Bio chap 14

Step one of how traits are transmitted from parents to offspring

Each parent cell has two alleles for each character

Step two of how traits are transmitted from parents to offspring

The two alleles segregate during gamete formation

Step three of how traits are transmitted from parents to offspring

Offspring inherit one allele from each parent

Gregor Mendel

Discovered the basic principles of heredity by breeding garden peas in carefully planned experiment

Other advantages of using peas

• Short generation time

• Large numbers of offspring

• Mating could be controlled

A character

A heritable feature that varies among individuals (such as flower color)

A trait

Each variant for a character, such as purple or white color for flowers

How did Mendel drive the law of segregation

By following a single character

The F1 offspring produced in this cross were ________, meaning that they were heterozygous for one character.

monohybrids

Monohydbrid cross

A cross between heterozygotes

P Generation

F1 generation

F2 generation

P generation

Parental generation

F1 generation

The first generation of offspring

F2 generation

Produced after F1 individuals are crossed

Homozygote

An organisms with two identical alleles for a gene

It is said to be ______ for the gene controlling that character

homozygous

Heterozygote

An organisms with two different alleles for a gene

it is said to be ____ for the gene controlling that character

heterozygous

Unlike homozygotes, heterozygotes are not _______

true-breeding

Phenotype

The observable physical or physiological traits of an organisms

Genotype

The actual genetic composition or combination of alleles an organisms carries (PP, Pp, or pp)

Ratio

3 purple : 1 white

Ratio

1 PP : 2 Pp : 1 pp

Crossing two true-breeding parents differing in two characters produces ______ in the F1 generation, heterozygous for both characters

dihybrids

Dihybrid cross

Can determine whether two characters are transmitted to offspring together as a unit or independently

Using a dihybrid cross, Mendel developed the

Law of Independent Assortment

Law of Independent Assortment

Each pair of alleles segregates independently of any other pair of alleles during gamete formation

The law of independent assortment only applies to?

Genes on different, nonhomologous chromosomes or those far apart on the same chromosome

Genes located near each other on the same chromosome tend to be?

Inherited together

Law of segregation

The two alleles for each gene separate during gamete formation

Law of segregation

Law of independent assortment

The multiplication rule

States that the probability that two or more independent events will occur together is the product of their individual probabilities

The rule of addition

The probability that any one of two or more mutually exclusive events will occur is calculated by adding together their individual probabilities

What can the rule of addition be used for?

To figure out the probability that an F2 plant from a monohydrbid cross will be heterozygous rather than homozygous

Rule of addition equation

P(A or B) = P(A) + P(B)

Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations

• When alleles are not completely dominant or recessive

• When a gene has more than two alleles

• When a gene produces multiple phenotypes

Complete dominance

occurs when the phenotypes of the heterozygote and dominant homozygote are identical

Incomplete dominance

The phenotype of F1 hybrids is somewhere between phenotypes of the two parental varieties

Codominance

Two dominant alleles affect the phenotype in separate, distinguishable ways

Most genes exist in population in ____

more than two allelic forms

The three alleles for the ABO blood groups and their carbohydrates

IA, IB, and i

The three alleles for the ABO blood groups and their carbohydrates

A, B, and none

Blood groups genotypes and phenotypes

IAIA or IAi, IBIB or IBi, IAIB, and ii

Blood groups genotypes and phenotypes

A, B, AB, O

Red blood cell appearances

Epistasis

A gene at one locus alters the phenotypic expression of a gene at a second locus

One gene determines the?

Pigment color

The other gene determines?

Whether the pigment will be deposited in the hair

Some traits may be determined by _______

two or more genes

Quantitative characters

Are those that vary in the population along a continum

Quantitative variation usually indicates

Polygenic inheritance

Polygenic inheritance

An additive effect of two or more genes on a single phenotype

Example of polygenic inheritance

Skin color in humans

Another departure form Mendelian genetics arise when the

phenotype for a character depends on environment as well as genotype

The phenotypic range is broadest for?

Polygenic characters

Polygenic traits

Traits that depend on multiple genes combine with environmental influences

An organisms phenotype includes?

Its physical appearance, internal anatomy, physiology, and behavior

An organisms’s phenotype reflects its overall

genotype and unique environmental history

A pedigree

A family tree that describes the interrelationships of parents and children across generations

(a)

A dominant trait

(b)

A recessive trait

Many genetic disorders are inherited in a

recessive manner

Carriers

Heterozygous individuals who carry the recessive allele but are phenotypically normal; most individuals with recessive disorders are born to carrier parents

Heterozygous (Aa)

Individuals carrying one dominant allele and one recessive allele. They do not show symptoms of the condition but can pass it on

Homozygous recessive (aa)

Individuals carrying two copies of the recessive allele, which results in the expression of the disorder

Inheritance probability

When two carrier parents have a child, there is a 25% chance that the child will inherit the recessive disorder

Albinism

A recessive condition characterized by a lack of pigmentation in skin and hair

Most genes have multiple phenotypic effects, a property called

Pleiotropy

Cystic fibrosis

The most common lethal genetic disease in the US, striking one out of every 2,500 people of European descent

Effects of the cystic fibrosis allele

Results in defective or absent chloride transport channels in plasma membranes leading up to a buildup of chloride ion outside the cell

Symptoms of cystic fibrosis

Mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine

What affects one out of 400 African Americans?

Sickle-cell disease

What is sickle cell disease caused by?

The substitution of a single amino acid in the hemoglobin protein in red blood cells

Sickle-cell disease in homozygous individuals

All hemoglobin is abnormal

Symptoms of sickle-cell disease

Physical weakness, pain, organ damage, and even paralysis

______ mating increase the chance of mating between two carriers of the same rare allele

Consanguineous

Consanguineous mating

Mating between close relatives

If a recessive allele that causes a disease is rare, then?

The chance of two carriers meeting and mating is low

Some human disorders are caused by dominant alleles

True

________ is a form of dwarfism caused by a rare dominant allele

Anchondroplasia

Huntington’s disease

A degenerative disease of the nervous system

Huntington’s disease has not obvious effects until the individual is about 35 or 40 years of age

True

No matter what our ______, our lifestyle has a tremendous effect on phenotype

genotype

Some ________ ________ can be detected at birth by simple tests that are now routinely performed in most hospitals in the US

genetic disorders

Description of complete dominance of one allele

Heterozygous phenotype same as that of homozygous dominant

Description of incomplete dominance of either allele

Heterozygous phenotype intermediate between the two homozygous phenotypes

Description of multiple alleles

In the population, some genes have more than two alleles

Description of epistasis

The phenotypic expression of one gene affects the expression of another gene

How could the botanist best determine whether the genotype of the green-pod plant is homozygous or heterozygous?

Cross the green-pod plant with a yellow-pod plant.

Suppose that the botanist carried out the test cross described in Parts A and B and determined that the original green-pod plant was heterozygous (Gg). Which of Mendel’s findings does her test cross illustrate?

law of segregation

During which part of meiosis (meiosis I or meiosis II) do the two alleles of a gene separate? During which phase does the separation occur?

meiosis I, anaphase

One character in peas that Mendel studied was yellow versus green seeds. A cross between a homozygous yellow line (YY) and a homozygous green line (yy) will result in F₁ plants that are heterozygous (Yy) for this trait and produce yellow seeds.

When an F₁ plant undergoes meiosis, what gamete types will it produce, and in what proportions?

½ Y ½ y

What is the probability that an F₂ seed chosen at random will be yellow?

¾

What is the probablity that an F₂ seed chosen at random from among the yellow seeds will breed true when selfed?

1/3

What is the probability that three F₂ seeds chosen at random will include at least one yellow seed?

63/64

What is the probability that three F₂ seeds chosen at random will include one green seed and two yellow seeds?

27/64

Autosomal dominant condition