GCU BIO 319: LATEST A+ QUESTIONS AND ANSWERS
GUIDE FOR ULTIMATE SUCCESS
Mendel performed two types of crosses
Self-fertilization:
- pollen and egg derived from same plant
- naturally occurs in peas because a modified petal isolates the reproductive structures
Cross-fertilization:
-pollen and egg derived from different plants (required removing and manipulating anthers)
Mendel studied 7 characters that bred true
- the morphological characteristics of an organism are termed characters
- the term trait describes the specific properties of a character
-- eye color is a character, blue eyes is a trait
- a variety that produces that same trait over several generations is termed a true-breeder
- each character showed two variants in the same species
- Mendel did not have a hypothesis to explain the formation of hybrids
-- empirical approach
- His first experiments involved crossing two variants of the same characteristic
-- monohybrid cross (a single characteristic is being observed)
Mendel's monohybrid cross
- This is called a P (parental) cross (also performed reciprocal crosses to eliminate gender-
related expression)
- These are the F1 (First filial) generation
- These are part of the F2 generation
- These are the F2 generation plants
Interpreting Mendel's monohybrid data
For all seven characteristics studied:
- the F1 generation showed only one of the two parental traits
- the F2 generation showed an ~3:1 ratio of the two parental traits
-- refuted a blending mechanism of heredity
- the data suggested a particulate theory of inheritance
What Mendel's data suggested
- a pea plant contains two discrete hereditary factors for a given character, one from each
parent
- the two factors may be identical or different
- when the two factors of a single character are different and present in the same plant...
,--one variant is dominant and its effect can be seen
-- the other variant is recessive and is not seen
- during gamete formation, the paired factors for a given character segregate from each other
(half receive one factor, half the other)
-- Mendel's Law of Segregation
Mendel's Law of Segregation Summary
- Mendelian factors now called genes
- alleles are different versions of the same gene
- an individual with two identical alleles is termed homozygous
- an individual with two different alleles is termed heterozygous
- genotype refers to the specific allelic composition of an individual
- phenotype refers to the outward appearance of an individual
Predicting the outcome of a cross
Punnett square: a grid used to predict the outcome of simple genetic crosses
1) Write down the genotypes of both parents: male parent=Tt, female parent=Tt
2) Write down the possible gametes each parent can make: male gametes: T or t, female
gametes: T or t
3) Create an empty Punnett square: male parent=Tt, female parent=Tt
4) Fill in the possible genotypes of the offspring by combining the alleles of the gametes
5) Determine the relative proportions of genotypes and phenotypes of the offspring: genotypic
ratio- TT=1, Tt=2, tt=1. phenotypic ratio- Tall=3, dwarf=1
The test cross
Mendel performed test crosses
- crossing an individual showing a dominant phenotype with another individual that is
homozygous for the recessive allele
Possibility I:
- Round pea producer WW (possible gametes: W) wrinkled pea producer ww (possible
gametes: w)
- Results of test cross: Ww (all Round pea producers)
Possibility II:
- Round pea producer Ww (possible gametes: W and w) wrinkled pea producer ww (possible
gametes: w)
- Results of test cross: 50% Ww (all Round pea producers) and 50% ww (wrinkled pea
producers)
, Mendel's dihybrid crosses
Mendel also performed dihybrid crosses
- crossing individual plants that differ in two characters
-- Character 1= seed texture (round vs. wrinkled)
-- Character 2= seed color (yellow vs. green)
1) Cross the true-breeding plants to each other... produces F1 generation seeds
2) Collect many seeds and record their phenotype
3) F1 seeds are planted and grown, and the F1 plants are allowed to self-fertilize. This produces
seeds that are part of the F2 generation
4) Analyze the characteristics found in the F2 generation seeds
Data from Mendel's dihybrid crosses
- Occurrence of nonparentals contradicts the linkage model...
The Law of Independent Assortment: During gamete formation, the segregation of any pair of
hereditary determinants is independent of the segregation of other pairs.
- predicted phenotypic ratio in F2 generation is 9:3:3:1
The dihybrid test cross
- Independent assortment also revealed by a dihybrid test cross: Example: TtYy X ttyy (Tall,
Yellow x dwarf, green)
- If the genes assort independently, the expected phenotypic ratio among the offspring is
1:1:1:1
Punnett squares
- Punnett squares can also be used to predict the outcome of crosses involving two
independently assorting genes
-- but if 3 or more independently assorting genes, becomes too cumbersome (64 squares for 3
genes!)
-Instead...
-- the forked-line method or
-- the multiplication method
add pic
Modern Genetics
- interested in the relationship between the molecular expression of genes and the outcome of
traits:
-- identify an individual with a defective copy of the gene
-- observe how this copy will affect the phenotype of the organism
--- loss-of-function alleles are commonly inherited in a recessive manner
Predicting outcomes (probability and statistics)
GUIDE FOR ULTIMATE SUCCESS
Mendel performed two types of crosses
Self-fertilization:
- pollen and egg derived from same plant
- naturally occurs in peas because a modified petal isolates the reproductive structures
Cross-fertilization:
-pollen and egg derived from different plants (required removing and manipulating anthers)
Mendel studied 7 characters that bred true
- the morphological characteristics of an organism are termed characters
- the term trait describes the specific properties of a character
-- eye color is a character, blue eyes is a trait
- a variety that produces that same trait over several generations is termed a true-breeder
- each character showed two variants in the same species
- Mendel did not have a hypothesis to explain the formation of hybrids
-- empirical approach
- His first experiments involved crossing two variants of the same characteristic
-- monohybrid cross (a single characteristic is being observed)
Mendel's monohybrid cross
- This is called a P (parental) cross (also performed reciprocal crosses to eliminate gender-
related expression)
- These are the F1 (First filial) generation
- These are part of the F2 generation
- These are the F2 generation plants
Interpreting Mendel's monohybrid data
For all seven characteristics studied:
- the F1 generation showed only one of the two parental traits
- the F2 generation showed an ~3:1 ratio of the two parental traits
-- refuted a blending mechanism of heredity
- the data suggested a particulate theory of inheritance
What Mendel's data suggested
- a pea plant contains two discrete hereditary factors for a given character, one from each
parent
- the two factors may be identical or different
- when the two factors of a single character are different and present in the same plant...
,--one variant is dominant and its effect can be seen
-- the other variant is recessive and is not seen
- during gamete formation, the paired factors for a given character segregate from each other
(half receive one factor, half the other)
-- Mendel's Law of Segregation
Mendel's Law of Segregation Summary
- Mendelian factors now called genes
- alleles are different versions of the same gene
- an individual with two identical alleles is termed homozygous
- an individual with two different alleles is termed heterozygous
- genotype refers to the specific allelic composition of an individual
- phenotype refers to the outward appearance of an individual
Predicting the outcome of a cross
Punnett square: a grid used to predict the outcome of simple genetic crosses
1) Write down the genotypes of both parents: male parent=Tt, female parent=Tt
2) Write down the possible gametes each parent can make: male gametes: T or t, female
gametes: T or t
3) Create an empty Punnett square: male parent=Tt, female parent=Tt
4) Fill in the possible genotypes of the offspring by combining the alleles of the gametes
5) Determine the relative proportions of genotypes and phenotypes of the offspring: genotypic
ratio- TT=1, Tt=2, tt=1. phenotypic ratio- Tall=3, dwarf=1
The test cross
Mendel performed test crosses
- crossing an individual showing a dominant phenotype with another individual that is
homozygous for the recessive allele
Possibility I:
- Round pea producer WW (possible gametes: W) wrinkled pea producer ww (possible
gametes: w)
- Results of test cross: Ww (all Round pea producers)
Possibility II:
- Round pea producer Ww (possible gametes: W and w) wrinkled pea producer ww (possible
gametes: w)
- Results of test cross: 50% Ww (all Round pea producers) and 50% ww (wrinkled pea
producers)
, Mendel's dihybrid crosses
Mendel also performed dihybrid crosses
- crossing individual plants that differ in two characters
-- Character 1= seed texture (round vs. wrinkled)
-- Character 2= seed color (yellow vs. green)
1) Cross the true-breeding plants to each other... produces F1 generation seeds
2) Collect many seeds and record their phenotype
3) F1 seeds are planted and grown, and the F1 plants are allowed to self-fertilize. This produces
seeds that are part of the F2 generation
4) Analyze the characteristics found in the F2 generation seeds
Data from Mendel's dihybrid crosses
- Occurrence of nonparentals contradicts the linkage model...
The Law of Independent Assortment: During gamete formation, the segregation of any pair of
hereditary determinants is independent of the segregation of other pairs.
- predicted phenotypic ratio in F2 generation is 9:3:3:1
The dihybrid test cross
- Independent assortment also revealed by a dihybrid test cross: Example: TtYy X ttyy (Tall,
Yellow x dwarf, green)
- If the genes assort independently, the expected phenotypic ratio among the offspring is
1:1:1:1
Punnett squares
- Punnett squares can also be used to predict the outcome of crosses involving two
independently assorting genes
-- but if 3 or more independently assorting genes, becomes too cumbersome (64 squares for 3
genes!)
-Instead...
-- the forked-line method or
-- the multiplication method
add pic
Modern Genetics
- interested in the relationship between the molecular expression of genes and the outcome of
traits:
-- identify an individual with a defective copy of the gene
-- observe how this copy will affect the phenotype of the organism
--- loss-of-function alleles are commonly inherited in a recessive manner
Predicting outcomes (probability and statistics)
