Chapter 8-9

What is heredity?

it is the transmission of traits from on generation to the next.

When did genetics begin?

Genetics (the scientific study of heredity) began with Gregor Mendel’s experiments.

What did Mendel cross?

Mendel crossed pea plants and trace traits from generation to generation.

What did Mendel hypothesize?

He hypothesized that there are alternative versions of genes (alleles), the units that determine heritable traits.

What did Mendel develop?

Mendel developed four hypotheses, described below using modern terminology

What is Mendel’s first hypothesis?

There are alternative versions of genes (called alleles) that account for variations in inherited characters.

What is Mendel’s second hypothesis?

For each character, an organism inherits two alleles of a gene, one from each parent.

What is homozygous?

An organism that has two identical alleles for a gene

What is heterozygous

An organism that has two different alleles for a gene

What is Mendel’s third hypothesis?

If the two alleles of an inherited pair differ, then one determines the organism’s appearance and is called the dominant alleles and other has no noticeable effect of the organism’s appearance and is called the recessive allele

What is Mendel’s fourth hypothesis?

A sperm or egg carriers only one allele for each inherited character because allele pairs separate (segregate) from each other during the production of gametes. This statement is called the law of segregation.

What does Mendel’s hypotheses explain?

It also explains the 3:1 ratio observed in the F₂ generation

What do the F₁ hybrids all have?

They all have a Pp genotype

What does the punnett square show?

It shows the four possible combinations of alleles that could occur when these gametes combine

What does every diploid cell have?

It has pairs of homologous chromosomes

What do the chromosomes in a homologous pair carry?

They carry alleles of the same genes at the same locations

What is monohybrid cross?

A cross between two individuals that are heterozygous for one character.

What is a dihybrid cross?

a mating of parental varieties that differ in two characters

What does Mendel’s law of independent assortment state?

It states that the alleles of a pair segregate independently of other allele pairs during gamete formation.

What can the offspring of a testcross reveal?

The offspring of a testcross, a mating between an individual of an unknown genotype and a homozygous recessive individual, can reveal the unknown genotype

What is the rule of multiplication?

calculating the probability of two independent evens both occurring

What is the rule of addition?

calculating the probability of an even that can occur alternative ways.

What follows Mendel’s Laws?

The inheritance of many human traits.

What do family pedigrees determine?

They can help determine individual genotypes

What are the genetic disorders listed in Table 9.9 known for?

They are known to be inherited as dominant or recessive traits controlled by a single gene

How are most people who have recessive disorders born?

They are born to normal parents who are both heterozygous — That is, parents who are carriers of the recessive allele for the disorder but are phenotypical normal

What carrier screening, fetal testing, fetal imaging, and newborn screening provide?

It can provide information for reproductive decisions but may create ethical dilemmas

What are Mendel’s laws valid for?

They are valid for all sexually reproducing species, but genotype often does not dictate phenotype in the simple way Mendel’s laws describe.

What did Mendel’s pea crosses always look like?

They always looked like one of the two parental varieties, a situation called complete dominance

What is incomplete dominance?

For some characters, the appearance of hybrids falls between the phenotypes of the two parental varieties.

What controls the ABO blood group?

The ABO blood group phenotype in humans is controlled by three alleles that produce a total of four phenotypes.

Which alleles are codominant?

The I^A and I^B alleles are codominant: Both alleles are expressed in heterozygous individuals (I^AI^B), who have type AB blood.

When does pleiotropy occur?

It occurs when one gene influences multiple characters

What is a human example of pleiotropy?

Sickle-cell disease

• This disease affects the type of hemoglobin produced and the shape of red blood cells and causes anemia and organ damage

• Sickle-cell and nonsickle alleles are codominant.

• Carriers of sickle-cell disease have increased resistance to malaria.

What are the many character results from polygenic inheritance?

Many characters result from a polygenic inheritance, in which a single phenotypic character results from the addictive effects of two or more genes a single phenotypic character

What is an example of polygenic inheritance?

Human skin color

How are many traits affected?

In varying degrees, by both genetic and environmental factors.

What does the chromosomes theory of inheritance state?

It states that genes occupy specific loci (positions) on chromosomes and chromosomes undergo segregation and independent assortment during meiosis.

What does Mendel’s laws correlate with

It correlates with chromosomes separation in meiosis

What did Bateson and Punnett study?

They studied plants that did not show a 9:3:3:1 ratio in the F2 generation. What they found was an example of linked genes which, are located close together on the same chromosomes and tend to be inherited together.

What does crossing over between homologous chromosomes produce?

it produces new combinations of alleles in gametes.

Linked genes can what?

They can be separated by crossing over, forming recombinant gametes.

What is recombination frequency?

The percentage of recombinant offspring among the total

How can recombination frequencies be used?

They can be used to map the relative positions of genes on chromosomes.

What is a genetic map?

an order list of the genetic loci along a chromosomes

What is a linkage map?

such a genetic map based on recombinant frequencies

In mammals, what are the male and female sex chromosomes?

A male has XY sex chromosomes, and a female has XX

What is a sex-linked gene?

A gene located on either sex chromosomes

What do X chromosomes carry?

They carry many X-linked genes that control traits unrelated to sex

What illustrates an X-linked recessive trait?

the inheritance of white eye color in the fruit fly

Most X-linked human disorder are due to what?

Recessive alleles and therefore are seen mostly in males.

What happens to a male who receives a single X-linked recessive allele from his mother?

They will have the disorder

What does a female must receive?

They must receive the allele from both parents to be affected

What can Y chromosomes provide?

They can provide data about recent human evolutionary history because they are passed on intact from father to son.

What is cell division?

It is at the heart of the reproduction of cells and organisms because cells originate only from preexisting cells.

What is asexual reproduction?

Some organisms go through this producing offspring that are all genetic copies of the parent and identical to each other.

What happens through sexual reproduction?

Other organisms reproduce through this creating a variety of offspring.

How do prokaryotic cells reproduce?

They reproduces asexually by binary fission, a term that means “diving in half.”

Where are most genes carried on?

in typical prokaryotes, they are carried on one circular DNA molecule that, with associated proteins, constitutes the organism’s chromosomes.

What happens when the cell replicates its single chromosome?

The copies move apart, and the plasma membrane pinches inward, and more cell wall is made, which eventually divides the parent cell into two daughter cells.

What has more genes, a eukaryotic cell or a prokaryotic cell?

A eukaryotic cell has many more genes than a prokaryotic cell, and they are groups into multiple chromosomes in the nucles.

What do each chromosome contain?

It contains one long DNA molecules.

What is visible under a light microscope?

Individual chromosomes are visible only when the cell is in the process of dividing otherwise, chromosomes are thin, loosely packed chromatin fibers too small to be seen.

What happens before a cell starts dividing?

The chromosomes duplicate, producing sister chromatids (containing identical DNA) that are joined together along their lengths by proteins, most closely at a region called the centromere

What does cell division involve?

it involves the separation of sister chromatids and results in two daughter cells, each containing a complete and identical set of chromosomes.

What is the cell cycle?

it is an ordered sequence of events that extends from the time a cell is first formed from a dividing parent cell until its own division.

What are the 2 parts of the cell cycle

Interphase and mitotic phase

What are the 3 major parts of the interphase?

G1 (first gap), S(DNA synthesis), G2 (second gap)

what are the two parts of the mitotic phase?

Mitosis, Cytokinesis

What does mitosis distribute?

It distributes duplicated chromosomes into two daughter nuclei

What happens after the chromosomes are coiled up?

A mitotic spindle made of microtubules moves the chromosomes to the middle of the cell.

What is separated and moved to the opposites poles of the cell?

The sister chromatids are separated and moved at which two new nuclei form.

I P P M A T C

Interphase, Prophase, Prometaphase, Metaphase, Anaphase, Telophase, Cytokinesis

What is cytokinesis?

Cytokinesis, in which the cell divides in two, overlaps the end of mitosis

How does a cleavage furrow form?

In animals, cytokinesis occurs when a cell contracts, forming a cleavage furrow

How does a cell plate form?

In plants, a membranous cell plate forms and then splits the cell into two.

When do most normal cells divide?

In laboratory cultures, they divide only when attached to a surface.

When do cultured cells stop dividing?

The cultured cells continue dividing until they touch one another.

When do animal cells divide?

They divide only when stimulated by growth factors, and some do not divide at all

What controls the cells cycle?

A set of proteins within the cell controls the cell cycle.

What determines whether a cell will go through the complete cycle and divide?

Signals affecting critical checkpoints in the cell cycle determine whether a cell will go through the complete cycle and divide.

What is necessary for cell division?

The binding of growth factors to specific receptors on the plasma membrane is usually necessary for cell division

What do cancer cells do?

They divide excessively to form masses called tumor

What do malignant tumors do?

They can invade other tissues.

What are the two types of cancer treatments?

Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division.

What are the mortality rates from cancer?

They vary by age of diagnosis, race, and other factors.

What do the somatic (body) cells contain.

Each stomatic (body) cells of each species contain a specific number of chromosome; for example, human cells have 46, consisting of 23 pairs of homologous chromosomes.

What do the chromosome of a homologous pair of autosomes carry?

They carry genes for the same characteristics at the same place, or locus.

What is a diploid?

Cells with two sets of homologous chromosomes.

What are gametes?

Eggs and sperm- are haploid cells with a single set of chromosomes

What do sexual life cycles involve?

They involve the alternation of haploid and diploid stages.

How is meiosis like mitosis?

Meiosis, like mitosis, is preceded by chromosome duplication, but in meiosis, the cell divides twice to form four daughter cells.

What does meiosis l start with?

The first division, meiosis l, starts with the pairing of homologous chromosomes

What happens when crossing over?

when crossing over homologous chromosomes exchange corresponding segments.

What happens in Meiosis l?

Meiosis l separated the members of each homologous pair and produces two daughter cells, each with one set of chromosomes.

How is meiosis ll essentially the same as mitosis?

In each of the cells, the sister chromatids of each chromosome separate. The result is a total of four haploid cells.

What do both mitosis and meiosis begin with?

They begin with diploid parent cells that have chromosomes duplicated during the previous interphase

What does mitosis produce?

it produces two genetically identical diploid somatic daughter cells

What does meiosis produce?

It produces four genetically unique haploid gametes.

When do each chromosomes of a homologous pair differ?

They differ at many points from the other member of the pair