Sex linkage

For generational continuity, reproduction is required. Distinct organisms have different ways of reproducing, and varied animals have different ways of determining sex. Environmental factors like temperature influence sex determination. In both humans and insects, sex is determined through genetic elements and sex linkage features.

Sex chromosomes

Apart from the 22 paired chromosomes defined as autosomes, both females and males have a single set of chromosomes termed as the sex chromosome. It’s called such since it determines a person’s sex. In females, all chromosomes are homozygous pair-XX, but in men, heterozygous pair-XY is present. Females create two X gametes, while males make 1 X gamete and 1 Y gamete during gamete production. As a result, this form of sex mechanism is referred to as the XX-XY or just XY type.

Sex linkage

Sex linkage, also known as sex linked inheritance, is the transmission of traits and their determining genes, as well as sex determining genes, that are carried on the sex chromosome and so passed down from one generation to the next generation. Morgan discovered a sex linkage while studying the inheritance of the red white eye colour characteristic in drosophila. The eyes of Drosophila are red, but a white-eyed mutant arose and freely mated with red-eyed females to produce red-eyed F1 individuals. The ratio of red-eyed to white-eyed people in F2 was 3:1, with white-eyed individuals being all males.

These findings matched Mendelian monohybrid ratio, in which one of the genes is dominant. Normally, half of each group of characters must be males and the other half females, so half of the white-eyed characters should be males and half females, however in this case, all of the white-eyed characters were found to be males. The theory that genes are carried on X – chromosome can explain this unusual behaviour of genes.

Sex Linked Genes 

Sex related genes are genes which are found on both sexes’ chromosomes and are inherited differently by males and females. In mammals, recessive genes on the X chromosome are more typically expressed in males since their only X chromosome includes this gene, whereas females carry a defective recessive gene on one X chromosome which is compensated by a healthy dominant gene on other X chromosome.

Sex Determination in Human

In humans, this is referred to as sex linkage. In human individuals, there are 22 pairs of autosomes. They have also one sex chromosome pair. Females are naturally homogametic. This implies that all of the ova produced by a female contain the same chromosomes, namely the X chromosomes. The Y chromosome is found in a 50 percent ratio in males, with the X chromosome accounting for the remaining 50%. As a result, males create two different types of chromosomes. And, at the time of fertilisation, the X or Y chromosomes have an equal chance of merging with the egg that only has the X chromosome.

As a result, we can conclude that either a girl or a male child has a 50% chance of being born. Sry is a gene found on the Y chromosome. This is the sex-determining area, which aids in the coding of testes-determining variables. This aids in the development of male characters, and if it is absent, feminine characters will develop. This is how a man’s sex connection works.

Sex-influenced genes

There are just two types of allele relationships which are dominance and blending. The existence of the dominant gene in the former situation hides the expression of the recessive allele, regardless of whether an individual is male or female. In the latter instance, where dominance is absent, heterozygous individuals mix. Baldness, for example, is caused by a gene that is more prevalent in men.

If we allow H, the baldness gene, to be dominant in men as well as its allele, h, to be dominant throughout women, the genotypes will be as follows: HH condition will result in baldness, both in men and women, Hh condition will result in non-bald women and bald men, and hh condition will result in non-bald men and non-bald women

Conclusion

If a gene mutation (allele) is found on a sex chromosome instead of a non-sex chromosome (allosome), it causes sex-specific inheritance and presentation patterns (autosome). X-linked recessive, X-linked dominant, and Y-linked are the terms used to describe these in humans. The inheritance and appearance of all the three are different based on the parent’s and child’s gender. This distinguishes them from recessiveness and autosomal dominance in a distinctive way.