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Mendelian Genetics/Pedigree/Meiosis Study Guide
heredity: the passing on of characteristics from parents to offspring through genes
traits: characteristics that are inherited
genes: a section on DNA that carries the information on what type of protein to make
genetics: the branch of biology that studies heredity
gamete: male and female sex cells; male = sperm, female =egg
monohybrid cross: when only one trait is compared, like eye color
allele: the different forms of a single gene—eye color has brown, blue, and green alleles
hybrid: when an organism has inherited different alleles from each parent (1 allele for brown
eyes, 1 for blue)
homozygous: when 2 alleles for a trait are the same
heterozygous: when 2 alleles for a trait are not the same
2. Who is regarded as the father of genetics? Gregor Mendel
3. What are Mendel’s 4 laws? Law of segregation, Law of Unit Factors, Law of Dominance, Law of
Independent assortment.
4. What is a dominant trait and how is it represented? “stronger” trait that shows up when the dominant
allele is present; represented by a capital letter
5. What is a recessive trait and how is it represented? “weaker” trait that shows up only when the
dominant allele is not present; represented by a lowercase letter
6. What is a phenotype? the physical appearance of an organism—what you can see
7. What is a genotype? genetic makeup of an organism—what you usually cannot see
8. What did Mendel experiment on? Pea Plants
Monohybrid Punnett Square
9. Matt recently met a cute brown-haired girl, Kayli, in Biology class. Use your knowledge of genetics to
answer the questions below.
(a) If Kayli’s father is a heterozygous (Bb) brown-haired and her mother has blonde hair (bb), what is her
genotype? Bb because she gets dominant from dad and recessive from mom. Heterozygous brown-haried
Create and complete the Punnett square to show the possible genotypes that would result to help
you determine Kayli’s genotype.
B
b
b
Bb
bb
Bb
bb
b
(b) Matt is heterozygous for his brown hair. What is his genotype? Bb
(c) Complete a Punnett square to show the possibilities that would result if Matt & Kayli had
children.
B
b
B
b
BB
Bb
Bb
bb
(d) List the possible genotypes and phenotypes for the kids. BB- Homozygous brown hair
Bb- Heterozygous Brown
bb- Homozygous Blonde
(e) What is the probability of kids with blonde hair? ¼ or 35%
(f) What is the probability of kids with brown hair? ¾ or 75%
10. Explain how a person inherits a recessive disorder. Both alleles must be recessive in the person to
inherit a recessive disorder.
11. Explain how a person inherits a dominant disorder. At least one of the alleles from mom or dad must
be dominant and present in the person.
12. What is a pedigree? When genetic inheritance is represented by a picture
***You also need to know how to read one.
13. Explain cystic fibrosis. What race does it mainly affect? A defective protein in the plasma
membrane of cells causes thick mucus to build up in the lungs and digestive system; white
Americans
14. Explain Tay-Sachs Disease. In some cases, when does death occur to a person with it? An absence of
an enzyme causes lipids to accumulate in the tissues and nerve cells of the brain; age 4
15. What happens to a person with Huntington’s disease? When do the symptoms start to appear?
Certain parts of their brain start to break down; Ages 30-50
16. If you see a phenotype that is a mixture of two dominant traits, is this codominance or incomplete
dominance? Ex. Red (R) and white (W) flower color produces a pink (RW) flower. Incomplete
17. If you see a phenotype that is shows both of the two dominant traits, is this codominance or
incomplete dominance? Ex. Black (B) and white (W) cats produce a white cat with black spots (BW).
Codominance
18. What is a sex-linked disorder? A disorder controlled by genes on a sex chromosome
19. Explain X-linked inheritance. . When a defective gene is carried on the X chromosome; passed along
from mother
20. Explain Y-linked inheritance. When a defective gene is carried on the X chromosome; passed along
only from father to son
21. What does polygenic inheritance mean? Would eye color and height be an example? When a trait is
determined by many genes; yes
22. In a karyotpe (a map of all of a person’s chromosomes), which ones are autosomes? Pairs 1-2223.
23. What are the 8 factors that can also influence gene expression?
1. Temperature
5. Infectious agents
2. Light
6. Hormones
3. Nutrition
7. Structural differences
4. Chemicals
8. Age
24.
1. diploid: a cell with two of each kind of chromosome
2. haploid: a cell with one of each kind of chromosome
3. meiosis: cell division that produces gametes (egg or sperm) containing half the number of
chromosomes as a parent’s body cell
4. sexual reproduction: type of reproduction that involves the production and fusion of egg and
sperm
5. homologous chromosomes: the two chromosomes of each pair in a diploid cell
6. crossing over: process that occurs during meiosis in which parts of the chromatids that make up
the homologous chromosomes break off and exchange their genetic information
7. genetic recombination: random reassortment of chromosomes and the genetic information they
carry during meiosis that provides a lot of variation (differences) in organisms.
8. nondisjunction: when homologous chromosomes fail to separate properly
9. Polyploidy: organisms with more than the usual number of chromosome sets; this is more
common in plants than in animals
25. A. What is the difference between a diploid cell and a haploid cell? Diploid has 2 of each
chromosome and are body cells whereas a haploid has 1 of each chromosome and are gametes
B. When diploid cells divide, what is this called? What about when haploid cells divide? mitosis;
meiosis
26. What gamete comes from a father? Sperm From a mother? Egg
27. Make a chart of the stages of meiosis (in order) and what happens during each phase.
Steps
Prophase I
Metaphase I
Anaphase I
What Happens
Tetrads condense and crossing over occurs
Tetrads line up in the middle
Tetrads split and move to opposite ends of the cell
Telophase I/
Cytokinesis
Prophase II
Metaphase
II
Anaphase II
Telophase
II/
Cytokinesis
2 separate daughter cells are made, each with a set of
homologous chromosomes that have been genetically mixed
(haploid)
Centrosomes appear and spindle fibers are formed
Replicated Chromosomes line up in the middle of the cell
Replicated Chromosomes separate and move to opposite ends of
the cell
New nuclei are formed and four daughter cells are made, each
containing one-half of replicated chromosome (Haploid)
28. Compare/contrast mitosis & meiosis.
Mitosis
o Division of body cells
Both
o Types of cell division
o Make 2 identical
diploid cells
o Contain chromosomes
o Used for growth,
repair, and
replacement
o Interphase
Meiosis
o Division of sex
cells (gametes)
o Make 4 nonidentical haploid
cells
o Used for
reproduction