Chromosome theory of Inheritance Flashcards
Define the chromosome theory of inheritance and the observations that lead to it.
genes are physically located on specific structures called chromosomes,
behavior of chromosomes during meiosis and fertilization accounts for the patterns of inheritance observed by Mendel.
This theory was supported by observations of sex chromosomes, linkage, and non-disjunction.
Describe Morgan’s key experiment supporting the chromosome theory of inheritance.
crossing a white-eyed male fruit fly with a red-eyed female fruit fly, and observing the eye color of the offspring.
He found that the eye color was linked to the sex of the flies
the white-eye trait was recessive and carried on the X chromosome.
This showed that genes can be located on specific chromosomes and that the X and Y chromosomes determine the sex of the flies.
Describe Bridge’s experiment proving the chromosome theory of inheritance
rare exceptions to Morgan’s experiment were caused by the non-disjunction of the X chromosomes in the female flies.
He showed that the white-eyed females were XXY and the red-eyed males were XO, and that the eye color was always associated with the X chromosome.
confirmed that the physical attachment of the genes to the chromosomes was responsible for the inheritance of traits.
How was the sex chromosome found and defined?
found and defined by studying the number and shape of chromosomes in different animals, and noticing that some chromosomes were different in males and females.
For example, Henking observed that firebug sperm cells had either 11 or 12 chromosomes, and that the extra chromosome was called X.
McClung suggested that the X chromosome could determine sex.
Sutton and Boveri observed that the X chromosome segregated independently from the other chromosomes during meiosis.
Stevens and Wilson identified the Y chromosome as the partner of the X chromosome in males, and that the ratio of X to autosomes determined the sex in fruit flies.
What are the main differences between mitosis and meiosis?
mitosis produces two identical diploid daughter cells from one diploid parent cell
meiosis produces four different haploid daughter cells from one diploid parent cell.
Mitosis involves one round of cell division,
meiosis involves two rounds of cell division.
Mitosis maintains the chromosome number,
meiosis reduces the chromosome number by half.
Mitosis is used for growth and repair,
meiosis is used for sexual reproduction and genetic variation.
What is crisscross inheritance?
phenomenon where a trait is inherited from the father to the daughter, and then from the daughter to the grandson.
This happens when the trait is carried on the X chromosome, and the male inherits only one X chromosome from his mother.
For example, in fruit flies, the white-eye trait is crisscross inherited from the white-eyed grandfather to the red-eyed daughter, and then from the red-eyed daughter to the white-eyed grandson.
How is sex determined in Drosophila melanogaster? How was it demonstrated?
ratio of X chromosomes to sets of autosomes (chromosomes 2, 3, and 4).
A ratio of 1 or more (such as XX or XXY) results in a female, a ratio of 0.5 or less (such as XY or XO) results in a male, and a ratio between 0.5 and 1 (such as X/3A) results in an intersex.
This was demonstrated by Bridges, who observed that the rare white-eyed females were XXY and the rare red-eyed males were XO, due to the non-disjunction of the X chromosomes in the female flies.
What is chromosome non-disjunction?
process where chromosomes fail to separate properly during cell division, resulting in daughter cells with an incorrect number of chromosomes.
This can occur during either meiosis or mitosis and can lead to conditions such as Down syndrome in humans, where an individual has an extra copy of chromosome 21.
In Drosophila melanogaster, non-disjunction of the X chromosomes can result in white-eyed females (XXY) and red-eyed males (XO).
What makes Drosophila melanogaster a good model organism?
Easy to grow and reproduce:
It can be cultured in empty milk bottles with mashed bananas, and it can produce 100 eggs per day per female.
It takes only 12 days from fertilized egg to mature adult.
Easy to distinguish sexes:
The male flies are smaller than the female flies, and have a different shape of the abdomen tip.
Detectable spontaneous mutants:
Different traits, such as eye color, body color, wing shape, etc., can be observed and followed in the progeny.
Small number of chromosomes:
It has only four pairs of chromosomes, two of which are sex chromosomes. This makes it easier to identify and analyze the genes on the chromosomes.
