80 Questions
What is the term used to describe the disturbances of red and green color vision caused by abnormal visual dyes?
Daltonism
What is a Y-body?
A highly fluorescent body in the interphase cell nucleus
In North European populations, which type of color vision disturbance is 4-5 times more common than protanopia?
Deuteranomaly
How many Y bodies are typically found in male cells?
Equal to the number of Y chromosomes
What is the term for a person who can see correctly but carries the gene for a type of color vision anomaly?
Correctvision
What is the term for the genetic cross between a daughter with protanomaly and a son seeing correctly with deuteranomaly?
XP1Y
What is Lyonisation?
Inactivation process of one of the X chromosomes
How is lyonisation described?
Independent, random, indivertible
What are Ishihara pseudoisochromatic tables used to check?
Color vision ability
In the Ishihara full test, how many tables are there typically?
36
When does lyonisation occur in female embryonic cells?
Around 16 days of embryonic life
'Deuteranomaly' affects approximately what percentage of men in North European populations?
~4-5%
What is the purpose of lyonisation?
To balance the gene expression from X chromosomes in XX and XY individuals
Which cells exhibit Y-drummer's sticks?
Neutrophils
'Protanopia' affects approximately what percentage of women in North European populations?
~0.5%
What happens to genes located in the pseudoautosomal region during lyonisation?
They are not inactivated
What is the most common type of mutation detected in Haemophilia B?
Missense mutations
Which type of mutation accounts for 11% of all mutations detected in Haemophilia B?
Splicing mutations
What level of factor VIII or IX in plasma is associated with the mild form of haemophilia?
0.05-0.40 IU/ml (5-40% norm)
Which type of bleeding is characteristic of severe haemophilia?
Prolonged bleeding after minor injuries
What dominates over the deuteranomaly allele Xd1 in terms of colour vision?
X-norm allele
How are women affected when they possess an abnormal colour vision gene on each X chromosome?
They see correctly
In Haemophilia B, what percentage of all mutations are characterized as gene rearrangements?
<1%
Which clinical form of haemophilia exhibits severe bleeding as a result of injuries and micro-trauma?
Severe
What is the inheritance pattern when a female carrier and a healthy man have children?
50% of sons will be sick and 50% healthy; 50% of daughters will be carriers and 50% healthy
What happens when an ill man (hemizygous) has children?
He does not pass the disease to sons, but all daughters will be carriers
What is the phenotype of hemizygous men and heterozygous women with a mutated gene?
Both get ill
What is the likelihood that sick women (heterozygotes) pass the mutant gene to both daughters and sons?
50% probability to both daughters and son
What is the effect of the mutant dominant gene in men?
It is often lethal
What is the phenotype of XAXA genotype in women?
Ill, most common lethal genotype
In the inheritance of sex-linked dominant traits, what is the phenotype of XAY genotype in men?
Ill, often a lethal feature
What is the genotype and phenotype of XaXa individuals?
'Invisible' carrier
What is a useful feature of fruit flies in genetic studies?
The presence of polytene chromosomes in salivary gland cells
How is the human karyotype classified?
23 pairs of chromosomes, 22 autosomes, and 1 heterosome
According to the classical division, which group do chromosomes 1-3 belong to?
Group B - Large submetacentric
In human karyotyping, how are autosomes arranged following the rules?
By size, followed by sex chromosomes X and Y
Which feature of chromosomes is used for their classification into groups A to G?
Length and centromere position
What system describes the rules for recording cytogenetic test results?
ISCN (The International System for Human Cytogenetic Nomenclature)
How are chromosomes stained in human karyotyping using Giemsa reagent?
G-bands are used for staining
What is the term used to describe the giant chromosomes in fruit fly salivary gland cells?
Polytene chromosomes
What type of inheritance is described as the transmission of traits from father to son?
Holandric inheritance
In the inheritance of recessive sex-linked traits, what is the phenotype of individuals with the genotype XAXa?
Clinically healthy, carrier
In the case of female carriers (heterozygotes) of a mutated gene, what is the probability of transmitting the gene to daughters and sons?
50% to both daughters and sons
What term describes individuals who have only one X chromosome and one copy of each gene linked to the X chromosome?
Hemizygous
In the inheritance of sex-linked dominant traits, what is the phenotype of individuals with the genotype XAY?
Healthy
What is the genotype of Illman?
XAY XaXa
What is the term for individuals with only one copy of a particular gene on the sex chromosomes?
Hemizygous
What is the genotype of Healthywoman?
XAY XaXa
In the inheritance of sex-linked dominant traits, what is the expected phenotype of a female with the genotype XDXd1?
Expresses the trait
When an Illwoman and Healthyman have offspring, what percentage of sons will be ill?
0%
When a woman who is a carrier for a recessive sex-linked trait has a son, what is the probability that the son will inherit the mutated gene?
50%
What is the genotype of a female carrier of the mutated gene for hemophilia B?
XAXa
For individuals with hemophilia B, what type of mutation accounts for approximately 11% of all identified mutations?
Splicing mutations
When a hemizygous man with haemophilia A has children with an Illwoman, what percentage of daughters are expected to be healthy carriers?
~50%
If a woman carries an abnormal color vision gene on each of her X chromosomes, what is her visual perception like?
Normal color vision
What is the inheritance pattern when an ill man (hemizygous) has daughters?
They will be healthy carriers
In the inheritance of sex-linked recessive traits, what is the phenotype of XaXa genotype in women?
Healthy
What is the phenotype of hemizygous men and heterozygous women with a mutated gene?
Sick
When a sick woman (heterozygote) passes the mutant gene, what is the likelihood that her sons will inherit it?
50%
What happens to genes located in the pseudoautosomal region during lyonization in female embryonic cells?
They are silenced
In North European populations, which type of color vision disturbance is about 4-5 times more common than protanopia, protanomaly, and deuteranopia?
Deuteranomaly
Which term is used to describe the disturbances of red and green color vision caused by the abnormal amount of visual dyes?
Daltonism
What is the term for a person who can see correctly but carries the gene for a type of color vision anomaly?
Hemizygous
When a female carrier and a healthy man have children, what is the inheritance pattern observed for the mutated gene?
X-linked recessive
What is the term used to describe the genetic cross between a daughter with protanomaly and a son who sees correctly with deuteranomaly?
Protandutic cross
What is the term for individuals who possess only one copy of a recessive gene on the X chromosome?
Hemizygous individuals
In the inheritance of sex-linked recessive traits, what is the phenotype of females who are carriers of the mutated gene?
Normal phenotype
When a female carrier and a healthy man have children, what is the likelihood that their sons will inherit the mutated gene?
25%
What is the term used to describe individuals who carry a gene for a certain trait but do not express the trait themselves?
Silent carriers
In sex-linked dominant trait inheritance, how are females affected when they possess an abnormal gene on one X chromosome?
They exhibit the trait mildly
What is the term for the graphical set of chromosomes typical for a given individual or species?
Karyotype
In the inheritance of sex-linked recessive traits, what is the phenotype of individuals with the genotype X^AX^a?
Hemophilia
When an ill man (hemizygous) has children, what is the likelihood that his daughters will be carriers of the mutated gene?
50%
In the inheritance of sex-linked dominant traits, what is the phenotype of individuals with the genotype X^AY?
Hemophilia
For female carriers (heterozygotes) of a mutated gene, what is the probability of transmitting the gene to their sons?
~25%
What is the term for a person who carries the gene for a type of color vision anomaly but can see correctly?
'Carrier' individual
In the case of female carriers (heterozygotes) of a mutated gene, what is the probability of transmitting the gene to their daughters?
~50%
Which type of mutation accounts for 11% of all mutations detected in Haemophilia B?
Gene rearrangements
'Protanopia' generally affects what percentage of women in North European populations?
~0.5%
'Deuteranomaly' typically affects what percentage of men in North European populations?
~4-5%
Study Notes
Genetic Studies of Fruit Flies
- Fruit flies are useful in genetic studies due to:
- Presence of polytene (giant) chromosomes in salivary gland cells
- High frequency of gene mutations affecting various morphological features
Human Karyotype
- Human karyotype consists of 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes (heterosomes)
- X and Y chromosomes are classified as sex chromosomes
- Sex chromosomes are arranged at the end of the karyotype, following the size and centromere position
Chromosome Classification
- Chromosomes are classified into seven groups (A to G) based on:
- Length
- Centromere position
- Table 1 shows the classical division of human chromosomes
Chromatin Y
- Chromatin Y (Y-body) is a condensed, heterochromatic part of the long arms of Yq12
- Visualized by the fluorescent method in the interphase cell nucleus
- Number of Y bodies is equal to the number of Y chromosomes
- Found in 30-50% of studied male cells, including sperm, lymphocytes, and oral epithelial cells
Lyonisation
- Lyonisation is the process of inactivation of one X chromosome in female cells
- Inactivation is:
- Independent
- Random
- Irreversible
- Compensatory mechanism to balance the level of gene expression on sex chromosomes
Inheritance of Sex-Linked Traits
- Inheritance patterns of sex-linked traits:
- Hemizygous men and heterozygous women both get ill
- Heterozygous women with a mutated gene usually have a mild form of disease
- Hemizygous men do not pass the disease to their sons, but all daughters will be carriers
- Sick women (heterozygotes) pass the mutant gene to both daughters and sons with 50% probability
Haemophilia
- Haemophilia A and B are recessive sex-linked diseases
- Caused by mutations in the genes F8C and F9, respectively
- Frequency of occurrence:
- Haemophilia A: 1:10,000 to 1:20,000 births
- Haemophilia B: 1:30,000 births
- Clinically, Haemophilia A and B do not differ from each other, symptoms appear in early childhood
Colour Vision
- Colour vision disturbances are caused by point mutations within the deutan gene
- In North European populations, red and green colour vision disturbances affect:
- About 8% of men
- About 0.5% of women
- Deuteranomaly is 4-5 times more common than protanopia, protanomaly, and deuteranopia
FISH Technique
- FISH (Fluorescence In Situ Hybridization) is a cytogenetic technique to detect a specific DNA sequence in genetic material
- Uses fluorescent DNA probes to identify specific DNA sequences
- Applications:
- Identification of additional genetic material (marker chromosomes)
- Evaluation of structural aberrations
- Detection of submicroscopic aberrations
- Rapid detection of aneuploidy/polyploidy in pre- and postnatal diagnosis
Test your knowledge on the inheritance patterns of sex-linked dominant traits, including scenarios involving female carriers and ill men. Learn about the different outcomes for sons and daughters based on the genetic makeup of the parents.
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