Genetics Study Guide
Short Answer
1. In Mendel’s experiments, what proportion of the plants in the F that had been absent in the F
1
generation?
2
generation had a trait
One fourth
2. Factors that control traits are called-genes
3. Scientists call an organism that has two different alleles for a trait a hybrid
4. What does the notation TT mean to geneticists?
It means the organism is homozygous dominant
5. What does the notation Tt mean to geneticists?
It means the organism is heterozygous-one dominant and one recessive allele
6. What is probability?
A number that describes how likely it is that an event will occur
7. What is the probability of producing a tall pea plant from a genetic cross between two hybrid tall pea plants?
75%
8. What does a Punnett square show?
The possible outcome of the genetic cross
9. If a homozygous black guinea pig ( BB ) is crossed with a homozygous white guinea pig ( bb ), what is the probability that an offspring will have black fur?
100%
10. An organism’s physical appearance is its phenotype
11. A purebred chicken with white feathers is crossed with a purebred chicken that has black feathers. Each of their offspring has both black and white feathers. Why does this happen?
Because of codominance, which means both alleles are dominant alleles
12. What is a mutation?
Changes in the gene or chromosomes
13. Which term refers to physical characteristics that are studied in genetics? traits
14. The different forms of a gene are called alleles
15. An organism that has two identical alleles for a trait is homozygous
16. A heterozygous organism has
Two different alleles for a single trait.

17. Chromosomes are made up of
Many genes joined together
18. Which of these traits is controlled by a gene with multiple alleles?
Blood type 1
19.What are multiple alleles?
When 2 or more alleles exist for a single trait
20. What controls variations in skin color among humans?
Many genes
21. Which combination of sex chromosomes results in a male human being?
X and y
22. Why are sex-linked traits more common in males than in females?
A recessive allele on the X chromosome will result in males having the trait
23. What is a pedigree?
a chart that traces the family members for a particular trait
24. Genetic disorders are caused by
Mutations in genes or abnormal number of chromosomes
25. Which genetic disorder causes the body to produce unusually thick mucus in the lungs and intestines?
Cystic fibrosis
26. What is a karyotype?
A picture of all chromosomes in a cell
27. Both parents of a child have type A blood. What might their child’s blood type be?
Type a or type o blood
28. Sex-linked genes are genes on
Sex Chromosomes -X
29. A carrier is a person who has
One dominant and one recessive allele
30. Hemophilia is caused by a(n)
Recessive allele on the X chromosome
31. Down syndrome most often occurs when-Chromosomes fail to split during meiosis
32. What genetic disorder results in abnormally shaped blood cells?
Sickle cell anemia
Use the diagram to answer each question .

33. Which trait—white flowers or purple flowers—is controlled by a dominant allele??
White flowers, it is capitalized
34. In which generation are the parents purebred? In which generation are they hybrids?
F1 is purebred, F2 is hybrid
35. In the F
1
generation, what is the genotype of the offspring? What is their phenotype?
Their genotype is 100% Ww, their phenotype is 100% white flowers
36. In the F
2
generation, what percent of the offspring have purple flowers? What is the genotype of the purple-flowered offspring? 25%, ww
37. Suppose one of the parents of the F
2
generation had been ww instead of Ww . What percent of the offspring would have purple flowers? What percent would have white flowers?
50% white
Use the diagram to answer each question .
38. What do the circles in the pedigree represent? What do the squares represent?

Circles represent a female , square represents a male, fully shades has the trait, half shaded is a carrier