Ch 1 (1.1, 1.2, 1.3): Mendel's Principles of Heredity

Genes

DNA segments that serve as the key functional units in hereditary transmission.

the biochemical units of heredity that make up the chromosomes; a segment of DNA capable of synthesizing a protein

heredity

the passing on of physical or mental characteristics genetically from one generation to another.

gene transmisison

genetics

The scientific study of heredity, gene transmission

Genetics is the study of biologically inherited traits, including traits that are influenced in part by the environment

Traits (characters)

Characteristics that are inherited

COMPLEX OR QUALITIVE

Traits that are governed by a single or few genes and that are not influenced by the environment - qualitative traits (for example, ABO blood group in humans)Traits that are governed by multiple genes and that are influenced by the environment - complex traits, are much more difficult to study (for example human height)

Complex traits

Complex traits - governed by multiple genes and influenced by the environment; exhibit a range of phenotypes (not distinct classes); difficult to analyze

HARDER TO STUDY

ex. height (genetic) + external environmental nutrition

qualitative traits

what we focus on with Medelian genetics

EASIER TO STUDY

Qualitative traits - governed by a single or few genes; not influenced by the environment; exhibit distinct phenotypic classes; easier to analyze (for example, ABO blood group in humans)

Alleles

different versions of a gene

Phenotype vs. Genotype

appearance vs gene allele ( genetic code)

- Phenotype: expressed physical traits

- Genotype: Genetic make-up

GENOTYPE CAN PREDIT PHENOTYPE BUT PHENOTYPE CANNOT PREDICT GENOTYPE

Mendelian Genetics

The pattern of inheriting characteristics that follows the laws formulated by Gregor Mendel

- there's variation of alleles for the gene in the pop.

- variation is essential for following genes

- variation is inherited according to inheritance patterns

- laws apply equally to all SEXUALLY reproducing organisms

- crosses produce PROBABILITIES not predetermined outcomes

recall that it excludes application to multiple alleles (>2), epistasis, pleiotropy, blood types, incomplete dominance/codominance, etc

artificial selection

Breeding organisms with specific traits in order to produce offspring with identical traits.

One limitation of selective breeding prior to Mendel's work was the inability to predict when offspring would inherit a valuable trait.

blending hypothesis of inheritance

an early, incorrect hypothesis of heredity. According to this view, the seeds that dictate hereditary traits are able to blend together from generation to generation. The blended traits would then be passed to the next generation.

Mendel disproved this theory by focusing on ONE TRAIT/ CHARATER with two alleles and uses a plant with fast growth. This made his theories more believable and set him apart from his peers.

Homunculus Theory

When the dad is holding a tiny person in his scrotum and it's then given to the mom and then how the child appears to be a lot closer to the mother since she give's birth

early misconception in genetics

Mendel's Peas

showed dominant vs. recessive genes. (aa+ AA homozygous a+A heterozygous) (Disproved "Blending Theory")

Good choice because they were easy to grow, they grew fast and they reproduced sexually.

uses self fertilization and cross fertilization to disprove his predecessors

focused on traits with ONLY 2 ALLELES for his studies (either white or purple pea plants)

Used true breeding pea plants as his P1 generation for consistency sake.

Mendel's explanation

1. Existence of genes- herreditary determinants of a particulate nature

2. Genes in pairs- alternative phenotypes of a character or trait are determined by different forms of a single type of gene- alleles

3. Principle of Segregation- members of the gene pair separate equally so that each allele is in each gamete (1 for 1)

4. Gametic content- each gamete carries one and only one allele for a gene pair

5. Random Fertilization- union of one gamete from each parent to form offspring

P1 generation

Parental generation; each parent was pure for a given trait. (true-breeding parents)

F1 generation

the first generation of offspring obtained from an experimental cross of two true breeding organisms

also called hybrids and share the same dominant allele as one of the parents.

F2 generation

Offspring resulting from interbreeding of the hybrid F1 generation.

3:1 PHENOTYPIC ratio with equal segregation of alleles

reciprocal cross

a cross in which the phenotypes of the male and female are reversed compared with a prior cross.

Both yield the exact same result so it does NOT matter which parent of the P1 generation is male or female.

white pea plant egg fertilized with purple pea plant sperm and vice versa

monohybrid cross

a cross in which only one characteristic (2 alleles) is tracked

a monohybrid cross is a cross between two organisms that are heterozygous for 1 trait

Whenever you see the word hybrid that means heterozygous

reveals the LAW OF SEGREGATION

3:1 PHENOTYPIC ratio with equal segregation of alleles

Law of Segregation

Mendel's FIRST law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

two copies of each gene in the parent separate so that each gamete only recieves one copy, at fertilization the two copies of the gene are restored in the zygote. One allele per gamete

Punnett Square

diagram that can be used to predict the genotype and phenotype combinations of a genetic cross

A chart that shows all the possible combinations of alleles that can result from a genetic cross

GENOTYPE DOES NOT EQUAL PHENOTYPE

product rule of probability (independent events)

The chance of two or more independent events occurring together is the product of their chance of occurring separately

Pr( Event 1 AND Event 2 occurring)= Pr(Event 1) x Pr(Event 2)

sum rule of probability (mutually exclusive)

states that the chance of an event that can occur in more than one way is the sum of the individual chances

Pr( Event 1 OR Event 2 occurring)= Pr(Event 1) + Pr(Event 2)

test crosses

used to determine the dominance of a certain allele over another and the genotype of the parents if given the offspring genotypes. ONE PARENT IS HOMOZYGOUS RECESSIVE

testcrosses are always with one parent homozygous recessive

used to determine the genotype of an organism expressing the dominant phenotype

genotype can predict phenotype but phenotype cannot predict genotype

dihybrid test crosses have a 1:1:1:1 genotypic ratio

dihybrid cross

A cross between two individuals, concentrating on two definable traits

TWO CHARACTERS

when doing a dihybrid cross, the parents will always have a heterozygous genotype for both characters

Whenever you see the word hybrid that means heterozygous

reveals the law of independent assortment

law of independent assortment

the law that states that genes separate independently of one another in meiosis

chromosomes assort randomly at the metaphase plate in metaphase 1 or meiosis

1:3:3:9 ratio for Aa Bb x Aa Bb crosses

the two characters being tested for are INDEPENDENT of eachother. Green pea plants should not have the tendency of having wrinkled seeds due to their color. These are separate genes.

16 BOXES

branched-line diagram

a method for systematically listing the expected results of multigene crosses

To find the number of unique gametes for a test cross with multiple characters like Aa Bb Cc Dd x Aa Bb Cc Dd.....

use the formula 2ⁿ where n is the number of different genotypes.

in the example there are 4 different genotypes so 2^4=16 different allele combinations

dominant allele, recessive allele

if two alleles at a locus differ, then one, the ________ ________ determines the organism's appearance; the other, the _______ _____, has no noticeable effect on the organism's appearance

usually the recessive allele follows the pattern of a limited or non functional protien--- but not always

ex. Dominant yellow peas Rr and RR but recessive green peas rr lack the pigment on a certain gene

single-gene trait

trait controlled by one gene that has two alleles

MORE LIKELY TO BE LIFE THREATENING/ A DISORDER IF RECESSIVE but not always true. Dominant alleles can cause disorders too.

ex. Huntington's disease (dominant), cystic fibrosis (recessive)

can be represented by mendelian genetics (mono/di- hybrid crosses, dominant/ recessive, pedigrees, etc)

multiple gene traits

2 or more genes control 1 trait

ex. eye color, skin color, etc

Pedigree

A diagram that shows the occurrence of a genetic trait in several generations of a family.

GENDER:

square= male

circle= Female

Diamond= sex unspecified

if any of the above are crossed out, they are deceased

RELATION:

single vertical line connecting parents: mating occurred

double vertical line connecting parents: mating occurred between relatives

horizontal line: children

CONDITION STATUS:

filled= has condition

unfilled= does not have condition

vertical pattern of inheritance

indicates a rare dominant trait

you know if vertical when about 50% of the offspring is effected by the genetic trait. At least one person is affected within each generation

horizontal pattern of inheritance

indicates a rare recessive trait where the parents are usually carriers but have affected children

occurs most often in matings between relatives

late-onset genetic trait

a genetic condition in which symptoms are not present at birth, but manifest themselves later in life

REALLY HARD TO KICK DIESEASE OUT OF POPULATION DUE TO THE LATENESS IT OCCURS IN LIFE. If people who are effected died at a young age, the allele would disappear from the population

cross-fertilization

process by which sperm from one flower's pollen fertilizes the eggs in a flower of a different plant

the process: In order to cross-fertilize two pea plants, a researcher must first remove the male sex organs from the flowers of one of the two plants

continuous traits vs discrete traits

continuous;

---determined by multiple genes (polygenic), such as height or hair color

ex. Amount of milk a cow produces in liters, Measurements of human blood pressure

discrete;

---- determined by one gene with two alleles

ex. Dog fur can be curly or straight, Flower color in pea plants can be purple or white

Mendel's qualitative approach

-He worked with large numbers of plants.

-He counted all the offspring of a cross.

-He compared his results with predictions based on his models.

recombiant types

offspring that have new combinations of phenotypic traits

Questions about heredity answered by Mendel

What is inherited? alleles of genes

How are they inherited? L.O.S and L.O.I.A

What is the role of chance? for each individual, inheritance is determined by chance, but within a population this chance operates in a context of strictly defined probabilities

# of different type of gametes

2^n where n= # of heterozygous loci (allele pairs) for ONE PARENT

# of different type of phenotypic classes

2^n

where monohybrid crosses (n=1)

dihybrid crosses (n=2)

# of different type of genotypic classes

3^n where n= # of heterozygous loci (allele pairs)

autosomal recessive traits

two copies of an abnormal gene must be present in order for the disease or trait to develop

- usually appear equally in males AND females

- tend to skip generations

- are more likely to appear among progeny of related parents

ex. cystic fibrosis

autosomal dominant traits

only need one copy to have the disorder

ex. Huntington's

ex. polydactyly

- appear in equal frequency in males and females; do not skip generations

-affected persons have at least ONE affected parent

-unaffected persons do not transmit the trait

autosomal vs sex-linked

If a trait is autosomal it will appear in both sexes equally. A sex-linked trait is a trait whose allele is located on the X chromosome so it is usually only seen in males

-sex-linked: gene is expressed on a sex chromosome

ex. huntington's, PKU

-autosomal: expressed on an autosomal chromosome

ex. hemophilia

Analyzing Pedigrees

-trial and error: consider one pattern of inheritance at a time for each mating in the pedigree and try to find evidence against it; repeat for each pattern of inheritance, for example, autosomal recessive or dominant, X-linked recessive or dominant, etc

-patterns of inheritance follow Mendelian rules; Mendelian ratios are rarely observed

-assumption: for rare traits unaffected people entering into a family pedigree (for example, by marriage) are considered homozygous normal

-result: pedigrees can frequently rule out, but not necessarily prove, a certain pattern of inheritance