You can recall that recessive traits are only shown if they are homozygous (both copies of the alleles are recessive). In some genetic diseases that are caused by sex-linked genes, for example haemophila, a color blindness trait, the allele for the disease is recessive. If the offspring is a girl, one of the X chromosomes comes from the mother and the other X chromosome comes from the father. If the offspring is a boy, the X chromosome comes from the mother and the Y comes from the father. Remember that a biological female carries 2 sets of X chromosomes (XX) and a biological male carries one set of the X and one set of Y chromosomes (XY). Sex-linked genes are genes that are inhererited through the X chromosome. 1 Illustration to show the inheritance of dominant and recessive alleles for eye colour. If a person has 2 copies of the blue eye allele (both recessive) then the person would have blue eyes. This is considered being homozygous, having the same 2 copies of alleles. Recessive alleles only show the traits if the person has 2 copies of the same alleles. If a person has one copy of the brown eye allele (dominant) and one copy of the blue eye allele (recessive) then that person is considered to be a carrier of the blue eye allele, since they would have brown eyes but still have the blue eye trait that is not shown. Recessive alleles are the genes that do not show the trait. If a person carries two copies of the brown eye allele, since they are codominant, the person would have brown eyes. For example, if the dominant trait is red for flowers and another dominant trait is white, then the flower will have both red and white as the dominant traits are expressed equally. When you have two copies of the alleles that are both dominant, this is called codominance. You would need at least one copy of the brown eye allele (B) to have brown eyes. For example, the brown eye allele is dominant, B.
If a person carries a heterozygous set of alleles (both uppercase and lower case letter of the gene) then the person will show the dominant trait (being that there is an uppercase letter present). With that being said, there are 2 sets of alleles that can be dominant or recessive. Remember that human cells carry 2 copies of each chromosome, one from the biological mother’s genes and one from the biological father’s genes. In order for a person to show the dominant trait, one of the person’s parents must have the dominant trait (which is an uppercase letter). Recessive alleles are seen as a lower case of a letter b. Alleles can be considered dominant or recessive, with dominant being the trait that is observed or shown and recessive being the trait is not seen.ĭominant alleles are seen as an uppercase of a letter for example, B. Different versions of a gene are called alleles.
Have you ever wondered why some people have blue or brown eyes? The coloring of the blue and brown eyes is an example of different versions of a gene. Understand why dominance sometimes doesn’t matter for sex-linked genes Know what it means for a gene to be dominant
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