Inheritance Flashcards
Phenotype
An observable or measurable feature of an organism
- anatomical
- biochemical
- behavioral
* can be almost anything
Genotype
The genetic makeup of an individual
- overall
- variants at a specific locus
Can an organism carry genetic information that is not observable?
YES; genotype is not always expressed in the phenotype!
Mendels experimental design
Peas
- self-fertilization
- created true-breeding strains (he was sure that phenotype corresponded directed to the genotype)
- he recorded the pedigree (parent and offspring relationships through many generations)
- the pea traits have two types (yellow and green)
- he had a large sample
- he repeated his experiment
Mendel’s Postulate 1: Hereditary characteristics are controlled by particulate unit factors that exist in pairs in individual organisms
There are units of inheritance in the form of particles (chromosomes)
- they are paired (one from each parent)
* these units of inheritance can have different versions
Alleles
Different versions of genetic information
Locus
The location of genetic information
Homozygous
Both copies of genetic information have the same allele
Heterozygous
Each copy of genetic information has a different allele
Mendels Law 2: Dominance- when an individual has two different unit factors responsible for a characteristic, only one is expressed; that unit factor is dominant over the other, which is recessive
One allele can cover up the expression of the other
Dominant
Allele that we can observe in the phenotype
Recessive
An allele that is in the genotype but not observable in the phenotype
Polygenic
Descriptor for a phenotypic trait that is influenced by more than one gene
Pleiotropic
Descriptor for a gene that affects more than one phenotypic trait
Sexual reproduction combines…
genetic information from two haploid gametes
Mendels Law 3: Law of Segregation
The paired units of inheritance (chromosomes) segregate and each sex cell receives one copy or the other with EQUAL likelihood
What helps us understand law of segregation?
Punnet squares help us answer this question: if these two specific individuals breed, what is the expected proportion of genotypes and phenotypes in the resulting generation?
Mendels Law 4: Law of Independent Assortment
Chromosomes get split up into gametes independently
- the segregation of any given pair of chromosomes does not affect segregation in other pairs of chromosomes, so that a gamete with “maternal” chromosome 1 will not necessarily contain “maternal” chromosome 2
Ex. the wrinkled-ness of the peas could get separated from the green-ness
- means that one person has the potential to generate over 8 million different possible gametes
Law of Independent Assortment
When genes are on different chromosomes
- every combination of alleles is possible
- every combination of alleles is equally likely (same frequencies)
When multiple genes are on the same chromosome, they will tend to be…
Inherited together
- linkage
- Genes A, T, and S are all linked but there are exceptions
Chromosomal mis-segregation (nondisjunction errors)
Down syndrome is fairly common in human populations
- extra chromosome 21
XXX syndrome is also fairly common and is one of many ways that people can be intersex
Turner syndrome is the inverse example: a person with only ONE X chromosome