Gregor Mendel conducted his experiments between 1850 and 1865. It was felt that the characters were transmitted to offspring and which mix in the child. Mendel disproved the second belief but served 40 years before his work was included.
The success of Mendel's research is due to a rigorous experimental design and use of the laws of probability.
The choice of study organism was assigned to the sweet pea : has a numerous progeny, it is easy to manipulate reproduction in that it can be pollinated or self-pollinated; 7 characters had chosen a complete dominance and were eriditati independently of each other. A
character is a feature observable body, once the form in which it occurs.
L ' intersection is severing the anthers to prevent self-pollination, and carrying pollen from one plant to another. Mendel had available lines of well, that self-pollinated gave the same character.
crossing two inbred lines (g enero parental P) with the opposite character traits and get a first filial generation F1 . In this there was a mixture, but a single stroke. He discovers that a trait is dominant and a recessive ( principle of dominance). In self-pollinated F2 generation produced by the stroke recurrence. To explain this
Mendel realized that both sections were left in the offspring, in terms of genotype traits are defined alleles. So if an individual has two alleles for different traits in the phenotype will manifest the dominant one. An individual is said
homozygous, homozygous recessive if the alleles are recessive or dominant and homozygous dominant if it has identical alleles for the character, and heterozygous if different alleles.
The first law Mendel's law of segregation that character said that during gamete formation the two alleles segregate (separate) ending on different gametes.
We now know that there are two alleles of its chromosomes and that the segregrazione of alleles occurs during meiosis.
Mendel used the square Punett to determine the amount of transmitted alleles, but could not understand what were the presence of heterozygotes, because the phenotype was identical. The only way that allowed him to understand was a cross check with the homozygous recessive ( dihybrid cross).
The second law of Mendel is used to refer to the way in which alleles of different traits assort is at crossroads: the
law independent assortment says that the alleles belonging to different genes segregate independently at the time of gamete formation and are inherited independently of each other.
But today we know that is not universally true, in fact when the genes controlling two characters are close in the same gene tend to be associated with offspring. A
allele is a sequence of a gene. Different alleles for a gene exist because are subject to mutations, a rare and random process that changes the genetic material. Geneticists call a wild-type gene if the allele is present in nature in most individuals.
dominance is not always complete because some genes are subject to multiple alleles (more than two alleles).
When a heterozygous subjects manifested an intermediate phenotype with respect to the generation partentale is said that the gene is subject to incomplete dominance. In some cases both alleles are dominant and you have the codomain (such as blood group AB).
Other alleles have multiple phenotypic effects and is called pleiotropic .
How genes interact?
A gene locus is the position of a gene on chromosome and is called polymorphic if it might present a mutant gene.
L ' epistasis is the influence of genes in phenotypic expression. In some phenotypic expression (height, skin color) the character is polygenic , ie more different genes work together to the final result. The genes associated
reside in the same chromosome and tend to be distributed contemporanenamente, with the exception of crossing over, recording the second law of Mendel, since the characters observed were located on different chromosomes. Probabilitàù with which the two genes on the same chromosome recombine is linked to their distance if they are close is low, if they will almost certainly far.
The laws of genetics and post-mendialiana medeliana can be used to predict the transmission of genetic diseases humans. The majority of genetic diseases are caused by a recessive allele. Generally
genetic diseases are due to defective production of an enzyme that cuts the pathway, but in the case of the heterozygous dominant allele can compensate.
A protein enzyme can easily be mutations that affect its overall performance, if the position is wrong or the amino acid has a charge different from the above we can create damage prevented the allosteric binding of the substrate with the active site. Genetic diseases
autosomal recessive: Cystic fibrosis, phenylketonuria, certain forms of diabetes, galactosemia. Generally
disease caused by a dominant allele from the population are removed quickly if the individual is unable to reproduce. Huntington's disease (HD) is a progressive neurodegenerative disease that takes over after 30 years in adulthood and results in dementia, unfortunately the progeny carrying a sick 50% of alleles.
Other genetic diseases are autosomal dominant achondroplasia dwarfism, polydactyly, neurofibtomatosi, galucoma chronic.
sickle cell anemia individuals heterozygous both red blood cells because the allele is codominant.
This mutation has survived because the sickled red blood cells resistant to infection of malaria. The cost is that an individual's offspring out of 4 present the homozygosity for allele and sickle cell anemia soppravviverà. 44/46
human chromosomes are the autosomes, that contain the same sequence of genes, but not exact sequence of DNA that can carry different alleles.
The remaining two are sex chromosomes or eterocromosomi . and are designated with X and Y, in the portion you are not homologous genes that allow sexual differentiation.
humans XX is an individual female (sex omogametico), and XY is a male (sex eterogametico ).
The female gametes are always X and X and Y sperm can be and have a different strength.
Some genes that are in non-homologous portion of the X chromosome, which therefore has no counterpart in Y, given the effects in males who do not have a dominant allele. Color blindness, hemophilia and are predominantly male disease produced dall'eterocromosoma maternal X. Mutations can be
gene or chromosome . The genetic mutation or
point are due to the substitution, deletion, insertion of nucleotide bases in DNA.
gene mutations caused by substitutions produce altered proteins and the consequences are of 3 types:
- silent mutation → relate to third base codon of mRNA that is often irrelevant to the amino acid.
- → a missense mutation of codon base alters the encoded amino acid (the genetic variation on which natural selection works).
- nonsense mutation → codon represents one amino acid instead of the start codon or stop, or vice versa.
In all deletion and insertion of the genetic code is translated and then following completely altered. Could be due to an error in DNA replication or physical agents (X or UV) or chemical mutagens.
mutations in the structure of chromosomes 4:
- → deletion of part of chromosome is lost (syndrome du cri du chat).
- → duplicating the chromosome is duplicated in the regulation of causing damage.
- → reversal after a break in the chromosome is assembled in an inverted position, gives no serious consequences except that we will be crossing over.
- → translocation following a break off a part of the chromosome and is inserted in a different chromosome, rendondo complicated pairing during meiosis.
The mutation of chromosome number (aneuploidy ) if, during meiosis a pair of chromosomes does not separate (nondisjunction) we have a cell with one chromosome less ( monosomy) and one with an extra chromosome ( trisomy ). No monosomy allows the development of the embryo, while trisomy of chromosome 21, it has Down syndrome. Aneuploidy affects 2 / 10 pregnancies. Down syndrome 1 / 700 and the age of the mother is directly proportional to the probability of the birth of a Down child. Aneuploidy
eterocromosomi causes less disturbance to the balance gene: X0 Turner syndrome, metafemmina XXX, XXY Klinefelter syndrome, XYY male normal.
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