BIO: Chapter 10 pattern of inheritance

What is the difference between a dihybrid cross and a monohybrid cross?

A monohybrid cross is defined as the cross happening in the F1 generation offspring of parents differing in one trait only A dihybrid cross is a cross happens F1 generation offspring of differing in two traits.

How does meiosis support Mendel's law of segregation?

As chromosomes separate into different gametes during meiosis, the two different alleles for a particular gene also segregate so that each gamete acquires one of the two alleles

Compare and contrast dominant/recessive with codominance.

If the alleles are different, the dominant allele usually will be expressed, while the effect of the other allele, called recessive, is masked. In codominance, however, neither allele is recessive and the phenotypes of both alleles are expressed.

Compare and contrast dominant/recessive with incomplete dominance.

Incomplete dominance is when a dominant allele, or form of a gene, does not completely mask the effects of a recessive allele, and the organism's resulting physical appearance shows a blending of both alleles.

inheritance pattern of a dominant allele on an autosome

autosomal dominant

condition caused by recessive allele on non-sex chromosome; expressed only if an individual inherits two copies of the allele

autosomal recessive

how are pedigrees helpful in determining a disorder's mode of inheritance?

by documenting family relationships and observing which individuals have a disorder over multiple generations, it is often possible to determine whether a disorder is autosomal or sex-linked and to determine whether it is dominant of recessive

How are chromosomes, DNA, genes, and alleles related?

chromosomes consist of DNA and associated proteins. The DNA in a chromosome is divided into genes, which are sequences of nucleotides that encode proteins. Alleles are different versions of one gene.

two alleles are both fully expressed in heterozygote

co-dominance

one allele masks the expression of another in a heterozygote

complete dominance

exchange of genetic material between homologous chromosomes during prophase 1 of meiosis

crossing over

mating between two individuals that are both heterozygous for two genes

dihybrid cross

an allele that is expressed if present in the genotype

dominant allele

Distinguish between dominant and recessive

dominant alleles appear in a phenotype whenever they are present recessive alleles contribute to the phenotype only if no dominant alleles are present

Why do males and females express recessive X-linked alleles differently?

each female has a pair of X chromosomes whereas a male has only one X chromosome any trait a male has on his X chromosome will be expressed. recessive alleles on a X chromosome of a female may be masked by dominant alleles on her other X chromosome

How can the same phenotype stem from many different genotypes?

each gene encodes one protein, but different proteins may interact in a single metabolic pathway. a mutation in a gene encoding any of these proteins may produce a similar phenotype

sequence of DNA that encodes a specific protein or RNA molecule

gene

an individuals combination of alleles for a particular gene

genotype

possessing two different alleles for a particular gene

heterozygous

possessing two identical alleles for a particular gene

homozygous

producing a mix of offspring for one or more trait; heterozygous

hybrid

what is a dihybrid cross, and what is the phenotypic ration expected in the offspring of the cross?

in a dihybrid cross two individuals that are each heterozygous for two genes are mated. the phenotypic ratio that is expected is 9;3;3;1 (9 dominant for both genes; 3 dominant for one gene and recessive for the other; 3 recessive for one gene and dominant for the other; 1 recessive for both genes)

two alleles confer an intermediate phenotype in a heterozygote

incomplete dominance

how do incomplete dominance and co-dominance increase the number of phenotypes observed in a population?

incomplete dominance and co-dominance produce phenotypes that are intermediate between or combinations of those produced by homozygous dominant or homozygous recessive individuals.

what is a test cross, and why is it useful?

its a mating between a homozygous recessive individual and and individual of unknown genotype. the genotype of the unknown parent can be deduced from the ratio of phenotypes among the offspring

Mendel's law stating that during gamete formation, the segregation of the alleles for one gene does not influence the segregation of the alleles for another gene

law of independent assortment

Mendel's law stating the the two alleles of each gene are packaged into separate gametes

law of segregation

group of genes that tend to be inherited together because they are on the same chromosome

linkage group

components of a homologous pair of chromosomes

made up of chromosome pairs (one from mom, the other from dad) of approximately the same length, centromere position, and staining pattern, each carry the same gene order, but the alleles of each trait may not be the same

mating between two individuals that are heterozygous for the same gene

monohybrid

one gene affects multiple, seemingly unrelated phenotypes

Pleiotropy

Why is a male hemizygous for a Y-linked trait?

Since males have only one copy of each sex chromosome, they are hemizygous for all sex-linked genes, and they always express the phenotype * of the allele * they get.

what is examined in a monohybrid cross?

The "mono" means a single trait is under examination; the "hybrid" means that the parents are heterozygous for the trait in question, that is, each parent has a dominant allele and a recessive allele.

How can you tell that you are dealing with an incomplete dominance situation?

You don't see either of the parent phenotypes. Offspring will likely not have the exact same height or hair color as one of their parents but will often have a blend between the two parent's phenotypes.

explain Mendel's law of segregation.

a diploid organism passes a randomly selected allele for a trait to its offspring, such that the offspring receives one allele from each parent.

what is a monohybrid cross, and what are the genotypic and phenotypic ratios expected in the offspring of the cross?

a monohybrid cross is a mating between two individuals that are each heterozygous for one gene. the genotypic ration expected in a monohybrid is 1:2:1 (homozygous: heterozygous: homozygous recessive) ; the phenotypic ration is 3:1 (dominant; recessive)

what is polygenetic inheritance, and how is it different from co-dominance?

a polygenetic trait is one that is controlled by multiple genes. co-dominance reflects the relationships among multiple alleles of the same gene.

one or two or more alternative forms of a gene

alleles

What does it mean for an organism to be "true breeding"? How could you test if an organism is "true breeding"?

always producing offspring identical to parent for one or more traits; homozygous parents must be both dominant or recessive

distinguish between heterozygous and homozygous

an individual is homozygous for a gene if both alleles are identical in a heterozygous individual the two alleles for a gene are different

What does it mean to be a "carrier"?

an individual who carries and is capable of passing on a genetic mutation associated with a disease and may or may not display disease symptoms.

distinguish between phenotype and genotype

an organisms phenotype is its appearance the genotype is the alleles an individual possesses

What is X-chromosome inactivation?

A process when one of the two X chromosomes is randomly "turned off."

How can you determine if a disease is dominant or recessive based on a pedigree?

Dominant traits will not skip a generation. If the trait is recessive, neither parent is required to have the trait since they can be heterozygous.

What does the word polyallelic mean?

Having multiple alleles at a genetic locus.

Why does crossing over (aka recombination) violate Mendel's law of independent assortment?

It doesn't but, Genetic linkage violates the law of independent assortment since linked traits would be inherited together and would not assort randomly/independently.

How does non-disjunction violate Mendel's law of segregation?

Nondisjunction is the failure of chromosomes to properly segregate during meiosis.

how genes and alleles are related.

One gene tells the cell how to make one protein. Different variations of a gene are called alleles. Each parent passes one allele to the child for each gene.

true breeding parents

P generation

How can the environment affect a phenotype?

The environment can directly affect the expression of some genes. For example, temperature can influence the expression of temperature-sensitive alleles. The environment can also affect the phenotype in other ways, as when infectious agents intensify a genetic disorder. Many aspects of the phenotype, including temperament and physical health, reflect not only genes but also upbringing, nutrition, and many other environmental variables.

Why does X inactivation occur in female mammals?

X inactivation prevents each cell of a female from receiving a double dose of X chromosome genes

condition caused by allele on the X chromosome

X-linked trait

a genotype, phenotype, or allele that is not the most common in a population or that has been altered from the wild type condition

mutant

What is pleiotropy?

occurs when a single gene has multiple, seemingly unrelated effects on the phenotypes. the gene may encode a protein that enters several different biochemical pathways or that affects more than one body part or process

what determines a persons sex?

one pair of chromosomes the sex chromosomes determines a persons sex. a female has two X chromosomes; a make has X and a Y chromosome

chromatid containing genetic information from only one parent

parental chromatid

chart used to determine a disorders mode of inheritance

pedigree

observable characteristics of an organism

phenotype

caused by more than one gene; polygenetic traits are typically expressed as a continuum of possible phenotypes

polygenetic

the chance of two independent events occurring equals the product of the individual chances of each event

product rule

diagram showing how the alleles in two parents gametes might combine at fertilization

punnett square

an allele whose expression is masked by dominant allele

recessive allele

chromatid containing genetic information from both parents as a result of crossing over

recombinant chromatid

what is the difference between recombinant and parental chromatids, and how do they arise?

recombinant chromatids are chromosomes that have a mixture of maternal and paternal alleles instead of alleles from just a single parent. crossing over produces recombinant alleles. in contrast, a parental chromatid carries the same combination of alleles that was inherited from a parent

describes genes or traits on the X and Y chromosome

sex linked

How do meiosis, fertilization, diploid cells, and haploid cells interact in a sexual life cycle?

specialized diploid cells undergo meiosis, a type of cell division that produces haploid cells. Haploid cells, in turn, combine during fertilization to form the diploid zygote, which is the first cell of the next generation

a mating of an individual of unknown genotype to a homozygous recessive individual to reveal the unknown genotype

test cross

how do biologists use crossover frequencies to map genes on chromosomes?

the father apart two linked genes are on chromosome, the more frequently they will cross over. analyzing crossover frequencies for multiple pairs of traits reveals which genes are close together and which are far apart. this information is used to deduce linkage maps, which show the relative positions of genes on chromosomes.

how do patterns of inheritance differ for unlinked versus linked pairs of genes?

the inheritance pattern of unlinked genes is predictable since allele combinations are not affected by crossing over. when pairs of genes are linked, they are carried on the same chromosome and are inherited together. crossing over can occur between linked genes, creating allele combinations that differ from those in either parent.

two does the law of independent assortment reflect the events of meiosis?

the law of independent assortment states that the segregation of alleles for one gene does not affect the segregation of alleles for another gene on a separate chromosome. this law is a consequence of the events of metaphase 1 in meiosis, during which each homologous pair of chromosomes is oriented independently of other chromosome pairs during metaphase 1 of meiosis

how can the product rule be used to predict the results of cresses in which multiple genes are studied simultaneously?

the product rule allows you to estimate the odds that an offspring will have a certain combination of alleles for multiple genes by multiplying the probability that each separate event will occur

How are Punnett squares helpful in following the inheritance single genes?

they show the genotypes of each parent as well as the genotypes of potential offspring. phenotypic and genotypic rations of offspring can be predicted from the data in punnet squares.

always producing offspring identical to the parent for one or more traits; homozygous

true-breeding

Explain law of segregation

two alleles of each gene are packaged into separate gametes; that is they "segregate" or move apart from each other during gamete formation

the most common allele, genotype, or phenotype

wild-type

distinguish between wild-type and mutant

wild-type allele is the most common form of a gene in a population a mutant allele arises when a gene undergoes a mutation

turning off all but one X chromosome in each cell of a mammal early in development

x inactivation