Practice poblems Flashcards
Give two misconceptions about genetics
- inherited features of offspring are contributed by the male parent ( forming a miniature off spring in the sperm)
- blended inheritance: parental traits become mixed and permanently changed in the offspring
list four things Mendel did that facilitated his elucidation of the fundamental laws of genetics
- reciprocal crosses
- pea plants (discrete traits)
- Meticulous
- pure-breeding
state Mendels law of segregation
the 2 alleles of each gene separate (segregate) during gamete formation and then reunites at random one from each parent at fertilization
state Mendel’s law of independent assortment
during gamete formation, different pairs of alleles segregate independently of each other
what are the characteristics of a recessive human pedigree?
- affected individuals can be the children of two unaffected carriers, particularly as a result of consanguineous (between relatives) mating
- all the children of two affected parents should be affected
- rare recessive traits show a horizontal pattern of inheritance
- recessive traits may show a vertical pattern of inheritance if the trait is extremely common in the population
what are characteristics of a dominant human pedigree
- affected children always have at least one affected parent
- as a result, dominant traits show a vertical pattern of inheritance
- two affected parents can produce unaffected children, if both parents are heterozygotes
Explain the difference between complete, co-dominance and incomplete dominance.
- complete dominance: hybrid resembles one of the two parents
- incomplete dominance: hybrid is intermediate phenotype of parents
- codominance: hybrid shows traits from both parents
Explain the concept of epistasis. What are the phenotypic ratios expected for recessive epistasis? Dominant epistasis?
- epistasis: the expression of one gene is modified (masked, inhibited, or suppressed) by the expression of one or more other genes
- dominant: one copy of an allele masks the other gene
- recessive: epistatic allele must be homozygous recessive
- ratios 9:3:4
- hypostatic: the gene that is masked is hypostatic to the other allele
What is a complementation test and what is its purpose?
- is used to determine if a particular phenotype arises from mutations in the same or separate genes
- can be applied only with recessive, not dominant, phenotypes
Explain the difference between penetrance and expressivity.
- penetrance: is the percentage of individuals with a particular genotype that show the expected phenotype (can be complete, 100%, or incomplete)
- expressivity: is the degree or intensity with which a particular genotype is expressed in a phenotype ( can be variable or unvarying)
Explain how the environment can contribute to a phenotype and the difference between permissive and restrictive conditions?
- temp. is a common element of the environment that can affect phenotype
- conditional lethal: mutations are lethal only under some conditions
- permissive conditions: mutant allele has wild-type functions
- restrictive conditions: mutant allele has defective functions
Describe how the extensions to Mendel’s laws as explained in Chapter 2 are compatible with real world observations of genetic inheritance such as blending and normal distributions of phenotypic variation.
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