5.1 Mendelian Inheritance

Question 1

1. Describe the pattern of inheritance Mendel observed when he crossed tall pea plants with short pea plants

Answer 1

When a tall and short plant are crossed, all the offspring are tall. If the offspring self-fertilize, they produce tall and short plants in a ratio of 3:1 in the next generation(F2)

Question 2

2. How does a homozygous genotype differ from a heterozygous genotype?

Answer 2

Homozygous: You inherit the same version of the gene from each parent, so you have two matching genes.
Heterozygous: You inherit a different version of a gene from each parent

Question 3

What is the difference between an organism’s genotype and its phenotype?

Answer 3

The genotype refers to the genetic material passed between generations
The phenotype is observable characteristics or traits

Question 4

What is probability?

Answer 4

The likelihood that a particular event will occur

Question 5

What are the two possible gametes that could be produced by a plant with the genotype Aa? Give the probability of producing each gamete.

Answer 5

Two possible types of gametes: A and a.
Since this is a random process, the individual will, on average, make equal numbers of each gamete. (Frequency of 1/2 for each gamete).

Question 6

In guinea pigs, rough coat is dominant to smooth coat. How could you determine
the genotype of a rough-coated guinea pig?

Answer 6

If they have a dominant allele (R)
Could be RR or Rr

Question 7

Differentiate between self-fertilization and
cross-fertilization of plants

Answer 7

-cross fertilization occurs between the male and female gametes of the different individuals of the same species
-key difference between the self and cross-fertilization is that self fertilization involves only ONE individual whereas cross fertilization involves TWO different individuals of the same species

Question 8

Define the term “hybrid” and give an example

Answer 8

-offspring that result from crossing two true-breeding
varieties of the same species
-e.g. Mendel produced hybrids by crossing tall-stemmed pea plants with short-stemmed pea
plants.

Question 9

What is meant by the terms “homozygous” and
“heterozygous?” Give an example to explain
each term.

Answer 9

homozygous: two inherited alleles are the same
-e.g. RR or rr
heterozygous: two inherited alleles are different
-e.g. Rr

Question 10

Genotype vs. Phenotype

Answer 10

genotype: complete set of genetic material and refers to the alleles

phenotype: individual’s observable traits, such as height, eye color and blood type

Question 11

Which allele will determine the trait that
shows up in a heterozygous individual: the
dominant allele or the recessive allele? Why?

Answer 11

dominant allele
-because there needs to be TWO copies of a recessive allele for it to be expressed as a trait in a heterozygous individual
-dominant allele only need ONE copy for it to be expressed

Question 12

What is the purpose of a test cross?

Answer 12

-used to infer the Mendelian alleles present in parental gametes based on the observation of offspring phenotypes

Question 13

What are separated during meiosis, according
to the law of segregation?

Answer 13

two alleles for a trait or gene segregate

Question 14

What does the Law of Segregation state?

Answer 14

-states that the two alleles for a trait or gene segregate during the phases of meiosis.
-with fertilization, each gamete donates one allele to make up the allele pair in offspring.

Question 15

Name two types of organisms that have been
used to study laws of inheritance. What makes
them useful as model organisms for genetic
studies?

Answer 15

-The fruit fly, Drosophila Melanogaster, is a useful genetic model because it produces large numbers of offspring relatively quickly

-peaplants because he could easily control their fertilization.
-pollen from the same flower (self-fertilization), or from another plant’s flowers (cross-fertilization)
-display simple dominant-recessive traits that are easy to isolate and observe, making them simple organisms to study

Question 16

Mendel used stocks of pea plants that were
true-breeding. What is meant by this term?
Give an example and explain why it was
necessary to use these particular plants in
the crosses.

Answer 16

true-breeding: plant, when self-fertilized, produces offspring identical in appearance to itself, generation after generation
-e.g. a true-breeding purple flower, if self-fertilized,
would only produce offspring with purple flowers.
-necessary to use these to study monohybrid plants
that differ in just ONE trait
-by experimenting with true-breeding pea plants, Mendel avoided the appearance of unexpected traits in offspring that might occur if the plants were not true breeding.

Question 17

How does the law of independent assortment
help explain the inheritance pattern for seed
colour and shape in pea plants?

Answer 17

-Mendel worked with pea plants by considering two characters, shape and colour of seed
-in the dihybrid cross, the phenotypes round yellow, wrinkled yellow, round green and wrinkled green appeared in the ratio 9:3:3:1
-the Punnett square can be used to understand the independent segregation of the two pairs of genes during meiosis and the production of eggs and pollen in the F1 RrYy plant.
-F1 gen has all round yellow plants(homoz. dom.)
-F2 gens has 9:3:3:1 ratio
(shows all alleles=segregated independently)

Question 18

What does Mendel’s law of independent assortment state?

Answer 18

Mendel’s second law, the law of independent assortment, states that genes that segregate independently in meiosis do not influence each other’s inheritance.

• alleles of two (or more) different genes get sorted into gametes independently of one another

Question 19

What is the difference between a monohybrid
and a dihybrid?

Answer 19

Monohybrid: parents that differ in ONE trait
Dihybrid: parents that differ in TWO traits

Question 20

What is a monohybrid cross?

Answer 20

hybrids with parents that differ in ONE trait are
crossed with one another

Question 21

How do Punnett squares help us to predict the
probable outcomes of genetic crosses?

Answer 21

diagram that shows the expected proportions of all
possible outcomes of a genetic cross

Question 22

List all possible allele combinations in the
gametes of an individual with genotype AaBb

Answer 22

-AB
-Ab
-aB
-ab

Question 23

How did Mendel show that traits were not
blended in offspring?

Answer 23

-when Mendel cross-pollinated one variety of purebred plant with another, these crosses would yield offspring that looked like either one of the parent plants, not a blend of the two
-e.g. when he cross-fertilized plants with wrinkled seeds to those with smooth seeds, he did not get offspring with semi-wrinkly seeds
-instead, the offspring from this cross had only smooth seeds

Question 24

Progeny meaning

Answer 24

offspring

Question 25

If the phenotype for a plant is tall, and the
long-stem allele is dominant to the short-stem
allele, describe how to determine the exact
genotype of this plant. Show an example cross.

Answer 25

Let L=long
Let l= short

LL x Ll
genotype: LL or Ll

Question 26

What would a diagram of how allele pairing
being related to the behaviour of chromosomes
during gamete formation and fertilization be of?

Answer 26

law of separation

Question 27

MENDEL’s WORK
What is the law of dominance

Answer 27

all traits have 2 forms (alleles)
one allele is dominant to the other form

Question 28

inheritance patterns

Answer 28

predictable patterns seen in the transmission of traits from one generation to the next
-e.g. white flower X white flower = all offspring
will have white flowers

Question 29

Inherited traits are also known as ________ traits

Answer 29

hereditary

Question 30

gregor mendel spent 7 years studying pea plants to better understand ___________

Answer 30

inheritance patterns

Question 31

Hypothesized that parents pass on separate and distinct “______” to their offspring that are responsible for _____ traits

Answer 31

factors; hereditary

Question 32

locus

Answer 32

location on chromosome

Question 33

Mendel began his experiments with true-breeding pea plants that produced _______ via _________

Answer 33

identical offspring; self-fertilization

Question 34

Using these plants, Mendel crossed plants that were true-breeding for one characteristic (e.g. purple flowers) with plants that were also true-breeding for a different variation of the same characteristic (e.g. white flowers)
- this is known as _____________

Answer 34

cross fertilization

Question 35

P Generation =

Answer 35

parental generation

Question 36

F1 Generation =

Answer 36

first generation of offspring (P x P)

Question 37

F2 Generation =

Answer 37

second generation of offspring (F1 x F1)

Question 38

genotype

Answer 38

Genotype = genetic make-up of an organism (e.g. PP)

Question 39

phenotype

Answer 39

Phenotype = physical expression/appearance of the organism (e.g. Purple)

Question 40

______________ depends on genotype

Answer 40

physical expression(phenotype)

Question 41

When crossing two different true-breeding organisms, the offspring are called ____

Answer 41

hybrids

Question 42

monohybrids

Answer 42

offspring of parents who differ in only one trait

Question 43

Genes can exist in different forms, known as

Answer 43

alleles
- e.g. alleles for pea seed shape are round or
wrinkled

Question 44

Offspring inherit one allele of a gene from each

Answer 44

parent

Question 45

if both alleles are the same = ___________ for that gene

Answer 45

homozygous

Question 46

if alleles are different = ____________ for that gene

Answer 46

heterozygous

Question 47

dominant alleles

Answer 47

dominant alleles are expressed in the heterozygous/homozygous dominant offspring (e.g. BB or Bb)

Question 48

recessive alleles

Answer 48

only expressed in the homozygous recessive offspring (e.g. bb)

Question 49

mendel’s law of segregation

Answer 49

During meiosis, alleles segregate into gametes
Only one allele for a trait appears in each gamete
Fertilization brings alleles into pairs again
Alleles, like traits, are therefore said to heritable

Question 50

We can predict the probability for the inheritance of an allele by using a grid diagram called a

Answer 50

Punnett Square

Question 51

test cross

Answer 51

breed the unknown individual with one that is homozygous recessive, and the phenotypes of the F1 offspring will reveal the genotype of the mystery parent.

Question 52

state mendels law of segregation

Answer 52

During gamete formation, the pair of alleles responsible for each trait segregate (separate) so that each gamete contains only one allele for each trait.

Question 53

state mendels law of independent assortment

Answer 53

During gamete formation, alleles segregate independently of each other

Question 54

dihybrid cross

Answer 54

A cross that involves 2 separate traits