Honors Genetics Test Review
1. What is the probability of flipping heads 4 times in a row? What is the probability of rolling a 6, six times in a row?
1/2 x 1/2 x 1/2 x 1/2 = 1/16.
1/6 x 1/6 x 1/6 x 1/6 x 1/6 x 1/6 = 1/46656
2. Curly hair is dominant to straight hair. A woman with heterozygous curly hair marries a man with straight hair. List
the genotypic and phenotypic ratios of their possible offspring.
Bb x bb =
Genotypic Ratios = 50% Bb 50% bb
Phenotypic Ratios = 50% curly hair: 50% straight hair
3. In some chickens, the gene for feather color is controlled by codominance. The allele for black is B and the allele for
white is W. The heterozygous phenotype is known as erminette.
*What is the genotype for black chickens? White chickens? Erminette chickens?
Black = BB White = WW Erminette = BW
4. Suppose you have two rose plants, both with pink flowers. You cross the two plants and are surprised to find that, while
most of the offspring are pink, some are red and some are white. What type of inheritance is this?
The is incomplete dominance
5. The normal body cell of a tiger has 38 chromosomes.
a. How many come from each parent? B. How many will the gamete have? C. How many pairs of chromosomes
does an elephant have? D. What is the haploid #? E. What is the diploid #?
a. 19 from each parent. B. Each gamete will have 19. C. 19 pairs of chromosomes. D. 19 E. 38
6. What is the difference between diploid and haploid cells? Where do we have each type of cell? Why do we need each
type of cell?
Diploid cells contain two complete sets of chromosomes. You receive one set from your mother and one set from
your father. Haploid cells contain only one set of complete chromosomes. The haploid number is always half of
the diploid number. All of our body cells are diploid. Haploid cells are only found in our sex cells (gametes) which
are produced in our gonads. We need diploid cells in order to function properly. We need haploid cells in order to
pass on our genetics through sexual reproduction. When two haploid cells combine to produce an organism that
organism will now contain the diploid number of chromosomes.
7. What is the difference between mitosis and meiosis? Be specific here. What is the purpose of each, the end product, the
differences between specific stages, etc.
Mitosis takes place in body cells and produces 2 diploid daughter cells that are identical to the parent cell.
Mitosis involves only 1 division. Mitosis does not change the number of chromosomes. Meiosis takes place in
the sex cells. It involves 2 different cell divisions and results in 4 different haploid daughter cells. Meiosis
reduces the chromosome number by half. During mitosis metaphase I, sister chromatids are separated and
pulled into opposite daughter cells. In meiosis metaphase I, homologous chromosomes are separated into
daughter cells. These daughter cells are now haploid. Meiosis goes through two complete phases of IPMAT.
8. What is karyotype? What is the karyotype notation for a normal, healthy female. A female with Down’s syndrome?
A karyotype shows the complete diploid set of chromosomes grouped together in pairs, arranged in order of
decreasing size. 46 XX 47 XX 21+
9. What is nondisjunction? When does/can this occur and what are the results? Illustrate an example of nondisjunction in
meiosis.
Nondisjunction is the failure of homologous chromosomes to separate correctly during anaphase I of meiosis.
The results are daughter cells that have abnormal number of chromosomes. One may have too many and one
may have too few. The far ranging results are organisms that have a disease of abnormal chromosome number
such as Klinefelter syndrome or Down syndrome. During meiosis, if chromosome 21 fails to separate
homologous chromosomes correctly, a child with Down Syndrome may result.
10. Illustrate the stages of meiosis, denoting what is occurring in each stage, and whether each stage is haploid or diploid.
11. What is the principle of independent assortment? What is the “coin flip?” Which phase of meiosis does it occur in?
The principle of independent assortment states that genes for different traits can segregate independently during
the formation of gametes. The coinflip is the random assortment of homologous chromosomes during
metaphase I of meiosis.
12. What is the difference between co-dominance and incomplete dominance?
Codominance is a type of inheritance where none of the alleles is dominant over the other. When you get a
heterozygote, the phenotype will show both of the codominant alleles. An example of this would be an erminette
chicken that shows both black and white alleles. Incomplete dominance is a type of inheritance where neither
alleles is dominant and the heterozygote will show a mixture of the two alleles. An example of this would be 4
o’clock flowers. The homozygous phenotypes are red and white but when you mix these to produce the
heterozygote you get a flower that is pink.
13. You are crossing a homozygous dominant tall, heterozygous purple plant with a heterozygous tall, heterozygous purple
plant. Find the phenotypes and genotypes possible.
TTPp x TtPp = TTPP ; TTPp ; TTpp ; TtPP ; TtPp ; Ttpp
Phenotypes possible. Tall purple and Tall white
14. Using a punnett square, show all the blood types possible for a cross between a heterozygous A man and a heterozygous B
woman.
IAi x IBi = IAIB AB blood, IAi A blood, IBi B blood, ii O blood
15. Hemophilia is a sex-linked trait. A woman who is a carrier for hemophilia marries a man who is normal. Using a punnett
square, list all possibilities for genotypes and phenotypes of their offspring.
XBXb x XBY = XBXB XBXb XBY XbY
Phenotypes: Normal female, Normal female (carrier) , Normal male , hemophiliac male
16. What is crossing over? When does it happen? When won’t it happen?
Occurs when homologous chromosomes physically cross over one another and exchange genetic material. It occurs
during Prophase I of meiosis. It will not happen during Prophase II of meiosis.
17. Review ALL your vocabulary!!!!!!!