Topic 2

mandelian Inheritance ch.9

Blending Inheritance is

a genetic theory proposing that offspring inherit a mixture of traits from their parents, rather than a strict combination of dominant and recessive traits. This concept suggests that traits blend together to form intermediate characteristics in the next generation.

Why is blending inheritance not correct fully

Because if blending inheritance was the mechanism the variation of traits would eventually diminish, leading to a uniform population over generations. This contradicts the observed genetic variability seen in populations.

Who was gregor mendel

A scientist known as the father of modern genetics who conducted experiments on pea plants. His work established the principles of heredity, including the concepts of dominant and recessive traits.

What is true breeding mean that medel used

True breeding refers to organisms that, when mated, produce offspring with the same traits as the parents, phenotypes . Mendel used true breeding plants to establish predictable patterns of inheritance. Always gave same phenotype when self crossed, homozygous for every trait

What are phenotypes

The observable physical characteristics or traits of an organism, resulting from the interaction of its genotype with the environment.

Genotypes are

the genetic makeup of an organism, representing the combinations of alleles inherited from its parents.

Progeny

The offspring resulting from the mating of two organisms, reflecting the genetic contributions of both parents.

How did Mendel test his hypothesis

True breeding homozygous pea plants to test if always given same outcome

focused on single trait at a time

Counted the progeny

F1 generation

result of crossing two parental genotypes, showing the first filial generation's traits, displays phenotype of dominant allele while masking the recessive one.

All heterozygous individuals Aa

Diffrence of dominat vs recessive alleles

Dominant allele codes for functional protein which allows for the presence of a functional enzyme that breaks down the chlorophyll and shows the dominant colour; recessive allele produces a non-functional protein, failing to mask the dominant allele's effect.

% chlorophyll breakdown will be for dominant vs recessive

a/a wil have less

a/A and A/A will have the same level of chlorophyll breakdown due to the presence of the dominant allele but the generations afterwards might express more of the recessive allele

What is segregation

The process during meiosis where alleles segregate so that each gamete receives only one allele for each gene, ensuring genetic variation.

Ratio of expressiopn of dominant vs recessive traits

dominant shown 3x more

Mandels principles of segregation

• Each organism is diploid; two allels

• Homozygous ones are the same producing one type of gamete

• Heterozygous alels are diffrent. two types of gametes

Generation 1 cross expected ratios

Phenotypic 1;2;1 Genotypic 3;1

Seeds in F2 generations showing the green colour are

aa, contain homozygous recessive trait

How to determine if you have hetero or homozygous zygote?

Test cross by mating with recessive genotypeto reveal the zygote's genotype., if hetero will display recessive gene

The organisms of a true-breeding line for a single trait, like those true-breeding lines of pea plants that Mendel used, are _____ for the trait of interest (such as seed colour or pod shape).

homozygous

A reproductive cell, or gamete, has:

only one allele for each gene.

is this true in Mandelians segregation “After many generations, it reduces heritable variation in a population”

No, Mendelian segregation maintains heritable variation in populations by randomly distributing alleles during gamete formation.

A single character controlled by multiple genes is known as a _____ character

polygenic

Seeds in F2 generation showing recessive green phenotype must be

homozygous recessive

Are the yellow pheonotype (dominant) seeds all equal in f2

no, some are Aa and others AA

Whats a test cross

Mating an unknownk genotype individual with a homozygous recessive genotype in order to tell genetic make up of unknown

Expected outcome of test cross for heterozygous vs homozygous

2;2 ration of P/P and P/p if heterozyous

all P/P is homozygous

Mandels hypothesis

• Adults carry two copies of factors (genes) that govern inheritance of character

• One is dominant over the other (recessive)

• The factors segregate during gamete formation, resulting in offspring inheriting one allele from each parent.

Probability Product Rule

If two independent events occur their probability is known by their product (x)

Independent probabilities multiplied

Sum rule

Probability of an outcome that can be achived by two or more mutually exclusive events is the sum of their individual probabilities

Individual probabilities are added

Monohybrid cross

Cross between two heterozygotes AaxAa 3;1 phenotype ration and 1;2;1 genotype ratio

Sperm production relavance in size of animal and quanitity

Typically larger animals produce more sperm but smaller size and small animals produce less sperm but long in length

Chromosomal theory of inheritance states;

• genes are located on chromosomes and are inherited according to Mendelian principles

• Chromosomes occur in pairs in diploid organisms

• seperation of each pair of chromosomes in meiosis is indapendent of other pairs

• Each gamete receives one chromosome from each pair.

When does segregation occur in meiosis

anaphase 1

Examples of when dominance is not universally observed

include incomplete dominance, and codominance

Incomplete dominance

Intermediate phenotype, mixture of 2 phenotypes caused as one allele is not completly dominnat to other allele

Represented by subscript letters or different letters for alleles in genotype C^R C^W

example. red and white flower make a pink one

In flowers for example how is incomplete dominance explained?

Dominant; red for example produces functional enzymethat allows for red pigment production, while the white recessive allele produces a non-functional enzyme. When both alleles are present, they result in a blend of colors, creating pink flowers. This is bc red enzyme is mixed with a non functional one, leading to an intermediate phenotype.

Incomplete dominance phenotype and genotype

Both 1;2;1 since the C^R C^W genotype has a distinct phenotype and the dominant dosent just mask over

Co-dominance

A genetic scenario where both alleles are expressed equally in the phenotype, resulting in a distinct expression for each allele, such as AB blood type in humans.

Not mixed together to create new variation but both allles are expressed without blending, showing distinct traits.

Polygenic/Pollyalleic/Pollymorphic genes

Genes that are influenced by multiple alleles

MHC Major Histocompatibility complex are

a group of genes important for immune system function, responsible for the recognition of foreign molecules.

How are alleles in MHC expressed

Alleles in MHC are expressed co-dominantly, meaning that both maternal and paternal alleles contribute equally to the phenotype in an individual. Highly polymorphic

Mandelian segregation preserves

the genetic variation during gamete formation by ensuring that alleles segregate independently into reproductive cells.

Discrete Mandelian traits are

One gene has 2 allels

Phenotypes consistent for genotypes

Ex; Co-dominance, Complete or Incomplete domiance

Complex Traits Non-Mandelian

Multiple genes and multiple alleles

Great Variation in phenotypes with the same genotype

Ex; Polygenic genes, eye colour, skin colour

Polygenic traits

Traits influenced by multiple genes, exhibiting a range of phenotypes in a continuous distribution ; more complex phenotypes and smoother distribution

is it possible for 2 individuals to have the same phenotype but different genotypes?

Yes, this can occur due to phenomena such as incomplete dominance, co-dominance, or environmental influences that affect phenotype expression.

Is same genotype but different phenotypes possible

Yes, same genotypes can lead to different phenotypes due to variations like environmental factors or gene interactions that influence how traits are expressed.

Mandelian segregation preserves

Genetic variation