Mendel and the Gene Iea

What is the P (parental) generation?

the first generation in a genetic cross (homozygous)

What is the F1 (first filial) generation?

The generation that is created by the parental generation. The alleles in this generation are 100% heterozygous (Aa)

What is the F2 (second filial) generation?

This generation is a cross between the products of the first filial generation. It yields:

25% homozygous dominant

50% heterozygous

25% homozygous recessive

What is the first concept that make up Mendel's model, explaining the 3:1 inheritance pattern that he observed among F2 offspring?

Alternative versions of genes account for variations in inherited characteristic among offspring (alleles).

What are alleles?

Different versions of a gene

What is the second concept that make up Mendel's model, explaining the 3:1 inheritance pattern that he observed among F2 offspring?

For each character, every sexually reproducing organism inherits one allele from each parent.

What is the third concept that make up Mendel's model, explaining the 3:1 inheritance pattern that he observed among F2 offspring?

If the two alleles are different, then the dominant allele will be expressed in the offspring, whereas the recessive allele will have no noticeable effect on the offspring.

What is the fourth concept that make up Mendel's model, explaining the 3:1 inheritance pattern that he observed among F2 offspring?

The two alleles for each character separate during gamete production.

What is a dominant allele?

A form of a gene that is fully expressed, even when two different alleles are present

What is a recessive allele?

An allele that is masked when a dominant allele is present.

What is Mendel's law of segregation?

states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization.

What is the law of independent assortment?

Genes for different traits are inherited independently of each other

What two chromosomes sort independently of each other?

maternal and paternal

What do homozygous organisms have?

two of the same alleles for a particular trait (ex. RR & rr)

What do heterozygous organisms have?

two different alleles for a trait (ex. Rr)

What is a phenotype?

physical characteristics of an organism

What is a genotype?

genetic makeup of an organism

What is a testcross?

A cross between an organism of unknown genotype with a homozygous recessive individual to determine if an individual showing a dominant trait is homozygous or heterozygous.

Why are testcrosses done?

to determine if an individual showing a dominant trait is homozygous or heterozygous.

What is a testcross always done between?

an unknown genotype an a homozygous recessive indiviual

What must happen if the unknown parent in a testcross is homozygous dominant?

all the offspring will show the dominant trait (RR x rr)

What must happen if the unknown parent in a testcross is heterozygous?

some of the offspring will show the recessive trait (Rr x rr)

What is a monohybrid cross?

A cross between individuals heterozygous for a single character

Why are monohybrid crosses done?

to study only one character (ex. flower color)

What is a dihybrid cross?

a cross that examines the inheritance of two different traits

Why is a dihybrid cross done?

to study two characters (ex. flower color and seed shape).

What governs Mendelian inheritance?

laws of probability

What are the two laws that are used directly in solving genetics problems?

the rule of multiplication and the rule of addition

What is the probability rule of multiplication?

When calculating the probability that any of two or more independent events will occur together in a specific combination, multiply the probabilities of each of the two events.

What is the probability law of addition?

When calculating the probability that any of two or more mutually exclusive events will occur, you need to add together their individual probabilities.

What should you do to calculate the chances of both event 1 and event 2 happening?

Multiply them together.

What should you do to calculate the chances of event 1 or event 2 happening?

Add them together.

What is complete dominance?

when phenotypes of the heterozygote and dominant homozygote are identical

What is incomplete dominance?

when one allele is not completely dominant over the other, causing a blending of traits (red+white=pink)

What is codominance?

when both alleles contribute to the phenotype

What are multiple alleles?

three or more forms of a gene that code for a single trait

What do many genes have?

they exist in more than two allele forms, meaning they have multiple alleles

What is polygenic inheritance?

inheritance pattern of a trait that is controlled by 2 or more genes

What may also influence gene expression?

environmental factors

What do many human traits follow?

Mendelian patterns of inheritance

What is a pedigree?

a chart that tracks which members of a family have a particular trait

What can pedigrees help with?

determining the genome of individuals that comprise them and predicting the genome of future offspring

What are recessively inherited disorders?

disorders that require two copies of the defective gene for the disorder to be expressed.

What are some examples of recessively inherited disorders?

cystic fibrosis, Tay-Sachs disease, Sickle-cell disease

What is cystic fibrosis?

It is a genetic disorder of the cell membranes. Causes thick, sticky mucus to build up in air passages and pancreas.

What is Tay-Sachs disease?

an autosomal recessive genetic disease that causes nervous system breakdown and death.

What is Sickle-cell disease?

It is an inherited blood disorder that causes the change in the primary structure of the hemoglobin, and it makes the cells look like sickles.

What are dominantly inherited disorders?

disorders that require only one copy of the allele in order for the disorder to be expressed.

When do lethal alleles activate?

later in life (ex. Huntington's Disease)

What is Huntington's disease?

degenerative disease of the nervous system cause by a lethal dominant allele

What is a common misconception about dominant alleles?

that they're more common than recessive alleles because dominant alleles are always expressed

What may be one to detect certain genetic disorders?

genetic testing of a fetus

What are the two common tests done on fetuses?

amniocentesis an chorionic villus sampling

What is amniocentesis?

the sampling of amniotic fluid using a hollow needle inserted into the uterus, to screen for developmental abnormalities in a fetus.

What is chorionic villus sampling?

a test made in early pregnancy to detect congenital abnormalities in the fetus. A tiny tissue sample is taken from the villi of the chorion, which forms the fetal part of the placenta.

What else can be done to detect genetic disorders in fetuse?

fetal cells and fetal DNA being isolated from the mother's blood and analyzed

Where does Mendelian inheritance find its physical basis?

in the behavior of chromosomes

What is the chromosome theory of inheritance?

Genes are carried from parents to offspring on chromosomes

What is a sex-linked gene?

gene located on a sex chromosome

What are the two types of sex chromosomes?

X and Y

What can sex-linked genes be?

either X-linked or Y-linked

What does each egg have?

an X chromosome

What does each sperm have?

they can either have an X or a Y chromosome

What is sex determined by?

chance and the sperm cell

To who do fathers pass X-linked genes to?

their daughters

To who do fathers pass the Y chromosome to?

their sons

What does not apply to a male pattern of sex-linked genes?

the terms homozygous and heterozygous

How do females express an X-linked trait?

exactly like any other trait

Where will males express X-linked traits?

only on the allele on the X chromosome they got from their mother

What are several X-linked disorders that have medical significance?

Duchenne muscular atrophy and hemophilia

What is Duchenne muscular atrophy?

an X-linked disorder characterized by a progressive weakening of the muscles and loss of coordination.

What is hemophilia?

An X-linked disorder in which blood doesn't clot normally

Why do linked genes tend to be inherited together?

because they are located near each other on the same chromosome

What are linked genes?

genes located on the same chromosome that tend to be inherited together

What is genetic recombination?

the production of offspring with combinations of traits differing from either parent

When does genetic recombination happen?

In prophase, it is the "crossing over" of chromosomes to share traits.

What do genetic crosses yield?

offspring with the same phenotype as one of the parents (parental types) and some of the offspring with phenotypes different from either parent (recombinants).

What are parental types?

offspring with a phenotype matching one of the parental phenotypes

What are recombinants?

individuals with new combinations of genes

What is crossing-over?

the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring.

What can crossing-over explain?

why some linked genes get separated during meiosis

Why do unlinked genes follow independent assortment during meiosis?

because they are located on different chromosomes

Why are linked genes not predicted to follow independent assortment?

they are found on the same chromosome

Why do genetic crosses sometimes give results that seem to indicate that some independent assortment has occurred even when genes are on the same chromosome?

crossing over

What does it mean if there is a high probability two genes will cross-over between each other?

it means that they are farther apart on a chromosome

What is a linkage map?

a genetic map of a chromosome based on recombination frequencies

What is a map unit?

A map unit is a unit of measurement of the distance between genes. One map unit is equivalent to a 1% recombination frequency.

What can cause some genetic disorders?

Alterations in chromosome number or structure.

What is nondisjunction?

An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell

What results from nondisjunction?

one gamete receives two of the same type of chromosome, and another gamete receives no copy

What happens if the faulty gametes resulting from nondisjunction engage in fertilization?

the offspring will have an incorrect chromosome number

What are some human disorders caused by nondisjunction?

Down syndrome, Klinefelter syndrome, and Turner syndrome

What is Down syndrome?

the result of having an extra chromosome 21 (trisomy 21). Own syndrome includes characteristic facial features, short stature, heart effects, and developmental delays.

What is Klinefelter syndrome?

occurs when a male possesses the sex chromosomes XXY (an extra X). Klinefelter males have male sex organs but are sterile.

What is Turner syndrome?

a monosomic condition in which the female has just one sex chromosome, often designated XO. Turner syndrome females are sterile because their reproductive organs do not mature. Turner syndrome is the only known viable monosomy in humans.

What are some exceptions to the standard inheritance patterns/

mitochondria an plastid genes as they are inherited only rom the mother because the zygote's cytoplasm comes only from the egg

Who do you inherit your mitochondrial DNA from?

your mother