Complex Patterns of Heredity PDF

Complex Patterns of Heredity Mendel’s principles offer a set of rules that predict various patterns of inheritance. The Big Idea There are exceptions to every rule, and exceptions to the exceptions.  + What are our possible outcomes for this combination of flowe...

Complex Patterns of Heredity Mendel’s principles offer a set of rules that predict various patterns of inheritance. The Big Idea There are exceptions to every rule, and exceptions to the exceptions.  + What are our possible outcomes for this combination of flower color? What if neither of the two traits was dominant to the other? I. Incomplete Dominance In incomplete dominance, both alleles are neither dominant nor recessive. RR WW RW  Heterozygous phenotype is intermediate between the two homozygous phenotypes. Homozygous parental phenotypes are not seen in F1 offspring. Green betta fish Steel blue betta fish Royal blue betta fish (GG) (BB) (GB) F1 generation R R RW RW W RW RW W Genotype: RW Phenotype: 100% pink flowers F2 generation R W RR RW R Red rose Pink rose W RW WW Pink rose White rose Genotype: RR, RW, WW Phenotype: 25%= red flowers 50%= pink flowers 25%= white flowers II. Co-Dominance Codominant alleles will both be completely expressed. Codominant alleles are neither dominant nor recessive. Ex: multi-colored red and white rose. Ex: In humans, ABO blood type. (A, B, AB, O) F1 generation R R RW RW W RW RW W Genotype: RW Phenotype: 100% red and white flowers F2 generation R W R RR RW W RW WW Genotype: RR, RW, WW Phenotype: 25% red flowers, 50% red-white flowers, 25% white flowers III. Multiple Alleles Some traits are controlled by more than 2 alleles for a certain gene. Human blood groups are controlled by 3 alleles - IA, IB, and i. IA and IB are codominant to each other, and dominant to i. There are 4 possible blood types - A (IAIA or IAi), B (IBIB or IBi), AB (IAIB), and O (ii). Sex Determination Sex chromosomes determine an individualʼs gender. The X chromosome is much larger than the Y chromosome. Therefore, it makes sense to assume that X chromosomes carry more genes and genetic information than the Y chromosomes.  IV. Sex-Linkage The presence of a gene on a sex chromosome is called sex linkage. Genes found on the X chromosome are called X-linked, and genes found on the Y chromosome are called Y-linked. The most common X-linked disorders are: a) Hemophilia b) Color Blindness Color Blindness: Colorblindness is an X-linked trait, carried by sex chromosomes. The allele for colorblindness is represented by XC, while the normal allele is X. A female must have two XC alleles in order to be colorblind, but if a male carries the XC allele, he will definitely be colorblind. Colorblindness Test In each of the circles, see if you can identify a hidden number. A person with normal vision will see the numbers, while a person who is colorblind will see only the circle. Hemophilia: Hemophilia is another example of a sex-linked trait. This rare disease causes blood not to clot properly. Failure of blood to clot may result in death. This trait is located on the X chromosome. Males are more likely to display this disorder since they only must have one copy of the allele.  V. Polygenic traits: Polygenic traits arise from the interaction of multiple pairs of genes. Traits controlled by two or more genes are said to be polygenic traits. Polygenic means “many genes.” Polygenic traits often show a wide range of phenotypes. The variety of skin color in humans comes about partly because more than four different genes probably control this trait.