Chapter 12.3 - Mendel Flashcards
Cystic Fibrosis Mutation Pedigree
SEE NOTES
Gregor Mendel’s 4 Major Contributions
- Segregation of traits in the gametes
- Alleles
- Dominance
- Alleles for different traits sort into gametes independently
*carefully contained crosses of pea plants with different characters. Pea plants were perfect organisms in this case because all offspring are carefully contained.
Character
A heritable feature that varies among individuals
Trait
A variant of a character
Phenotype
The physical appearance of a particular character
Inheritance see graph right under this
How a trait behaves when it’s passed from one generation to the next
Self-Fertilization
Offspring will always be the same. The same phenotypein the next generation.
Alleles
Alternative alleles (versions of genes) account for variation in inherited characters. DIAGRAM
Alleles encode an enzyme that code for synthesis of a separate pigment.
Locus
A defined region of a chromosome where a given gene is located. Alleles are the same genes on the same locus
Exon
Encodes portion of the protein
Intron
Spliced out of the mRNA
Dominance
- if two alleles at a locus differ, the dominant allele determines the phenotype
- dominant alleles are a capital letter and recessive are lowercase
Genotype
The specific genetic makeup of an individual usually referring to a particular gene
Homozygous
Same two alleles at a locus
Heterozygous
Different alleles at a locus
The Law of Segregation
- Parental traits (alleles) randomly segregate to the gametes
- Mendel uses a monohybrid (heterozygous for one character) cross to conclude that alleles segregate independently (in gametes)
- Meiosis is the mechanism for segregating alleles
- genotype ratio vs. phenotype ratio*
Incomplete Dominance
- Heterozygotes have an intermediate phenotype resulting from not having enough of one enzyme that synthesizes a particular trait ex: pigment via pink flower
- EXAM Q: Phenotypic and Genotype ratios are the same in this case
Dihybrid Cross DIAGRAMS
- Mendel also used plants with variations in TWO different characters. In his example, the two characters were seed shape and seed colour
- In the F1 Generation is only the dominant phenotype
- The F2 Generation had a ratio of 9 round yellow: 3 green round: 3 yellow wrinkled: 1 green wrinkled
The Law of Independent Assortment
- Genes conferring different characters (ex: seed colour, seed shape) sort independently from one another during gamete formation
- Mendel used a dihybrid to show independent assortment
- Meiosis is the mechanism for independent assortment: alignment of tetrads at metaphase plate
Punnet Squares - 4 vs. 16
NEXT DIAGRAM
4: Dependent Ratio of 3:1. Colour and shape are linked
16: Independent Ratio of 9:3:3:1 (dihybrid ratio) colour and shape are independent
X-Linked Genes in Humans
- colour blindness
- haemophilia
- Duchenne muscular dystrophy
*about 1100 genes on x chromosome (x-linked) and 75 on Y chromosome diagrams
Probability Rules
Multiplication Rule and Addition Rule
Multiplication Rule
“What is the probability of getting a white flower in a Pp x Pp monohybrid cross?”
> Probability of 2 independent events occurring together is the product of their individual probability
Addition Rule
“What is the probability of getting a purple flower in a Pp x Pp monohybrid cross?”
> The probability that any one of two mutually exclusive events occurring is the sum of their individual probabilities
