Ap Bio Chapter 15 the Chromosomal Basis of Inheritance
Chapter 15
The chromosomal basis of inheritance
Key ideas:
1) Mendelian Inheritance has its physical basis in the behavior of chromosomes during sexual life-cycle.
2) Morgan traced a gene to a specific chromosome.
3) Linked genes tend to be inherited together because they are located on the same gene.
4) Independent assortment of chromosomes and crossing over produce genetic recombinants.
5) Geneticists use recombination data to map a chromosome’s genetic locus.
1900 Biology finally caught up with Mendel.
Independently, Corren, Tschermak, and Vries all found that Mendel had explained the same result 35 years go.
Resistance remained about Mendels laws until evidence had supported it.
Chromosoems and genes are both present in pairs of diploid cells.
Homologous chromosomes separate and alleles segregate during meiosis.
Fertilization restores the paired condition for both chromosomes and genes.
Around 1902, the chromosome theory of inheritance began to take form.
Thomas Hunt Morgan was the first t associate a specific gene with a specific chromosome in the early 20th century.
Like Mendel, Morgan made an insightful choice as an experimental animal, he chose fruit flies.
Advantages of fruit flies: Prolific breeders, generation time of 2 weeks, 3 pairs of autosomes and a pair of sex chromosomes (XX in females, XY in males)
Morgan spent a year looking for variants in the fruit flies. Most had red eyes but he found 1 male with white eyes.
Normal phenotypic characteristics are called wild type.
Alternative traits are called mutant phenotypes.
When Morgan crossed his white eyed male with a red eyed female, all the offspring’s had red eyes. Therefore the allele for red eyes is dominant over the one for white eyes.
When he crossed the F1 offspring, it produced a 3:1 ratio in the F2 generation. 3 red, 1 white.
The white eyes appeared only in males. Half the males and all the females had red eyes.
His conclusion: eye color is linked to sex.
The chromosomal basis of inheritance
Key ideas:
1) Mendelian Inheritance has its physical basis in the behavior of chromosomes during sexual life-cycle.
2) Morgan traced a gene to a specific chromosome.
3) Linked genes tend to be inherited together because they are located on the same gene.
4) Independent assortment of chromosomes and crossing over produce genetic recombinants.
5) Geneticists use recombination data to map a chromosome’s genetic locus.
1900 Biology finally caught up with Mendel.
Independently, Corren, Tschermak, and Vries all found that Mendel had explained the same result 35 years go.
Resistance remained about Mendels laws until evidence had supported it.
Chromosoems and genes are both present in pairs of diploid cells.
Homologous chromosomes separate and alleles segregate during meiosis.
Fertilization restores the paired condition for both chromosomes and genes.
Around 1902, the chromosome theory of inheritance began to take form.
Thomas Hunt Morgan was the first t associate a specific gene with a specific chromosome in the early 20th century.
Like Mendel, Morgan made an insightful choice as an experimental animal, he chose fruit flies.
Advantages of fruit flies: Prolific breeders, generation time of 2 weeks, 3 pairs of autosomes and a pair of sex chromosomes (XX in females, XY in males)
Morgan spent a year looking for variants in the fruit flies. Most had red eyes but he found 1 male with white eyes.
Normal phenotypic characteristics are called wild type.
Alternative traits are called mutant phenotypes.
When Morgan crossed his white eyed male with a red eyed female, all the offspring’s had red eyes. Therefore the allele for red eyes is dominant over the one for white eyes.
When he crossed the F1 offspring, it produced a 3:1 ratio in the F2 generation. 3 red, 1 white.
The white eyes appeared only in males. Half the males and all the females had red eyes.
His conclusion: eye color is linked to sex.