Mendelian Genetics

Question 1

What did Mendel Study?

Answer 1

The principles of heredity

Question 2

What’s are the two Hypotheses for heredity?

Answer 2

1. The “blending” hypothesis is the idea that genetic
   material from the two parents blends together to produce a trait.
2. The “particulate” hypothesis is the idea that parents pass genetic material as discrete heritable units that interact to produce a trait.

Question 3

Why did Mendel use pea plants? (A,B,C)

Answer 3

Mendel used pea plants as a model organism to study heredity.

A. There are many varieties of these plants with distinct traits for various heritable characters.
B. Matings can be controlled.
C. Matings produce several offspring (from seeds)

Question 4

Characters in Pea Plants

Answer 4

Mendel tracked characters that varied in an either-or manner such as purple or white flowers. Character = flower colour
Trait = Purple or White flower

Question 5

True breeding plants

Answer 5

produce offspring of the same variety (traits) when they self-pollinate

Question 6

Mendel’s Experimental Design

Answer 6

Parental Generation (P)
True-breeding (trait 1) x True-breeding (trait 2)
First filial generation offspring (F1)
Cross results in hybrids
First filial generation offspring (F1)
Second filial giration offspring (F2)

Question 7

Mendel’s Three Principles

Answer 7

The principle of:
1. Segregation
2. Dominance
3. Independent Assortment

Question 8

P generation

Answer 8

• true-breeding parents (ex: purple flowers x white flowers)
• When Mendel crossed true-breeding white and purple flowered pea plants, all of the F 1 hybrids were purple.

Question 9

F1 generation

Answer 9

-hybrids
- When Mendel crossed the F1hybrids, many of
the F2 plants had purple flowers, but some had white.

Question 10

F2 Generation

Answer 10

Mendel discovered a ratio of about 3:1, purple to white flowers, in the F2 generation.

Question 11

Mendel’s observations + results

Answer 11

• Mendel observed the same pattern of inheritance in six other pea plant characters.
• His results support the particulate hypothesis of heredity.
• Mendel developed a model to explain the 3:1 inheritance pattern he observed in F 2 offspring.

Question 12

Mendel’s Model (5 points)

Answer 12

1. For each character, an organism inherits one heritable factor from each parent.
2. Alternative versions of these heritable factors account for variations in inherited characters. These alternate versions are alleles.
3. One allele is dominant while the other is recessive.
4. These heritable factors segregate (separate) during gamete formation and are packaged into different gametes.
5. Sex of the parent passing on the allele does not affect the inheritance pattern.

Question 13

Punnett Square

Answer 13

A Punnett square is a matrix where the rows represent the possible gametes of one parent, the columns the possible gametes of another parent, and the boxes the possible combinations in offspring.

Question 14

What does a Punnett square allow you to predict?

Answer 14

Can allow you to predict the probability of an offspring’s genotype and phenotype for a particular set of parents.

Question 15

Genetic ratios

Answer 15

• Phenotype vs genotype
• Phenotype = Purple, purple, purple, white = 3:1 ration
• Genotype= PP (homozygous dominant), Pp (heterozygous), Pp (heterozygous), pp (homozygous recessive) = 1PP: 2Pp: 1pp

Question 16

What makes an Allele Dominant?

Answer 16

• When the effects of an allele can be detected regardless of the alternative allele, then that allele is described as dominant.
• If the effect of an allele is masked in the heterozygous condition, then the allele is described as recessive.

Question 17

Mendelian Genetics and Human Disorders

Answer 17

• Mendelian traits in humans can be disorders.
• These disorders are caused by one gene (monogenic disorders).
• The disorder can be inherited as a recessive or dominant trait depending on the allele involved in the disorder.

Question 18

Albinism

Answer 18

A recessive disorder

Question 19

Heterozygotes

Answer 19

are referred to as carriers when the disorder is recessive.
- They are not affected by the disease but they are carriers of the disorder allele.

Question 20

Achondroplasia

Answer 20

• a type of dwarfism
• a dominant disorder

Question 21

What about the inheritance of two characters?

Answer 21

• Mendel constructed his model and derived the law of segregation by following a single character in monohybrid crosses.
• Mendel identified his third law of inheritance by following two characters at the same time in dihybrid crosses.

Question 22

Two hypotheses exist

Answer 22

1. Traits are inherited as a package; alleles are linked and assort dependently into the same gamete
2. Traits are not inherited as a package; alleles are not linked and are independently assorted into gametes.

Question 23

Dependant assortment

Answer 23

Parental combinations only

Question 24

Independent assortment

Answer 24

Parental but also new combinations

Question 25

The two hypotheses…

Answer 25

(Dependant and independent assortment) predict different phenotypic ratios in the F2 offspring when F1 dihybrids self-pollinate

Question 26

Mendel’s model makes sense! Now we know…

Answer 26

1. Chromosomes are the vehicles of heredity. 2. How meiosis works and shuffles alleles into unique combinations.

Question 27

What does Mendel’s model explain

Answer 27

The laws of segregation and independent assortment. 1. Genes are the units of heredity. 2. What genes are, how they work, and how mutation can change them. 3. How alleles arise and that some can be dominant.

Question 28

Chromosome are Vehicles of Heredity

Answer 28

All our genes contributing to a specific character can be found at specific locations (loci) within a specific chromosome.

Question 29

For every chromosome what do we inherit?

Answer 29

We inherit a pair called homologous chromosomes and, therefore, pairs of each gene.

Question 30

These pairs of genes can differ at…

Answer 30

can differ at their nucleotide sequence and encode different versions of proteins (different alleles) or they can be identical and encode identical proteins (same alleles).

Question 31

Different proteins

Answer 31

Can lead to different traits

Question 32

The chromosome theory of inheritance

Answer 32

Was used to explain Mendel’s model in the early 1900s

Question 33

Principle of segregation

Answer 33

The alleles for a seed color segregate during gametogenesis because they are located on homologous chromosomes and these chromosomes are separated during Meiosis I.

Question 34

Principle of independant assortment

Answer 34

The alleles for seed shape and seed color assort independently because the genes are located on different chromosomes. During Meiosis I, maternal and paternal chromosomes from homologous sets are randomly distributed into daughter cells.

Question 35

Genes are

Answer 35

Units of heredity A. Genetic information flows from dna to rna to proteins - Mice with this DNA sequence have dark coats B. Differences in genotype may cause differences in phenotype (physical traits that are a product of the proteins produced) - Mice with this DNA sequence have light coats

Question 36

Explanation for a dominant Allele

Answer 36

- Many recessive alleles are alleles that have been changed through mutation (called mutant allele) and produce non-functional proteins. - In complete dominance, having one copy of the normal allele produces enough functional protein to produce a normal phenotype.

Question 37

Protein P

Answer 37

- functions as an enzyme - the amount of functional protein P is the molecular connection between the genotype and the phenotype - the normal (dominant) allele encodes a functional enzyme

Question 38

Genotype is

Answer 38

The amount of functional protein P produced

Question 39

Phenotype is

Answer 39

The relationship of the normal (dominant) and mutant (recessive) alleles display simple Mendelian inheritance Physical traits that are a product of the proteins produced

Question 40

Mendel’s model doesn’t explain it all

Answer 40

Not all characters are Mendelian characters! The inheritance pattern of MOST characters do not follow his simple model.