Genes Flashcards
What chemical is the basis of inheritance
DNA
Whereas DNA found
Nucleus in chromosomes
What is a small section of DNA that determines a particular feature
A gene
How do genes determine features
Instruct cells to produce particular proteins which leads to development of the feature
What does mitosis form
A genetically identical cell with the same type and amount of DNA
What is a molecule of DNA made of
Two strands of nucleotides so it is polynucleotide
What does each nucleotide contain
Nitrogenous base , phosphate group and sugar molecule
What are the nitrogenous base pairs and how do they work
Complimentary base pairs always bind with each other
Adenine and thymine
Customise and guanine
Which part of DNA codes for manufacture proteins
Sense strand , the other strand is the anti sense strand
What views for one amino acid
A sequence of three nucleotides . The base sequence codes for the amino acid . 3 bases = 1 amino acid. DNA code is a triple code . The sequence of based that codes for all the amino acids in a protein is a gene
What is a mutation
A change in the DNA of a cell An happen in individual genes or whole chromosomes
How does mutation happen
When DNA is replicating mistakes are made and the wrong nucleotide is used . The result is a gene mutation that can alter the sequence of bases in a gene that can lead to the gene coding for the wrong protein
What is duplication
Form of mutation . The nucleotide is inserted twice instead of once and the entire base sequence is altered - each triplet after the point where the mutation has altered . Whole gene is different and codes for an enitirely different protein
What is deletion
Mutation. Nucleotide is missed out. Entire base sequence altered each triplet after mutation changed whole gene different codes for different protein
What is substitution
Different nucleotide used. Triplet of bases where mutation occurs is changed and may code for different amino acid . If it does the structure of protein moclecuke will be different. This may be enough to produce an alteration in the functioning of the protein or lack of function . Triplet may not code for a different amino acid as they normally have more than one code
Inversions
Sequence of bases in the triplet is reversed. Only one triplet affected may or may not result in a different amino acid and altered protein structure
What happens to harmful mutations
Mutations in body cells affect that particular cell. If they are harmful the cell will die and then mutation will b lost
What happens to non harmful mutations
If the mutation does not affect the functioning of the cell in a major way the cell may not die if the cell then divides the mutation will be passed on
How can mutations be passed on to next generations
Organism dies , mutations die with it unless mutations are in sex cells or cells that divide to form sex cell then mutation will be passed on to next genration and genetic diseases begin
When are mutations advantageous
As a result of random mutations bacteria can become resistant to anti biotic . They become advantageous over non resistant bacteria and They will survive antibiotic treatment and reproduce and the mutation will be passed on. Proportion of resistant bacteria will increase as they survive
What are mutagens
Agents that increase mutations
- ionising radiation ( X-ray , uv light , gamma rays
- chemicals such as mustard gas , nitrous oxide , tar ,
What is DNA cooked around in chromosomes
Histones . Each chromosome contains one double stranded DNA molecule that is folded and coiled around proteins called histones
How many chromosomes on a diploid
46
Matching chromosomes
Homologous pairs . Carry genes for the same feature in the same sequence
How many chromosomes on a haploid and a red blood cell
Haploid - 23
Red blood cell - none
How are sex cells fromed
Meiosis. Each cell formed has one chromosome from a homologous pair . Haploid cell
What happens when sex cells fuse in fertilisation
Two nuceli join to form a single diploid cell - a zygote - . This cell has chromosomes in homologous pairs and two copies of every gene
What is an allele
Different forms of a gene . Homologous chromosomes carry genes for the same feature in the same sequence but the Alleles of the gene might not b the same
What does the domainant allele do
Cancels out recessive allele to give you the phenotype
What do human body cells contain
46 chromosomes in 23 homologous pairs
What happens in mitosis
Produces two daughter cellsgenetically identical to parent cell
What must happen for mitosis
- cell must copy chromosomes before it divides. DNA replicates and more proteins are added to strructure . Each daughter cell can then recueve a copy of each chromosome .
- it must divide in a way that each daughter cell revives one copy of every chromosome otherwise they will not contain all the genes
What is DNA structure
Double helix
Polymer - a long chain made up of lots of monomers ( the nucleotides )
What is varaition due to
Genes environment or both
When is DNA copied
Before mitosis - chromosome duplicated into chromatids
Interphase
Cell has not yet divided - clear nucleus , nuclear membrane , individual chromosomes that cannot be seen.
Prophase
DNA replicates . Chromosomes condense and become visible . Nuclear membrane disappears . Spindle starts to form in cytoplasm.
Metaphase
Nuclear membrane disappeared . Chromatids line up on equator of cell. Spindle forms from either pole or cell and attaches to centre of chromatids ( centromere)
Anaphase
Spindle fibres pull chromosomes towards pole of the cell . Chromatids split with one member of each pair going other way
Telophase
Chromosomes reach pole of cell and spindle begins to break down and nuclear membrane starts to reform . Cytoplasm begins to cleave among the equatior
Cytokinesis
Two new daughter cells are firmed with the same DNA as patent cell
Homozygous
Two identical alleles
Heterozygous
Two different alleles
Recessive
You need two copies of recessive Allele to receive phenotype
Genotype
Your combination of alleles
Phenotype
Physical characteristic resulting from genes and environment
How are all cells in our body formed except sex cells
From mitosis from the zygote
Why do cells divide by mitosis
Growth , to replace skin cells that have been lost by skin , cells scraped off the lining in the gut as foood passes on , cells divide to produce replacements , cancer cells - cells divide mitosis and produce genetically identical cells including the Mutation that makes them divide uncontrollably
What does meiosis produce
4 haploid cells not genetically identical
What must cell do to divide my meiosis
Copy each chromosome for enough genetic material to be shared between 4 daughter cells
Divide twice so each daughter cell receives just one chromosome from each homologous pairs.
What happens in meiosis
DNA duplicates
Homologous pairs of chromosomes line up( independent assortment )
Crossing over ( nucleus membrane disappears )
Homologous chromosomes move to each end of cell
Cell divides into two daughter cells ( end of meiosis one )
Divides into 4 new cells meiosis 2. Non identical cells and have half the normal number of chromosomes
Why is there variation in meiosis
Crossing over - maternal and paternal chromosomes exchange sections of their DNA that alters combinations of genes on a chromosome
2. Independent assortment which is the random position of maternal and paternal chromosomes at metaphase 1
Why is there variation in offspring from sexual reproduction
Random sperm fertilises random egg
What is asexual reproduction
Part of organism grows breaks away from parent organism and divides my mitosis
What is each feature controlled by
A gene found on a chromosome
What do the sex cells have
One copy of each chromosome and each gene so one allele
What is codominant
If two alleles are expressed in the same phenotype
What is sex determined by
X and y chromosomes . Two X chromosomes in females . One x and one y in all male cells . If the y chromosome is present when the zygote is developing it will be a boy
Where are plural membranes
Surrounding lungs
Why do alveoli have permeable walls
To allow gases to diffuse easily
Where are stomata located
Tiny pores on leaf surface
Purpose of biconcave
Large surface area for absorbing and relaxing oxygen can
