16 Multiple AllelesSome human traits are controlled by a single gene that has two or more alleles.Three or more forms of a gene that code for a single trait.In this pattern of inheritance, the genes have more than two alleles controlling them.
17 Multiple Alleles Even though a gene may have multiple alleles, a person canonly carry two of those alleles.Chromosomes exist in pairs –Each chromosome in a paironly carries one allele for eachgene
18 Multiple AllelesBlood type in humans is an example of this inheritance pattern.The four different blood groups:A, B, O, and ABAre produced by three different alleles:A, B, and O
20 Blood Type Practice Problems: A mother is AB and a father is O. Draw the Punnett square.A BOWhat is the probability their offspring will have A type blood? ____Can they have an offspring with O blood?
28 Genetic DisorderAn abnormal condition that a person inherits through genes orchromosomes.Genetic disorders are causedby mutations.Down syndrome and cystic fibrosis are two examples of genetic disorders.
29 Genetic Recessive Disorders Many human genetic disorders are caused by recessive genes.Occur when both parents have the recessive allele for the disorder.Parents may be heterozygous and have no symptoms and pass the trait onto any offspring.
31 Boy or Girl?The gender of a baby is determined by genes on chromosomes.There are 23 pairs of chromosomes in each of our cells. One of pair ofchromosomes are called sexchromosomes.
32 Boy or Girl? The sex chromosomes determine whether a person is male or female.The sex chromosomes are the only pair of chromosomes that do not always match.
33 FemalesTwo sex chromosomes match XXSince both chromosomes are X, all eggs carry one X chromosome.
34 MalesTwo sex chromosomes don’t match XY, so sperm cells will either carry an X or a Y chromosome.
35 Sex-Linked Genes Some human traits occur more often in one gender than the other.Sex-Linked Genes: Genes on the X and Y chromosomes, whose alleles are passed from parent to offspring on sex chromosomes
36 Sex Linked GeneIn females, a dominant allele on one X chromosome will mask a recessive allele on the other X chromosome.In males, there is no matching allele on the X and Y chromosome. As a result, any allele on the X chromosome will produce the trait in a male who inherits it.
37 Sex-Linked GenesBecause males have only one X chromosome, males are more likely than females to have a sex-linked trait that is controlled by a recessive allele.
38 Sex-Linked Punnett Square Let C = Normal Vision c = ColorblindCross: Normal Male ( ) x Carrier Female ( )