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Chapter 14 & 15 - Coggle Diagram
Chapter 14 & 15
monohybrid cross experiment
- starting point: true-breeding purple flower plant x true-breeding white flower plant
- F1 Generation: 100% purple flowers
- disproved blending hypothesis
- indicated that the white trait was masked, not destroyed
F2 generation (from self-pollinating F1):
- 3:1 phenotypic ratio (3 purple : 1 white)
- white trait reappeared, showing it was masked in F1
principle of segregation:
- each individual has two alleles for each gene
- These alleles separate (segregate) during gamete formation, so each gamete receives only one allele
- alleles recombine randomly during fertilization
genotypes and phenotypes in monohybrid cross:
- parental (P) generation: Big P Big P (purple) x Little P Little P (white)
- F1 Generation: Big P Little P (all purple phenotype)
- F2 Generation (from Big P Little P x Big P Little P):
- genotypic ratio: 1 Big P Big P : 2 Big P Little P : 1 little p little p(1:2:1)
phenotypic ratio: 3 purple : 1 white (3:1)
Dihybrid Cross Experiment
- starting point: true-breeding round yellow peas x true breeding wrinkled green peas
- F1 Generation: 100% round yellow peas
- confirmed round and yellow as dominant traits
F2 Generation (from self-pollinating F1):
- phenotypic ratio: 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green (9:3:3:1)
- observed new combinations of traits (round green, wrinkled yellow), which were not present in the parental generation
Principle of Independent Assortment:
- alleles for different genes (seed shape and seed color) assort independently of one another during gamete formation
- the new trait combinations in the F2 generation
- correlates with independent assortment of homologous chromosomes during meiosis I
gregor mendel: the father of modern genetics discovered basic principles of heredity through breeding garden peas
- understanding heredity without knowledge of chromosomes or genes
- genetic crosses in the monastery gardens.
- studied science at the university of vienna, learning proper scientific study methods and botany
blending hypothesis: idea before Mendel suggesting offspring are a blend of parental traits mendel's work didnt approve
monohybrid cross:I
- involved crossing true-breeding parents differing in one character (purple x white flowers)
- F1 generation: All offspring displayed the dominant trait (all purple)
- F2 generation (from self-pollinating F1): showed a 3:1 phenotypic ratio of dominant to recessive traits
- led to the principle of segregation: each one has two alleles for each gene, and these alleles segregate during gamete formation, with each gamete receiving only one allele
dihybrid cross:
- involved crossing true-breeding parents differing in two characters (round yellow peas x wrinkled green peas)
- F1 generation: All offspring displayed dominant traits for both characters (all round yellow)
- F2 generation (from self-pollinating F1): showed a 9:3:3:1 phenotypic ratio
- led to the principle of independent assortment: Alleles for different genes assort independently of one another during gamete formation
Genetic Terminology:
- gene: modern term for mendel's "character."
- allele: term for Mendel's "trait" (diferent versions of a gene)
- genotype: the genetic makeup or allele combination of an organism (big P little p)
- phenotype: the observable physical traits of an organism (purple flower)
- homozygous: having two identical alleles for a gene (big P big P or Little p little p)
- heterozygous: Having two different alleles for a gene (big P little p)
pea plants: a organism due to diverse varieties, short generation time, large number of offspring, and controllable mating (self-pollination or cross-pollination)
- character: heritable feature that varies among individuals (flower color)- trait: variant for a character (purple or white flower color)- true breeders: organisms that produce offspring identical to themselves when self-pollinated
genomic impriting
- Genomic imprinting involves the silencing of certain gene depending which parent passes it on
- only the paternal allele of this gene is expressed
- may affect small part of mammalian genes
chromosome structure
- deletion, removes a chromosomal fragment
- duplication, repeats a segment
- inversion, reverses orientation of a segment within a chromosome
- translocation, moves a segment from one chromosome to another
polyploidy is a condition in which an organism has more than two complete sets of chromosomes
- triploidy (3n) is three sets of chromosomes
- tetraploidy (4n) is four sets of chromosome
monosomic zygote has only one copy of a particular chromosome
trisomic zygote has three copies of a particular chromosome
aneuploidy, the fertilization of gametes in which nondisjunction occurred
The Chromosomal Basis of Sex
- a gene that is located on either sex chromosome is called a sex-linked gene
-X chromosomes have genes for many characters unrelated to sex
- y -linked genes are related to sex determination
- genes that are located on the same chromosome tend to be inherited together and are called linked genes
- genetic recombination, the production of offspring with combinations of traits differing from either parent
- offspring with a phenotype matching one of the parental (p) phenotypes are called parental types
- offspring with nonparental phenotypes are called recombinant types, or recombinants
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advantages of pea plants for genetic studies
- variety: many distinct varieties with different "characters" (heritable features) and "traits" (variations of characters)
- examples: flower color (purple/white), seed color (yellow/green), seed shape (round/wrinkly), pod color (green/yellow), pod shape (inflated/constricted), stem length
- short generation time: quick growth allows for multiple generations in a short period
- large number of offspring: each pea is an embryo, leading to many plants for statistical analysis.
controlled mating:
- self-pollination: plants can fertilize themselves (sperm and egg in the same flower)
- cross-pollination: pollen from one plant can fertilize another Mendel could prevent self-pollination by removing anthers
tay-sachs disease is a fatal inherited disorderca dysfunctional enzyme causes an accumulation of lipids in the brain
in epistasis, expression of a gene at one locus alters the phenotypic expression of a gene at a second locus
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