WORKSHEET
7.1-7.2
SECTION 7.1 - CHROMOSOMES AND PHENOTYPE
1. In humans, how does a gamete from a male determine the sex of offspring?
A female can only pass on X chromosomes, but a male can pass on either X or Y chromosomes.
2. What type of genes are on the Y chromosome?
Male characteristics
3. What are the patterns of expression for sex-linked genes?
Males will express all sex-linked genes because they have only one copy of each gene. females express sexlinked genes similar to autosomal genes. However, one X chromosome in each cell is randomly turned off.
4. What is a carrier
A carrier has one normal, dominant allele and one recessive, disease-causing allele, and does not have the
disorder but can pass it on to an offspring.
5. What is X chromosome inactivation?
In females, one of the two X chromosomes in every cell is randomly “turned off.”
6. What are sex-linked genes?
Genes on the sex chromosomes
7. What are sex chromosomes?
Chromosomes that determine an organism’s sex
8. What are autosomes?
All other chromosomes that do not directly affect an organism’s sex
9. How is a carrier different from a person who has a genetic disorder?
A carrier does not show symptoms of a disorder but can pass the disorder to offspring
10. How might a scientist determine whether a trait is sex-linked by observing the offspring of several genetic crosses?
If more males than females have a particular phenotype, the trait is probably sex-linked
11. What are sex-linked genes
Genes that are located on the sex chromosomes
12. What is a polygenic trait?
A trait produced by two or more genes.
13. Fill out the two Punnett squares below and write inside the possible genotypes for the offspring (DD, Dd and/or dd),
and also write in the phenotype (no disorder, carrier, or disorder) inside for each box.
Autosomal Recessive
Autosomal Dominant
D
d
D
DD,
no disorder
Dd
carrier
d
Dd
carrier
Dd
disorder
D
d
D
DD
disorder
Dd
disorder
d
Dd
disorder
dd,
no disorder
14. Fill in the Punnett square below to show the pattern of inheritance for sex chromosomes.
Sex Chromosome Inheritance
X
Y
X
X
XX
female
XX
female
XY
Male
XY
male
SECTION 7.2 – COMPLEX PATTERNS OF INHERITANCE
15. What is incomplete dominance?
Two alleles interact to produce an intermediate phenotype
16. What is codominance?
Two alleles are both completely and separately expressed
17. What is a polygenic trait?
A trait produced by two or more genes
18. How is codominance the same as having no dominant and recessive relationship at all between two alleles?
Both are neither completely dominant nor completely recessive. Incomplete dominance produces an
intermediate phenotype; codominance produces both traits in a phenotype.
19. Describe what happens in epistasis.
One gene affects the expression of other genes
20. How is incomplete dominance different from a dominant and recessive relationship?
In incomplete dominance neither allele is completely dominant nor is one allele not hidden in a heterozygote.
The heterozygous phenotype is somewhere between the homozygous phenotypes
21. How is codominance different from a dominant and recessive relationship?
In codominance both alleles are completely expressed and the heterozygous phenotype contains the separate
products of both alleles.
22. What is a multiple-allele trait?
A trait for which a gene has more than two alleles
23. Provide an example of incomplete dominance
Betta fish (green, steel blue, royal blue); 4 o’clock plant (white, red, pink)
24. Provide an example of codominance
Blood type (A, B, AB,)
25. List and explain two examples of how environment and genotype can interact.
Sex determination in sea turtles depends on both genes and the temperature at which sea turtle eggs mature.
Human height is affected both by genes and such factors as nutrition and health care.