Mendelian Genetics

Question 1

What is blending inheritance?

Answer 1

Traits in the mother and father blend together to form the traits in their offspring. Source was mixing of blood.
White and black sheep produce gray sheep.
Analogy: Mixing of paints

Question 2

When did Mendel determine rules of inheritance?

Answer 2

1865

Not really known until 1900’s

Question 3

Who were Sutton and Boveri and what did they determine?

Answer 3

1903, Sutton and Boveri independently linked patterns of inheritance with chromosomes and reduction in chromosome number (meiosis) restored at fertilization.

Question 4

What did Thomas H. Morgan discover?

Answer 4

1907, T. H. Morgan and other biologists described details of sex determination by studying fruit flies.

Question 5

Why was Mendel successful?

Answer 5

Excellent observer and record keeper
Quantitative approach
Picked a really good model organism for his research (relatively easy to manipulate)
Some luck involved
The traits he studied were relatively simple and straightforward
The traits he studied happened to be unlinked with each other

Question 6

What are Mendel’s rules of inheritance?

Answer 6

units of inheritance are “particles of inheritance” (material elements) => genes are nucleotide sequences on DNA coding for proteins

particles of inheritance come in pairs that do not blend together => gene alleles come in pairs on homologous chromosomes and form definite traits

particles retain their character through generations => chromosomes replicate to be passed on to each following generation

particles of inheritance separate during formation of gametes => alleles on homologous chromosomes separate during meiosis I, ending in different gametes

Question 7

Define Character

Answer 7

Qualities or attributes of an organism that are visible or discernable (height to protein primary structure)
Ex: Seed shape, seed color

Question 8

Define Trait

Answer 8

Variations in a character

Ex: round, wrinkled, yellow, green

Question 9

Define genotype

Answer 9

Genetic makeup that determines trait of a character will be expressed

Question 10

Define phenotype

Answer 10

The visible or determinable expression of the genotype

Question 11

Define homozygous

Answer 11

An organism has two identical alleles of a gene for a given character

Question 12

Define heterozygous

Answer 12

An organism has differing alleles for a gene for a given character

Question 13

Define dominant

Answer 13

An allele that is expressed in the heterozygous condition

Question 14

Define recessive

Answer 14

An allele that is not expressed in the heterozygous condition

Question 15

Describe Mendel’s Law of Segregation

Answer 15

Mendel: the particles of inheritance for green and yellow color segregate but remain unchanged during reproduction

Question 16

Mendel’s Rules of Inheritance

Answer 16

Males and females contribute equally to the genotype of their offspring.
Some alleles are dominant to other alleles. (certain traits “recede” but are still present)

Question 17

Are homozygous alleles identical genetically?
Yes, both alleles express the same phenotype

No, the alleles will differ slightly in
DNA base pair code

Answer 17

Both are correct, the same phenotype can be expressed even though the underlying DNA sequence can be different (remember third position changes in DNA).

Question 18

How did Mendel disprove the idea of “blending” in heredity?

Answer 18

There was no “blending” of traits
no intermediate or transitional forms
therefore,
“particles of inheritance” that did not change
“pairs” that did not blend
“recessive” expressed only in absence of dominant

Question 19

How does a Punnet square work?

Answer 19

If you can’t figure this out you don’t deserve to pass the class >_<

Question 20

Punnet square example: a cross between Yy and Yy (monohybrid)
What is the phenotype in the next generation?
What is the genotype in the next generation?

Answer 20

Many more yellow than green the expected is 3:1 yellow versus green
1:2:1 ratio of homozygous yellow: heterozygous yellow and homozygous green

Question 21

Why would the actual counts of pea color only be expected to approximate the 3:1 ratio?
because science is not exact
because of experimental error
according to Mendel’s laws, there would be an exact 3:1 ratio

Answer 21

B is correct because some peas may be lost or miscounted, some will shrivel up and won’t be counted, etc.

Question 22

How does a punnet square work with dihybrid crosses?

Answer 22

Same as a normal punnet square but you have two variables like X and Y for the genotype

Question 23

Describe what is meant by incomplete dominance

Answer 23

Some traits appear to blend (in this case red and white snapdragon flowers)
A cross of red and white yields a F1 generation of all pink.
The F2 generation will have a 1:2:1 ratio of red:pink:white
Genotypic and phenotypic ratios are the same for incomplete dominance

Question 24

Describe what is meant by codominance.

Answer 24

There are A, B, AB and O blood types in humans
A means one kind of surface protein on red blood cells, B another and O means that cells lack both A and B.
AB blood has both
Both A and B are dominant to O
Presence of A and B alleles means that both proteins are expressed
An individual can only have two alleles for these blood types

Question 25

Understand what is meant by multigenic (or polygenic traits)

Answer 25

Multigenic traits are controlled by a series of genes.
Examples in humans include skin color, height, certain diseases like susceptibility to heart disease and complex behaviors (extroversion, schizophrenia)
The phenotypes approximate a bell shaped curve and variation appears to be smooth or continuous.

Question 26

Why is color blindness more prevalent in men than women?

Answer 26

Because it is an allele located on the X sex-chromosome. It is a recessive allele so since men only have one X chromosome it is easier to occur. Women have two X chromosomes so both would need to have the recessive allele for color blindness