1C - Mendelian Concepts

Question 1

Describe what consanguinity is?

Answer 1

This is sharing the same ancestor

Question 2

Based on your knowledge of the royal inbreeding, describe how inbreeding can be disadvantageous?

Answer 2

Inbreeding is a common practice seen in royalty
While this was important in political boundaries, this was genetically limiting. This is a bad practice because this can allows deleterious alleles to emerge within children

Question 3

Define genes

Answer 3

These are DNA sequences that code for heritable traits that can be passed from one generation to the next. These determine physical and biochemical characteristics

Question 4

Define alleles

Answer 4

These are different versions of the same gene!

Question 5

Compare and contrast genotype from phenotype

Answer 5

Genotype - this is the genetic combination possessed by an indv
Phenotype - this is the manifestation of a given genotype as an observable trait

Question 6

How do homologues affect gene expression?

Answer 6

Homologues describes chromosomes as pairs. Each chromosomes are paired because an indv receives one copy from each parent
These pairs of chromosomes mirror one another, meaning, they have the same genes on the same locus/location on each chromosome, but these genes can have different versions of the gene = alleles
Different alleles can have different dominance and therefore affect the expression of the alleles

Question 7

Contrast dominance from recessive genotype

Answer 7

These terms describe the number of alleles needed for gene expression.
Dominance - This allele only needs one copy of the allele to be expressed
Recessive - this is the allele needs 2 copies of the allele in order to be expressed

Question 8

Oftentimes genes are referred to as having penetrance. For instance, with Huntington’s disease, individuals with 40 sequence repeats have full penetrance or 100% penetrance. What does this mean?

Answer 8

Penetrance is a population measure defined as a proportion of the indv in the population carrying the alleles who actually express the phenotype. This means that individuals with this allele will show 100% of the Sx of Huntington’s disease.

Question 9

Contrast the different levels of penetrance that can be seen in population

Answer 9

Penetrance can be viewed as a scale: 100% - this means that the those indv with this allele will have Sx/Pheno of this gene
High penetrance - most indvs with this allele of high penetrance may show pheno of this geno, some may not
Reduced Penetrance
Low penetrance - most don’t show a pheno
Nonpenetrance - 0% show a pheno

Question 10

Contrast expressivity from penetrance

Answer 10

Both are related with slight differences
Expressivity - this describes the phenotypes that result from the same geno. Therefore this is the different manifestations of the same geno across the population and more on the indv level
Penetrance - this is a population measure. This is the proportion (%) of the population with a given genotype who actually expresses the pheno

Question 11

Upon assessing the genetic components of autism, you come to find that these genes have a variable expressivity. What does this means? What is it in contrast to?

Answer 11

Variable expressivity - then individuals with the same genotype may have different phenotypes
Variable expressivity is in contrast to constant expressivity - this refers to how all indv with a given geno express the same pheno

Question 12

In the disease of neurofibromatosis type II, there is a range of phenotypes associated with carrying the affected allele. Many patients have debilitating tumors of the vestibulocochlear nerve, which is needed for hearing and balance. Some have cataracts. Others have tumors in the skin called neuromas. Describe the levels of penetrance and expressivity among indv with this allele

Answer 12

Penetrance - hard to identify but from this stem it appears that there is a high penetrance/high % of the population with the genotype who expresses the pheno
Expressivity - variable

Question 13

What does it mean for a genotype to be homozygous? Heterozygous? Hemizygous?

Answer 13

· Homozygous: is one in which the 2 allele are the same

· Heterozygous: the geno is one in which the 2 alleles are different

· Hemizygous: genotype in which only one allele is present for a given genes (such as part of the X chromosome in males

Question 14

You’re visiting your vet friend and you note that this particular cat here has a parent of with a recessive genetic mutation where they have a limp, yet this cat doesn’t have this characteristic. As you have knowledge in mendelian genetics, describe the pattern of dominance seen in this cat

Answer 14

This cat’s alleles are said to be complete dominance where the one allele received from the normal parent. In this case, the presence of one dominant allele leads to expression of it and the other allele is muted

Question 15

In the discussion of blood type, A antigen and B antigen are proteins which both are equally expressed in erythrocytes. Explain what type of pattern of dominance is seen when and indv has both alleles in their genome

Answer 15

This is said to have codominance - when one dominant allele exists for a given gene, and both are present and are both equally expressed.

Question 16

Contrast incomplete dominance from codominance

Answer 16

Incomplete dominance - this is when heterozygote expresses a phenotype that is intermediate between the 2 homozygous genotypes.
Codominance - when one dominant allele exists for a given gene, and both are present and are both equally expressed

Question 17

With which phase does each of Mendel’s laws most closely correlate?

Answer 17

Mendel’s first law of segregation - describes independent assortment (which is seen in Anaphase I)
Mendel’s second law of independent assortment - most similar to recombination as seen in prophase I of meiosis

Question 18

While Mendel’s laws are quite accurate to what has been found true in modern times about genetic diversity processes during meiosis, how does it slightly differ?

Answer 18

Mendel names how laws backwards to what we would come to think of them as today.
His first law - law of segregation describes a process in which 2 alleles are separated into indv eggs. In modern discovery, this is in fact called law of independent assortment!
His second law - law of independent assortment is the process in which modern discovery has termed it to be recombination

Question 19

Segregation by Mendelian 
A. Anaphase I
B. Prophase I 
C. Metaphase I
D. Crossing Over

Answer 19

A. Anaphase I. Mendelian’s law of segregation is independent assortment as seen in meiosis I

Question 20

Mendelian’s independent assortment
A. Anaphase I
B. S phase 
C. Metaphase I
D. Crossing Over

Answer 20

D. Crossing over. This is his description of recombination as seen in prophase I

Question 21

Define gene pool

Answer 21

This is the collection of genes in a population

Question 22

Describe the importance of genetic variability

Answer 22

This is important in the survival of a species especially in the face of changing environments

Question 23

How are genetic variability introduced into a gene pool?

Answer 23

There are many mechanisms that this can be achieved!

Mutations, leakage, genetic drift

Question 24

Suppose that in a mammalian species, the allele for black hair (B) is dominant to the allele for brown hair (b) and the allele for curly hair (C) is dominant to the allele for straight hair (c). When an organism of unknown genotype is crossed over against one with straight, brown hair, the phenotype ratio is as follows: 
I. 25% curly black hair 
II. 25% straight black hair
III. 25% curly brown hair 
IV. 25% straight brown hair
What is the genotype of the unknown parent? 
A. BbCC
B. bbCc
C. Bbcc
D. BbCc

Answer 24

D. All the geno of the children are 25% which is a ratio seen only when parents are heterozygous. This can be figured out on the punnett square/test cross - just remember that this is a dihybrid problem with a double recessive indv crossed with an indv of unknown genotype.

Question 25

If a male with hemophilia (XhY) is crossed with a female carrier of both color blindness and hemophilia (XcXh), what is the probability that a female child will be phenotypically normal? 
A. 0% 
B. 25%
C. 50%
D 100%

Answer 25

C. The definition of phenotypically normal refers to normalcy in each indv phenotypes. The affected alleles are found on different X chromosomes. Based on the Punnett square, we see that 25% of the offspring will be female hemophiliacs (XhXh) and 25% will be female carriers of both alleles (XcXh). This question is asking what percentage of females will have a normal phenotype, which would be half of the females (those who are carriers for both traits)

Question 26

Which of the following definitions is false?
A. Penetrance - the percentage of indv in the population carrying the allele who actually express the phenotype associated with it
B. Expressivity - the percentage of indv in the population carrying the allele who do not express the phenotype associated with it
C. Incomplete dominance - occurs when the phenotype of the heterozygote is an intermediate of the phenotypes of the homozygotes
D. Codominance - occurs when multiple alleles exist for a given gene and more than one of them is dominant

Answer 26

The definition given in the answer choices is a much better definition (additional) for penetrance (or really, one minus the penetrance). Expressivity refers to the variable manifestations of a given genotype as different phenotypes; the degree to which various phenotypes are expressed.