ArianaMejiaCh14 Genes and Mendel (True-breeding (Monohybrids (F1 progency…
ArianaMejiaCh14 Genes and Mendel
Mendelian patterns of inheritance
Widow's peak- is due to a dominant allele, W. Homozygous recessive,ww.
A diagram of a family tree with conventional symbols, showing the ocurrence of heritable characters in parents and offspring over multiple generations.
Three- generation pedigree that traces the ocurrence of a pointed contour of the hairline on the forehead.
Dominantly inherited disorders
Behavior of recessive alleles
Albinism is a recessive condition characterized by a lack of pigmentation in skin and hair
Most individuals with recessive disorders are born to carrier parents
Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal
Show up only in individuals homozygous for the allele
Recessively inherited Disorders
Huntington's disease, is caused by a lethal dominant allele that has no obvious phenotypic effect until the individual is about 35 to 45 years old.
Achondroplasia is a form of dwarfism caused by a rare dominant allele
Dominant alleles that cause a lethal disease are rare and arise by mutation
Can be performed starting at the 15th week of pregnancy
The liquid that bathes thevfetus is removed and tested.
Chorionic villus sampling(CVS)
Is that it can be performed as early as the 10th week of pregnancy.
A sample of the placenta is removed and tested.
Other techniques, such as ultrasound, allow fetal health to be assessed visually in
At the molecule level, the alleles are codominant
At the biochemical level, the phenotype is incompletely dominant
At the organismal level, the allele is recessive
Is fatal: a dysfunctional enzyme causes an accumulation of lipids in the brain
Degrees of Dominance
occurs when phenotypes of the heterozygote and dominant homozygote are identical.
Ex: Mendel's classic pea crosses, The flowers on Mendel's pea plant are an example of complete dominance, or when the dominant allele completely covers up the recessive allele
The phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties.
Seen when red snapdragons are crossed with white snapdragons: All the F1 hybrids have pink flowers
Two dominant alleles affect the phenotype in separate, distinguishable ways
The human MN blood group is determined by codominant alleles fro two specific molecules located on the surface of red blood cells, the M and N molecules.
Frequency of Dominant Alleles
Sex-linked gene- a gene located on eighter sex chromosome. Most sex-linked genes are on the X chromosome and show distinctive patterns of inheritance
Polygenic inheritance:- an additive effect of two or more genes on a single phenotypic character.
Pleiotropy-most genes have multiple phenotypic effects, a property
Ex: pleitropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle cell disease.
Epistasis-expression of a gene at one locus alters the phenotypic expression of a gene at second locus
Ex: in Labrador retrievers and many other mammals, coat color depends on two genes
A heritable feature that varies among individuals
Ex: flower color
One of two or more detectable variants in a genetic character
Such as purple or white color for flowers
Advantages of using peas
Large numbers of offspring
Mating could be controlled : plants could be allowed to self-pollunate or could be cross-pollunated.
Short generation time
Crossing pea plants
Removed stamens from purple flower
Transferred sperm bearing pollen from stamens of white flower to egg bearing carpel of purple flower
Waited for pollinated carpel to mature into pod.
Planted seeds from pod.
Examined offspring: all purple flowers
Law of Segregation
The fourth and final part of Mendel's model
States that the two alleles for a heritable character segregate during gamete formation and end up in different gametes.
P generation- true breeding parents
Hybridization- typical experiment, Mendel mated two contrasting , true breeding varieties
F1 generation- hybrid offspring of the p generation
F2 generation- produced ehen F1 individuals self pollinate or cross pollinate with other F1 hybrids
F1 progency produced in his crosses of true breeding patents
Meaning that they were heterozygous for the one particular character being followed in the cross.
Monohybrid cross- a cross between such heterozygotes.
Individuals heterozygous for the two characters being followed in the cross
Dihybrid cross: a cross between F1 dihybrids, can determine whether two characters are transmitted to offspring as a pachage or independently