Technology of storage and primary processing of agricultural products

14- LABORATORY WORK.

Topic: The transmission of sex-linked traits

The purpose of the work. Living organisms are divided into two sexes, male and female. It consists of gaining an understanding of the chromosomes that control the sexes in the body, that is, the sex chromosomes, and studying the inheritance of the genes located on the sex chromosomes in the offspring.
The content of the work. In the early stages of the development of the chromosome theory of heredity , important events were identified, such as the continuity and number of chromosomes in cells, their equal distribution to new daughter cells during meiosis, the reduction of chromosomes during gamete maturation, and the recovery of diploid numbers in fertilization .
T. Morgan's scientific work (1910) raised the doctrine of the material basis of heredity to a higher level. Experimental proof that genes are located on chromosomes was the second step in the development of the chromosome theory of heredity. 
T. Morgan conducted his experiments on fruit mosquito drozofila because it was a very convenient object for genetic research. 
The chromosomal theory of heredity has been of great importance in determining the presence of sex chromosomes in certain sex organisms and their effect on heredity in the development of the problem of sex mark development and identification .
It is known that all somatic cells have an even number of chromosomes, and that each pair of chromosomes has exactly the same shape and size . Observations have shown that in most animals and some genus plants, the sum of the chromosomes of male and female individuals differs from each other by a pair of chromosomes, which (the X and U chromosomes) are called the sex chromosome. The remaining chromosomes are similar in male and female individuals and are called autosomal chromosomes (A) . In humans, mammals, Drosophila, and some other species, the female sex somatic cell has a pair of similar sex chromosomes (two X chromosomes) that form the same gamete (homogametalac). The male sex has different sex chromosomes (having X and U chromosomes) and therefore forms different gametes (heterogametal). The female Drosophila has 6 autosomes and an X, X chromosome. When a gamete is formed, the egg cell has 3 autosomes and one X chromosome . Sperm, on the other hand, have 3 different autosomes, but half of them are X chromosomes and the other half are U chromosomes.
The chances of an X-chromosomal egg cell fertilizing are only two different. Sometimes it can happen with an X-chromosomal sperm, and sometimes with a U-chromosomal sperm.
6A + XX x 6A + XU
gametes 3A + X, 3A + X 3A + X, 3A + U
6A + XX, 6A + XU, 6A + XX, 6A + XU
The fertilized egg zygote is a 6A + XX or 6A + XU chromosome, which is formed in equal amounts. The sex-to-divorce ratio is 1: 1.
If the genes are located on autosomal chromosomes, it does not matter which sex (male or female) of these dominant or recessive genes is inherited through chromosomes in the generation of characters .
If the genes are located on the sex chromosomes, the transmission and separation of this trait depends on the state of the sex chromosomes in meiosis and their addition during fertilization.
The characters in the X chromosomes and a gene transfer is called gender colluded with the transfer. This phenomenon has been proven in T. Morgan's experiment with the Drosophila fly, which shows the effect of chromosomes on heredity . In the Drosophila fly, the gene that controls eye color is located on the X chromosome . Therefore, this sign is given from mother to son, from father only to girls . The gene is located on the X chromosome on the sex chromosome . For example, when a white-eyed female and a red-eyed male Drosophila fly are intertwined, the gametes propagate as follows.
W - red eye, dominant character
w - white eye, recessive character
X ^W x ^W x ^w
Gametes X ^W X ^w , U
X ^W X ^w X ^W U
girl boy
The eyes of the resulting girl's body are red because she received the dominant W gene from the mother, and the boy's eyes are red because he received the dominant W gene from the mother. By interbreeding the F ₁ hybrids, we can observe the following changes.
X ^W X ^w x X ^W U
Gametes X ^W , X ^w X ^W , U
X ^W X ^W , X ^W X ^w , X ^W U, X ^w U
The white-eyed (boy) Drozfila received the W gene in the mother, and the red -eyed (girl) received the W-gene from the father.
It has been found that a person has a number of sex-linked traits . These characters are paired with sex chromosomes - X or U. Some inherited diseases are associated with the X chromosome, and such a disease occurs in a son who receives an X chromosome from his mother. Some inherited disease is linked to a chromosome that is passed from father to son. For example, the presence of a veil between the paws of some men’s feet is related to the U chromosome. The disease is harmless and occurs only in the male sex of the offspring. In humans, a disease that cannot distinguish between red and green ( color blindness) is associated with the X chromosome . Daltonizm disease -carrying X chromosome in women, regardless of who her husband with this disease to the sons.
Below we observe the transmission of this gender-related trait from generation to generation. For example, if a woman in a family is healthy and a man is colorblind (chromosome , healthy with color blindness ), let's define them as follows: mother XX =, father X U = . From their marriage a daughter and a son are born. An abnormal X chromosome is passed from father to daughter, a normal U chromosome to a son, and a normal X chromosome to a mother . This means that the girl will be the carrier of the disease (XX = ) and the boy will be healthy (XU =). The girl marries a healthy young man and has two daughters and two sons. First her father and maternal chromosomes (XX * normal, healthy girl, this is not a carrier of the disease. The second father to the mother of a normal X daltonizm gene of chromosome XX the past, it is considered normal, but daltonlar illness a secret.
The first son has normal X chromosomes from the mother, U chromosomes from the father (XU *), and he is healthy. The second son is passed from the mother to the X chromosome, which contains the abnormal color blindness gene, and from the father to the U chromosome (XU * ). This means that it cannot distinguish color, i.e. it is colorblind. This example shows that 50% of boys who have passed the X chromosome from their mother have the color blindness gene .