Where are we going with this? The information on this page should increase understanding related to this standard: Identify patterns of inheritance to predict genotype/phenotype and solve punnett square problems.
- Genetic information is carried by DNA.
- DNA is organized into structures called chromosomes.
- Chromosomes carry information for specific traits in sections called genes.
- Genes having different versions or variations of a trait are alleles.
- Some traits are dominant, some are recessive, some are incompletely dominant, and some are codominant.
- Some traits require information from more than one gene; these are polygenic.
- Humans have 46 chromosomes organized into 23 pairs; on chromosome from each pair comes from the mother and the other comes from the father.
- How many chromosomes an organism has
- Sex of the organism
- Presence of a chromosomal disorder
Sex-linked traits: traits that are carried on the sex chromosomes.
In the image above, the Y chromosome does not have the genes labeled A, B, and C. (This is an example and does not necessarily model real genes exactly.) Therefore, whatever traits are controlled by those genes will come through in the child. The Y chromosome has no alternative to offer; the gene of the X chromosome will be expressed.
Many people can think of someone who is color blind. If you can, are they male or female? You probably answered that they were male. Why?
Hemophilia is a recessive, sex-linked disorder. Both males and females can have it.In the image to the right, the father has the recessive trait on the X chromosome. He has no allele for that trait on the Y chromosome. The female has one X with, and one X without the trait.Therefore, the presence of hemophilia is determined by which of th X chromosomes the female passes.The four possible outcomes are shown in among the daughters and sons.
Some Examples of Sex-linked Traits:
- Red-green colorblindness
- Male Pattern Baldness
- Duchenne Muscular Dystrophy
Aneuploidy can occur in both the autosomes and in the sex chromosomes. There are a numerous kinds of aneuploidy caused by nondisjunction. A few of them are illustrated below:
Monosomy is when the offspring only received one copy of a chromosome.Trisomy is when the offspring received three copies of a chromosome.