Topic 1

Question 1

Compare monohybrid and dihybrid crosses.

Answer 1

Monohybrid crosses look at a single trait/gene and dihybrid crosses look at 2 traits/genes

Question 2

What is a test cross?

Answer 2

Determining unknown genotypes by crossing with homozygous recessive

Question 3

Compare parental cross, first generation, and second generation offspring.

Answer 3

Parental cross: homozygotic true breeding; one recessive one dominant
F1: heterozygous and only shows dominant phenotype with hidden genotypes
F2: shows all possible phenotypes and all genotypes can be inferred

Question 4

Why was Mendel successful in his discovery?

Answer 4

Not only are peas easy to grow, have a short life cycle, controlled mating, and have two easily distinguishable states (short and tall);
There is no gene linkage, meaning the traits are controlled by a single gene.
As well as, Mendel kept detailed record of the crosses that were used to find statistical evidence and used true breeding lineages (good controls)

Question 5

What is the first Mendelian law?

Answer 5

Alleles of a gene separate independently (randomly) from each other during transmission from parent to offspring (meiosis)

Question 6

The dominant phenotype appears at _____% in the F1 generation and _______% in the F2 generation

Answer 6

100%; 75%

Question 7

Define locus.

Answer 7

a specific region on a chromosome, usually a gene
(plural loci)

Question 8

How do you predict the results of a dihybrid cross in a punnet square?

Answer 8

You put all the possible allele combinations for each parent.
Ex) a parent that is YyRr has all the possible combinations for their gametes:
YR Yr yR yr

Question 9

What is the second Mendelian law?

Answer 9

Law of Independent Assortment
Alleles of two (or more) genes (loci) segregate independently during transmission from parent to offspring
9 AA: 3 Aa: 3aA: 1aa

Question 10

Derivations of the Second Law?

Answer 10

(3/4D+1/4r)^n
where n is the number of genes involved in the cross

Question 11

How do you find the probability of an organism having multiple, independent genotypes? Phenotypes?

Answer 11

Multiply them.
If inheritance is independent, the expected frequencies are of the genotypes are their products:
Ex) P(dd)=1/2; p(tt)=1/4; and p(gg)=1/8
P=1/21/41/8= 1/64

P(AA)=0.25
P(Aa)=0.5
P(aa)=0.25

So, the probability of getting a dominant phenotype is 75% and the probability of getting a recessive phenotype is 25%. To find the probability of these phenotypes in combination use the multiplication rule.
Ex) P(round, yellow, and tall)=(0.75)^3
or P(round, green, and short)=(0.75)(0.25)(0.25)

Question 12

How do we calculate the frequency of genotypes in crosses?
AKA the total possible allele combinations

Answer 12

We can use probability to determine the expected frequencies of genotypes in a progeny based on the assumption of equal segregation of alleles (First Mendelian Law) and independent assortment of alleles (Second Mendelian Law).

(1) Apply the Second Law to predict frequencies:
(2) Consider every locus separately
(3) How many gamete genotypes can from from each parental genotype
(a) if the alleles at the locus are the same (homozygotic) then there is effectively only one allele
(4)

Question 12

How do we calculate the frequency of genotypes in crosses?

Answer 12

We can use probability to determine the expected frequencies of genotypes in a progeny based on the assumption of equal segregation of alleles (First Mendelian Law) and independent assortment of alleles (Second Mendelian Law).

(1) Apply the Second Law to predict frequencies:
(2) Consider every locus separately
(3) How many gamete genotypes can from from each parental genotype
(a) if the alleles at the locus are the same (homozygotic) then there is effectively only one allele
(4) Multiply all the possible outcomes
(5) then raise the product to the power of the number of segregating loci

Question 13

True or false? Not all sets of genes are ‘Mendelian’ or follow Mendel’s laws.

Answer 13

True

Question 14

How do you statistically test if genes are Mendelian?

Answer 14

preform a Chi-squared test

Question 15

How do you preform a Chi-Squared test?

Answer 15

Step 1: Predict expected numbers based on hypothesis
Ex) 9:3:3:1 for a dihybrid cross

Step 2: Calculate how well the data fits hypothesis use the chi-squared formula (with observed and expected frequencies)

Step 3: Determine the degrees of freedom
- you can then use a table (df vertical, 0.05 horizontal) to find the CV
Note: df= n-1
where n is the number of categories (amount of phenotypes)

Step 4: Accept or reject the hypothesis by comparing the chi-squared statistic to the critical value
Ex) H0: there is no difference between the observed phenotypic ratio and the expected ratio
Either determine if the chi-squared is larger than the CV OR calculate the p-value on the computer
If the p-value is less than 0.05 it may be significantly different (reject null hypothesis)

Question 16

How do you determine the expected number of a phenotype or genotype when the expected frequency is known?

Answer 16

Total # of offspring x expected frequency

Question 17

There is no way to know ___________ expected ratios ahead of time.

Answer 17

non-Mendelian

Question 18

What is the chi2 test usually used for?

Answer 18

To discard Mendelian inheritance for the genes in question and to further understand the linkage of those genes

Question 19

Describe the human genome.

Answer 19

• 23 pairs of chromosomes (2n=46)
• 22 pairs of autosomes (homologous chromosomal pairs)
• 1 pair of sex chromosomes (X and Y)

Question 20

_______ are Mendelian, while _______ chromosomes display different, non-Mendelian inheritance patterns.

Answer 20

autosomes; sex

Question 21

Many human diseases are caused by mutations in single genes. This means they _____ but not _______.

Answer 21

Heritable but not contagious

Question 22

What are some obstacles in Human Genetic Analysis?

Answer 22

(1) Incomplete or incorrect family records
(2) small number of progeny
(3) Uncontrolled environment (phenotypic plasticity, infidelity)

Question 23

What are pedigrees?

Answer 23

Diagrams that show the relationships among the members of the family and represent the inheritance pattern of a specific characteristic/condition

Question 24

When viewing pedigrees what is a tell that a trait is recessive? That the parents are heterozygous?

Answer 24

If the parents aren’t affected but they have affected offspring, the trait must be recessive.
If there are both affected and unaffected offspring in the same generation with the same parents this indicates heterozygous parents.

Question 25

When it comes to pedigrees, what are two rules of recessive trait inheritance?

Answer 25

Recessive traits may occur in individuals whose parents are not affected.
Rare recessive traits are most likely to appear in a pedigree when spouses are related to one another.

Question 26

Recessive mutations are…
Hint: theres 3

Answer 26

(1) Most common causes of human genetic disease
(2) usually lack function (fail to make a product/protein or make a non-functional product)
(3) usually, a single wildtype allele (heterozygote) will make enough of the normal product to have the normal phenotype (haplosufficiency)

Question 27

Compare genes and alleles.

Answer 27

A gene is a recipe for a protein, an allele is a variation on that recipe.

Question 28

Recessive traits often occur rarely in a pedigree because…

Answer 28

recessive alleles are hidden in heterozygotes (as carriers)

Question 29

Describe the interpretation of pedigrees

Hints: 2 rules, 2 guidelines, and 2 when genetic condition is rare

Answer 29

Often, a pedigree is consistent with only a particular mode of inheritance (dominant or recessive).

Rules:
(1) Dominant trait– unaffected parents can’t have an affected child
(2) Recessive trait– unaffected parents can have an affected child

Guidelines:
(1) Dominant trait– tends to appear in every generation
(2) Recessive trait– tends to skip generations

If a genetic condition is rare:
(1) It will be present in very few families in a population
(2) Unaffected individuals that marry into the family with the condition, are likely homozygous for the normal allele rather than heterozygous

Question 30

Describe the inheritance of a dominant trait (4).

Answer 30

• Every individual who carries the dominant allele manifests the trait and unaffected individuals cannot be carriers
• Every affected individual is expected to have at least one affected parent
• The trait tends to show up in every generation
• If both parents are heterozygotes they will both be effected but can have unaffected children

Question 31

Which genotype can be hard to prove in a pedigree and why?

Answer 31

Homozygous dominant can be hard to prove without a large sample size
(1) Both parents must be affected
(2) All offspring must be affected

Question 32

How do autosomal dominant traits arise?
Note: such mutations are not as common as recessive, lack-of-function mutations

Answer 32

Autosomal dominant traits are caused by a mutant allele that is dominant over the normal allele.
This can be due to: production of too much of a normal protein or one functional copy of a gene does not make enough gene product.

Question 33

In the case of autosomal dominance when one functional copy of a gene does not produce enough, how does this result in a dominant phenotype?

Answer 33

Production of abnormal variant of a protein that interacts incorrectly with the normal protein or with some other structure in the cell.
or
Production of protein with some entirely new function or normal function in new place (gain-of-function).

Question 34

What does P, F1, and F2 stand for?

Answer 34

P: Parental cross
F1: first generation
F2: second generation

Question 35

What does true-breeding mean?

Answer 35

A true-breeding organism, sometimes also called a purebred (biology slang: pure line or true-breeding line), is an organism that always passes down certain phenotypic traits (i.e. physically expressed traits) to its offspring of many generations.
aka homozygous

Question 36

Define test cross.

Answer 36

Mendel’s experimental cross of an individual organism of dominant phenotype but unknown genotype and an organism with a homozygous recessive genotype (and phenotype).

Question 37

What is a recombinant phenotype?

Answer 37

Phenotype that is result of recombination and therefore, different than their parents

Question 38

What is the parental phenotype?

Answer 38

The chromosomes that are similar to their parents are referred to as parental chromosomes. The chromosomes that are different from their parents are referred to as recombinant chromosomes.

Question 39

What is segregation in genetics?

Answer 39

When the alleles of a gene loci are separated into gametes

Question 40

What are all the Mendelian ratios?

Answer 40

A cross of two F1 hybrids, heterozygous for a single trait that displays incomplete dominance is predicted to give a 1:2:1 ratio among both the genotypes and phenotypes of the offspring.

Both male and female dihybrids exhibiting independent assortment will generate four types of gametes, in a 1 : 1 : 1 : 1 ratio

This 9:3:3:1 phenotypic ratio is the classic Mendelian ratio for a dihybrid cross in which the alleles of two different genes assort independently into gametes.