Genetics Study Guide

Key to Success on the Test

1. What scientist experimented with pea plants to establish

modern genetics?

• Gregor Mendel

2. What is the difference between a monohybrid and a dihybrid cross

• Monohybrid examines 1 trait, Dihybrid examines 2 traits

3. What is the difference between a gene and an allele?

• Genes are a segment of DNA that code for a trait. Alleles are alternate forms of that gene.

• Gene: Pea Pod Color

• Alleles: Yellow pod color or Green pod color

4. What is the difference between genotype and phenotype?

• Genotype is the code or letter that represent a trait

• Phenotype is the physical way that the trait is expressed

• Genotype: YY

• Phenotype: Yellow

5. What is the difference between homozygous and heterozygous?

• Homozygous means that you have 2 same alleles for a trait (YY or yy)

• Heterozygous means that you have 2 different alleles for a trait (Yy)

6. What is the difference between a hybrid and a purebred?

• Hybrids have 2 different alleles from the parent(s) Yy

• Purebreds have two same alleles from the parent(s) YY or yy

7. What is the difference between dominant and recessive?

• Dominant alleles have the ability to mask a recessive allele.

• With the genotypes YY and Yy the dominant trait will be expressed

• With the genotype yy, the recessive trait will be expressed

8. What are Punnett Squares used for?

• To find out the possible outcomes for a genetic cross

9. Create a Punnett Square for a monohybrid cross for two

individuals that are heterozygous for brown eyes

(Bb). Brown eyes are dominate to blue eyes.

10. Give 3 reasons that Mendel used pea plants for his studies.

• Short growing period/Easy to Grow

• 7 traits in 2 distinct forms

• Produces many offspring

11. Mendel’s Laws

– The Law of Segregation-During Meiosis each pair of alleles separate

– The Law of Independent Assortment-gene pairs separate randomly and independently of each other

– The Law of Dominance-dominant allele masks recessive allele

12. What are 3 ways you can show probability?

• Ratio

• Percent

• Fraction

13. Define trait.

• Anything that can be passed down from parent to offspring

14. What are carriers?

• Individuals who are heterozygous for a recessive trait. They carry the trait, but they are not affected by it.

15. What is a pedigree used for?

• To examine inheritance patterns in families.

• Circles are females

• Square are males

• Individuals that exhibit the trait are shaded in

• Individuals that carry the trait are partially shaded in

16. What is the difference between sex chromosomes and

autosomes?

• Sex chromosomes determine the sex of the offspring and X-linked traits. Autosomes carry the genes that affect the rest of the individual.

17. What is the genotype for a female and what is the genotype for

a male

• FEMALE: XX

• MALE: XY

18. What is one difference between X and Y chromosomes?

• Size. The X chromosome is significantly larger than the Y chromosome

19. When babies are made, which gamete controls the sex of the

offspring?

• Male gamete - Sperm

20. What are sex-linked traits?

• Sex-linked traits are from genes located on the X chromosome of the sex chromosome.

21. Create a Punnett Square to show the recessive sex-linked trait “male pattern

baldness” Cross a carrier female with a normal male.

Give Ratios.

22. What are karyotypes?

• Diagram that shows the cell’s chromosomes organized from smallest to largest.

• It allows people to determine gender and find out if the individual has any chromosomal disorders.

23. How many chromosomes do people with Down Syndrome

have?

• 47. They have 3 chromosomes located on chromosome 21

24. What do you observe about this karyotype? Is it going to

produce a “normal” offspring?