Chapter 10 Flashcards
Gregor Johann Mendel
father of modern genetics; quantitatively analyzed garden peas
why did he study peas?
Greg or Mandel performed experiments with garden peas because there are many varieties available with easily distinguishable traits that can be quantified; they are small, easy to grow, and produce large numbers of off spring quickly; their reproductive organs can be easily manipulated so that pollination can be controlled, they can self fertilize
what is true breeding/homozygous?
plants that have been self fertilized for several generations; each variety contained only one type of trait
genotype
genetic make up
phenotype
external appearance
what is characteristic?
heritable features
what is trait?
alternative forms of character
when is a trait considered dominant?
trait expressed in the F1 generation; Purple
when is a trait. considered recessive?
trait not expressed in the F1 generation; white
what is an F1 and F2 generation?
Mendel had a specific experimental design: he first established true breeding varieties by allowing plants to self fertilize for several generations, he ensured that each variety contained only one type of trait. He named these parental lines the P generation. he then crossed two varieties exhibiting alternative traits. He named the resulting offspring the F1 generation. He then allowed the plants from the F1 generation to self fertilize. He named the offspring the F2 generation.
what Mindel observed
Mindel counted the number of each type of plant in the F2 generation. He found a consistent proportion in expressed traits for his different crosses. Three fourths of the F2 individuals expressed the dominant trait while one fourth express the recessive trait. The dominant: recessive ratio among the F2 plants was always close to three: one.
what Mindel observed
Mindel reasoned that the recessive trait must somehow be hidden in the F1 generation but just not expressed. He allowed the F2 to self fertilize and form the F3 generation. He found that one fourth of the plants from the F2 that were recessive were true breeding in the F3. He found that the three –fourths of the plants from the F2 that were dominant: only one –third were true breeding in the F3. The remaining two– thirds showed both traits.
what Mindel observed
he determined that the ratio of three: one that he observed in the F2 generation was in fact a disguised 1:2:1 ratio (True breeding dominant: not true breeding dominant: true breeding recessive:
Mendel proposes a theory
hypothesis one: parents don’t transmit traits directly to their offspring. Parents transmit information about the trade in the form of what Mindel called Factors.
hypothesis 2: each parent contains two copies of the factor governing each trait. The two copies of the factor may or may not be the same. Homozygous individuals have 2 similar copies. Heterozygous individuals have two different copies.
Mendels laws
Mendel’s first law: segregation: the two alleles of a trait separate from each other during the formation of gametes,so that half of the gametes will carry one copy and half will carry the other copy
Mendel’s 2nd law: independent assortment: genes located on different chromosomes are inherited independently of one another
polygenic
several genes affect one character; for example, height in humans
pleiotropic effects
an allele that has more than one effect on the phenotype is considered pleiotropic – one gene affects many characters. these effects are characteristic of many inherited disorder, such as cystic fibrosis and sickle cell anemia.
pleiotropic affects of the cystic fibrosis gene
defective CF gene produces faulty chloride transport channels – causing mucus to build up in The liver, pancreas, lungs, sweat glands.
incomplete dominance
not all alternative alleles are either fully dominant or fully recessive in heterozygotes. In such cases, the alleles exhibit incomplete dominance and produce a heterozygous phenotype but is intermediate between those of the parents. For example, crossfertilizing a red flower with A white flour will result in a pink flower.
environmental effects
The degree to which many alleles are expressed depends on the environment. for example: some alleles are heat – sensitive. Arctic foxes only produce for a pigment when temperatures are warm. The CH allele in Himalayan rabbits and Siamese cats encodes a heat – sensitive enzyme, called tyrosinase, that that controls pigment production. tyrosinase is in active at high temperatures.
Epistasis
in some situations, two or more genes interact with each other, such that one gene contributes to or masks the expression of the other gene. In epistasis, one gene modifies a phenotypic expression produced by the other. For example, in corn, to produce and deposit pigment, a plant must possess at least one functional copy of each of two genes. One gene controls pigment deposition. The other Gene controls pigment production.
how epistasis affects corn kernel color
white (AAbb) and white (aaBB) are crossfertilized to form F1 generation purple (AaBb) which is then cross fertilized with a female AaBb. It produces 9/16 purple and 7/16 white. You need to have both a dominant A gene and dominant B gene in order to have purple kernels.
The effect of epistasis interactions on coat color in dogs
no dark pigment in for: yellow lab
eebb– Yellow fur; brown nose, lips, Eye rims
eeB_-gold fur: Black nose, lips, Eye rims
E_bb-Brown fur, nose, lips, eye rims
E_B_-Black fur, nose, lips, eye rims
codominance
A gene may have more than two alleles in a population. Often, in heterozygotes, there’s not a dominant allele but, instead, both alleles are expressed. These alleles are said to be codominant. for example, spotted or Roan offspring or human blood groups.
