Maternal gametes Maternal gametes Maternal gametes Maternal gametes 00 00 match on the Y in a allele erne is located on a sex the The ey loss: Many genes on the X do not have ol be by a allele. esult is that by the is usually Sex Linkage F1 seen only in the heterogametic sex (XY) and occurs rarely in the homogametic sex (XX). In humans, recessive sex linked genes are responsible for a number of heritable disorders in males, e.g. hemophilia. Women who have the recessive alleles on their chromosomes are said to be carriers. Ides: Many genes on the X chromosome do not have ol therefore be masked by a dominant allele. inkage is a special case of linkage occurring when a is located on a sex chromosome (usually the X). The Hemophilia is an inherited genetic disorder linked to the N-chromosome that results in ineffective blood clotting when a blood assel is damaged. The most common type, hemophilia A, occurs n Lin 5000 male births. Any male who carries the gene will express the phenotype. Hemophilia is extremely rare in women. Parents Carrier Normal female male 1. A couple wish to have children. The woman knows she a carrier for hemophilia. The man is not a hemophiliac. Use the notation Xh for hemophilia and XH for the dominant allele to complete the diagram on the right including the parent genotypes, gametes and possible fertilizations. Write the genotypes and phenotypes in the table below. Gametes Genotypes Phenotypes Possible pou Male fertilizations children Paternal gametes Paternal gametes Female children 00 00 a) A second couple also wish to have children. The woman knows her maternal grandfather was a hemophiliac, but neither her mother or father were. Determine the probability she is a carrier (XHxh) Use the Punnett squares, right, to help you: Paternal gametes Paternal gametes (b) The man is a normal non-hemophiliac male. Determine the probability that their first male child will have hemophilia. Use the Punnett squares, right, to help you: 00 ay 3. The gene for red-green colour vision is carried on the X chromosome. If the gene is faulty, colour blindness (X°) ill occur in males. Red-green colour blindness occurs in about 8% of males but in less than 1% of females. Parents Non colour Colour blind female blind male A colour blind man has children with a woman who is not colour blind. The couple have four children. Their phenotypes are: 1 non colour blind son, 1 colour blind son, 2 non colour blind daughters. Describe the mother's: (a) Genotype: (b) Phenotype: Gametes (C) Identify the genotype not possessed by any of the children: Possible fertilizations, WER