5.1 Mendelian Inheritance Flashcards
- Describe the pattern of inheritance Mendel observed when he crossed tall pea plants with short pea plants
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)
- How does a homozygous genotype differ from a heterozygous genotype?
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
What is the difference between an organism’s genotype and its phenotype?
The genotype refers to the genetic material passed between generations
The phenotype is observable characteristics or traits
What is probability?
The likelihood that a particular event will occur
What are the two possible gametes that could be produced by a plant with the genotype Aa? Give the probability of producing each gamete.
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).
In guinea pigs, rough coat is dominant to smooth coat. How could you determine
the genotype of a rough-coated guinea pig?
If they have a dominant allele (R)
Could be RR or Rr
Differentiate between self-fertilization and
cross-fertilization of plants
-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
Define the term “hybrid” and give an example
-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.
What is meant by the terms “homozygous” and
“heterozygous?” Give an example to explain
each term.
homozygous: two inherited alleles are the same
-e.g. RR or rr
heterozygous: two inherited alleles are different
-e.g. Rr
Genotype vs. Phenotype
genotype: complete set of genetic material and refers to the alleles
phenotype: individual’s observable traits, such as height, eye color and blood type
Which allele will determine the trait that
shows up in a heterozygous individual: the
dominant allele or the recessive allele? Why?
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
What is the purpose of a test cross?
-used to infer the Mendelian alleles present in parental gametes based on the observation of offspring phenotypes
What are separated during meiosis, according
to the law of segregation?
two alleles for a trait or gene segregate
What does the Law of Segregation state?
-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.
Name two types of organisms that have been
used to study laws of inheritance. What makes
them useful as model organisms for genetic
studies?
-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
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.
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.
How does the law of independent assortment
help explain the inheritance pattern for seed
colour and shape in pea plants?
-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)
What does Mendel’s law of independent assortment state?
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
What is the difference between a monohybrid
and a dihybrid?
Monohybrid: parents that differ in ONE trait
Dihybrid: parents that differ in TWO traits
What is a monohybrid cross?
hybrids with parents that differ in ONE trait are
crossed with one another
How do Punnett squares help us to predict the
probable outcomes of genetic crosses?
diagram that shows the expected proportions of all
possible outcomes of a genetic cross
List all possible allele combinations in the
gametes of an individual with genotype AaBb
-AB
-Ab
-aB
-ab
How did Mendel show that traits were not
blended in offspring?
-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
Progeny meaning
offspring
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.
Let L=long
Let l= short
LL x Ll
genotype: LL or Ll
What would a diagram of how allele pairing
being related to the behaviour of chromosomes
during gamete formation and fertilization be of?
law of separation
MENDEL’s WORK
What is the law of dominance
all traits have 2 forms (alleles)
one allele is dominant to the other form
inheritance patterns
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
Inherited traits are also known as ________ traits
hereditary
gregor mendel spent 7 years studying pea plants to better understand ___________
inheritance patterns
Hypothesized that parents pass on separate and distinct “______” to their offspring that are responsible for _____ traits
factors; hereditary
locus
location on chromosome
Mendel began his experiments with true-breeding pea plants that produced _______ via _________
identical offspring; self-fertilization
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 _____________
cross fertilization
P Generation =
parental generation
F1 Generation =
first generation of offspring (P x P)
F2 Generation =
second generation of offspring (F1 x F1)
genotype
Genotype = genetic make-up of an organism (e.g. PP)
phenotype
Phenotype = physical expression/appearance of the organism (e.g. Purple)
______________ depends on genotype
physical expression(phenotype)
When crossing two different true-breeding organisms, the offspring are called ____
hybrids
monohybrids
offspring of parents who differ in only one trait
Genes can exist in different forms, known as
alleles
- e.g. alleles for pea seed shape are round or
wrinkled
Offspring inherit one allele of a gene from each
parent
if both alleles are the same = ___________ for that gene
homozygous
if alleles are different = ____________ for that gene
heterozygous
dominant alleles
dominant alleles are expressed in the heterozygous/homozygous dominant offspring (e.g. BB or Bb)
recessive alleles
only expressed in the homozygous recessive offspring (e.g. bb)
mendel’s law of segregation
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
We can predict the probability for the inheritance of an allele by using a grid diagram called a
Punnett Square
test cross
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.
state mendels law of segregation
During gamete formation, the pair of alleles responsible for each trait segregate (separate) so that each gamete contains only one allele for each trait.
state mendels law of independent assortment
During gamete formation, alleles segregate independently of each other
dihybrid cross
A cross that involves 2 separate traits
