AB biology: Mendel and Different forms of Inheritance Flashcards
Blending Hypothesis
The idea that genetic material contributed by 2 parents mixes in a manner analogous to the way blue and yellow plaints blend together to make green
Particulate Hypothesis of inheritance
The Gene Idea
parents pass on discrete heritable units: genes
Gregor Mendel studied and used peas for his work because:
They are available in many varieties
Could be strictly control which parents mated with which
Lots of offspring
Easily observable traits
Reasoning as to why when Mendel crossed the F1 plants, they had a ratio of 3:1
In the F1, only the purple flower factor was affecting flower color in these hybrids.
Purple flower color was dominant, and white flower color was recessive
Mendel’s model to explain the 3:1 ratio
- alternative version of genes: account for variations in inherited characters (ALLELES)
- For each character, an organism inherits 2 alleles: a gene locus represented twice
- If 2 alleles at a lovus differ, the dominant allele determines the organisms appearance. The other allele, recessive allele has no noticeable effect on organisms appearance
- Law of segregation
Trait
a copy of a gene or an inherited characteristic
Law of dominance
If one allele is present in a genotype, it will hide the other allele
Law of Segregation
derived by following a single trait
The 2 alleles for a heritable character segregate during gamete formation and end up in different gametes
Law of Independent assortment
Each pair of alleles segregates independently during gamete formation
Due to genes that are being followed are on separate chromosomes.
Test Cross
allows one to determine the genotype of an organism with the dominant phenotype, but unknown genotype
Crosses an individual with the dominant phenotype with an individual that is homozygous recessive for a trait
Characteristics of inheritance
inheritance patterns are often more complex than predicted by simple mendelian genetics
The relationship between the phenotupe and genotype is rarely simple.
Complete Dominance
occurs when the phenotypes of the heterozygote and dominant homozygote are identical
Codominance
2 dominant alleles are expressed at the same time
chickens and cows have multiple feathers and hair colors and the human blood group AB
Multiple alleles
most genes exist in populations in more than 2 allelic forms
ie: blood types ABO in humans
incomplete dominance
F1 is a mix of dominant and recessive
3 phenotypes
Dominant inheritance
ie: Achandroplasia
a form of dwarfism that is lethal when homozygous for the dominant allele
Huntingtons disease
A degenerative disease of the nervous system
has no obvious phenotypic effects until about 35 - 40 ys old.
Multifactorial disorders
many human diseases have both genetic and environmental components
ie heart disease and cancer
Gene Testing and counseling
genetic counselors can provide info to prospective patients concerned about a family history for a specific disease
Pleiotropy
a gene has multiple phenotypic effects
ie: cystic fibrosis causes more than one symptom to occur (lungs, sodium channels, etc)
polygenic traits
may be determined by 2+ traits
end up with a spectrum of phenotype possibilities
lots of traits follow this: eye color, hair color, height, skin color
Quantitative variationusually indicates polygenic inheritance
an additive effect of 2 genes on a single phenotype
Epistasis
a gene at one locus alters the phenotypic expression of a gene at a second locus
if one gene is fully recessive, it can prevent expressions of a dominant allele
Nature and Nurture
The environmental impact on phenotype
another departure from simple mendelian genetics arises when the phenotype for a character depends on environment as well as on genotype
The norm of reaction
The phenotypic range of a particular genotype that is influenced by the environment
