Mendelian Genetics

Question 1

What is HEREDITY?

Answer 1

The passing of traits from parents to offspring

Question 2

What is GENETICS?

Answer 2

The branch of biology that studies the ways in which hereditary information is passed from parents to offspring

Question 3

Who is Gregor Mendel? What did he study?

Answer 3

He’s a monk who began the study of heredity by carrying out experiments with pea plants

Question 4

Why were pea plants useful to study? (Three reasons.)

Answer 4

1. Several traits of the peas existed in only two options (tall/short, purple/white)
2. Mating can be easily controlled because male and female parts are enclosed within the same flower
3. Peas grow easily. They mature quickly and produce many offspring

Question 5

What are two methods of mating of pea plants?

Answer 5

1. Self-fertilized

2. Cross-pollination: transferring the pollen from one plant to another flower in a different plant

Question 6

What does a MONOHYBRID CROSS study?

Answer 6

The inheritance of one pair of contrasting traits (like purple or white flowers)

Question 7

What are the three steps of a monohybrid cross?

Answer 7

1. Mendel first allowed each plant to self pollinate for several generations in order to make sure each was a true-breeding plant, henceforth known as parent (P) generation
2. Then, he cross-pollinated two different P plants to make the F1 generation
3. Finally, he allowed F1 to self pollinate to make F2

Question 8

What is a TRUE-BREEDING plant?

Answer 8

It only produces offspring of its same type

Question 9

What did Mendel see in the F1 generation?

Answer 9

They all had one trait - all were purple and the white trait disappeared

Question 10

What did Mendel see in the F2 generation?

Answer 10

The trait that went missing in the F1 reappeared in a 3:1 ratio.

Question 11

What did scientists think about traits in offspring before Mendel? Did Mendel’s experiments prove or disprove this?

Answer 11

That the traits were a blending of the parents.

Mendel’s experiments disproved this

Question 12

What are the four parts of Mendel’s Hypothesis?

Answer 12

1. An individual has two copies of every gene for a specific trait, one from each parent
2. There are alternate versions of genes, called ALLELES (like purple and white for flower color)
3. When there are two different alleles in an organism, one may be expressed while the other is hidden. In all of his experiments, there was always one dominant and one recessive allele.
4. Gametes that are formed during meiosis have only one allele for each trait, and when they unite during fertilization, each gamete contributes one allele

Question 13

What is a dominant trait?

Answer 13

One that is observable, always expressed

Question 14

What is a recessive trait?

Answer 14

A trait that isn’t expressed when in presence of a dominant allele

Question 15

What is an ALLELE?

Answer 15

Different versions of genes, like purple and white for flower color

Question 16

How are dominant alleles represented?

Answer 16

First letter of trait as a capital letter

Ex purple flowers: P

Question 17

How are recessive alleles represented?

Answer 17

First letter of dominant trait in lowercase

Ex white flowers: p

Question 18

What does HOMOZYGOUS mean?

Answer 18

Same two alleles for a specific gene

PP or pp

Question 19

What does HETEROZYGOUS mean?

Answer 19

Two different alleles for a gene. The dominant one is expressed, while the recessive one is masked
Pp

Question 20

What is a PHENOTYPE?

Answer 20

The physical appearance of a trait

Ex purple

Question 21

What is a genotype?

Answer 21

The alleles that an individual has

Ex Pp

Question 22

What is the Law of Segregation? What does it explain?

Answer 22

It explains the behavior of chromosomes during meiosis.
It states that two alleles separate from each other when gametes are formed, making sure that only one option is passed on from each parent

Question 23

What is the Law of Independent Assortment? How did Mendel test for this?

Answer 23

The inheritance of one trait doesn’t affect the inheritance of any other trait because the alleles of different genes separate independently from one another during gamete formation.
Mendel used a dihybrid cross, when he studies two traits to see if they affected each other. They didn’t.

Question 24

What does a dihybrid cross study?

Answer 24

Two pairs of contrasting traits, like height (tall/short) and flower color (purple/white)

Question 25

What is a punnet square?

Answer 25

A diagram that predicts the outcome of genetic crosses by considering all possible genetic combinations of gametes in the cross
It can be used to predict the outcome of a cross between two plants that are both heterozygous for a certain trait

Question 26

When doing a monohybrid cross for two plants that are both heterozygous for a certain trait, what is the phenotypic ratio? Genotypic ratio?
(Feel free to draw one!)

Answer 26

Phenotypic ratio: 3:1

Genotypic ratio: 1:2:1

Question 27

Why would we do a test cross?

Answer 27

Because it’s impossible to find out just by looking at an organism with a dominant phenotype if it’s heterozygous or homozygous for a trait.

Question 28

In a test cross, what genotype do we cross the unknown genotype with?

Answer 28

Homozygous recessive

Question 29

How will we know the unknown genotype after a test cross?

Answer 29

If only the dominant trait is expressed, it must have been homozygous dominant.
If there is a mix, and some express the dominant trait and others the recessive, it must have been heterozygous.

Question 30

What us incomplete dominance? What is an example of an organism that shows this?

Answer 30

When the inheritance of a dominant trait and a recessive trait results in a blending of traits that is not exactly like either of the plants.
This is shown in four-o-clock flowers, which can have red, white, or pink flowers

Question 31

What is codominance? How is it represented? What is an example?

Answer 31

When two dominant traits are visible at the same time. Use capital letters with superscripts to represent the alleles
An example is cattle - red + white = roan; each individual hair is either all red or all white, but overall has both colors of hair

Question 32

What does it mean if there are multiple alleles? What is an example?

Answer 32

When there are more than two possible alleles for a certain trait. Each individual will only inherit two of the possibilities.
For example, there are three different alleles for blood type: A (I^A), B (I^B), and O (i). You can only have two of these alleles.

Question 33

What do the A, B, and O alleles code for in blood typing? What types of traits are they?

Answer 33

The A and B code for the presence of certain markers on the surface of the red blood cells. The O codes for no labels.
A and B are codominant, so if both are there, the AB phenotype occurs. O is recessive.

Question 34

What is an autosomal trait?

Answer 34

A trait that is located on an autosome- not a sex chromosome

Question 35

What is a sex-linked (or X-linked) trait? How is it expressed in males and females?

Answer 35

A trait whose allele is located on the X chromosome
Because males only one X, it will be expressed.
Because females have two X chromosomes, if it is a recessive trait, it has to be on both chromosomes to be expressed

Question 36

What is an example of a sex-linked trait?

Answer 36

Color blindness.

Question 37

What is a pedigree?

Answer 37

A family history constructed by geneticists that shows how a trait is inherited over several generations. This is especially important if the trait is a genetic disorder and the family members want to know if they are carriers or if their children might get the disorder

Question 38

What are the three facts about a trait that a scientist can determine from a pedigree?

Answer 38

1. Is the trait autosomal or sex-linked? If it’s sex-linked, it will appear in more males than females.
2. Is it dominant or recessive? A dominant trait will appear in every generation, while a recessive one may skip a generation
3. Is a person’s genotype heterozygous or homozygous? If the phenotype shows the recessive characteristic, he must be homozygous recessive. If his phenotype shows the dominant trait, he must be either homozygous dominant or heterozygous

Question 39

What is a polygenic trait? What are two examples?

Answer 39

A trait that is influenced by many genes. These can be locate on the same chromosome or on different chromosomes.
Ex eye color, skin color

Question 40

How can many different combinations of genes happen?

Answer 40

Independent assortment and crossing over

Question 41

What can influence traits other than genes?

Answer 41

The environment
Examples:
1. Hydrangea plants are affected by the pH of the soil; they have different color flowers depending on how acidic or basic it is.
2. Arctic fox is affected by temperature. During the summer, their fur is darker, reddish brown, while in the winter it’s white so they can blend into the snow.
3. Humans: exposure to sun can darken skin; nutrition can affect your height or weight; environment can affect your personality.