down the middle of the cell. Spindle fibres attach to them and pull them apart
- the first division creates two non-identical cells
- the second division creates 4 haploid cells
- 4 gametes are formed
Compare mitosis and meiosis:
- 1 division vs 2 divisions
- 2 daughter cells vs 4 daughter cells
- identical cells vs non-identical cells
- diploid vs haploid
- growth,repair, aseual reproduction vs sexual reproduction
How is the diploid number of chromosomes maintained during fertilisation?
each gamete has 23 chromosomes so 23 (sperm) + 23 (egg) = 46 (zygote-fertilised egg)
What are the advantages of sexual reproduction?
- introduces variation into offspring.
- can lead to natural selection and evolution over time
- artificial selection can be used to selectively breed desired traits
What are the advantages of asexual reproduction?
- faster and more energy efficient
- doesn’t require another parent/mate
- lots of clones can be made if the environment is favourable
What organisms use both asexual and sexual reproduction?
malrial parasite, fungi and some plants
How do malarial parasties use both sexual and asexual reproduction?
- asexual reproduction in humans
- sexual reproduction in mosquitos
How do fungi use both sexual and asexual reproduction?
- asexual reproduction in spores
- sexual reproduction when required (ie. limited resources)
How do some plants use both sexual and asexual reproduction?
- asexually with cuttings/runners
- sexually with seeds
What determines sex in an embryo and when?
The sex chromosomes (pair 23) at about 6 weeks after fertilisation
What chromsomes do females possess?
XX
What chromosomes do males possess?
XY
What type of chromsome does an egg have?
X
What type of chromsomes do sperm have?
50% X and 50% Y
How many copies of each gene do we have? Why?
Two copies of each gene as we have two copies of each chromosome
What is an allele?
A different version of a gene
How many genes control fur colour in mice?
1
What are the two mice fur alleles and which is dominant and which is recessive?
Black fur (dominant) and brown fur (recessive)
What are the symbols for black fur and brown fur?
B and b
What is the genotype of an organism?
The combination of dominant and/or recessive genes which an organism receives from their parents (e.g. BB for mice fur)
What is the phenotype of a mouse?
The fur colour
What is a mouse with a genotype BB called? WHat colour fur does it have?
A homozygous dominant - black
What is a mouse with a genotype Bb called? What colour fur does it have?
A heterozygous - black
What is a mouse with a genotype bb called? What colour fur does it have?
A homozygous recessive - brown
What is a carrier?
An organism which carries a recessive gene in one of their two chromosomes so can pass it on to their offspring but display the dominant gene
What does polygenic mean?
Means a characteristic is defined by many genes
What type of diseases are cystic fibrosis and polydactyl?
Monogenic hereditary diseases
What is cystic fibrosis?
- living condition where a patient produces very thick sticky mucus which builds up in lungs, digestive system, reproductive system
- it is recessive so 2 carries have a 1/4 chance of their child having cystic fibrosis
What is polydactyly?
- where someone grows extra fingers or toes
- it is dominant so a patient cannot be a carrier of it as the heterzygous individual will be a sufferer
What are the disadvantages of sexual reproduction?
- takes time and energy to find a mate or spread gametes so is less efficient
- often slower than asexual reproduction
WHat are the disadvantages of asexual reproduction?
- if the environment changes, all offspring are at risk since they are genetically identical and may not survive
Compare asexual and sexual reproduction:
- Asexual requires one parent whereas sexual requires 2
- fertilisation is used in sexual reproduction and mitosis in asexual reproduction
- offspring from sexual reproduction are genetically different to one another and their parents whereas asexually reproduced offspring are genetically identical to their parent
What does sexual reproduction in plants involve?
The joining of pollen and an ovule in fertilisation
How do plants reproduce asexually?
runners form at the ends of exisiting stems by mitosis
How will the genome project help identify which rare diseases are inherited?
- the genome of a person with a rare disease can be compared to the genome of a relative
- if the relative has the disease, DNA sequences that are similar can be looked for
- if the relative does not have the diesease, scientists can look for DNA sequences that are different
- these genes may be linked to the disease and mean it is inherited
How will the genome project help to develop treatments for rare diseases?
- if genes that are linked to diseases are identified, treatments can be developed
- this could be genetic engineering to change a gene
What is non-coding DNA?
- DNA around a gene which switches the gene on and off but doesn’t actually code for a protein
What is gene expression?
when a protein, coded for by a gene, is synthesised in a cell
What can be used to show genetic crosses?
Punnett squares and family trees
