Study Guide for the Genetics Unit
Name __________
The Work of Gregor Mendel

Explain who Gregor Mendel is.

Define the term “heredity”.

Define the term “genetics”.

Identify the parent generation in a cross.

Identify the F1 and F2 generations in a cross.

Explain why when Mendel crossed a purebred short pea plant with a purebred tall
pea plant, the resulting F1 generation only had tall pea plants.

Explain why when Mendel allowed the F1 generation of all tall pea plants to selfpollinate, short pea plants reappeared in the F2 generation.

Define the term “gene”.

Define the term “allele”

Define the terms “dominant” and “recessive”.

Properly abbreviate the alleles that an individual possesses for a trait.

Define the terms “genotype” and “phenotype”.

Define the terms “homozygous” and “heterozygous”.

Identify the phenotype and genotype of different individuals for a given trait.

Explain what a Punnett Square is.

Use a Punnett Square to predict the possible offspring that may result from a
cross.

Define the term “probability”.
 Explain the role of probability in genetics.
Patterns of Heredity

Explain what a pedigree chart is.

Use a pedigree chart to track the presence of a trait in a family.
 Identify the different symbols used in a pedigree chart.
Circle = female;
Square = male,
horizontal line connecting two = marriage
Line coming down from a marriage = offspring from the parents
Shaded in = affected by the trait
half-shaded = carrier/heterozygous
 Define the term “carrier”.
An individual that has the recessive gene but is not affected by its trait
 Explain simple recessive inheritance.

Explain simple dominant inheritance.

Explain incomplete dominance.

Explain codominance.

Explain multiple phenotypes from multiple alleles.

Explain how the sex of an individual is determined.

Define the term “autosome”.

Define the term “sex chromosome”.

Explain sex-linked inheritance.

Define the term “sex-linked trait”.
Study Guide for Genetics - KEY
The Work of Gregor Mendel
 Explain who Gregor Mendel is.
“Father of genetics” – did experiments breeding pea plants to learn about heredity
 Define the term “heredity”.
The study of how traits are passed on from one generation to the next
 Define the term “genetics”.
Study of the actual genes that organisms possess and how they interact
 Identify the parent generation in a cross.
 Identify the F1 and F2 generations in a cross.
 Explain why when Mendel crossed a purebred short pea plant with a purebred tall
pea plant, the resulting F1 generation only had tall pea plants.
Tall is dominant over short and they were all heterozygous “Tt”
 Explain why when Mendel allowed the F1 generation of all tall pea plants to selfpollinate, short pea plants reappeared in the F2 generation.
Crossing two heterozygotes will give you all three genotypes “TT” “Tt” & “tt”
 Define the term “gene”.
A segment of DNA that codes for a single protein
 Define the term “allele”
One possible variation of a gene; like a flavor that the gene can come in
 Define the terms “dominant” and “recessive”.
Dominant alleles will be expressed over recessive alleles when they are both present
 Properly abbreviate the alleles that an individual possesses for a trait.
Alleles are designated by the letter of the dominant trait
 Define the terms “genotype” and “phenotype”.
Genotype tells you the genes that an organism has, phenotype tells you the trait
 Define the terms “homozygous” and “heterozygous”.
Homozygous = two of the same allele (“TT” or “tt”)
heterozygous = two different alleles (“Tt”)
 Identify the phenotype and genotype of different individuals for a given trait.
Homozygous dominant, heterozygous = dominant trait;
homozygous recessive = recessive trait
 Explain what a Punnett Square is.
A tool for finding out what the probably outcomes of a genetic cross are
 Use a Punnett Square to predict the possible offspring that may result from a
cross.
 Define the term “probability”.
The chances or odds that a certain outcome will happen, usually in a ratio or percentage
 Explain the role of probability in genetics.
Using a punnett square, you can find the probability that a certain genetic outcome will
occur, but it only tells you the probability, not a guarantee
Patterns of Heredity
 Explain what a pedigree chart is.
A way of looking at the genes and traits that are passed down through a family tree

Use a pedigree chart to track the presence of a trait in a family.
 Identify the different symbols used in a pedigree chart.
Circle = female;
Square = male,
horizontal line connecting two = marriage
Line coming down from a marriage = offspring from the parents
Shaded in = affected by the trait
half-shaded = carrier/heterozygous
 Define the term “carrier”.
An individual that has the recessive gene but is not affected by its trait
 Explain simple recessive inheritance.
When a trait is recessive, an individual must have two copies of it in order to have the
trait. If they have one recessive and one dominant allele, they will be a carrier.
(“aa” = affected; “Aa” = carrier – not affected)
 Explain simple dominant inheritance.
When a trait is dominant, an individual can have one or two copies of it and be affected
by the trait.
(“AA” or “Aa” = affected by the dominant trait)
 Explain incomplete dominance.
When two alleles are both present, the outcome is a third phenotype which is a blend of
the other two (“RR” = Red; “rr” = White; “Rr” = Pink)
 Explain codominance.
When two alleles are both present, the outcome is both phenotypes are expressed
together, but not blended. (“RR” = Red; “WW” = White; “RW” = both Red and White
 Explain multiple phenotypes from multiple alleles.
Like blood types, sometimes there can be more than two alleles possible for a gene,
which leads to a wider spectrum of possible outcomes
 Explain how the sex of an individual is determined.
The sex chromosomes determine the sex of the offspring (XX = female, XY = male)
 Define the term “autosome”.
A normal chromosome; in humans, one of the 22 other pairs
 Define the term “sex chromosome”.
One of the chromosomes that determines gender; there are two possibilities: X & Y
 Explain sex-linked inheritance.
If a trait is found on the X chromosome, males will only have one copy of it, so they
can’t possibly be carriers. Males only need one copy of the recessive gene to have it.
 Define the term “sex-linked trait”.
A trait whose gene is found on the X chromosome (or occasionally Y)