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