mendel’s studies of traits

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Mendel’s Studies of Traits

• The passing of traits from parents to offspring is called heredity.

Chapter 4 The Origins of Genetics

• The patterns that Mendel discovered form the basis of genetics, the scientific study of heredity.



Mendel’s Studies of Traits, continued

Mendel’s Breeding Experiments

• Gregor Mendel is considered to be the father of genetics. He was an Austrian monk who did work with pea plants in the mid 1800’s.




Mendel’s Studies of Traits, continued

Chapter 4 Principles of Genetics

• Parental generation- first pair of plants or animals in a study

•First Filial generation (F1)—the results of the parental cross

•Second Filial generation (F2) -offspring produced by the first filial generation.

•Chromosomes(found in nucleus)-> DNA->Genes



Mendelian Theory of Genetics

1. For each inherited trait, an individual has two copies of the gene, one from each parent.

** It takes at least two genes to express a trait **2. Geneticist use symbols to represent genes. The

term allele refers to either member of a pair of genes that expresses a trait. It is an alternative version of a gene. It is these alternative versions of genes that account for variation of inherited characteristics.

Ex. Eye color, hair color, textures, shape, etc.




Mendalian Theory of Genetics, contd.

3. Principle of Dominance - states that one allele (or gene) in a pair may prevent the other allele (or gene) in the pair from being expressed.

• A gene that masks or over-rides another gene in the pair is called dominant (capital letter). The hidden or repressed gene is called recessive (lowercase letter).

• 2 gene pairs are identical-TT or tt –homozygous• Both alleles are dominant (TT)-homozygous

dominant• Both alleles are recessive (tt)-homozygous recessive




Mendalian Theory

• When 1 allele is dominant and the other recessive (Tt) it is called heterozygous.

• Genotype-pair of alleles that make up a trait. Ex: TT, tt. or Tt.

• Phenotype-what is actually seen or expressed physically in the organisms appearance.

• Wild Type -a phenotype that is the most common expression of a particular gene in a population.

• Mutation-change from the wild type• Mutant-an allele that arises as a result of mutation

from the wild type. Is a variation and is not necessarily harmful.




• Law of Segregation -states that members of each pair of genes separate when gametes are formed. Thus, an egg and sperm receive only one of the genes that are present in two copies in the somatic cells of the organism.



• Law of Independent Assortment – states that the alleles of different genes (for traits) separated independently of onel another during gamete formation. Ex: alleles for plant height separate from alleles for plant color




• Punnett square – named for Sir Reginald Punnet (British geneticist), helps you visualize probable results of genetic crosses.

Symbols for all possible gametes from the male goes across the top of the grid.Symbols for all possible gametes from female appear along the left side.

• Monohybrid cross- a cross involving one trait (one pair of alleles)

• Dihybrid cross- a cross involving 2 traits and therefore at least 4 alleles.




Monohybrid Cross: Homozygous Plants

Chapter 4



Monohybrid Cross: Heterozygous Plants

Chapter 4



Incomplete Dominance

Chapter 4



Modes of Inheritance -pattern in which Mendelian traits appear in families.

• It designates whether the gene is carried on an autosome or on the X chromosome.

• It reveals whether the associated phenotype to the gene is dominant or recessive.



Modes of inheritance includes:

1) Autosomal dominant –trait can appear in either sex since the gene is carried on an autosome. Since it is dominant, if a child has the trait at least 1 parent must also have it.

2) Autosomal recessive –trait can appear in either sex, 2 carriers (hetero.) parents who do not have the trait typically are surprised to give birth to a child who has it.

3) Sex-Linked dominant –Ch.64) Sex-Linked recessive –Ch.6

Consanguinity –shared bloodlines: occurs when blood relatives have children together. Sometimes a rare autosomal recessive illness may occur in families in which parents are blood relatives.



Pedigree –a chart consisting of symbols for individuals connected by lines that depict blood relationships and transmission of inherited traits.• Helps to track of relationships and traits• Squares indicate males• Circles indicate females• Vertical lines represent generations• Horizontal lines that connect shapes at their centers depict

parents• Shapes connected by vertical lines joined by horizontal lines

above them indicate siblings.• Colored shapes indicate individuals who express the trait under

study, and half-filled shapes represent known carriers• Symbols for heterozygotes are half-shaded.Pedigrees help families identify the risk of transmitting an inherited

illness and as starting points for gene searches.



• Propositus – male individual afflicted with genetic disorder that led to the construction of pedigree

• Proposita – female individual

mendel’s studies of traits

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