Exam 3 Flashcards
Pangenesis Hypothesis
Inheritance by means of each organ sending information to the gametes. - Explains why children resemble their parents (not true)
Blending Hypothesis
averaged between parents (not true)
Natural Selection
More offspring produced than will survive.
Individuals with favorable traits will survive.
Traits are inherited from parents to offspring.
What happens when varieties with opposing traits are mated (monohybrid cross)?
One trait is completely lost in the first generation.
The missing trait returns in the second generation with 25% of the offspring/
Homozygous vs Heterozygous
Homozygous - PP or pp
Heterozygous - Pp
What happens when two traits are followed simultaneously (dihybrid cross)?
Dependent vs independent assortment.
Independent - 4 kinds of gametes from each plant, 16 possible genotypes with 4 phenotypes in f2 generation (9:3:3:1)
Dependent - if 1 trait depends on another, dihybrid crosses should resemble monohybrid crosses (3:1 ratio)
Independent Assortment - By chance, any two alleles for two different genes should only be inherited together in 50% of the offspring. This is not true for genes that are on the same chromosome, without homologous recombination, they should be inherited 100 percent of the time.
Independent Segregation
(monohybrid vs dihybrid)
Monohybrid Crosses - The two alleles for a trait segregate equally in gametes.
Dihybrid Crosses - Alleles for different traits assort independently (not always correct).
What are Mendel’s “factors”?
Alleles on chromosomes.
Meiosis explains inheritance patterns.
Most traits in plants and animals do not follow simple mendelian inheritance patterns, because most traits are governed by multiple alleles of multiple genes.
Mendel’s laws still apply to each individual gene (allele pair).
Are recessive alleles ever nonfunctioning alleles.
Yes, in many cases (not all).
Do any human traits follow Mendel’s observations?
Yes, only ones that are encoded by a single (dominant/recessive) gene.
Are any heritable disorders carried by a single allele.
Yes.
Sickle cell anemia, cystic fibrosis - single recessive allele.
Sickle cell allele selection hypothesis:
Sickle cell anemia provides some protection against malaria and may have been selected for in population that are exposed to malaria.
Give the family history of a trait, can the genotype of individuals be determined?
Yes
What are quantitative/continuous traits?
Continuous or quantitative traits are characteristics that demonstrate a wide range of phenotypes and are usually influenced by multiple genes, often in combination with environmental factors. These traits can take on a spectrum of values rather than distinct, categorical outcomes.
What can quantitative traits result from?
- Incomplete dominance or co-dominance of alleles.
- More than two alleles are present in a population.
- Multiple genes (with multiple alleles) contribute to the trait.
- Genes can interact with the environment.
Co-dominant alleles
Both effect the phenotype and may appear to blend in heterozygotes.
Incomplete dominance
Occurs when two copies of an allele are needed for one phenotype and a single copy gives a different phenotype.
Can blending occur?
Yes, when alleles are co-dominant or incompletely dominant. (Mechanism 1)
If there are more than 2 alleles for a given gene, does this mean that there can be more variations on a trait?
Yes (Mechanism 2)
Polygenic traits
Influenced by multiple genes.
Most traits in animals and plants. (Mechanism 3)
If enough genes influence a trait it will be considered continuous or quantitative rather than either or because there are intermediates between extremes.
Multifactorial traits
Traits that have a genetic basis but also respond to the environment.
What is a gene?
Something that codes for a protein
Diprosopia and Cyclopia
Diprosopia - Born with two faces.
Cyclopia - Born with one eye.
What causes Diprosopia and Cyclopia?
Too much or too little SHH expression in the midline leads to holoprosencephaly conditions. Too little or too much causes not enough or too much division.