Chapter 9 - Genetic Inheritance

Question 1

What plant did Gregor Mendel do a lot of detailed work?

Answer 1

Pea plants! 🫛

Question 2

When was Mendel’s work published and when was it noticed and proven by the scientific community?

Answer 2

Published in 1866.
Noticed and proven in 1900.

Question 3

What is a character (characteristic)?

Answer 3

A heritable feature that varies among individuals, such as flower colour or
seed colour.

Question 4

What is a trait?

Answer 4

Each variant of a character (i.e., white or purple flowers, green or yellow seeds)

Question 5

What is self fertilization (in plants)?

Answer 5

When an organism can fertilize itself. When the pollen of the plant fertilizes the egg of the same plant.

Question 6

What is cross fertilization?

Answer 6

Fertilization in which the gametes are produced by separate individuals.
i.e. fertilization of one plant with the pollen of another plant.

Question 7

What is a hybrid?

Answer 7

The offspring of two different varieties.

Question 8

What is a P generation?

Answer 8

True-breeding parental organisms.

Question 9

What is a F1 generation?

Answer 9

First filial generation – these are the hybrid offspring from crossing two different true-breeding varieties.

Question 10

What is a F2 generation?

Answer 10

Second filial generation – the result of crossing 2 F1 hybrids together.

Question 11

What is a monohybrid cross?

Answer 11

A cross of 2 true-breeding plants that differ in only one character – i.e. flower colour.

Question 12

What is a dihybrid cross?

Answer 12

Crossing two true-breeding plants that differ in 2 characters - i.e. seed shape and seed colour.

Question 13

What is an allele?

Answer 13

An alternate version of a gene that resides at the same locus on homologous chromosomes.

Question 14

What is a phenotype?
What is a genotype?

Answer 14

P: the set of observable physical traits. i.e. purple flowers.
G: An organism’s genetic information. i.e. Pp

Question 15

What is true-breeding? What are true-breeding organisms?

Answer 15

A kind of breeding where the parents would produce offspring that would carry the same phenotype (homozygous for each trait and are all identical to the parent organism).
True-breeding organisms are homozygous for the traits being studied.

Question 16

What were Mendel’s 4 hypotheses that he derived from all of his experiments?

Answer 16

1. There are alternate versions of genes (alleles).
2. For each character, an organism inherits 2 alleles, one from each parent.
3. There are dominant and recessive alleles.
4. A sperm or egg carries only one allele for each inherited character (the law of segregation).

Question 17

What is the law of segregation?
How is this related to meiosis?

Answer 17

It says that allele pairs separate from each other during the production of the gametes.
We saw this in meiosis anaphase 1.

Question 18

What is the law of independent assortment?
How is this related to meiosis?

Answer 18

It says that the separation of the alleles into the gametes is random and independent. Inheritance of one character does NOT influence the inheritance of another.
Happens at metaphase 1 of meiosis (chromosomes line up randomly).

Question 19

What is a dominant allele?
What is a recessive allele?

Answer 19

When a dominant allele is present it will always show its trait. A recessive allele only shows its trait when no dominant allele is present.

Question 20

What does it mean to be genetically homozygous?
What about heterozygous?

Answer 20

Homo: having two identical alleles for a given gene. Can be dominant or recessive. i.e. QQ or qq
Hetero: having two different alleles for a given gene. i.e. Qq

Question 21

If someone has 2 dominant alleles they are ________ dominant for the trait.
If they have 2 recessive alleles they are __________ recessive for the trait.

Answer 21

Homozygous dominant.
Homozygous recessive.

Question 22

When asked to:
“Work out a Punnett square for the F1 monohybrid cross for seed colour”
Which generation are you supposed to look at to answer the related questions?

Answer 22

Working out the F1 means using the F1 generation to find out what the next generation will look like. So really you’re looking at the F2 generation to find answers to phone/genotype, etc.

Question 23

When can you tell the genotype by looking at an organism?
When can’t you tell the genotype?

Answer 23

You can tell the genotype when a known recessive trait is visible.
You cannot tell the genotype when the dominant trait is visible. It could be heterozygous or homozygous dominant.

Question 24

What is the phenotypic ratio of the F2 generation for a monohybrid cross? What about the genotypic ratio?

Answer 24

Phenotype = 3:1
Genotype = 1:2:1

Question 25

What is the phenotypic ratio of the F2 generation for a dihybrid cross?

Answer 25

Phenotype = 9:3:3:1

Question 26

What are homologous chromosomes?

Answer 26

Homologous chromosomes code for the same characters, but may express different traits (alleles). Found in pairs, one from mom, one from dad.

Question 27

What is the rule of addition?

Answer 27

Key word: OR
It states that the probability for all possible outcomes of an event to occur must always add up to 1.
i.e. 0.5 + 0.5 = 1
Also the probability that an event can occur in two or more alternative ways is the sum of their separate probabilities.
i.e. 0.25 + 0.25 = 0.5.

Question 28

What is the rule of multiplication?

Answer 28

Key word: AND
The probability of two independent events happening at the same time is the product of them happening individually.
i.e. 0.5 x 0.5 = 0.25

Question 29

If an organisms with 3 pairs of chromosomes (2n=6) can make 23 or 8 types of gametes, an organism with 12 pairs of chromosomes (2n=24) can make 212 or ______ different types of gametes.

Answer 29

???????

Question 30

What is a test cross?

Answer 30

A way to find if an organism with the dominant phenotype is homozygous dominant or heterozygous for a trait.
Done by breeding the dominant phenotype with a homozygous recessive phenotype. The phenotypic ratio of the offspring can reveal the parent’s genotype.

Question 31

If 100% of the offspring from a test cross show the dominant phenotype, you know the parent with the dominant phenotype is ________ for the trait. If there are any offspring that show recessive traits, you know that the dominant parent was _________ for that trait.

Answer 31

Homozygous.
Heterozygous.

Question 32

What assumptions are made in Mendelian Genetics? Are these assumptions always true?

Answer 32

We assume that the traits are on different chromosomes (not linked), there are only 2 alleles in the population, only one gene codes for one trait, and that dominance is complete. This isn’t always the case.

Question 33

What is epistasis?
What example of this did we look at?

Answer 33

When the expression of one gene interferes with the expression of another.
In labrador retrievers coat colour one gene codes for colour (B) and another gene allows the colour to be expressed in their coat (E). The E gene can interfere with the B gene.

Question 34

What is incomplete dominance?
Is the result of incomplete dominance permanent?

Answer 34

Where the F1 offspring look like a blend of the parents.
Homozygous dominant shows one phenotype, homozygous recessive shows another phenotype and heterozygous shows both!
No, we get the dominant and recessive traits back in the F2 generation.

Question 35

In the case of incomplete dominance, what are the phenotypic and genotypic ratios in the F2 generation of a monohybrid cross?

Answer 35

The ratios are identical in the F2 generation because heterozygotes display a different phenotype than homozygous dominant individuals.

Question 36

What is co-dominance? What example did we look at?

Answer 36

Where both alleles are fully expressed.
The ABO blood groups where the allele for type A blood and type B blood are both fully expressed as antigens on the person’s blood cells. This creates the AB blood type.

Question 37

What are multiple alleles? What example did we looked at?

Answer 37

When there are more than 2 types of alleles present in a population.
The ABO blood group is an example of this.

Question 38

What is the universal donor and universal acceptor of blood types?

Answer 38

O is the universal donor because it has no antigens on its surface.
AB is the universal acceptor because it already has A and B antigens and O has no antigen so it doesn’t matter.

Question 39

A and B are __________ with each other but are __________ relative to O

Answer 39

Co-dominant.
Dominant.

Question 40

What is pleiotropy? What example did we look at?

Answer 40

When a single gene can affect many phenotypic characters.
i.e. Sickle-cell disease which causes the production of abnormal haemoglobin (it’s also an example of co-dominance, heterozygous individuals are usually healthy tho).

Question 41

What are the effects of abnormal haemoglobin production due to sickle-cell disease?

Answer 41

Under conditions of moderately low oxygen, the cells will sickle and block small blood vessels, cause organ damage, pain, fever, joint problems, anaemia, and the immune system destroy the sickled blood cells.

Question 42

What is polygenic inheritance? How many genes code for skin colour?

Answer 42

When multiple genes affect a single phenotypic character. The opposite of pleiotropy.
At least 3 genes that code for skin colour. The dominant alleles code for darker skin, the recessive alleles code for pale skin.

Question 43

What did humans evolve from? Why did humans evolve dark skin and then re-evolve light skin?

Answer 43

Chimp ancestors with light skin under dark fur. Early humans lost their fur in order to dissipate extra heat from having bigger brains. But pale skin was more likely to burn and develop skin cancer. UV also destroys vitamin B9 (folate) needed for healthy pregnancies.
More skin pigmentation = reduced the risk of skin cancer and also protects folate.
Humans migrated north and needed paler skin to produce enough vitamin D.

Question 44

Many characteristics result from a combination of ________ and __________. However only ________ influences are inherited.

Answer 44

Genetics and environment.
Only genetic influences are inherited.

Question 45

Define epigenetics.

Answer 45

Heritable changes in gene expression that are, unlike mutations, not attributable to alterations in the sequence of DNA. Environment, diet, etc. can turn various genes on or off and that can be passed on to offspring.

Question 46

One major way genes can be turned off if by DNA ___________ .

Answer 46

Methylation

Question 47

Epigenetics may help explain the correlations that researchers have found between _______ and risk of disease.

Answer 47

Lifestyle

Question 48

What is the chromosome theory of inheritance? When was it created?

Answer 48

It states that genes occupy specific loci on chromosomes and it is the chromosomes that undergo segregation and independent assortment during meiosis.
Created in the early 1900s.

Question 49

What are linked genes?

Answer 49

Genes found on the same chromosome tend to be inherited together. The closer the genes are to each other, the less likely they will
be separated during a cross over event.

Question 50

What is a sex-linked gene?

Answer 50

A gene that codes for something other than sexual determination, that is on a sex chromosome.

Question 51

Why are sex-linked genes often called x-linked?

Answer 51

Because the X chromosome contains many genes not found on the Y chromosome.

Question 52

Why are X-linked genes are often inherited differently in males and females?

Answer 52

Males only have 1 X chromosome,
so there is no match for the majority of X-linked genes in males. They will express their X-linked gene whether the allele is dominant or recessive because it’s the only one they have.

Question 53

Why are haemophilia, Duchene Muscular Dystrophy and red-green colour blindness more common in males than females?

Answer 53

They are all X linked recessive traits.

Question 54

How many recessive X-linked alleles must females and males receive to express a disease?

Answer 54

Females must receive 2 recessive alleles, one from their mother and one from their father.
Males must only receive one recessive allele from the mother.