Chapter 14: Gentetics Flashcards
Gregor Mendel
Founder of modern genetics, as a monk documented inheritance in peas
– used experimental method
– used quantitative analysis
– excellent example of scientific method
Self-Pollination
Pollen from the anther is transferred to the stigma of the same plant
Cross-Pollination
when pollen from a plant is transferred to the stigma of another plant
What exactly was Mendel’s process with observing the pea plants?
P=parental
f=Filal Generation
1st: Cross-Pollinate true breeding parents pea plants (Plants that are not heterozygous)
2nd: Raise seeds & then observe traits (F1)
3rd: Allowed offspring to self-pollinate & observed next generation (F2)
What did Mendel discover?
He leaned that after breeding two pure pea plants that the dominant trait will only appear in the F1. However, If the F1 cross or self-pollinate the recessive trait will show up again about 25% of the time.
Alleles
Traits come in alternative versions.
different alleles vary in sequence of nucleotides at the specific locus of a gene.
Ex: Purple-flower allele & white-flower allele are two DNA variations at the flower color locus.
For each characteristic, an organisms inherit….
2 alleles , 1 from each parent
diploid organism
- inherits 2 sets of chromosomes, 1 from each parent
-homologous chromosomes
What did Mendel’s findings of the purple and white flower traits of the pea plants mean?
some traits masks others
Dominant allele
functional protein
masks other alleles
a.k.a: wild type
Recessive allele
allele makes a malfunctioning protein.
- mutant
Phenotype
description of an organism’s trait
the “physical”
Genotype
description of an organism’s genetic makeup
What are the proportion of genotypes?
1:2:1
Wat are the proportions of phenotype?
3:1
Homozygous
same alleles
Ex: PP, pp
Heterozygous
different alleles Pp
Is it possible for 2 organisms can have same phenotype but have different genotypes?
Yes
Test Cross
breed the dominant phenotype– the unknown genotype– w/ a homozygous recessive(pp) to determine the identity of the unknown allele.
What is Mendel’s 1st law of hereditary?
Law of Segregation
- during meiosis, alleles segregate
- homologous chromosomes separate
- each allele for a trait is packaged into a separate gamete
monohybrid cross
- single trait
Which stage of meiosis creates the law of segregation?
Metaphase 1
Monohybrid Cross
Following the inheritance of single characters
Ex: flower color, seed color
Dihybrid Cross
Following the inheritance of 2 different characters
Ex: seed color & seed shape
Mendel’s 2nd Law of Heredity
Law of independent assortment
- different loci (genes) separate into gametes independently
- non-homologous chromosomes algin independently
- classes of gametes produced in equal amounts
- YR= Yr=yR=yr
- only true for genes on separate chromosomes or on same chromosome but so far apart that crossing over happens frequently
dihybrid (or more) crosses
Which stage of meiosis creates the law of independent assortment?
Metaphase 1
Mendel’s law of segregation and independent assortment reflect what rules?
The rules of probability
How is the rule of addition used in genetics?
Rules of Addition: The probability that any one of two or more exclusive event will occur is calculated by probabilities.
It can used to figure out the probability that an F2 plant from a monohybrid cross will be heterozygous rather than homozygous.
How do you apply the multiplication and addition rules of probabilities to genetics?
These rules are used to predict the outcome pf crosses involving multiple characters.
A dihybrid or other multicharacter cross is equivalent to two or more independent monohybrid crosses occurring simultaneously.
In calculating the chances for various genotypes, each character is considered separately and then the individual probabilies are multiplied.
Incomplete Dominance
Heterozygote shows an intermediate blended phenotype.
RR –> red flowers
rr –> white flowers
Rr –> pink flowers
P: true breeding red x true breeding white flower
F1: 100% pink flowers
F2: 25%: red 50%: Pink 25%: White
Co-dominance
2 alleles affected the phenotype equally & separately
- not blended phenotype
- human ABO blood groups
-3 alleles
Ia & Ib are codominant that explains why AB blood exists.
i is recessive which explains having 2 i make you O
+ is dominant
- is recessive
Pleiotropy
one gene affects more than one phenotypic character.
1 gene affects more than one trait.
Ex: dwarfism
Epistasis
One gene completely masks another gene
coat color in mice = 2 separate genes
C(pigment) c (no pigment)
more pigment (B=black) or less (b=brown)
cc = albino no matter B allele
same thing w/ Labradors
Polygenic Inheritance
Some phenotypes determined by additive effects of 2 or more genes on a single character.
- phenotypes on a continuum
- human traits
- skin color
- weight
- height
- behaviors
What controls phenotypes ?
Environment & genes
