Chapter 13 Biology Study Guide

Gene

Known as the functional unit of DNA that carries instructions for a specific way.

Heritable units of information/ DNA instructions for a trait.

Allele

The Alternative form of a gene, you inherit one of these from each parent.

Where different molecular forms of the same gene differ.

Homozygous dominant

This is written as AA and are basically 2 dominant alleles.

Example would be A=Brown eyes

Homozygous Recessive

This is written as aa and are 2 recessive alleles

Example would be a=blue eyes

Heterozygous

The genotype in which homologous chromosomes have different alleles at the same locus.

Basically 2 different alleles for a gene.

Aa or Bb

Phenotype

The persons observable traits.

Example. Would be physical appearance like height, hair, skin color.

Genotype

The set of alleles that are carried by a individuals chromosomes

An example would be = A=eye, B=hair, T=Height

Dominant traits

Refers to an allele that masks the effect of a recessive allele paired with it in heterozygous individuals.

Basically if a genotype is Aa, then A is shown and a is hidden because A is dominant.

Recessive traits

Opposite to dominant

Basically this only shows in aa, not Aa or AA.

Monohybrid cross

The ratio for this is 3:1.

It is the study of how one trait is passed from parents to offsprings.

The type of cross that is between TWO heterozygous individuals for ONE gene

Example Aa x Aa

Dihybrid Cross

Ratio = 9:3:3:1

A genetic cross that looks at inheritance of TWO traits at the same time.

Example AaBb x AaBb

Test Cross

The method of determining the genotype of an individual with a dominant phenotype.

Example - A check because you don’t know if someone’s genotype is what it is because it could be AA or Aa - they both look dominant.

Law of segregation

2 Alleles of any gene locus are distributed into separate gametes.

Means they separate and each gamete gets only 1 allele

Law of independent Assortment

Alleles at 1 gene locus on chromosomes tend to be distributed into gametes independently at other loci.

Means genes for different traits separate INDEPENDENTLY during gamete formation.

Complete dominance

100% dominant appearance in heterozygotes.

Incomplete dominance

One allele is not completely dominant over another. When the heterozygote shows a blended immediate trait.

Codominance

When both alleles are expressed equally.

Polygenic Inheritance

The form of a single trait is collectively determined by alleles of several genes

Multiple Allele systems

A gene has MORE THAN 2 alleles in the population at relatively high frequency

Pleiotropy

Has many effects, when 1 gene effects multiple traits in an organism.

Epistasis

A form of polygenic inheritance in which the effect of an allele on a trait masks the effect of a different gene.

Continuous variation

Range of small differences in a trait.

What type of cross is between two heterozygous individuals for one gene.

Dihybrid cross

What are heritable units of information called

Genes

How do different molecular forms of the same gene differ

Alleles

What describes an organism with a genotype AaBb?

Heterozygous for both traits

What are the phenotypic ratios expected in a monohybrid vs Dihybrid cross?

3:1 and 9:3:3:1

What pattern of inheritance shows a blended phenotype between two alleles?

Incomplete dominance

What pattern shows both alleles expressed equally in heterozygotes

Codominance

What term describes a gene that affects more than one trait?

Pleiotropy

What kind of inheritance involves multiple genes influencing a single trait?

Polygenic

What does it mean if one gene masks the effect of another?

Epistasis

What kind of variation is shown by traits like height, skin color and weight?

Continuous variation