Genetics

Although the processes of DNA replication and mitosis are extremely accurate and efficient, the huge number of repetitions of these processes throughout the body ensures that mistakes do happen and that changes to the genome can occur. Define mutation

Mutations are important not only for the individual carrier, but as a crucial source of _____ _____ within populations, without which ______ could not occur. Mutations can be ______ (occurring due to _____ _____ in the natural process of replication and genetic recombination) or ______ (occurring due to physical or chemical agents called ______, which can damage DNA and increase the frequency of mutation above the baseline frequency of spontaneous mutations).

The effects on the cell are the same in either case. The effect of a mutation on an organism's fitness may be ______ or ______, or there may be ___ ____ at all. Mutations may occur at the level of the ______ or the level of the _______.

Define Gene mutation and chromosomal mutation
In multicellular organisms, a mutation in a somatic cell (Greek: soma~body) is called a ______ mutation

A somatic mutation of a single cell may have very _____ effect on an organism with millions of cells. In contrast, a mutation in a germ cell, from which all other cells arise, can have _____ consequences for the offspring produced.

Under normal conditions, mutations are _____. Only about one out of every _____ gametes will carry a mutation for a given gene. Different types of mutations are categorized both by the effect of the change on the ______ of the genetic sequence and by the effect on the sequence's ______.

Define point mutation and base substitution mutation

Define Transition mutation and Transversion mutation

Define Addition mutations and Deletion mutation

If a mutation has no effect on an organism's fitness, that mutation is said to be _____. A neutral mutation could change the ____ ____ sequence of a protein without changing its ______ or could result in no change to an amino acid sequence (e.g. changing the codon AAA to AAG through a base substitution would still result in the amino acid lysine.) The type of neutral mutation in which the amino acid sequence is unchanged is called a _____ mutation.

Some nucleotide mutations can cause significant changes to the function of a gene. Define missense mutation

Missense mutations can be ______ and result in completely functional proteins. However, missense mutations can also significantly change a polypeptide's ______. Explain the sickle cell anemia example

Define a nonsense mutation

Nonsense mutations tend to have serious consequences for the cell (why?)

The addition and deletion of nucleotides, which are also considered point mutations, can result in a frameshift mutation (define).

Why does an addition or deletion of one or two nucleotides change the reading frame of the code?

An altered reading frame means that the entire sequence after the mutation will be shifted so that the three base sequences are grouped incorrectly. For instance, if a single T nucleotide were inserted into the series: AAA|GGG|CCC|AAA, so that it reads AAT|AGG|GCC|CAA|A, each 3 nucleotide sequence downstream from the mutation would be altered and therefore each amino acid coded for could change.

On the other hand, if three T nucleotides were inserted randomly, the downstream sequence would not be shifted, and only one or a few 3-nucleotide sequences would be changed: AAT|TAG|GTG|CCC|AAA. This is a ____ _______ mutation.

Non-frameshift mutations may still result in a ______ or even ______ _____ protein, while frameshift mutation most often result in ______ _____ ______ proteins. Frameshifts may also result in _______ mutations if the new reading frame includes a premature stop codon.

Changes at the chromosomal level often have ______ consequences for the organism. Structural changes may occur to a chromosome in the form of ______, _______, ________, and ________.

When do chromosomal deletions occur?

Define duplications and Gene duplication

Deletion or duplication can occur with entire chromosomes (______) or even entire sets of chromosomes (______).

Define translocation and inversion

Translocation and inversion can be caused by _______. Transposition takes place in both prokaryotic and eukaryotic cells. The DNA segments called ______ _____ or ______ can excise themselves from a chromosome and reinsert themselves at another location. Transposons can contain one gene, several genes, or just a control element.

A transposon within a chromosome will be flanked by ______ ______ _______. A portion of the flanking sequence is part of the transposon. Three possibilities of transposons when in motion

_______ is one mechanism by which a somatic cell of a multicellular organism can alter its genetic makeup without meiosis.

Define cancer

However, cancer also has a genetic component that is related to mutation. Certain genes that stimulate normal growth in human cells are called _____ ______. Proto-oncogenes can be converted to ______, genes that cause cancer, by mutagens such as ____ ______ or ______, or simply by _______ mutations.

Mutagens that can cause cancer are called _______. The genome also contains _______ ______ ______ that help regulate normal cell growth. When the normal functions of _____ _____ _____ are inactivated by mutation, cells growth may proceed uncontrolled.

_____ can be thought of as a special case of mitosis that takes place solely in the reproductive organs. _____ reproduction takes place when genetic information from two individuals merge to produce offspring. For sexual reproduction to occur, reduction division of the genetic information is needed in order to create ______ reproductive cells, or ______, from diploid parent cells.

In humans, only the ________ and the _______ undergo meiosis. All other cells are ______ cells and undergo ______ only. Meiosis is an important part of sexual reproduction and occurs only in _______. This section details the process of meiosis in animals, which is how it is most likely to be seen on the MCAT®.

While meiosis, like mitosis, is a form of cell division, the goals and end products of meiosis are different. What is the purpose of mitosis? What is the purpose of meiosis?

During mitosis, a cell undergoes _____ round(s) of nuclear division to produce ____ ______ ______ cells, each bearing ______ genetic information. In contrast, during meiosis, germ cells undergo ____ round(s) of nuclear division to produce _____ ______ ______ cells, the ______, each with a unique genetic makeup. The primary difference in the mechanisms of mitosis and meiosis can be found in ______ of meiosis I in how the chromosomes align. *Regulation of meiosis takes place in much the same way as that of mitosis

Meiosis consists of two rounds of division called ______ and ______. Each round of meiosis consists of successive stages of ______, ______, _______ and ______.

Explain how the mechanisms of Meiosis work (6-story)

In the case of the female, one of the oocytes, called the first polar body, is much ______ and _______. This occurs in order to conserve _______, which is only contributed to the zygote by the ______.

Meiosis II proceeds through prophase II, metaphase II, anaphase II, and telophase II, appearing much like _____ under the light microscope. The final products are _____ ______, each with ____ chromosomes. In the case of the spermatocyte, _____ sperm cells are formed. In the case of the oocyte, a ______ _____ is formed after the degeneration of the polar bodies. (In the female, telophase II produces _____ ______ and a ______ _____ _____.)

If during anaphase I or II the centromere of any chromosome does not split, this is called _______. As a result of primary nondisjunction (nondisjunction in anaphase I), one of the cells, will have ____ _____ ______ (a complete extra chromosome) and the other will be missing a chromosome. The extra chromosome will typically line up along the ______ plate and behave normally in meiosis II.

Nondisjunction in anaphase II will result in one cell having _____ ______ _____ and one cell lacking ____ _____. Nondisjunction can also occur in mitosis, but the ramifications are ____ severe (why?) One possible outcome of nondisjunction is having three copies of a single chromosome (a condition known as _____), which can have significant effects. For example, Down syndrome is caused by ______ of chromosome 21.

The purpose of meiosis is to make ______ gametes that can be used in sexual reproduction . The production of gametes, or ________, occurs in several stages. Gametogenesis occurs via similar paths in males and females, with some key differences. The process in males is more straightforward . Once a male reaches sexual maturity, _______ is ongoing, replenishing the body's supply of gametes as needed.

In males, the diploid progenitor cells responsible for giving rise to gametes through the process of meiosis are called _______ (define).

Each primary spermatocyte undergoes the reduction division of meiosis l to become ____ _____ ______ ______. After the division of meiosis II, each secondary spermatocyte becomes _____ ______. A spermatid undergoes a process of maturation in which it loses its ______ and gains a _____ to become a mature male gamete known as ______.

There are many parallels between the process of gamete production in males and females. In females, the diploid progenitor cell for gametogenesis is known as the _______. The oogonium _______ mitosis to produce ______ ______ ______. Unlike in males, this step in females primarily takes place before a female is born and the process does not proceed further until the female has reached ______.

Primary oocytes remain arrested in ______ of meiosis until they receive the hormone signal to participate in the ______ _____ (see the Endocrine System Lecture in Biology 2: Systems for more information on menstruation and ovulation).

In preparation for ovulation, a primary oocyte completes meiosis I, producing a _____ ____. At this step, again, males and females differ. While meiosis I in males produces ____ _____ _____ from each primary spermatocyte, the contents of a primary oocyte are not divided _____ among its daughter cells. One daughter cell receives all of the ______ and becomes a secondary oocyte. The other daughter cell, which receives no ______, is the first polar body and is ______.

The resulting secondary oocyte, now ______, begins the process of meiosis II but is arrested at the stage of _______. In this arrested state, the secondary oocyte is released from the ______ and travels down the ______ _____. The secondary oocyte completes meiosis II only when penetrated by a sperm during the act of _______.

The penetration of the sperm immediately initiates the completion of ______, dividing the secondary oocyte into a _____ _____ ______, which is also discarded, and an _____, which matures into an _____. The joining of the genetic material of the sperm and the ovum produces a ______.

He found that when he crossed purple flowered plants with white flowered plants, the ____ ____, or F1 generation, included only purple flowers. He called the purple trait ______, and the white trait ______. Mendel examined seven traits in all, and each trait proved to have dominant and ______ alternatives.

When Mendel self-pollinated the Fl generation plants, the F2 generation contained some plants that expressed the dominant trait and some that expressed the recessive trait in a ratio of ____ (which is now referred to as the _______ ratio)

When the F2 generation was self-pollinated, 33% of the ______ produced only dominants, and the rest of the dominants produced the _______ ratio. The _____ flowered plants produced only white flowered plants. Mendel used this data to conclude that, even if plants expressed the dominant trait (purple), they might still retain _______ information on the recessive trait (white) (why?)

The key to understanding Mendel's experiments is to examine the alleles involved. For any one trait, a diploid individual will have ____ ______ containing separate genes that each code for that trait. These two chromosomes are _______ by definition. Their corresponding genes are located at the same _____, or position, on their respective chromosomes.

Each gene contributes one _____, which codes for a specific outcome in that trait. There may be _____ or _____ allele types possible at each locus. For example, one chromosome may carry the allele coding for purple flowers (represented by P), while the other chromosome may carry the allele for white flowers (represented by p). The "normal" or most common allele type for a certain trait within a population is deemed the _____ _____ allele.

With regard to alleles for a certain trait, an individual's genetic makeup is called a _____ while the expression of the trait (i.e. the way the organism actually looks) is called the ______. In the example given, the possible genotypes are PP, Pp, and pp, while the possible phenotypes are _____ and _____. The phenotype is expressed through the action of enzymes and other structural proteins, which are encoded by genes.

In complete dominance , as is the case with Mendel's purple and white flowers, the dominant allele _____ expression of the recessive allele. This concept is demonstrated by the outcome that flowers with the genotype Pp appear purple.

An individual with a genotype having two dominant (PP) or two recessive (pp) alleles is said to be ______ for that trait. An individual with a genotype having one dominant and one recessive allele (Pp) is said to be ______ for the trait, and is called a _____.

Explain Mendel's First Law of Heredity, the Law of ______

Define Penetrance and Expressivity

Unlike penetrance, which is based on a binary condition (_______ vs. not ______), expressivity describes the degree of ______ of a certain trait. When a heterozygous individual exhibits a phenotype that is intermediate between its homozygous counterparts, the alleles are said to demonstrate _______ ______.

By convention, alleles showing incomplete dominance are represented with the same capital letter, and distinguished with a _____ or ______. For instance, a cross between red flowered sweet peas and white flowered sweet peas may produce _____ flowers. The genotype for the pink flowered individual would be expressed as either _____ or _____.

If the heterozygote exhibits both (parental) phenotypes, the alleles are _______. Human blood type alleles are co-dominant (why?)

Figure 2.25 shows a helpful tool called a Punnett square, used for predicting ______ ratios of offspring from parent genotypes. The genotypes of all possible ______ of one parent are displayed to the left of the column, and all possible ______ of the second parent are displayed above the first row. The alleles are then combined in the corresponding boxes to show the possible genotypes of the offspring. According to the law of _______, each gametic genotype is equally likely. Therefore, each offspring genotype is also ______ likely.

State Mendel's Second Law of Heredity, the law of _______ _______

(Notice that the Law of Independent Assortment discusses _____ genes that code for _____ traits, in contrast to the law of Segregation, which instead discusses different _____ of a single gene.)

If two genes are located on the same chromosome, the likelihood that they will remain together during gamete formation is indirectly proportional to the _____ _____ them. Thus, the _____ they are on the chromosome, the more likely it is that they will not be separated by ______ _______ and instead will remain together.

The expression of some traits is dependent on the sex of the individual (explain). In humans, the 23rd pair of chromosomes establishes the sex of the individual, and each partner in the pair is called a ____ chromosome.

_____ chromosomes are designated as either X or Y. Human females usually carry ____ X chromosomes, while males usually have one X and one Y chromosome. In comparison to the X chromosome, the Y chromosome is greatly _______ and contains only a few genes.

Genes located on the sex chromosomes are said to be ____ _____. Generally, the Y chromosome does not carry the allele for the ____-____ trait; thus, the allele that is carried by the X chromosome in the male is expressed whether it is ______ or ______.