Chapter 14 Flashcards
2 possible explanations for how genes/heredity are passed down from parent to offspring
1) Blending hypothesis
2) “Particulate” hypothesis or Gene Idea
Blending Hypothesis
genetic material contributed by two parents mixes
i.e blue + yellow paint = green
“Particulate” Hypothesis
Gene Idea
parents pass on discrete heritable units, called genes, that retain their identities in future offspring
Gregor Mendel
- discovered the principles of heredity
- 1st to document particulate inheritance
- utilized an experimental and quantitive approach to genetics
~1857, studied principle of heredity by breeding garden peas
Why Mendel worked with peas
1) available in many varieties
provided both distinctive heritable features or characters with different traits
2) control cross breeding
4) food source
4) easily observable
5) grow relatively quickly in cooler climates
Character
a heritable feature
i.e. hair or eye color
Trait
a variant of a character
i.e. brown, blond, red hair color
Mendel’s Experiments
- began breeding “true-breeds”
- then would mate the two contrasting, true-breeds
- used pea plants, studying petal color (purple vs. white)
- 3:1 phenotype ratio
- 1:2:1 genotype ratio
“True-Breeding”
the same variety
always produce the same color
Hybridization
- mating two contrasting, true-breeding varieties
- studied the process of inheritance
What did Mendel use to determine the process of inheritance in future generations?
pea plant Petal Color
-purple vs. white
“P” generation
the true-breeding parents
Hybrid Offspring
from the “P” generation
create F1 generation
had all dominant trait, regardless of source of pollen
i.e. all purple flowers
F1 cross with F1
Self-polination
- create F2 generation
- disproved the hybridization theory
i. e. 3/4 purple; 1/4 white
- 3:1 ratio
Dominant
i.e. purple petals
if dominant trait was present, that was the trait that was seen
Recessive
i.e. white petals
only seen if both recessive genes were passed down
4 related concepts that make up Mendel’s 3:1 ratio model (long version)
1) Alternative versions of genes account for variations in inherited characters, called alleles
2) Each character an organism inherits 2 alleles, one from each parent (genetic locus is represented twice)
3) If 2 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 the organism’s appearance
4) the Law of Segregation: 2 alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes
4 related concepts that make up Mendel’s 3:1 ratio model (short version)
1) alternative version of genes (alleles)
2) 2 alleles per character are inherited
3) Dominant allele will determine appearance
4) Law of Segregation: alleles separate in meiosis
Alleles
inherited characters
found on chromosomes
Law of Segregation
2 alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes
- for a single trait
Pungent Square
can be used to predict the results of a genetic cross between individuals of known genotype
Homozygous organism
a pair of identical alleles for that gene and exhibits true-breeding
Heterozygous organism
a pair of alleles that are different for that gene
Phenotype
an organism’s physical character
Genotype
an organism’s genetic makeup
2 organisms can have ….
the same phenotype but different genotype
- one homologous, one heterologous
Testcross
allows us to determine the genotype of an organism with the dominant phenotype, but unknown genotype
crosses an individual with the dominant phenotype with an individual that is homozygous recessive for a trait
Monohybrid Cross
- law of segregation for a single trait
- heterozygous for one character
Dihybrid Cross
- looking at 2 inherited characters at the same time
- crossing two, true-breeding characters that produces dihybrids in the F1 generation
- produces 4 phenotypes
- 9:3:3:1 ratio
- are the two characters transmitted from the parents as a package?
Law of Independent assortments
alleles are sorted into gametes and inherited independently
-each pair of alleles segregates independently during gamete formation
Laws of probability govern…
Mendelian inheritance and Mendel’s law of segregation and independent assortment reflect the rules of probability
can use these rules of probability to predict the outcome of crosses involving multiple characters
Multiplication Rule
the probability that two or more independent events will occur together is the product of their individual probabilities
in calculating the chances for various genotypes from crosses, each character first is considered separately and then the individual probabilities are multiplied together
The relationship between genotype and phenotype is
Rarely Simple and the inheritance of characters by a single gene may Deviate from Simple Mendelian patterns
3 types of dominance
Complete dominance, Co-dominance, Incomplete dominance
Complete Dominance
Dominant character is shown, recessive character is suppressed
i.e. Mendel’s pea plants
Co-Dominance
both phenotypes are fully expressed
i.e. ABO blood type
Incomplete dominance
the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental variations
i.e. snapdragons
Red + White => Pink F1s
Recessive Inherited Disorders
many genetic disorders are inherited in a recessive manner and show up only in individuals homozygous for the allele
Carriers (parents) are heterozygous individuals who carry the recessive allele but are phenotypically normal…
can give their offspring a recessive gene and giving them a recessive inherited disorder
2 types of recessive inherited disorders
1) Cystic fibrosis
2) Sickle Cell Disease
Cystic Fibrosis
include mucus buildup and abnormal absorption of nutrients in internal organs
transduction channel doesn’t pump water and protein correctly
- mostly Caucasian, descendants from Europe
Sickle Cell Disease
a mutation that affects the hemoglobin protein in red blood cells
- hemoglobin protein in RBCs that transport oxygen is not folded correctly
- symptoms: physical weakness, pain, organ damage, even paralysis
- affects 1 out of 400 African-Americans
