Mendelian Genetics - Quiz 2 Genetics

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Mendelian Genetics:

Gregor Mendel(1888) - Father of genetics

Discovered the fundamental laws of inheritance

Applied mathematics to the study of heredity

Worked on plants

Mendels Law of segregation:

Explains the pattern of inherited traits

For each characteristic (tall, dwarf, etc.) each plant has a pair of alleles or factors that could be identical, or different

one allele could express itself(dominant) while the other allele is not expressed(recessive) if both alleles are found together

LAW: Members of a pair of alleles for a given trait are segregated or separated when gametes are formed

Mendelian Genetics:

Phenotype: Observable characteristics of an organism ie/ tall vs dwarf plant

Genotype: The genetic characteristics of an organism

Capital letters designate dominant traits(T)

lower case letters designate recessive traits(t)

Homozygous: Two dominant alleles or two recessive alleles ( ie. TT or tt)

Heterozygous: one dominant and one recessive allele (ie. Tt)

Alleles: Variations of the same gene (T and t gene for height)

Punnet square:

Represents all possible gametes that a parent could form for a particular allele.

Parent 1: Homozygous green (GG)

Parent 2: Heterzygous green (Gg)

Genotypes: 2 GG: 2 Gg

Phenotypes: 4 green pea plants

NOTE: heterozygous zygotes are always dominant phenotype plants, 0 yellow pea plants in this case

Variations in Heredity:

Incomplete Dominance:

the pattern of gene expression in which the phenotype of a heterozygous individual is intermediate between those of the parents

Cases in which one allele is not completely dominant over the other

ie: Down below

Codominance:

The condition in which both alleles in a heterozygous organism are expressed

BOTH alleles contribute to the phenotype

The 2 alleles don't blend but are rather both present In the offspring

Multiple Allelism:

When there are more than 2 alleles possible for a given gene

Allows for a larger number of genetic and phenotypic possibilities

Multifactoral:

Traits whose phenotype expression is controlled by genes found at many loci

Sex-linked Traits and Pedigrees:

Sex-linked traits:

Genes found on one of the sex chromosomes(X or Y) but not the other are called sex chromosomes

mostly found on the X chromosome as its longer than the Y

Different from the traits on autosomes chromosomes where both sexes have the same possibility of expressing the trait

ie: Hemophilia is recessive on the X chromosomes

Below is the proper execution of this type of question

Pedigree Charts:

A chart that traces the inheritance of traits among family members

We can use a pedigree to determine if a trait is dominant or recessive, sex-linked or not sex-linked

NOTE: If ost males in the pedigree are affected, the disorder is sex-linked

If it even between female and male, the disorder is likely autosomal

For the autosomal (aka non-sexlinked) pedigrees the easiest way to start is to find that "smoking gun child" aka the one child who has a different phenotype than either of the parents. This child MUST be homozygous recessive and both parents MUST be heterozygous. Then you go from there (find the rest of the homozygous recessive first, then what MUST their parents be for them to be homozygous recessive and go from there).

Dihybrid crosses:

Two genes of interest at the same time

Assume the two genes are on different chromosomes so crossing over isn't occurring

IE: Pea plant homozygous dominant tall and homozygous dominant round peas

GENOTYPE: TTRR - The possible Gametes are TR

IE: Pea plant homozygous recessive dwarf and heterozygous round pod

GENOTYPE: ttRr - The possible gametes are; tR and tr

PROBABILITY:

ie. Calculate the probability of the offspring

In this case, tale the probability of each event and multiply them all together!

Parent 1: AAbbccDd Parent 2: AABbCcDd

Odds:

AbcD; 0.5 x 1 x 1 x 0.5 = 0.25 AbcD: 1x0.5x0.50.5 = 0.125

Multiply gamete possibilities: 0.25 x 0.125 = 0.03125

Therefore, there is a 3.125% chance of that offspring from those aprents

Multitrait Inheritcane:

Dihybrid crosses + The law of independent assortment:

dihybrid crosses: a cross that involves 2 genes, each consisting of heterozygous alleles

Heterozygous individual for 2 characteristics will produce 4 possible gametes

Law of independent assortment: If genes are located on separate chromosomes, they will be inherited independently of one another

NOTE, each allele is independent of the other, and not two alleles are linked to eachother

TEXTBOOK:

Mendelian Inheritance ~ Page 184-193

Traits: a particular version of an inherited characteristic ( ie eye color)

Mendels Pea Plants:

peas reproduce quickly and he could control which parents produced offspring

offspring of two different true-breeding plants = hybrid

Mendels Experiment:

The breeding of two different organisms with different traits is called a cross

Mendel crossed true-breeding plants that differed from each other in only one characteristic ie. Flower colors

These plants - Parent generation or P gen

Hybrid offspring of the p gen cross were the F1 generation

F1 generation different from each other in only one characteristic, making them monohybrids

The pattern in the experiment:

n f1 generation - Only one of two traits was present

In the f2 generation - both traits were present

Conclusion:

Mendel called for a factor that was expressed in all the f1 generation the dominant factor

The factor that reminded hidden but was expressed in the f2 generation is the recessive factor

Law of segregation:

FOr each characteristic(ie. Flower color) or organisms carrier two factors(genes): One from each parent

Parent organisms drove only one of each gene in their gametes

Alleles: Alternate forms of a gene

Each forms a gene that is called an allele

Calle s have 2 alleles for each gene

1 allele; inherited one the chromosome from 1 parent, and another allele is inherited on the homologous chromosome from other parents

If 2 alleles for a particular gene are the same, the individual is homozygous for that allele

If one allele is coded for white flowers while the other coded for purple flowers, alleles will be heterozygotes

A set of alleles that an individual has is its genotype(ie. Gg or GG or gg)

remember, genotype includes all forms of individual genes, even if the same genes remain hidden

the traits of an individual make up its phenotype (brown-haired, long shared, etc.)

Alles that are expressed determines an individual's phenotype!

Dominant and Recessive Alleles:

Dominant allele: An allele that expresses its phenotype effect whenever it's present in the individual

Recessive Allele: Expressed only when both alleles are of the recessive form

Influence of alleles on phenotype:

Whenever an individual has at least one copy of the dominant allele, that allele is expressed

Variations in Heredity (pg 194- 196)

Complete dominance - Only one of the alleles is expressed, despite the presence of others

NOTE: Dominance is not always complete

Incomplete and Codominance:

Incomplete dominance: A situation where neither allele dominates the other and both have an influence on the individual; results in partial expression of both traits

Codominance: A situation where both alleles are expressed fully to produce offspring with a 3rd phenotype

Codominance and Dominance: ABO Blood Types

Blood type genotypes, 3 possible alleles: I^A, I^b, and i.

I^A I^A = Type A I^A i = Type A

I^bI^b = Type B I^b i = Type B

I^AI^b = Type AB

ii = Type O

If i is paired w I^A or I^b, then the individual expresses the dominant allele and is either type a or b

So, Type I^bi and I^A i are examples of dominant alleles

Pedigrees - Tracking Inheritance (Pages 97-201)

Pedigree charts:

Pedigree: A chart that traces the inheritance of a certain trait among members of the family

Shows connections between parents and offspring, sex of individuals in each generation, and the presence or absence of a trait

Birth order is left to right, so oldest to youngest

An example is below;

Sex linkage:

Follows the X and Y chromosomes

If an allele is found on an autosome, it is said to be under the control of the autosomal inheritance

Both males and females are affected equally, no difference between the autosomes of males and autosomes of females

Some alleles that cause genetic disorders are found on the sex chromosomes (specifically X)

Females have 2 copies of the gene (XX) and males have a single copy (XY)

Since allele with the disorder is found o the x chromosomes and is recessive, the type of inheritance is sex-linked or x linked.

If a male inherits the x chromosome from their mother who carries a recessive allele, he will express the disorder because the y chromosomes cannot mask the effect of that allele

Males cannot inherit x linked disorders from father

FEMALES must inherit 2 copies of the recessive gene in order t express the disorder, one from the father, one from the mother