Mendelian Inheritance:
Gregor Mendel figured out Meiosis - how alleles segregate and shuffle during the production of eggs and sperm.
Law of Segregation: allele pairs separate or segregate during gamete formation, and randomly unite at fertilization.
Law of Independent assortment: alleles for a trait separate when gametes are formed. These allele pairs are then randomly united at fertilization.
Punnet Squares: represent Meiosis, followed by fertilization.
- 1:1, 3:1 = Monohybrid cross
- 1:1:1:1, 9:3:3:1 = Dihybrid cross
http://biology.about.com/od/geneticsglossary/g/law_of_segregation.htm
http://biology.about.com/od/mendeliangenetics/ss/independent-assortment.htm
Law of Segregation: allele pairs separate or segregate during gamete formation, and randomly unite at fertilization.
Law of Independent assortment: alleles for a trait separate when gametes are formed. These allele pairs are then randomly united at fertilization.
Punnet Squares: represent Meiosis, followed by fertilization.
- 1:1, 3:1 = Monohybrid cross
- 1:1:1:1, 9:3:3:1 = Dihybrid cross
http://biology.about.com/od/geneticsglossary/g/law_of_segregation.htm
http://biology.about.com/od/mendeliangenetics/ss/independent-assortment.htm
Inheritence:
Chromosomes # 1-22 are autosomal
Chromosome # 23 is sex-linked (x or y chromosome)
Dominant - The allele that is expressed when present in a heterozygote
Recessive - The allele that is not expressed in the phenotype of a heterozygote
Chromosome # 23 is sex-linked (x or y chromosome)
Dominant - The allele that is expressed when present in a heterozygote
Recessive - The allele that is not expressed in the phenotype of a heterozygote
Complete Dominance:
Complete dominance occurs when the dominant allele of a heterozygous gene is fully expressed over the recessive allele.
Incomplete Dominance:
Incomplete dominance occurs when neither allele is completely dominated by the other.
Co-dominance:
Co-dominance occurs when the heterozygote expresses both alleles equally.
Pedigrees:
As you begin to work with pedigrees, as yourself:
1) What is the male to female ratio of affected individuals?
2) Are there people that are unaffected that pass the trait on to their offspring?
1) What is the male to female ratio of affected individuals?
2) Are there people that are unaffected that pass the trait on to their offspring?
Choices for the "mode of inheritance" are:
Autosomal Dominant
Autosomal Recessive
X-Linked Dominant
X-Linked Recessive
Y-Linked
Mitochondrial
Autosomal Dominant
Autosomal Recessive
X-Linked Dominant
X-Linked Recessive
Y-Linked
Mitochondrial
Examples: Huntington’s, short-limbed dwarfism. Occurs when there is one parent affected and there is one parent carrier (heterozygote) = 50% normal, 50%
affected. Affected males and females have an equal opportunity of passing the trait to their offspring and affected individuals are heterozygous for the
trait.
affected. Affected males and females have an equal opportunity of passing the trait to their offspring and affected individuals are heterozygous for the
trait.
Examples: cystic fibrosis, tay-sachs, hemochromatosis. This occurs if 2 heterozygotes mate = 25% will be normal, 50% will be carriers, and 25% will be affected. There is no gender bias and only appears when the individual is homozygous for the mutant allele.
Ratio of 2 females affected: 1 male. There is no transmission of the mutant gene from father to son. All of the daughters of an affected male will have the mutant gene since the male only contributes one X-chromosome to daughters. There is a 50% chance that an affected woman will have offspring that
are also affected.
are also affected.
Examples: muscular dystrophy, hemophilia, congenital deafness. X-linked recessive skips a generation. Females are often not affected because they have 2 X chromosomes and would need both of them to carry the affected gene for it to appear in the phenotype. There is also father to daughter conduction or mother to daughter and/or son conduction.
ALL MALES AFFECTED
Females pass it on to all offspring. Males will not pass on the trait to their offspring because they do not give mitochondria to offspring.
Blood Typing:
Blood Types-
A, B, and O alleles
A person can be:
AB, AO, AA
BA, BO, BB
Blood Types Tutorial: http://www.biology.arizona.edu/human_bio/problem_sets/blood_types/genotypes.html
If someone has blood type A, they must have at least one copy of the A allele, but they could have two copies. Their genotype is either AA or AO. Similarly, someone who is blood type B could have a genotype of either BB or BO.
A blood test of either type AB or type O is more informative. Someone with blood type AB must have both the A and B alleles. The genotype must be AB. Someone with blood type O has neither the A nor the B allele. The genotype must be OO.
Blood type Possible genotypes Blood Type Possible genotypes
A AA AO AB AB
B BB BO O OO
A, B, and O alleles
A person can be:
AB, AO, AA
BA, BO, BB
Blood Types Tutorial: http://www.biology.arizona.edu/human_bio/problem_sets/blood_types/genotypes.html
If someone has blood type A, they must have at least one copy of the A allele, but they could have two copies. Their genotype is either AA or AO. Similarly, someone who is blood type B could have a genotype of either BB or BO.
A blood test of either type AB or type O is more informative. Someone with blood type AB must have both the A and B alleles. The genotype must be AB. Someone with blood type O has neither the A nor the B allele. The genotype must be OO.
Blood type Possible genotypes Blood Type Possible genotypes
A AA AO AB AB
B BB BO O OO