16. Chromosomes, genes and proteins Flashcards
Describe chromosomes, gene, allele, inheritance of sex in humans with reference to X and Y chromosomes
chromosomes are made of DNA, which contains genetic information in the form of genes.
gene- a length of DNA that codes for a protein
allele- an alternative form of a gene
Describe what determines sequence of AA, how function of DNA is controlled and expression of genes
the sequence of bases in a gene determines the sequence of amino acids used to make a specific protein as different sequences of amino acids give different shapes to protein molecules.
DNA controls cell function by controlling the production of proteins, including enzymes, membrane carriers and receptors for neurotransmitters.
most body cells in an organism contain the same genes, but many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs
Explain how a protein is made
- the gene coding for the protein remains in the nucleus
- messenger RNA (mRNA) is a copy of a gene
- mRNA molecules are made in the nucleus and move to the cytoplasm
- the mRNA passes through ribosomes
- the ribosome assembles amino acids into protein molecules
- the specific sequence of amino acids is determined by the sequence of bases in the mRNA
Types of Nucleus and their no. of chromosome
a haploid nucleus as a nucleus containing a single set of chromosomes
a diploid nucleus as a nucleus containing two sets of chromosomes
in a diploid cell, there is a pair of each type of chromosome and in a human diploid cell there are 23 pairs
Describe mitosis
mitosis- nuclear division giving rise to genetically identical cells
role of mitosis- growth, repair of damaged tissues, replacement of cells and asexual reproduction.
exact replication of chromosomes occurs before mitosis
during mitosis, the copies of chromosomes separate, maintaining the chromosome number in each daughter cell
Describe meiosis
meiosis is involved in the production of gametes
meiosis- reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells
Describe stem cells
unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions
Describe inheritance, genotype & phenotype
inheritance- the transmission of genetic information from generation to generation.
genotype- the genetic make-up of an
organism and in terms of the alleles present
phenotype- as the observable features of an organism
Describe homozygous, heterozygous, dominant allele, recessive allele
homozygous- having two identical alleles of a particular gene. two identical homozygous individuals that breed together will be pure-breeding
heterozygous- having two different alleles of a particular gene
a heterozygous individual will not be pure-breeding
a dominant allele- an allele that is expressed if it is present in the genotype
a recessive allele- an allele that is only expressed when there is no dominant allele of the gene present in the genotype
Explain how to use a test cross to identify an unknown genotype
perform a test cross ;
by breeding with, homozygous recessive / king cheetah ;
if any of the offspring of the test cross are king cheetahs it confirms 17 is heterozygous ;
Describe codominance with an example
Describe codominance as a situation in which both alleles in heterozygous organisms contribute to the phenotype.
phenotypes are A, B, AB and O blood groups and
alleles are IA, IB and Io
IA and IB are codominant but both are dominant to IO.
Describe a sex-linked characteristic
a feature in which the gene responsible is located on a sex chromosome and that this makes the characteristic more common in one sex than in the other
red-green colour blindness is an example of sex linkage as it is more likely to be inherited by males because allele is on X chromosome.
