Quiz 2 (3.1- 3.3)

Question 1

Define the following terms used in classical genetics: genes

Answer 1

the basic physical and functional unit of heredity

Question 2

locus

Answer 2

Individuals inherit two copies of each of the chromosomes
both chromosomes has same genes in same place (locus)

Question 3

alleles

Answer 3

Sometimes individual has 2 genes have the same sequence
Other times individual have genes with different sequences
That is, have two different versions of a gene (alleles)

Question 4

genotype

Answer 4

Genetic makeup of an individual at one or more genes

Question 5

phenotype

Answer 5

Observable physical properties of an organism

Question 6

characteristic

Answer 6

qualities or features that describe the distinctive nature or features of an individual organism or of a group

Question 7

heterozygote

Answer 7

The presence of two different alleles at a particular gene locus

Question 8

homozygote

Answer 8

The presence of two identical alleles at a particular gene locus

Question 9

dominant trait

Answer 9

trait observed in the F1 generation

Question 10

recessive trait

Answer 10

the trait that disappeared in the F1 generation

Question 11

Explain what Mendel discovered in his monohybrid crosses, including

Answer 11

Cross between parents that differ in a single characteristic

Question 12

Explain what meant by the P, F1, and F2 generation

Answer 12

P generation: (Parental)
F1 generation: (Filial 1)
F2 generation: “grandchildren” of P generation

Question 13

State which phenotypes he observed in the F1 generation of crosses between 2 “true-breeding” pea plants

Answer 13

Mendel examined the progeny resulting from the cross of two plants with different trait
Observed that all of the progeny resembled only one of the two parents

Mendel repeated the same experiment with 6 other traits:
Always for the same result:
When 2 “true-breeding” plants were crossed:
All offspring had trait of one of the parents

Question 14

Explain the Mendel’s observations from a monohybrid cross using modern terminology (gene, allele, chromosome, meiosis), including how we would know describe:
The two different “genetic factors” that each plant has.
That one of the plant’s two “genetic factors” goes into each gamete that they make.
That the two type of “genetic factors” of an individual plant separate with equal probability into the gametes.

Answer 14

Each plant must have two different “genetic factors”
Since F2 generation had plants with traits from both type of the P generation, Mendel concluded:
Each plant has 2 genetic factors for each characteristic
They get one “genetic factor” from each parent
We now know: The 2 “genetic factors” for each characteristic are the 2 copies of every gene
There can be different versions of those genes (alleles)

The two “genetic factors” in each plant separate when gametes are formed
one “genetic factor” goes into each gamete
We now know:
For each gene, each individual gives one of two copies of gene to their offspring
And so
offspring inherits one allele
from each parent

Mendel concluded that there are two different type of traits:
a dominant gene and a recessive gene
We now know that (for this type of gene):
when an individual gets two different alleles for that gene,
one of the alleles determines the trait
Mendel’s terms (dominant and recessive) are still used

Question 15

Explain how the principle of independent assortment results from the separation of chromosomes in meiosis

Answer 15

Through the Principle of Independent Assortment, he explained how genes segregate (or separate) in homologous chromosomes during meiosis. During this process, the alleles of different genes are sorted in gametes and inherited independently. This results in genetic diversity and recombination.

Question 16

State that different alleles have different genetic sequences, and explain how a difference in the sequence of a gene can alter the function of a protein produced by that gene.

Answer 16

Different sequences in genes result in different proteins
Different proteins function differently
These different functions result in different phenotypes

Question 17

Explain the Concept of Dominance and how phenotypes are determined by genotype.

Answer 17

Concept of dominance:
When an individual gets two different alleles for that gene:
one of the alleles determines the trait
Allele that determines phenotype = dominant allele
Allele that has no effect on phenotype = recessive allele

Question 18

Explain how the principle of segregation and the concept of dominance account for the results of a genetic cross.

Answer 18

1. If 2 alleles of genotype Rr are located on homologous chromosomes
2. which replicate in the S phase of meiosis
3. In prophase I of meiosis, crossing over may or may not rake place
4. In anaphase I, the homologous chromosomes separate
5. If no crossing over has taken place, the 2 chromatids of each chromosome segregate in anaphase II and are identical
6. If crossing over has taken place, the 2 chromatids are no longer identical, and the different alleles segregate in anaphase II

Question 19

Predict the phenotype and genotype of the progeny of a monohybrid cross, based on the genotype of their parents, using a Punnett square

Answer 19

Punnett square
Simple, shorthand method for predicting outcomes of monohybrid genetic crosses
Gets very cumbersome with more that one gene

Predicts ratio of genotype of offspring from genotype of parents
Based on fact that the two chromosomes of each parent distribute equally to their gametes

Question 20

State the genotypes of parents, based on the phenotypes of their progeny.

Answer 20

Example:
For alleles at MC1R gene
Allele for having freckles (F) is dominant
Allele for no freckles (f) is recessive
First: determine genotype of parents:
Father = Ff
Mother = ff

Question 21

Explain the function of a testcross, and how it can be used to determine the genotypes of an individual with a dominant phenotype based on their offspring.

Answer 21

Testcrosses determine genotype of individual with a dominant trait without sequencing

Can determine the genotype by performing a testcross:
By crossing the individual with dominant phenotype with an individual with recessive trait
two recessive alleles

Question 22

Use the Multiplication Rule to determine the probabilities of combinations of events occurring together, and to use the Addition Rule to determine the probabilities of one or the other event occurring

Answer 22

Multiplication Rule:
The probability of two or more independent events occurring together is calculated by multiplying their independent probabilities.

Addition Rule:
The probability of any one of two or more mutually exclusive events is calculated by adding the probabilities of these events.

Question 23

Use probability to predict the progeny produced in a cross with two or more loci, using either of the methods discussed in class (“one gene at a time” or “the forked-line method”).

Answer 23

calculate probabilities one GENE at a time

The fork line method can be used by figuring the occurrence of each gene or set of genes to be found in the gamete, and then multiply them together