Biology 1
Unit 7
Genetics: Punnett squares, Monohybrid and Dihybrid Crosses, Codominance and
Incomplete Dominance, Multiple Alleles, Sex-linked Traits, Pedigrees
Terms also refer to: Prentice Hall, Biology book by Miller and Levine, Unit 4 Genetics,
Chapter 11 Introduction to Genetics, Section 11-1 What is Science pp. 263-266 and,
Section 11-4 Meiosis, pp. 275-278, Section 11-5 Linkage and Gene Maps, pp. 279-280 and
the Glossary
Biology I SATP 2 Review Guide
Section 10.1
Introduction to Mendelian Genetics, page 213
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Gregor Mendel – an Austrian monk whose study of garden peas earned him the
title Father of Genetics
Genetics – the study of heredity
Heredity – the passing of traits from one generation to the next
Gene – a section of DNA that determines a specific trait such as eye color
Alleles – different forms of the same gene; for example, blue and brown are
different alleles for eye color
Dominant –a trait that is expressed over another trait
Recessive – a trait that can be hidden by another trait
Genotype – the combination of alleles for particular trait (homozygous or
heterozygous)
Homozygous (or pure) – having two of the same alleles for a trait
Heterozygous (or hybrid) – having two different alleles for a trait
Phenotype – the physical characteristics of an organisms that show how genes
are expressed
Terms also refer to: Prentice Hall, Biology book by Miller and Levine, Unit 4 Genetics,
Chapter 11 Introduction to Genetics, Section 11-2 Probability and Punnett Squares, pp.
267-269
Biology I SATP 2 Review Guide
Section 10.2
Monohybrid Crosses
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Law of Segregation – a natural law explaining that alternative forms of a gene
separate during the formation of gametes (sex cells); they do not mix to form a
new trait
Monohybrid cross – crossing one trait from two parent organisms
Biology 1

Punnett square – a diagram that shows all possible gene combinations for a
cross
Terms also refer to: Prentice Hall, Biology book by Miller and Levine, Unit 4 Genetics,
Chapter 14 The Human Genome, Section 14-1 Human Heredity, pp. 341-348
Biology I SATP 2 Review Guide
Section 10.3
Human Autosomal/Genetic Diseases, page 223
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Autosomes – all chromosomes except the sex chromosomes (X and Y)
Autosomal disease – genetic disease that is carried by a gene on an autosome
Carrier – a person who has one recessive gene for a recessive genetic disease;
will not display symptoms of the disease but can pass on the gene to offspring
Cystic Fibrosis – a genetic disease that causes the body to produce unusually
thick, sticky mucus; decreases life expectancy
Phenylketonuria (PKU) – a genetic disease where a person is born without the
enzyme to break down use phenylalanine, an essential amino acid
Tay-Sachs – a fatal genetic disease that causes fatty material to build up in the
nerves and brain
Terms also refer to: Prentice Hall, Biology book by Miller and Levine, Unit 4 Genetics,
Chapter 11 Introduction to Genetics, Section 11-2 Probability and Punnett Squares, pp.
267-269, Section 11-3 Exploring Mendelian Genetics pp. 270-274
Biology I SATP 2 Review Guide
Section 11.1
Dihybrid Crosses
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Dihybrid cross – studying two traits crossed from parent organisms
Law of Independent Assortment - a natural law that explains how traits are
inherited independently of other traits
Terms also refer to: Prentice Hall, Biology book by Miller and Levine, Unit 4 Genetics,
Chapter 11 Introduction to Genetics, Section 11-3 Exploring Mendelian Genetics pp. 270274
Biology I SATP 2 Review Guide
Section 11.2
Incomplete Dominance and Codominance
 Incomplete dominance – having alleles that do not have complete dominance
so the resulting trait is a mix of two alternate traits; for example, red snapdragons
crossed white snapdragons produce pink snapdragons
Biology 1
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Codominance – having two or more alleles that are equally dominant for a trait
so that both traits are expressed; for example, roan cattle have both red hair and
white hair (not pink)
Sick cell anemia – a genetic disease caused by a codominant gene
Terms also refer to: Prentice Hall, Biology book by Miller and Levine, Unit 4 Genetics,
Chapter 14 The Human Genome, Section 14-2 Human Chromosomes, pp. 349-353
Biology I SATP 2 Review Guide
Section 11.3
Linked and Sex-Linked Genes
 Law of Independent Assortment – a natural law that ecplains how traits are
inherited independently of other traits
 Sex Chromosomes – the one pair of X and Y chromosomes that determine
gender
 Sex-linked genes – genes that are found on either the X or the Y sex
chromosomes
 Red-green color blindness – a sex-linked disorder that is carried on the X
chromosome
 Hemophilia – a sex-linked disease that is carried on the X chromosome
 Pedigree – a diagram used by geneticists to chart a trait from one generation to
another