Biology I - Chapter 5B - Basic Genetics

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For Biology I students at Christian Life School

Know about Gregor Mendel

Born in 1822 on a farm in Austria.
Became a monk at 21.
Studied science and math at the University of Vienna.
Bred pea plants to study their genetics.
Called the "Father of Genetics"

Genetics

The study of heredity

Self-pollination

When the pollen naturally fertilizes the pistil of the same flower.

Cross-pollination

When the pistil is fertilized by the pollen of another flower.

P1

Symbol for the parent plant (generation).

F1

Offspring of the P1 generation; known as the first filial generation

F2

Offspring of the F1 generation; known as the second filial generation

Concept of Unit Characteristics

States that an organisms characteristics are caused by factors that occur in pairs.

Concept of Dominant and Recessive

States that some factors will express themselves and others will be masked or hidden and show up in future generations.

Concept of Segregation

States that when a cell forms gametes, the genes on the chromosomes separate so that there is only one characteristic in each gamete.

Phenotype

The physical expression of an organisms genes; what an organism is like.

Examples of phenotypes

Tall, short, blue eyes, brown eyes, red flowers, white flowers

Phenotypic ratio

A ratio that tells the possibilities for the physical characteristics of an organism in a Punnett square.

Genotype

The specific genes an organism has often expressed as letters in Biology.

Examples of genotypes

Tt, ZZ, rr, Hh, Ss, ss, FF

Genotypic ratio

A ratio that tells the possibilities for the genes of an organism in a Punnett square.

Locus

The site on a chromosome where a specific gene is located.

Allele

An alternate form of a gene that occupies the same locus on homologous chromosomes.

Homozygous

When both alleles in a particular gene are the same; also known as purebred. (TT, ss, FF, pp)

Heterozygous

When both alleles in a particular gene are not the same; also known as hybrid. (Tt, Ss, Ff, Pp)

Monohybrid cross

A cross between two organisms that deals with only one trait. (Eye color OR hair color OR seed shape)

Dihybrid cross

A cross between two organisms that deals with two traits. (Eye color AND hair color; Seed shape AND seed color)

Punnett squares

A method used to show genetic crosses and determine the possibility of an offspring being a particular genotype or phenotype.

Incomplete Dominance

Occurs when two or more alleles are expressed, resulting an a phenotype that is a blending of the two traits.

Codominance

Occurs when two alleles for a gene are both expressed at the same time in a heterzygous offspring.

Multiple Alleles

When there are more than two alleles that code for a specific gene at the same locus.

Sex chromosomes

Chromosomes determining whether an organism will be a male or a female.

Autosomes

The 22 pair of non-sex determining chromosomes that make up the body cells.

Sex-linked traits

Traits that have their genes on the X chromosome and not on the Y chromosome.

Female sex chromosomes

XX

Male sex chromosomes

XY

Carrier

An individual that does not show the physical characteristic for a trait, but does carry the gene for a trait.

Know how to set up and complete Monohybrid (one-factor...4 square) Punnett Squares

Determine the genotypes (genes expressed as letters) for each individual.
Separate the genotypes and place the genes for the mom on the top of the squares and place the genes for the dad on the left side of the boxes. There should be one letter above each box and one letter to the left of the boxes (see example).
Combine all genes to show the possibilities for genes for their children.
Figure out the genotypic ratio: look in the first box and see what that genotype is; count how many of that specific genotype are found in the four squares; write that number down or write a percentage making sure to include the genotype with the percentage; continue counting the genotypes until all four boxes are accounted for.
Figure out the phenotypic ratio: look in the first box and figure out what the physical characteristic is; count how many of that specific phenotype are found in the four squares; write that number down or write a percentage making sure to include the physical characteristic with the percentage; continue counting the phenotypes until all four boxes are accounted for.

Know how to set up and complete Dihybrid (two-factor...16 square) Punnett Squares

Determine the genotypes (remember that there should be 4 letters...two for each trait) for each individual.
Use the FOIL method (First, Outside, Inside, Last) and multiply each pair of genes together to determine the letters that will placed on top of each box and on the left of each box (remember that one of each of the letters must be represented in each pairing).
Place the letters on top and to the left of each box and then combine them. There should be 4 letters inside each box after combining.
Determine the genotypic and phenotypic ratios for the boxes.

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