Sex linked traits, inheritance of gender sex traits
genes exist in varieties called alleles;
46 chromosomes occur in human somatic cells;
sex chromosomes are marked with the letters X and Y.
explain why some traits are coupled with sex;
present with help of a genetic cross the ways of inheriting hemophilia and colour blindness.
Sex linked traits
Sex linked traitsSex linked traits determined by genes located on the X chromosome are determined (in the case of a determinate sex, as in a human, by the XY system). These traits are inherited in the same way as sex. They are not passed on to the offspring independently, but along with other genes located on the X chromosome.
The most famous traits of a sex‑linked disorder are the inability to properly distinguish colours (colour‑blindness) and hemophilia – a disease, manifested by congenital abnormalities in blood coagulation. The appearance of these traits is conditioned by the recessive allele, which is why they occur relatively rarely in the population. In addition, these characteristics are less likely to occur in women than in men. Men can get a recessive allele from their mothers along with their X chromosome. This is enough to reveal the characteristic, because on the Y chromosome there is no corresponding dominant allele. In order for a woman to show a sex linked traits, she would have to inherit two recessive alleles, one for each parent. Women who are heterozygous for sex linked traits and have a dominant allele and a recessive allele in their genotype, are referred to as carriers. In their phenotype, the recessive allele usually does not reveal itself, but they can pass it on to their children.
Using different sources of information, look for examples of sex‑related traits other than those listed in the handbook.
Inheritance of sex‑linked traits
Daltonism is one of the kinds of colour blindnesscolour blindness, characterized by incorrect perception of green colour and frequent confusion with red. The cause of colour blindness is the recessive allele of a gene located on the X chromosome. The dominant D‑element of the same gene determines the correct perception of colours. Men mainly suffer from colour blindness (8% of the population) who received a recessive allele from their carrier mothers. Among women, only 0.5% are colour‑blind. There are two recessive alleles in their genotype, one inherited from the mother and the other from the father.
HemophiliaHemophilia it is a very rare genetic defect that does not result in selected blood coagulation factors in the body. It occurs in 1 in 10 thousand people. Their bodies are often bruised and they bleed from the noses. Even minor injuries cause inflammation and pain in the muscles and joints. Treatment of hemophilia patients involves the administration of synthetic blood coagulation factors throughout their lives.
Hemophilia is inherited in the same way as colour blindness. It is conditioned by the recessive h gene located on the X chromosome.
Determine the probability that in a family of a man who is not colourblind and a woman who is, a child with colourblindness will be born. Answer the answer with appropriate genetic crosses.
Diseases such as colour blindness and hemophilia are mainly suffered by men. Indicate all the reasons why this happens.
- These diseases are transmitted along with a recessive copy of the gene on the X chromosome.
- In order for a woman to have symptoms of the disease she would have to have two X chromosomes containing the disease-allele.
- Because a man has only one X chromosome, it will be enough to inherit symptoms of the disease inheriting a defective copy of the gene on this chromosome.
- These diseases are transmitted together with a defective copy of the gene found on the Y chromosome, and the Y chromosome is only present in men.
Match the feature to the factor that determines it.
the presence of a defective gene on both X chromosomes, presence of a defective gene on the only X chromosome, the presence of the Y chromosome in somatic cells, the presence of appropriate genes on one of the autosomes
| male sex in a human | |
| curly hair in humans | |
| colour blindness in a woman | |
| hemophilia in a man |
A woman who was the carrier of the allele conditioning the onset of hemophilia, she married a man who was a colour blind. On the basis of the appropriate genetic cross, indicate the true statement.
- Each daughter of this couple will be the carrier of the allele conditioning the occurrence of color blindness.
- Each son of this couple will suffer from haemophilia.
- The probability of having a son suffering from haemophilia is 50% for this couple.
- The probability of having a son who is colour blindness is in the case of this pair 50%.
Summary
Sex linked traits, such as colour blindness and hemophilia, are conditioned by recessive alleles of genes located on the X chromosome.
Sex linked traits are much more common in men than in women.
Determine what percentage of children in the marriage in which the father suffers from haemophilia and the mother is free from the symptoms of this disease may be haemophiliacs. Assume that none of the mother's family members showed signs of disease. Save the appropriate genetic crossword.
Keywords
hemophilia, colour blindness, sex‑linked traits
Glossary
cechy sprzężone z płcią – cechy warunkowane przez geny położone na chromosomie X, np. ślepota barw, hemofilia
hemofilia – choroba genetyczna warunkowana przez recesywny allel znajdujący się na chromosomie X; jest efektem braku odpowiednich białek uczestniczących w procesie krzepnięcia krwi
kariotyp – zestaw chromosomów obecnych w komórkach somatycznych organizmu
ślepota barw – zaburzenie widzenia uwarunkowane przez recesywny gen umiejscowiony na chromosomie X; występuje w kilku odmianach, z czego jedna, zwana daltonizmem, polega na nieprawidłowym postrzeganiu barwy zielonej i jej częstym nieodróżnianiu od barwy czerwonej; w skrajnym przypadku ślepota barw powoduje widzenie jedynie w odcieniach szarości