Biology 102 Chapter 7 - Mendelian Genetics
Genetics
Gregor Mendel: Typical experiment of Mendel:
● Augustinian friar ● Start with true-breeding plants that
● The 1850s and 60's in the modern-day differ in one trait. They are designated
Czech Republic the "P" generation.
How are traits transferred from one generation ● Cross the two different varieties -
to the next? hybridization.
Conducted observational experiments with ● Collect and plant the seeds-"F1" (first
pea plants. filial) generation.
Trait: Any inherited characteristic of an ● Cross (or self) F1 individuals to
organism. produce an "F2".
● Physical ● Keep meticulous notes about the
● Biochemical plant's traits.
● Behavioral (Thousands of replications)
Mendel had access to different pea varieties – ● F1-all purple
plants that differed in some traits. ● White flowers returned in the F2.
● The heritable factor for white flowers
was never lost.
● The purple trait is dominant; the white
trait is recessive.
Furthermore, no matter the white trait he was
experimenting with, the F2 consistently
resulted in:
● ¾ with the dominant trait
● ¼ with the recessive trait
3:1 ratio
Mendel's Model
1. Alternate versions of heritable factors account for the variation in inherited traits.
2. For each trait, an organism inherits two copies of the factor, one from each parent.
3. If the 2 copies are different, one is dominant and the other is recessive.
1
, Biology 102 Chapter 7 - Mendelian Genetics
In modern terms:
Genes = heritable factors
Alleles = alternate versions
(Locus-: a gene's position on the chromosome)
Mendel's first law
● Law of segregation
○ During gamete formation, the two copies of a gene segregate from each other and
end up in different gametes.
Today, we know exactly why this happens – Anaphase 1
Doing genetics problems
● Designate a letter to represent the gene.
● The dominant allele is represented by the uppercase and the recessive allele by the
lowercase.
● Always use the same letter for both alleles.
● Make a Punnett square to simulate random fertilization.
Some common genetics terminology:
Genotype: the specific alleles/genetic makeup of an organism
Phenotype: a trait the organism has due to its genotype
Homozygous: both copies of a gene are the same allele.
Heterozygous: two different alleles.
True (pure) breeding: homozygous
This is called a monohybrid cross.
Probabilities and Expectations
The 3:1 ratio that underlies a monohybrid cross can be interpreted as 2 things.
Probability - ex. If a body is on its way, what is the probability that it will have a certain trait?
Exception - ex. If an oak tree produces 1000 acorns, how many of those are expected to have a
certain trait?
If 4 offspring are born, we'd expect 3 to be dominant, but that doesn't mean they necessarily.
2
Genetics
Gregor Mendel: Typical experiment of Mendel:
● Augustinian friar ● Start with true-breeding plants that
● The 1850s and 60's in the modern-day differ in one trait. They are designated
Czech Republic the "P" generation.
How are traits transferred from one generation ● Cross the two different varieties -
to the next? hybridization.
Conducted observational experiments with ● Collect and plant the seeds-"F1" (first
pea plants. filial) generation.
Trait: Any inherited characteristic of an ● Cross (or self) F1 individuals to
organism. produce an "F2".
● Physical ● Keep meticulous notes about the
● Biochemical plant's traits.
● Behavioral (Thousands of replications)
Mendel had access to different pea varieties – ● F1-all purple
plants that differed in some traits. ● White flowers returned in the F2.
● The heritable factor for white flowers
was never lost.
● The purple trait is dominant; the white
trait is recessive.
Furthermore, no matter the white trait he was
experimenting with, the F2 consistently
resulted in:
● ¾ with the dominant trait
● ¼ with the recessive trait
3:1 ratio
Mendel's Model
1. Alternate versions of heritable factors account for the variation in inherited traits.
2. For each trait, an organism inherits two copies of the factor, one from each parent.
3. If the 2 copies are different, one is dominant and the other is recessive.
1
, Biology 102 Chapter 7 - Mendelian Genetics
In modern terms:
Genes = heritable factors
Alleles = alternate versions
(Locus-: a gene's position on the chromosome)
Mendel's first law
● Law of segregation
○ During gamete formation, the two copies of a gene segregate from each other and
end up in different gametes.
Today, we know exactly why this happens – Anaphase 1
Doing genetics problems
● Designate a letter to represent the gene.
● The dominant allele is represented by the uppercase and the recessive allele by the
lowercase.
● Always use the same letter for both alleles.
● Make a Punnett square to simulate random fertilization.
Some common genetics terminology:
Genotype: the specific alleles/genetic makeup of an organism
Phenotype: a trait the organism has due to its genotype
Homozygous: both copies of a gene are the same allele.
Heterozygous: two different alleles.
True (pure) breeding: homozygous
This is called a monohybrid cross.
Probabilities and Expectations
The 3:1 ratio that underlies a monohybrid cross can be interpreted as 2 things.
Probability - ex. If a body is on its way, what is the probability that it will have a certain trait?
Exception - ex. If an oak tree produces 1000 acorns, how many of those are expected to have a
certain trait?
If 4 offspring are born, we'd expect 3 to be dominant, but that doesn't mean they necessarily.
2
