Download Genetics Study Guide

Genetics Study Guide
Vocabulary- Know the meaning of the following terms:
trait allele
dominant allele
recessive allele
Punnett Square
heterozygous
homozygous
 Trait: Characteristics that are passed down from parents to offspring.
 Allele: Different forms of a gene.
 Dominant allele: The allele that is always expressed if it is present. Recessive allele:
The allele that is expressed only if the dominant allele is not present.
 Punnett Square: A tool used to visualize all the possible combination of alleles from
the parents.
 Heterozygous: The two alleles on the gene are different.
 Homozygous: The two alleles on the gene are the same (both dominant or both
recessive)
Concepts

What is heredity?
- Heredity: The passing on of characteristics from parents to offspring.

Know the difference between genotype and phenotype.
- Genotype is the combination of alleles (for example Bb) you get one allele from
your mom and one from your dad.
- Phenotype is the physical trait we can actually see.

Know the genotypes for male and female.
- male: XY
- female XX

Explain what a chromosome is and where it is located within the cell.
A chromosome is tightly wound DNA that is made up of genes. It is located in the
nucleus of the cell.

Explain what genes are made up of. Genes are made up of short segments (pieces) of
DNA.

Explain probability. Probability is the likelihood of something happening.

Differentiate between heterozygous, homozygous recessive, and homozygous
dominant.
- Heterozygous: The genotype is made up of two different alleles (one dominant and
one recessive). It is represented with a capital letter and a lower case letter (Xx).
- Homozygous recessive: The genotype is made up of two of the same alleles (both
recessive). It is represented with two lower case letters (xx).
- Homozygous dominant: The genotype is made up of two of the same alleles (both
dominant). It is represented with two upper case letters (XX).

Punnett Squares: What does a punnett square tell you? A punnet square shows the
probability (likelihood) of a child having certain traits based on the parents’
genotypes.
o Be able to create and work a punnett square (analyze the results by explaining the
probability of the offspring’s genotypes and phenotypes).
o Be able to solve problems similar to this:
Parent A, with the genotype Dd has dimples. Parent B, also has the genotype Dd
and has dimples.
D= dimples
d= no dimples
Use this genetic cross (Dd x Dd) to answer a-c
a. Draw and solve a Punnett square:
b. State the probability for the possible genotypes. DD= 25%, Dd=50%,
dd=25%
c. State the probability for the possible phenotypes. Dimples or no dimples
Meiosis: Know which cells are created through meiosis. Sex cells (egg or sperm)
o How many cells are created? 4
o How are these cells compared to the original cell? Sex cells are NOT exact
copies of the original cell and they have HALF as many chromosomes.

Know the difference between asexual and sexual reproduction.
- Asexual reproduction requires one parent. The offspring is identical to the parent.
It is common in single celled organisms.
- Sexual reproduction requires a male and female parent. The offspring is a
combination of the parents’ DNA. It is common in multicelled organisms.

What is the joining of egg and sperm called? Fertilization

Know how many chromosomes are in a human body cell: 46

Know how many chromosomes are in a human sex cell: 23

Compare and contrast Mitosis and Meiosis by completing the Venn Diagram below:
Mitosis

Both
Meiosis
What is a mutation? Mutation: A change in a gene or chromosome.