Chromosomes and Inheritance by Owen Borville August 29, 2024
Chromosomal Theory of Inheritance is the theory proposing that chromosomes are the genes' vehicles and that their behavior during meiosis is the physical basis of the inheritance patterns that Mendel observed.
The Chromosomal Theory of Inheritance was consistent with Mendel’s laws, which the following observations supported:
During meiosis, homologous chromosome pairs migrate as discrete structures that are independent of other chromosome pairs. Chromosome sorting from each homologous pair into pre-gametes appears to be random. Each parent synthesizes gametes that contain only half their chromosomal complement.
Even though male and female gametes (sperm and egg) differ in size and morphology, they have the same number of chromosomes, suggesting equal genetic contributions from each parent. The gametic chromosomes combine during fertilization to produce offspring with the same chromosome number as their parents.
Research by Eleanor Carothers and Thomas Hunt gave further evidence to support the Chromosomal Theory of Inheritance.
Homologous recombination is the process by which homologous chromosomes undergo reciprocal physical exchanges at their arms, also crossing over.
Parental types are a progeny (offspring) that exhibits the same allelic combination as its parents.
Nonparental (recombinant) types are progeny that result from homologous recombination that exhibits a different allele combination compared with its parents.
Genetic Maps are a chromosome map that is a linear representation of gene order and relative distance on a chromosome (by Alfred Sturtevant).
Recombination frequency is the average number of crossovers between two alleles; and is observed as the number of nonparental types in a progeny's population.
Centimorgans (cM) are a genetic chromosome map unit relative distance that correspond to a 0,01 recombination frequency (1 cM).
Chromosome Identification by isolation and microscopic observation forms the basis of cytogenetics and is the primary method by which clinicians detect chromosomal abnormalities in humans. Karyotypes are an individual's chromosome number and appearance which includes the size, banding patterns, and centromere positions. A karyogram is a karyotype's photographic image.
Autosomes (body chromosomes) are the non-sex chromosomes in a human karyotype and are usually organized in order of size from largest to smallest (chromosome 1-22).
Translocation is the process by which one chromosome segment dissociates and reattaches to a different, nonhomologous chromosome, or a different part of the same chromosome. Karyotypes can identify translocations. Certain cancers are associated with translocations.
Nondisjunction is the failure of synapsed homologs to completely separate and migrate to separate poles during the meiosis' first cell division, usually identifiable by a karyogram. Non-disjunction causes chromosome number disorders, chromosome number abnormalities including duplicating or losing entire chromosomes, or changes in the number of complete sets of chromosomes.
Aneuploidy is an abnormal number of chromosomes (euploid means an individual with the correct number of chromosomes). An individual with an abnormal number of chromosomes is called an aneuploid. The error can be caused by chromosome segment deletions and duplications. Monosomy is the losing of one chromosome, while trisomy is the gaining of an extra chromosome duplication.
Polyploidy is when an individual has an incorrect number of chromosome sets (two for diploid species). An individual with more than the correct number of chromosome sets is called a polyploid. Polyploid animals are rare and sterile.
X-inactivation is a molecular process of condensing X chromosomes into Barr bodies (inactive X chromosome) during embryonic development in females to compensate for the double genetic dose of trisomies and monosomies.
In addition to losing or gaining an entire chromosome, a chromosomal segment may duplicate or lose (delete) itself, often producing offspring that survive but exhibit abnormalities.
Chromosome inversion is a structural rearrangement in chromosomes which is the detachment and 180 degree rotation and chromosome arm reinsertion, caused by mechanical shear or from certain DNA enzymes. An inversion can be pericentric and include the centromere, or paracentric and occur outside the centromere.
A translocation occurs when one chromosome segment dissociates and reattaches to a different, non-homologous chromosome (associated with cancer and schizophrenia.
Chromosomal Theory of Inheritance is the theory proposing that chromosomes are the genes' vehicles and that their behavior during meiosis is the physical basis of the inheritance patterns that Mendel observed.
The Chromosomal Theory of Inheritance was consistent with Mendel’s laws, which the following observations supported:
During meiosis, homologous chromosome pairs migrate as discrete structures that are independent of other chromosome pairs. Chromosome sorting from each homologous pair into pre-gametes appears to be random. Each parent synthesizes gametes that contain only half their chromosomal complement.
Even though male and female gametes (sperm and egg) differ in size and morphology, they have the same number of chromosomes, suggesting equal genetic contributions from each parent. The gametic chromosomes combine during fertilization to produce offspring with the same chromosome number as their parents.
Research by Eleanor Carothers and Thomas Hunt gave further evidence to support the Chromosomal Theory of Inheritance.
Homologous recombination is the process by which homologous chromosomes undergo reciprocal physical exchanges at their arms, also crossing over.
Parental types are a progeny (offspring) that exhibits the same allelic combination as its parents.
Nonparental (recombinant) types are progeny that result from homologous recombination that exhibits a different allele combination compared with its parents.
Genetic Maps are a chromosome map that is a linear representation of gene order and relative distance on a chromosome (by Alfred Sturtevant).
Recombination frequency is the average number of crossovers between two alleles; and is observed as the number of nonparental types in a progeny's population.
Centimorgans (cM) are a genetic chromosome map unit relative distance that correspond to a 0,01 recombination frequency (1 cM).
Chromosome Identification by isolation and microscopic observation forms the basis of cytogenetics and is the primary method by which clinicians detect chromosomal abnormalities in humans. Karyotypes are an individual's chromosome number and appearance which includes the size, banding patterns, and centromere positions. A karyogram is a karyotype's photographic image.
Autosomes (body chromosomes) are the non-sex chromosomes in a human karyotype and are usually organized in order of size from largest to smallest (chromosome 1-22).
Translocation is the process by which one chromosome segment dissociates and reattaches to a different, nonhomologous chromosome, or a different part of the same chromosome. Karyotypes can identify translocations. Certain cancers are associated with translocations.
Nondisjunction is the failure of synapsed homologs to completely separate and migrate to separate poles during the meiosis' first cell division, usually identifiable by a karyogram. Non-disjunction causes chromosome number disorders, chromosome number abnormalities including duplicating or losing entire chromosomes, or changes in the number of complete sets of chromosomes.
Aneuploidy is an abnormal number of chromosomes (euploid means an individual with the correct number of chromosomes). An individual with an abnormal number of chromosomes is called an aneuploid. The error can be caused by chromosome segment deletions and duplications. Monosomy is the losing of one chromosome, while trisomy is the gaining of an extra chromosome duplication.
Polyploidy is when an individual has an incorrect number of chromosome sets (two for diploid species). An individual with more than the correct number of chromosome sets is called a polyploid. Polyploid animals are rare and sterile.
X-inactivation is a molecular process of condensing X chromosomes into Barr bodies (inactive X chromosome) during embryonic development in females to compensate for the double genetic dose of trisomies and monosomies.
In addition to losing or gaining an entire chromosome, a chromosomal segment may duplicate or lose (delete) itself, often producing offspring that survive but exhibit abnormalities.
Chromosome inversion is a structural rearrangement in chromosomes which is the detachment and 180 degree rotation and chromosome arm reinsertion, caused by mechanical shear or from certain DNA enzymes. An inversion can be pericentric and include the centromere, or paracentric and occur outside the centromere.
A translocation occurs when one chromosome segment dissociates and reattaches to a different, non-homologous chromosome (associated with cancer and schizophrenia.