Topic 17 Flashcards
Chromosone
Made of DNA, which contains genetic information in the form of genes
Gene
A length of DNA that codes for specific protein -> controls our characteristics
Allele
Different versions of the same gene
Sex chromosones
Responsible for sex determination -> either labelled as X or Y
Sex chromosones -> males
X and Y chromosone (XY) -> Y chromosome causes male characteristics
Sex chromosones -> females
X and X chromosome (XY) -> XX combination causes female charactersitics
Sex chromosones -> sperm
Can carry either and X or Y chromosone so sex determination in humans depends on what chromosome is carried by speem that fertilises egg -> 50:50 chance of sperm carrying either chromosome
Haploid VS diploid cells -> haploid cell
Haploid nucleus: contains a single set of chromosones
-> 23 chromosomes
-> Example: gametes (sex cell)
Haploid VS diploid cells -> Diploid
Diploid nucleus: contains two sets of chromosomes -> there’s a pair of each type of chromosome (23 pairs/ 46 chromosomes)
-> Example humand body cells (except gametes)
Protein synthesis: DNA and genes
DNA strands contain bases which make up genes -> sequence of bases in a gene is the genetic code that determines the order (sequence) of amino acids in a protein
1. Each amino acid is coded for by a sequence of three bases in the gene
2. Amino acids are joined together to make specific proteins -> depending on order of gene’s bases
3. When a chain of amino acids has been assembled, it folds into a unique shape which allows protein to perform the task it’s meant to do -> different sequences of amino acids result in proteins with differenct shapes
DNA
Controls cell function by controlling production of proteins including enzymes, membrane carriers (carrier proteins) and neurotransmitter receptors
Protein production
- Gene coding for the protein remains in the nucleus
- Messanger RNA (mRNA) is a copy of a gene
- mRNA molecules are made in the nucleus and move to the cytoplasm
- mRNA passes through ribosomes
- Ribosome assembles amino acids into protein molecules
- The specific sequence of amino acids is determined by the sequence of bases in the mRNA
Body cells
Most body cells in an organsim have the same genes, but cells don’t express (make proteins from) all of their genes -> cells only express those genes that lead to the production of the specifi proteins they need to carry out their function
Mitosis
Nuclear division of a diploid cell that results inntwo genetically identical cells -> used in growth, cell replacement and repair of damaged tissues
Before mitosis happens
Cell’s chromosones are replicated -> end up with twice as many chromosones
During mitosis
Chromosones copies seperate and nucleus divides so one copy of each chromosone ends up in daughter cell -> mantains original chromosone number in each daughter cell
Stem cells
Unapecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions
Meiosis
A reduction division, which halves chromosome number from diploid to haploid (sperm + egg) forming four genetically different cells
Monohybrid inheritance->Inheritance
Transmission of genetic information (DNA) between generations
Monohybrid inheritance->Genotype
Alleles and organism has it’s genetic make-up) -> determines phenotype
Monohybrid inheritance->Phenotype
Observable features of an organism
Monohybrid inheritance->Homozygous
Having two identical alleles for a particular gene
Monohybrid inheritance->Heterozygous
Having two different alleles for a particular gene
Monohybrid inheritance->Dominant allele
Allele that’s always expressed if it’s present
Monohybrid inheritance-> Recessive allele
Allele that’s only expressed when dominant version of allele isn’t present in orgnism’s genotype
Monohybrid inheritance: Inheriting genes
Yo have two alleles of every gene in your body -> one from each parent
. Two identcial homozygous individuals that breed together will be pure-breeding -> can only pass one type of allele and so only one phenotype
. Heterozygous individual won’t be pure-breeding -> can pass on two different allels
Dominant and recessive alleles
Dominant alleles (shown with capital letters) overrrule recessive alleles (shown with small letters)
Dominant and recessive alleles: Displaying dominant characteristics
. Two dominant alleles
-> Example: CC
. One dominant and one recessive allele
-> Example: Cc
Dominant and recessive alleles: displaying recessive characteristics
Both alleles must be recessive
-> Example: cc
Genetic diagrams
Show the possible alleles of offspring and therefore probability of offspring having certain characteristics -> doesn’t tell exactly what will happen
Genetic diagrams: monohybrid cross
When you cross two parents to look at just one characteristic
Genetic diagrams: punnett square
Show genetic crosses
Genetic diagrams: pedigree diagram
Shows how characteristics are inherited
Carrier
Someone who doesn’t have the disorder but can pass it on
Genetic diagrams: test crosses
Used to identify unknown genotypes by analysing ratio of phenotypes in specific offspring using genetic diagrams -> a homozygous recessive individual must be involved to do this
Sex-linked genetic disorders: sex-linked characteristic
Feature that’s coded for by a gene located on a sex chromosone, making it more common in one sex than in the other -> Y chromosome is smaller than X chromosome and so carries fewer genes so most genes in sex chromosomes are only carried on X chromosome
Sex-linked genetic disorders: male
Only have one X chromosome so often only have one allele for sex-linked genes so characteristic of this allele is shown eve; if it’s recessive -> makes men more likely than a woman to show recessive characteristics for genes that are sex linked
Sex-linked genetic disorders
Disorders caused by faulty alleles located on sex chromosomes
Blood type in humans
A, B, AB and O (phenotypes) -> gene for blood type in humans has three different alleles I^A, I^B and I^O (genotypes)
Ineritance of blood groups: Codominance
Bothe alleles in heterozygous organism are expressed and so both determine the organism’s phenotype
