Please enable JavaScript.
Coggle requires JavaScript to display documents.
Biology Ch. 14 (Ch 14.4 (Genetic Testing and Counseling (Genetic…
Biology Ch. 14
Ch 14.4
-
-
-
Cystic Fibrosis
Cystic fibrosis is the most common lethal genetic disease in the United States, striking one out of every 2,500 people of European descent
The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes, leading to a buildup of chloride ions outside the cell
Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine
Sickle-Cell Disease
-
It is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells
In homozygous individuals, all hemoglobin is abnormal (sickle-cell)
Symptoms include physical weakness, pain, organ damage, and even paralysis
-
About one out of ten African Americans has sickle-cell trait, an unusually high frequency
Heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being heterozygous in regions where malaria is common
-
Multifactorial Disoders
Many diseases, such as heart disease, cancer, alcoholism, and mental illnesses, have both genetic and environmental components
No matter what our genotype, our lifestyle has a tremendous effect on phenotype
-
-
Fetal Testing
In amniocentesis, the liquid that bathes the fetus is removed and tested
In chorionic villus sampling (CVS), a sample of the placenta is removed and tested
Other techniques, such as ultrasound, allow fetal health to be assessed visually in utero
Ch 14.3
-
Degrees of Dominance
-
incomplete dominance
-
Ex: when red snapdragons are crossed with white ones all the F1 generation are pink. neither allele is completely dominant
codominance
two dominant alleles affect the phenotype in separate, distinguishable ways
Ex: the human MN blood group is determined by codominant alleles for two specific molecules located on the surface of red blood cells
Ex: in Mendel pea flower experiemnt the F1 generation was all purple flowers which showed complete dominance
-
-
Multiple Alleles
-
For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme that attaches A or B carbohydrates to red blood cells: IA, IB, and i
The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither
Pleiotropy
Most genes have multiple phenotypic effects, a property called pleiotropy
For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease
Epistasis
In epistasis, expression of a gene at one locus alters the phenotypic expression of a gene at a second locus
For example, in Labrador retrievers and many other mammals, coat color depends on two genes
-
The other gene (with alleles E for color and e for no color) determines whether the pigment will be deposited in the hair
If heterozygous black labs (genotype BbEe) are mated, we might expect the dihybrid F2 ratio of 9:3:3:1
However, a Punnett square shows that the phenotypic ratio will be 9 black to 3 chocolate to 4 yellow labs
Epistatic interactions produce a variety of ratios, all of which are modified versions of 9:3:3:1
Polygenic Inheritance
-
Quantitative variation usually indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype
-
-
-
Ch. 14.1
Mendel
-
He studied that characteristics, a heritable feature that varies, of the pea plant (flower color)
Also studied the traits, a variant for a charcter, of the flower such as purple or white color
Also started with varieties that were true-breeding (plants that produce offspring of the same variety when they self-pollinate
In his experi,ent he mated two contrasting, true-breeding varieties, a process called hybridization
True-breeding parents are the P generation which were the true-breeding white and purple flowered pea plant in Mendel's experiment
The hybrid offspring of the P generation are called the F1 generation. In Mendels experiment these ended up being all purple flowered
When F1 individuals self-pollinate or cross-pollinate with other F1 hybrids, the F2 generation is produced. Mendel discovered a ratio of about 3 purple and 1 white flower in the F2 generation
Law of segregation
-
-
The factor for white flowers was not diluted or destroyed because it reappeared in the F2 generation
Mendel's Model
-
For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers
-
-
Second
Second: for each character, an organism inherits two alleles, one from each parent
-
The two alleles at a particular locus may be identical, as in the true-breeding plants of Mendel’s P generation
Or the two alleles at a locus may differ, as in the F1 hybrids
Third
Third: if the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance
In the flower-color example, the F1 plants had purple flowers because the allele for that trait is dominant
Forth
Fourth (the law of segregation): the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes
Thus, an egg or a sperm gets only one of the two alleles that are present in the organism
This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis
Genetic
-
-
An organism with two different alleles for a gene is a heterozygote and is said to be heterozygous for the gene controlling that character
Unlike homozygotes, heterozygotes are not true-breeding
We distinguish between an organism's phenotype, physical apperence, and its genotype, genetic makeup
Ex: flower color in pea plants, PP and Pp plants have the same phenotype (purple) but different genotypes
Testcross
-
To determine the genotype we can carry out a testcross: breeding the mystery individual with a homozygous recessive individual
If any offspring display the recessive phenotype, the mystery parent must be heterozygous
-
-