Chapter 17 Inheritance Flashcards
Define inheritance
the transmission of genetic information from generation to generation
Define chromosomes
thread like structures of DNA, carrying genetic information in the form of genes
Define allele
A version of a gene
Describe the inheritance of sex in humans
One of the 23 pairs controls the inheritance of biological gender
males have two diff sex chromosomes (XY)
females have two X chromosomes (XX)
The ratio of female to male offspring is 1:1
on average, half the offspring will be girls and half will be boys
Define a gene
A length of DNA that codes for a protein
N.I.S How is the DNA molecule packaged?
In the nucleus of each cell, the DNA molecule i packaged into thread like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure
Define haploid nucleus and diploid nucleus
Haploid nucleus (n): a nucleus containing a single set of unpaired chromosomes present (e.g. sperm and egg cells) Diploid nucleus (2n): a nucleus containing two sets of chromosomes present (e.g. in body cells)
Explain genetic code
Each nucleotide carries one of four bases (A,T,C, or G)
A string of nucleotides therefore holds a sequence of bases. This sequence forms a code, which instructs the cell to make particular proteins.
Proteins are made from amino acids linked together. The type and sequence of the amino acids joined together determines the kind of protein formed.
It is the sequence of bases in the DNA molecule that decides which amino acids are used and in which order they are joined. Every three bases code for one amino acid.
A gene, then, is the sequence of triplets of the four bases, which specifies an entire protein.
The chemical reactions that take place in a cell determine what sort of cell it is and its functions. These chemical reactions are in turn, controlled by enzymes.
Enzymes are proteins. It follows, therefore, that the genetic code of DNA, in determining which proteins, particularly enzymes, are produced in a cell, also determines the cell’s structure and function. In this way, the genes also determine the structure and function of the whole organism.
Other proteins coded for in DNA include antibodies and receptors for neurotransmitters.
Describe the manufacture of proteins in cells
DNA molecules remain in the nucleus, but the proteins they carry the codes for are needed elsewhere in the cell. A molecule called messenger RNA (mRNA) is used to transfer the information from the nucleus.
mRNA is much smaller than a DNA molecule and is made up of only one strand. Also it contains slightly different bases (A,C,G and U). Base U isuracil.
To pass on the protein code, the double helix of DNA unwinds to expose the chains of bases.
One strand acts as template. A messenger RNA molecule is formed along part of this strand, made up of a chain of nucleotides with complementary bases to a section of the DNA strand.
The mRNA molecule carrying the protein code then passes out of the nucleus, through a nuclear pore in the membrane. Once in the cytoplasm it attaches itself to aribosome.
Ribosomes make proteins. The mRNA molecule instructs the ribosomes to put together a chain of amino acids in a specific sequence, thus making a protein.
In a diploid cell, there is a pair of each type of chromosome and in a human diploid cell there are ___ pairs
In a diploid cell, there is a pair of each type of chromosome and in a human diploid cell there are 23 pairs
Explain gene expression
All 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 to fulfil its function.
Define mitosis and describe it
Mitosis is nuclear division giving rise to genetically identical cells
It also plays a role in growth, repair of damaged tissues, replacement of cells and asexual reproduction.
For example, basal cells of the skin, which keep dividing to make new skin cells, and cells in the red bone marrow, which constantly divide to produce the whole range of blood cells. These are stem cells (which are unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions.)
Describe the process of mitosis
Each chromosome duplicates itself and is seen to be made up of two parallel strands, called chromatids. This occurs before mitosis happens.
When the nucleus divides into two, one chromatid from each chromosome is separated so that two different chromatids exist in the daughter cells. Later they will REPLICATE themselves ready for the next cell division.
Mitosis producestwo genetically identical cellsin which the number of chromosomes is the same as in the original cell.
Define and describe meiosis
meiosis is nuclear division which gives rise to cells that are genetically different.
It is a reduction division in which the chromosomes number is halved from diploid to haploid resulting in four genetically different haploid cells.
It is involved in the production of gametes (haploids) and it occurs in the gonads of animals
Meiosis produces variation by forming new combinations of maternal and paternal chromosomes
Define genotype
Genotype is the genetic make-up of an organism in terms of the alleles present.
