1Law of Segregation
two alleles for a single gene separate during gamete formation so that each gamete receives only one allele
2Law of Independent Assortment
During gamete formation, different pairs of alleles segregate INDEPENDENTLY of each other
3Phenotypic Ratio for Heterozygous F2 DIHYBRID
9:3:3:1
4Genotypic Ratio for Heterozygous F2 in a TESTCROSS
1:2:1
6Testcross
1. YY x yy
2. Yy x yy
7Testcross on dihybrids
1. YYRR x yyrr
2. YyRR x yyrr
3. YYRr x yyrr
4. YyRr x yyrr
8The number of different gametes =
2^n # of different traits
9How many genotypes in Aa Bb Cc Dd?
256: 2^4 = 16, 16 x16 = 256
10Cross Aa Bb Cc Dd × Aa Bb Cc Dd
What proportion of progeny will be AA bb Cc Dd?
.25 x .25 x .5 x .5 = 1/64
11Molecular explanation for Mendel’s pea shape
- R allele encodes Starch branching enzyme (Sbe1).
- r allele does not make Sbe1. Sucrose and unbranched starch build up, leading to wrinkled peas.
12Molecular explanation for Mendel’s pea color
- Y allele encodes the Stay green enzyme (Sgr). Sgr helps break down chlorophyll.
- y allele does not make Sgr. Chlorophyll is not broken down and the peas remain green.
13Two general molecular principles
1. A specific gene determines a specific protein, whose activity may affect the phenotype
2. A dominant allele usually determines a normally functioning protein, and a recessive allele usually does not encode a functional protein
14What do human pedigrees look like if the disease is dominant?
Vertical pattern
15Dominant Trait Disease example and explanation
Huntington's: produces abnormal Htt protein which damages nerve cells
16What do human pedigrees look like if the disease is recessive?
horizontal
17Recessive Trait Disease example and explanation
cystic fibrosis: encodes abnormal CFTR protein
CFTR protein regulates passage of Cl- across cell membrane.
18How to recognize dominant traits in pedigrees (3)
1. Affected children always have at least one affected parent
2. vertical pattern of inheritance
3. Two affected parents CAN produce unaffected children, if both parents are heterozygotes
19How to recognize recessive traits in pedigrees (4)
1. Affected individuals can be the children of two unaffected carriers, particularly as a result of consanguineous (between relatives eww) mating
2. ALL children of two affected parents ARE affected
3. horizontal pattern of inheritance
4. Recessive traits may show a vertical pattern of inheritance if the trait is extremely common in the population