Introduction to Mendelian Genetics

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Introduction to Mendelian Genetics

Packet #19

Chapters 6 & 7

Friday, April 21, 2023

Mendelian GeneticsWho is Mr.

Gregor Mendel?

What is he famous for?

Describe the experiments of Gregor Mendel


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Introduction I

Heredity The biological similarity

of offspring and parents

Gene Region of DNA, found

on the chromosome, that controls a discrete hereditary characteristic of an organism


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Introduction II

Allele One of several alternate

forms of a particular gene

Locus Particular place along

the length of a chromosome where a given gene is located


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Introduction III


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Genotype The specific allele

composition of a cell The combination of

alleles located on homologous chromosomes that determines a specific characteristic or trait.

Introduction IV

Phenotype The observable physical

or biochemical characteristics of an organism, as determined by organism’s genetic makeup (genotype).


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Introduction V

Dominant AlleleAn allele that expresses its phenotype effect even

when combined with a recessive allele.

Recessive AlleleAn allele whose phenotype effect is not expressed

unless it is combined with another recessive allele.

However, there are exceptions to this rule in specific genetic disorders.More to come in future packets…Please hold those

questions until then.


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Introduction VI

A = dominant allele

A = recessive allele

AA = homozygous dominant genotype

Aa = heterozygous genotype

aa = homozygous recessive genotype

Genotype Variations Homozygous dominant

Two dominant alleles Heterozygous

One recessive allele One dominant allele

Homozygous recessive Two recessive alleles

Incomplete Dominance

Occurs when hybrids, with a heterozygous genotype, have an appearance between the phenotypes of the parental varieties.


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Incomplete Dominance II


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Codominance

Situation in which the phenotypes of both alleles are exhibited in a heterozygote


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Epistasis

Phenomenon in which one gene alters the expression of another gene that is independently inherited.


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Epistasis II


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Sex-Linked Genes

Sex-linked genes Genes that are found on

the sex chromosomes.

Multiple Alleles

On some occasions, there is more than two alleles (forms) of a particular gene. Example: - Alleles for blood

group.

When discussing genotypes for blood groups, there are three alleles that one must consider i iA

iB

More to come on blood types later and how blood types are determined in a couple’s offspring and how blood groups impact the blood transfusions.

Punnett Squares

Punnett Square A diagram used in the

study of inheritance Shows the result of

random fertilization in genetic crosses. Shows the probable

results of crossing over. More to come in

the next packet.


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Mendel’s Laws

Mendel’s Laws

When Mendel carried out his research, the processes of mitosis and meiosis had not yet been discovered.

However, Mendel knew, through his experiments, that genes (alleles) existed.

From Mendel’s research, he devised two laws. Principle of Segregation Principle (Law) of

Independent Assortment

Principle of Segregation

Principle of Segregation The principle states that

in diploid organisms genes come in pairs and that when sex cells get produced each gamete gets one gene at random.

Principle of Segregation II

When developing this idea Gregor Mendel conducted a series on monohybrid (test) crosses using pea plants. A monohybrid is when

only one allele is investigated.

Principle of Independent Assortment

The Law of Independent Assortment states that the alleles (or separate members of a gene pair) separate independently to form the gamete. To do this, one must be comparing

at least TWO traits. Dihybrid cross

By doing so, the traits are transferred independent from one another. This allows for much more

variation in the offspring since the alleles are randomly matched with the gamete from the other parent to form the zygote. According to how many traits

are in question, the number of possible variations can become quite high.

Dihybrid Cross

A dihybrid cross involves an investigation of two alleles at the same time.

Principle of Independent Assortment II

Mendel concluded that alleles (traits) are transmitted to offspring independently of one another.

If the genes are transmitted independently, then the genes are determined as being unlinked.

If the genes are transmitted together, the majority of the time, then the genes are determined as linked genes. Hence, the principle

of independent assortment does not apply.

Principle of Independent Assortment III

This law holds true as long as the two genes (traits) in question are: - Located on separate

chromosomes Not linked together if they

are located on the same chromosome. Unlinked genes

More to come later in AP Biology

The principle of independent assortment allows/results in recombination The presence of new gene

combinations not present in the parental (P) generation.

Principle of Independent Assortment IV

The principle of independent assortment allows/results in recombination The presence of new

gene combinations not present in the parental (P) generation.

Genetic Crosses

Monohybrid (Test) Cross

Examples

Dihybrid Crosses

Examples

Parent #1 Genotype FfEe

Parent #2 Genotype FfEe

Review

Documents

Introduction to Mendelian Genetics