Hemophilia is crossed in a 2 x 2 Punnet square using the technique for single hybrid, sex-linked crosses. The trait in question, hemophilia, should be denoted with a superscript on the X chromosome. Typically a capital H is used for the normal gene; the lower case h is used to denote the gene for hemophilia. Filling out the Punnet square gives the predicted percentages of normal, carrier or hemophiliac children.Know More
In order to set up the Punnet square properly, there is some information necessary about the gene in question. For hemophilia, it is important to know that it is sex-linked, carried on the X chromosome and recessive. This means that women will only have hemophilia if both X chromosomes contain the hemophilia gene because a normal gene on one of the X chromosomes is dominant over the hemophilia gene. Women with only one hemophilia gene are carriers. Men with the hemophilia gene are afflicted with hemophilia because they only have one X chromosome.
To use a Punnet square on a cross between two people, draw a 2 x 2 square. Write the woman's chromosomes down the left side, noting if each chromosome is XH or Xh. Next, write the man's chromosomes across the top, noting if his X chromosome is XH or Xh. Then, carry out the cross as you would in any other Punnet square. As an example, when crossing a man with hemophilia and a woman who is a carrier, the children will be as follows: 25 percent female carrier, 25 percent female with hemophilia, 25 percent normal male, and 25 percent male with hemophilia.Learn more about Molecular Biology & DNA
The self-fertilization of a pea plant with yellow, round seeds that is heterozygous for both the color and shape of the seeds is an example of a dihybrid cross. Yellow is the dominant allele for color. Green is the recessive allele. Round is dominant for shape, and wrinkled is recessive.Full Answer >
A monohybrid cross is a type of genetics breeding experiment between two parent organisms that each have a different homozygous trait. An example is a cross between a pea plant with a dominant green seed and one with a recessive yellow seed. The offspring are all born with green seeds.Full Answer >
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Assuming each gene has two alleles, or alternate genes, there are 64 squares in a trihybrid cross Punnett square. When there is an independent assortment of genes, the number of combinations is two raised to the power of the number of genes.Full Answer >