Human karyotype contains 46 chromosomes, out of which 22 homolog pairs are autosomes and one pair contain sex-chromosomes (X and Y).

d. 46

Colorblindness is a recessive trait that is determined by a sex-linked gene. The three genes that are responsible for the color vision are found on the X chromosome.
Since the X is dominant over the Y chromosome, colorblindness will appear in males if it is inherited from their mother. In females, the recessive trait will appear if the recessive allele is inherited from both of the parents.
If a mother carries a recessive allele for colorblindness (red X chromosome), while the father does not, there is a 25 percent chance for that trait to appear in their offspring (genotype {color{Red}X}{color{Blue}Y}), while females (genotype {color{Blue}X}{color{Red}X}) are the carriers whose male children may be colorblind.

begin{center}
begin{tabular}{ c c c}
& {color{Blue}X} & {color{Red}X}\
{color{Blue}X} & {color{Blue}XX} & {color{Blue}X}{color{Red}X}\
{color{Blue}Y} & {color{Blue}X}{color{Blue}Y} & {color{Red}X}{color{Blue}Y}
end{tabular}
end{center}

c. recessive and located on the X chromosome

Mendel discovered that alleles for different traits can be dominant or recessive. However, if alleles are codominant, then the features that are determined by both dominant and recessive allele appear in the phenotype of a heterozygous offspring. Therefore, if a person inherits both A and B alleles that determine the blood type in the ABO system, we can conclude that his blood type would be AB.

d. AB

Every cell in our body has a diploid number of chromosomes. These cells contain 23 pairs of homologous chromosomes. Only gametes (sperm and eggs) are haploid, which means that these cells contain 23 chromosomes. Since we inherit one set of chromosomes from a father and the other one from a mother, that would make a total of 46 chromosomes.

A universal donor has O blood type and he is able to donate blood to any person, no matter what blood type does he has. A person with O blood type doesn’t have antigens on erythrocyte surface so it is unable to induce the immune response of the recipient.

The mosaic expression is a phenomenon that occurs in females because of inactivation of one X chromosome. The genotype of females is 46, XX but only one of the sex chromosomes can be active while the inactivated genes in the other are condensed into a Barr body. The mosaic expression occurs when certain genes on the one X chromosome are active in a number of cells, but in the rest of the organism’s cells, the expressed genes are located on the other X chromosome, while the first one is here inactive. An example is the expression of orange and black colors in the cat fur, where the gen for orange is located on one, while the gene that determines black fur color is found on the other X chromosome. Since males have only one X chromosome, they can inherit black or orange fur, but not both.

The family tree provides more information than the pedigree chart. In the family tree, the whole family is described, while the pedigree chart contains only the direct relatives of the person that we are interested in. Therefore, making a pedigree chart is more effective in exploring the rules of inheritance of genetic disorders and certain traits in the family.

The pedigree chart on the picture consists of four generations. Generations are labeled in Roman numerals, while individuals are labeled in Arabic numbers.

The Huntington’s disease is an autosomal dominant recessive disorder that leads to the damage and death of nerve cells. In this illness, a CAG sequence is abnormally repeated in a gene known as Huntingtin, which results in the synthesis of altered protein. This Huntingtin protein causes the changes in the nervous system that are also known as Huntington’s chorea. Some of the symptoms include mood changes, uncontrollable movements, or altered gait. They usually appear in the middle age.

d. Huntington’s disease

Cystic fibrosis is an autosomal recessive genetic disorder which results in the synthesis of altered cystic fibrosis transmembrane conductance regulator (CFTR) protein. This defect protein disables transport of chloride ions through the cell membrane.

b. the CF allele is recessive

Nondisjunction can occur during meiosis I when chromosomes are unable to accurately divide, or during meiosis II, when sister chromatids don’t separate correctly. At the end of a meiotic division, there will be four daughter cells, some of which may be haploid and others aneuploid. When a haploid gamete merges its genetic material with aneuploid gamete that will result in aneuploidy. The zygote will contain one or three sets of chromosomes.
Down syndrome (trisomy 21), Turner’s syndrome (45, X0), and Klinefelter’s syndrome (47, XXY) are all aneuploidies.
The sickle cell disease is a genetic disorder that is caused by substitution of thymine for adenine in one strand of the DNA molecule, which changes codon of the mRNA for a beta-globin from GAG (glutamic acid) to GUG (valine).

d. sickle cell disease

The sickle cell disease is a genetic disorder that is caused by substitution of thymine for adenine in one strand of the DNA molecule, which changes codon of the mRNA for a beta-globin from GAG (glutamic acid) to GUG (valine). This change in amino acid alters the structure of hemoglobin molecule making it less soluble which lead to the formation of sickle-shaped erythrocytes. However, it is discovered that persons who have one copy of the sickle cell allele are less prone to malaria because this allele provides them protection from the parasite.

Cystic fibrosis is an autosomal recessive genetic disorder which results in the synthesis of altered cystic fibrosis transmembrane conductance regulator (CFTR) protein. This defect protein disables transport of chloride ions through the cell membrane. It is found that normal CFTR protein serves as a receptor for Salmonella Typhi in the intestine. Therefore, an altered protein cannot bond to this bacteria which prevent the occurrence of typhoid fever.

Nondisjunction represents a disability of chromosomes or sister chromatids to separate during cell division. Turner’s syndrome is caused by nondisjunction during meiosis. The genotype of females with this illness is 45, X0.

Klinefelter syndrome is a genetic disorder that occurs because of nondisjunction during meiosis among sex chromosomes. Males with this condition have an extra X chromosome, so their genotype is 47, XXY. They can have more than one extra chromosome, but such cases are extremely rare. Usually, the symptoms and signs appear during puberty and they include reduction of secondary sexual characteristics, gynecomastia, and infertility. Therapy is a hormonal substitution.

Adopted children should know the medical history of biological parents because of their own health and lifestyle. Many diseases are hereditary, while others, such as some types of cancer, diabetes mellitus or hypertension, have a higher incidence among family members. This means that people with positive family history for certain illness should start screenings earlier in life than other people who have a negative family history. Also, a child could be the allele carrier for certain diseases, such as sickle cell, Tey-Sachs, or Huntington disease, in which case, knowing medical family history could be very important when this person wants to start a family.

Scientists are now able to explore genome with technics that allows them to cut, separate and read DNA molecule.
A DNA is a large molecule that first has to be cut into smaller pieces before the reading begin. Some bacterial enzymes known as restrictive enzymes are used in the laboratory for this very purpose. They are able to cut DNA into fragments of only several hundred bases long.

c. cutting the DNA into manageable pieces

Scientists are now able to explore genome with technics that allows them to cut, separate and read DNA molecule.
A DNA is a large molecule that first has to be cut into smaller pieces before the reading begin. Some bacterial enzymes known as restrictive enzymes are used in the laboratory for this very purpose. They are able to cut DNA into fragments of only several hundred bases long.

c. cutting the DNA into manageable pieces

The electrophoresis is a process during which negatively charged DNA fragments move through the porous gel after an electric voltage is been applied. The smaller DNA fragments will pass faster, and after usage of a particular stain that makes them visible, scientists get a model of bands based on the size of these DNA pieces.

b. separate DNA fragments

A human genome contains 46 chromosomes, about 3 billions of nucleotide pairs, and around 20 000 genes. Only 2 percent of a human genome is included in protein synthesis.

A human genome contains 46 chromosomes, about 3 billions of nucleotide pairs, and around 20 000 genes. Only 2 percent of a human genome is included in protein synthesis. Up to 10 percent of the whole genome contains sequences that are included in the regulation of gene expression. However, more than 50% of the DNA molecule consists of repetitive nucleotide sequences, whose purpose is currently unknown.

DNA molecules of two unrelated people match base for a base in a high percentage. The difference between genomes makes one base in about 1200 bases. These single base differences are known as single nucleotide polymorphisms or SNPs. Some SNPs are carriers of certain traits or diseases among people. As science makes progress, medical treatment could become highly personalized in the future because of the ability to read a patients genome. If the genome shows a certain pattern in SNPs, the scientist can conclude which diseases a person is prone to. Based on the results, a person may make lifestyle changes, be included earlier in life in the screening process for a certain illness, or begin a medical treatment.

The Genetic Information Nondiscrimination Act passed the Congress in 2008. This act is meant to prevent genetic discrimination in health insurance and employment. Health insurers are barred from refusing coverage to a healthy person or charging him higher premiums only because he has a genetic predisposition for a certain disease, which may or may not develop in his life. This act also prevent employers to make resolutions about hiring, firing, job position, or promotion based on the genetic predispositions of employes or potential employes.

Epigenetics studies changes in phenotype which are heritable but do not involve changes in the nucleotide sequence of the DNA molecule. These changes could be caused by methylation of nucleotide bases, chromatin remodeling, histone modification, as well as non-coding RNA mechanisms. These processes don’t alter the nucleotide sequence but they affect gene expression.
Genomic imprinting represents epigenetic changes that are heritable and are associated with certain traits or diseases. An example of an illness that is linked to genomic imprinting is an Angelman syndrome. The gene that is called UBE3A is located on a chromosome 15. A healthy child inherits an expressed gene from a mother and a silenced gene from a father. If the mother’s genome has a deletion of this particular gene and the father’s gene is silenced, the Angelman syndrome will appear.

In females, the recessive trait, that is determined by a sex-linked gene, will appear if the recessive allele is inherited from both of the parents. If a female has a disease, that tells us that she has the homozygous recessive genotype and that she has recessive alleles on both of her X chromosomes. This disease will appear in the male offspring if the recessive allele is inherited from their mother, which is the case in this particular example.
An experiment would include a cross between sick female and a healthy male fruit fly. If the gene for this illness is sex-linked, the male offspring is the only one that would be affected.

Colorblindness is a recessive trait that is determined by a sex-linked gene. The three genes that are responsible for the color vision are found on the X chromosome.
Since the X is dominant over the Y chromosome, colorblindness will appear in males if it is inherited from their mother. In females, the recessive trait will appear if the recessive allele is inherited from both of the parents.

If a mother carries a recessive allele for colorblindness (red X chromosome), while the father does not, there is a 25 percent chance for that trait to appear in their offspring (genotype {color{Red}X}{color{Blue}Y}), while females (genotype {color{Blue}X}{color{Red}X}) are the carriers whose male children may be colorblind.

begin{center}
begin{tabular}{ c c c}
& {color{Blue}X} & {color{Red}X}\
{color{Blue}X} & {color{Blue}XX} & {color{Blue}X}{color{Red}X}\
{color{Blue}Y} & {color{Blue}X}{color{Blue}Y} & {color{Red}X}{color{Blue}Y}
end{tabular}
end{center}
If a mother is also colorblind (genotype {color{Red}X}{color{Red}X}), while the father does not, that trait will appear only in their male offspring.

begin{center}
begin{tabular}{ c c c}
& {color{Red}X} & {color{Red}X}\
{color{Blue}X} & {color{Blue}X}{color{Red}X} & {color{Blue}X}{color{Red}X}\
{color{Blue}Y} & {color{Red}X}{color{Blue}Y} & {color{Red}X}{color{Blue}Y}
end{tabular}
end{center}
If a mother is healthy but carries the allele for colorblindness, while the father is colorblind, that trait will appear in 50% of their offspring.

begin{center}
begin{tabular}{ c c c}
& {color{Red}X} & {color{Blue}X}\
{color{Red}X} & {color{Red}X}{color{Red}X} & {color{Blue}X}{color{Red}X}\
{color{Blue}Y} & {color{Red}X}{color{Blue}Y} & {color{Blue}X}{color{Blue}Y}
end{tabular}
end{center}
If both parents are colorblind, that trait will appear in all of their children.

begin{center}
begin{tabular}{ c c c}
& {color{Red}X} & {color{Red}X}\
{color{Red}X} & {color{Red}X}{color{Red}X} & {color{Red}X}{color{Red}X}\
{color{Blue}Y} & {color{Red}X}{color{Blue}Y} & {color{Red}X}{color{Blue}Y}
end{tabular}
end{center}

A karyotype represents a picture of all chromosomes that a cell contain, arranged from the biggest to the smallest.
Cystic fibrosis is an autosomal recessive genetic disorder which results in the synthesis of altered cystic fibrosis transmembrane conductance regulator (CFTR) protein. Since this illness is caused by changes in a single gene, it will not reflect in the karyotype because this alteration of a DNA molecule is too small.

The sticky ends are made when the restriction enzymes cut DNA strands in several bases part. This result in two double-stranded DNA fragments that both have an overhang region, which can easily bind with a different DNA fragment.
Therefore, the restriction enzymes that produce sticky ends are BamHI, HindIII, and EcoRI. All the restriction enzyme recognition sites are sequences that read the same in both directions.

In females, the recessive trait, that is determined by a sex-linked gene, will appear if the recessive allele is inherited from both of the parents. If a female has a disease, that tells us that she has the homozygous recessive genotype and that she has recessive alleles on both of her X chromosomes. This disease will appear in the male offspring if the recessive allele is inherited from their mother, which is the case in this particular example.
An experiment would include a cross between sick female and a healthy male fruit fly. If the gene for this illness is sex-linked, the male offspring is the only one that would be affected.

Is there a linear relationship between an organism’s complexity and its genome size?
Among prokaryotic organisms, there is a linear relationship between a genome size and a number of genes it contains. However, that is not the case in eukaryotes. For example, mustard weed has a larger genome and more genes than a roundworm. This is called the C-paradox. The genome size in eukaryotes is measured in haploid cells and it is constant for a species, so it is called a C-value.

Is there a relationship between genome size and a number of genes?
Some organisms have a large genome compare to the gene number it contains because of the repetitive DNA sequences which are the non-coding part of the molecule.

Is there a relationship between a number of genes and the complexity of an organism?
There is a linear relationship between a number of genes and the complexity of an organism. For example, people have about 25 000 genes, mice have around 24 000, while roundworm has 19 000 genes. However, there are exceptions, mustard weed has a smaller genome than humans, but the estimated gene number is about 25 500.

The mosaic expression is a phenomenon that occurs in females because of inactivation of one X chromosome. The mosaic expression occurs when certain genes on the one X chromosome are active in a number of cells, but in the rest of the organism’s cells, the expressed genes are located on the other X chromosome, while the first one is here inactive. An example is the expression of orange and black colors in the cat fur, where the gen for orange is located on one, while the gene that determines black fur color is found on the other X chromosome.
Since males have only one X chromosome, they can inherit black or orange fur, but not both.
However, a genetic disorder can occur in the male cat because of nondisjunction during meiosis among sex chromosomes. Males with this condition have an extra X chromosome, so their genotype is 47, XXY. This is very rare, but the result is a male calico cat, with an expression of both fur colors – black, and orange.

Mutations present permanent and heritable changes in the genome. Gene mutations are known as point mutations because they affect only up to several nucleotides. Since amino acids that build a protein are determined by codons (which are made by three nucleotides in a row) even one nucleotide change can alter the codon and make a change in an amino acid that builds a protein. An altered protein may cause small changes in the appearance of an organism, while others cause large changes, both harmful and helpful. However, not all mutations alter an organism’s phenotype. Some mutations occur in a non-functional part of a DNA or they change the codon, but not the amino acid that corresponded to the original codon.
A beneficial mutation improves the health of an organism. Some examples include mutations in bacterial genome that causes their resistance to antibiotics, or mutation that affects the CCR5 gene, that codes a protein found in the surface of leukocytes, which causes HIV resistance in human. Polyploidy is another example of beneficial mutations, in which a plant’s genome contains more than two sets of chromosomes. That makes these plants bigger and stronger.
However, there are far more examples of harmful mutations. An example of point mutation that alters the phenotype of a person is the sickle cell disease. The cause of this genetic disorder is a substitution of thymine for adenine in one strand of the DNA molecule, which changes codon of the mRNA for a beta-globin from GAG (glutamic acid) to GUG (valine). This change in amino acid alters the structure of hemoglobin molecule making it less soluble which lead to the formation of sickle-shaped erythrocytes. However, it is discovered that persons who have one copy of the sickle cell allele are less prone to malaria because this allele provides them protection from the parasite.

Scientists must cut, separate and read DNA molecule in order to explore the genome.
A DNA is a large molecule that has to be cut into smaller pieces before the reading begin. Some bacterial enzymes known as restrictive enzymes are used in the laboratory for this very purpose. They are able to cut DNA into fragments of only several hundred bases long. Some bacteria contain these enzymes so they could dissolve the genome of bacteriophage, which is a type of virus that invade bacteria. In this way, bacteria protect itself from viruses as by disabling their reproduction.

The Punnett square shows possible genotypes of a child if a mother is homozygous dominant (AA), while a father is heterozygous (Aa) for the LCT gene.

begin{center}
begin{tabular}{ c c c}
& {color{Blue}T} & {color{Blue}T}\
{color{Blue}T} & TT & TT\
{color{Blue}t} & Tt & Tt
end{tabular}
end{center}

We can conclude that their children wouldn’t express lactose intolerance, but half of their children will be the carriers of the recessive allele.

The Punnett square shows possible genotypes of a child if a mother is homozygous dominant (AA), while a father is heterozygous (Aa) for the LCT gene.

begin{center}
begin{tabular}{ c c c}
& {color{Blue}T} & {color{Blue}T}\
{color{Blue}T} & TT & TT\
{color{Blue}t} & Tt & Tt
end{tabular}
end{center}

We can conclude that their children wouldn’t express lactose intolerance, but half of their children will be the carriers of the recessive allele.

The ratio in genotypes is:
– 50 percent homozygous dominant and
– 50 percent heterozygous.
Therefore, the ratio of phenotypes is 100 percent normal.

If a mother is homozygous dominant (AA), while a father is heterozygous (Aa) for the LCT gene, we can conclude that their children wouldn’t express lactose intolerance, but half of their children will be the carriers of the recessive allele.
The ratio in genotypes is:
– 50 percent homozygous dominant and
– 50 percent heterozygous.
Therefore, the ratio of phenotypes in their children is 100 percent normal, which matches to the pedigree chart.
Persons 8, 9, and 10 are not lactose intolerant. Their father is homozygous recessive, but their mother is eighter homozygous dominant or heterozygous, so their children inherited one recessive allele from a father and a dominant allele from their mother, which makes them heterozygous.
Persons 11 and 12 are lactose intolerant, so their genotype is aa, which means that their parents are both heterozygous for the LCT gene.

People have the right to keep their genetic information in private in order to avoid discrimination.
The Genetic Information Nondiscrimination Act passed the Congress in 2008. This act is meant to prevent genetic discrimination in health insurance and employment. Health insurers are barred from refusing coverage to a healthy person or charging him higher premiums only because he has a genetic predisposition for a certain disease, which may or may not develop in his life. This act also prevent employers to make resolutions about hiring, firing, job position, or promotion based on the genetic predispositions of employes or potential employes.
However, adopted children should know the medical history of biological parents because of their own health and lifestyle even if the parents wouldn’t give a consent. Many diseases are hereditary, while others, such as some types of cancer, diabetes mellitus or hypertension, have a higher incidence among family members. This means that people with positive family history for certain illness should start screenings earlier in life than other people who have a negative family history. Also, if a child could be the allele carrier for certain diseases, such as sickle cell, Tey-Sachs, or Huntington disease, knowing medical family history could be very important when this person wants to start a family.

Right before the start of the meiotic division, genetic material is being doubled. Nondisjunction can occur during meiosis I when chromosomes are unable to accurately divide, or during meiosis II, when sister chromatids don’t separate correctly. At the end of a meiotic division, there will be four daughter cells, some of which may be haploid and others aneuploid. When a haploid gamete merges its genetic material with aneuploid gamete that will result in aneuploidy. The zygote will contain one or three sets of chromosomes.
Klinefelter syndrome is a genetic disorder that occurs because of nondisjunction during meiosis among sex chromosomes. Males with this condition have an extra X chromosome, so their genotype is 47, XXY.
The genotype of females with Turner’s syndrome is 45, X0.
Down syndrome is a trisomy 21, which means that persons with this condition have an extra chromosome 21.

A pedigree shows us the appearance of the certain traits among the direct relatives of the person that we are interested in. Based on a pedigree, we can conclude whether the allele is the dominant or recessive, autosomal or sex-linked.
In the pedigree chart, males are marked as squares, while females are represented with circles. The shaded symbol means that the trait is expressed in that person, while symbols that are not shaded tells us that these persons doesn’t express the studied trait. Half shaded symbols determines the carriers for autosomal traits, while the circle with the dot in its center represents the carrier for an X-linked trait.
Generations are labeled in Roman numerals, while individuals are labeled in Arabic numbers.
Vertical lines represent marriage, while horizontal represents children. Breeding among relatives is marked with double lines.
In order to understand better the pedigree chart, we should know the way that the studied trait is inherited – is it recessive or dominant. If it is more common among males, it is probably X-linked, but if the ratio of expression is similar among males and females the trait is presumably autosomal.

Scientists are now able to explore genome with technics that allows them to cut, separate and read DNA molecule. A DNA is a large molecule that has to be cut into smaller pieces before the reading begin.
1. Bacterial enzymes known as restrictive enzymes are used in the laboratory for cutting DNA into fragments of only several hundred bases long
2. The next step is electrophoresis, where DNA fragments are put in the porous gel
3. The electric voltage is been applied which cause negatively charged DNA fragments to move through the porous gel. The smaller DNA fragments will pass faster.
4. The particular stain is used that makes DNA fragments visible
5. Scientists get a model of bands based on the size of these DNA pieces.
6. In the next step, they join single-stranded DNA with DNA polymerase and nucleotide bases that are chemically stained.
7. DNA polymerase forms new DNA strand based on the one they put in
8. Because nucleotides this enzyme use are colored, scientists are able to read a complementary sequence of the examined DNA fragment.