B13 - Reproduction Flashcards
What is a gene
A section of DNA on a chromosome that codes for the animo acid sequence of a specific protein
What are alleles
Different versions of the same gene
How many chromosomes are there in a normal human cell
23 pairs
What are gametes, how many chromosomes and how are they made
- Sex cells - sperm in men and eggs in females or pollen and eggs in plants
- They have 23 single chromosomes
- They are made by meiosis
Features of sexual reproduction
- Fusion of male and female gametes - the offspring has a mixture of genetic information from both parents
- Every gamete is different - this causes variation in the offspring
- Gametes are made by meiosis
Features of asexual reproduction
- Only one parent involved - doesn’t involve gametes
- Offspring are all genetically identical so they are clones
- Only involves mitosis not meiosis
How are gametes produced by meiosis
- Only takes place in reproductive organs - testes and ovaries
1. All of the chromosomes are copied/DNa replicated and sub celluar structures are duplicated
2. Cell divides into two
3. The two cells then divide again to form 4 cells, halving the number of chromosomes in all cells so each cell only has a single set (divides twice)
4. Each gamete is genetically different from each other
Stages in fertilisation and after
- Gametes fuse in fertilisation restoring the number of chromosomes to 23 pairs
- The cell then divides by mitosis producing an embryo - a clump of identical cells
- The cells then differentiate into different cell types
Advantages and disadvantages of sexual reproduction
Advantages
* Produces variation in the offspring
* Allows more offspring to survive due to changes in the environment (GREATER CHANCE OF SURVIVAL)
* This can be used by humans in selective breeding
Disadvantages
* Slower than asexual
* Takes time and energy to find a mate, spread gametes
Advantages and disadvantages of asexual reproduction
- only one parent needed
- no need to find a mate so more efficient in boht time and energy
- Faster than sexual reproduction
- Useful to produce identical offspring when conditions are favourable
Disadvantages
* If conditions become unfavourable, all offpsring may die due to lack of variation
organisms that reproduce both sexually and asexually
- malaria parasite - in humans uses asexual, in mosquitos uses sexual
- Fungi - asexually by producing spores and they can reproduce sexually
- Strawberry plant - asexually by strawberry runners, sexually by flowers
- Daffodils - asexually by bulb divisions, sexually by flowers
Structure of DNA
- Made of 2 polymer strands that wind around each other to make a double helix shape
- The monomers that make up the polymer starnd are called nucleotides
- A nucleotide has a phosphate group (circle) a sugar molecule (pentagon) and a base attached to the sugar molecule
- The phosphate group joins to the sugar of another nucleotide forming a sugar-phosphate backbone
- There are 4 different bases that a nucelotide can have - A,T,C or G
- The DNA strands are complementary as A attaches to T and C attaches to G and vice versa
defenition of a genome
the entire genetic material that makes up an organism
Benefits of having studied the entire human genome
- Enables scientists to search for genes linked to a disease e.g. that increase risk of cancer
- Helps us understand and treat inherited disorders
- Can trace human migration patterns - ancestry
- Paternity determination
Stages of protein synthesis
- Transcription - base sequence of the gene is copied into a complementary template molecule (mRNA)
- mRNA passes into the cytoplasm as it is small
- Translation - mRNA molecule attaches to a ribosome
- Amino acids are brought to the ribosome on carrier molecules (tRNA) so each tRNA has 3 bases
- The ribosome reads the triplet of bases and uses this to join the correct amino acids brought by the tRNA together
- Once the protein chain is complete, it folds into its unique shape
What can proteins strands be used for in the body
- Enzymes
- Hormones
- Forming structures e.g. collagen
How many bases code for a specific amino acid
3
How can non-coding parts of DNA affect gene expression
They can switch genes on or off
What is a mutation
the change in the sequence of bases in DNA
They are spotaneuous and happen frequently
How can mutations cause problems in the coding region of DNA
- Most mutations have no effect of structure or function
- Some mutations cause a change in the sequence of bases in mRNA leading to a drastic change in the amino acids sequence which means the folded shape of the protein will be different
- This could have a dramatic effect e.g. the active site of an enzyme changing shape or it alters the strength of a structural protein
How can mutations cause problems in the non-coding region of DNA
- Affects how genes are switched on or off
- Gene may be turned on when its meant to be turned off
- This could cause an unwanted protein to be produced
- This could lead to problems e.g. uncontrolled cell division and cancer
What is cystic fibrosis
- A disorder of cell membranes
- It is controlled by a single gene
- Is caused by a recessive allele and to have it, both parents have it
What is polydactyly
- Where people have extra fingers or toes
- Caused by a dominant allele
issues around embryo screening
- Expensive - money should be spent elsewhere in the NHS
- LArge number of embryos are created but only a few are used - means some healthy embryos are destroyed which is unethical
- Designer babies - screen embryos to produce offspring with desriable features e.g. taller, smarter
- Chance of miscarriage during fetal cell harvesting
- Terminating a pregancy will have massive mental health affects and may go against people’s religions
