Period 2
Polydactyly is a condition in which a person has more than five fingers per hand or five toes per foot. Polydactyly occurs in the womb; instead of developing only one thumb and four fingers an extra finger is added Usually the hand is formed in the womb and when it is being split it is made into 4 fingers, 1 thumb. However sometimes an extra split occurs and abnormal number of fingers is produced It is a autosomal dominate characteristic
The cause of the disorder is usually found on chromosome 13. However for some cases it is not known There is another gene or chromosome that the mutation could happen in that could cause polydactyly
Mode of Inheritance Polydactyly is autosomal dominant. Autosomal dominant means that an offspring can get this disease by having it passed down from just one parent. Polydactyly occurs because of genetic disorders or errors in fetal development. Polydactyly can also be a symptom for another disease. Ex. – Bardet-Biedl syndrome Ex. – Bloom’s syndrome Ex. – Jeune’s thoracic dystrophy syndrome
What are Alleles? A person has two alleles per gene You get one of the two alleles in a gene from your father and the other from your mother Recessive alleles are represented by the letter of the characteristic in lower-case form Dominant alleles are represented by the letter of the characteristic in capital R – Dominant r – Recessive The dominant alleles and the recessive alleles both represent two different possible characteristics. The “characteristic” will be dominant if the gene has one dominant allele or two dominant alleles The “characteristic” will be recessive if the gene has two recessive genes only
GGGr gg Gg GgGg Ww w w WWWW Heterozygous Homozygous hh hhhh
GGGg gg G g GgGg Ratio 1GG 2Gg 1gg Percentage 25% -GG 50% - Gg 25% - gg 75% chance of getting Polydactyly 25% chance of not getting Polydactyly
GGGg gg G g GgGg GG – two dominant alleles Gg – one dominant allele and one recessive allele gg – two recessive alleles Phenotype GG = Recieve polydactyly Gg = Receive polydactyly gg = Normal amount of fingers Genotype GG = Homozygous dominant Gg = Heterozygous dominant gg = Homozygous recessive Top – Father Left – Mother
GGGg gg G g GgGg Phenotype - Ratios- 3 for polydactyly : 1 for normal - Percentage – 75% chance of polydactyly 25% chance of normal # of f fingers Genotype - Ratios- 1 GG : 2 Gg : 1 gg - Percentages- 25% GG : 50% Gg : 25%gg
G g GgGg Genotype Ratio – 1 GG; 2 Gg; 1gg Percentage – 75% chance receive disease 25% chance of not getting disease Phenotype Ratio – 3 with Polydactyly; 1 without Polydactyly Percentage – 75% of getting Polydactyly GGGg gg
Female – circle Male – Square All green – homozygous recessive gene, person doesn’t have the disease, person has 2 healthy alleles Half green, half black (or star) – heterozygous gene, person has the disease because you only one dominant gene with the disease to get it All black homozygous dominant. Has the disease.
Student Practice Key – circle – female square – male shaded in (black) – two dominant alleles not shaded (red) – two recessive alleles half shaded – one dominant and one recessive allele
If two parents are homozygous dominant, how likely would it be for a child not have the disease? If two parents are homozygous dominant, how likely would it be for a child not have the disease? If one parent is homozygous dominant but another is homozygous recessive, is it possible for one of the children not to obtain the disease? If one parent is homozygous dominant but another is homozygous recessive, is it possible for one of the children not to obtain the disease? If one parent were heterozygous dominant and homozygous recessive, how likely is it for a child to get the disease? If one parent were heterozygous dominant and homozygous recessive, how likely is it for a child to get the disease? Questions???????? 0% child would wind up homozygous dominant 0% child would wind up homozygous dominant Each of the children will wind up heterozygous dominant Each of the children will wind up heterozygous dominant 50%