BIOL 113
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1. What is Mendel's Law of Segregation?: The two forms of a gene (alleles) present in each parent
segregate independently.
2. What experimental results led to the formulation of Mendel's Law of Segre-
gation?: Results from monohybrid crosses between true-breeding individuals differing in one character, where al
F1 progeny resembled one parent, and both parental traits appeared in the F2 generation in a 3:1 ratio.
3. What is the significance of dominant and recessive traits in Mendelian inher-
itance?: One trait is dominant and masks the recessive trait, which is not lost in the F1 generation.
4. What is Mendel's Law of Independent Assortment?: Each pair of alleles assorts indepen-
dently of each other during gamete formation.
5. How was Mendel's Law of Independent Assortment formulated?: It was formulated
by studying the inheritance of two characters simultaneously through dihybrid crosses, resulting in a 9:3:3:1 phenotypic
ratio.
6. What would happen if independent assortment did not occur?: The alleles for two
traits would be inherited together, resulting in only two types of gametes and no recombinants in the F2 generation.
7. How does segregation of alleles account for the outcome of a monohybrid
cross?: Each organism has two alleles that segregate during gamete formation, leading to four different combina-
tions in the offspring, three of which contain the dominant allele.
8. What is a testcross and how is it used?: A testcross determines the genotype of an individual with
a dominant phenotype by crossing it with a homozygous recessive individual.
9. What are the expected outcomes of a testcross if the dominant phenotype
individual is heterozygous?: The F1 progeny would show a 50-50 outcome of two phenotypes.
10. What are the expected outcomes of a testcross if the dominant phenotype
individual is homozygous?: The F1 progeny would be 100% the dominant phenotype.
11. How do you combine probabilities to solve complex genetic problems?: Mul-
tiply the individual probabilities for each trait.
12. What are the key events of interphase in meiosis?: Chromosomes replicate into homolo-
gous pairs to form a diploid cell.
13. What happens during Meiosis I?: Homologous chromosomes separate to form two haploid cells
with replicated chromosomes.
14. What happens during Meiosis II?: Sister chromatids separate into haploid cells with unreplicated
chromosomes.
, BIOL 113
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15. What are the main differences between meiosis and mitosis?: Mitosis occurs in
somatic cells with one division, producing two identical diploid cells; meiosis occurs in germ line cells with two divisions,
producing four non-identical haploid gametes.
16. What is unique to meiosis that is not found in mitosis?: Synapsis, the pairing of
homologous chromosomes.
17. What is the chromosomal theory of inheritance?: Mendel's heritable factors (genes) are
located at specific positions (loci) on chromosomes, which undergo segregation and independent assortment.
18. How do Mendel's Laws relate to the behavior of chromosomes during meio-
sis?: Sutton linked chromosome behavior during meiosis to Mendel's laws, observing that chromosome pairs
segregate equally into gametes and assort independently.
19. What explains Mendel's Law of Segregation in terms of chromosome behav-
ior?: Each allele is on a different member of a homologous pair of chromosomes and moves to opposite poles during
anaphase I.
20. What explains Mendel's Law of Independent Assortment in terms of chro-
mosome behavior?: Homologous pairs line up randomly on the metaphase plate during meiosis I, leading
to equal probabilities of genotype combinations in gametes.
21. What are the main sources of genetic variability in sexually reproducing
organisms?: Mutation, independent assortment, crossing-over, random fertilization.
22. What is crossing over and when does it occur during meiosis?: Crossing over is
the process of genetic recombination that occurs during the pachytene phase of prophase I, where homologous
chromosomes exchange genetic information at the chiasma.
23. How does linkage interfere with independent assortment?: Linked genes are located
on the same chromosome and tend to be inherited together, violating the principle of independent assortment during
gamete formation.
24. What are some reasons for deviations from Mendelian ratios?: Sex-linkage, incom-
plete dominance, co-dominance, pleiotropy, polygenic inheritance, and epistasis.
25. What is the difference between incomplete dominance and co-dominance?-
: Incomplete dominance occurs when a dominant allele does not completely mask a recessive allele, resulting in
an intermediate phenotype (e.g., snapdragon flower color). Co-dominance occurs when both alleles are expressed
distinctly in the phenotype (e.g., ABO blood group system).
26. What is pleiotropy?: Pleiotropy is when a single gene has multiple effects on the phenotype, such as a
pea gene affecting both flower and seed color.
, BIOL 113
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27. What is polygenic inheritance?: Polygenic inheritance is when a single trait is determined by
multiple genes, resulting in continuous variation in the population.
28. Give examples of polygenic inheritance in humans.: Height, weight, skin pigmentation,
hair color, eye color.
29. What is epistasis and how does it affect Mendelian ratios in a dihybrid
cross?: Epistasis occurs when one gene masks or modifies the expression of another gene, leading to modified
ratios, such as a 9:3:4 ratio in mice coat color.
30. Why is a recessive sex-linked gene always expressed in male Drosophila or
humans?: Males have only one X chromosome, so a recessive allele on the X is expressed, while females need two
copies of the allele for expression.
31. What are the steps to make a karyotype?: 1. Draw blood and culture in growth medium. 2. Add
phytohemagglutinin to stimulate mitosis. 3. Treat with colcemid to stop mitosis. 4. Centrifuge and lyse cells. 5. Stain
and examine chromosomes under a microscope.
32. Distinguish between aneuploidy and polyploidy.: Polyploidy involves extra whole sets of
chromosomes, while aneuploidy involves missing or extra individual chromosomes.
33. What causes aneuploidy?: Aneuploidy is caused by non-disjunction of homologous chromosomes
during meiosis I or sister chromatids during meiosis II.
34. What are some features associated with Down's syndrome?: Characteristic facial
features, short stature, learning disabilities, heart defects, susceptibility to leukemia and Alzheimer's, and growth failure.
35. What is Turner's syndrome and how does it demonstrate the role of the
Y chromosome in sex determination?: Turner's syndrome (XO) occurs when there is a missing X
chromosome in females, demonstrating the necessity of at least one X for female development.
36. What is Klinefelter's syndrome and its relation to the Y chromosome?: Kline-
felter's syndrome (XXY) occurs in males with an extra X chromosome, showing that the presence of a Y chromosome
determines male sex characteristics.
37. What is the modified phenotypic ratio resulting from incomplete domi-
nance?: The modified phenotypic ratio is 1:2:1.
38. How does epistasis modify the expected Mendelian ratio?: Epistasis can lead to
modified ratios such as 9:3:4 instead of the expected 9:3:3:1 in a dihybrid cross.
39. What is the significance of the synaptonemal complex during crossing over?-
: The synaptonemal complex is a protein structure that holds homologous chromosomes together during synapsis,
facilitating crossing over.
Study online at https://quizlet.com/_htkstb
1. What is Mendel's Law of Segregation?: The two forms of a gene (alleles) present in each parent
segregate independently.
2. What experimental results led to the formulation of Mendel's Law of Segre-
gation?: Results from monohybrid crosses between true-breeding individuals differing in one character, where al
F1 progeny resembled one parent, and both parental traits appeared in the F2 generation in a 3:1 ratio.
3. What is the significance of dominant and recessive traits in Mendelian inher-
itance?: One trait is dominant and masks the recessive trait, which is not lost in the F1 generation.
4. What is Mendel's Law of Independent Assortment?: Each pair of alleles assorts indepen-
dently of each other during gamete formation.
5. How was Mendel's Law of Independent Assortment formulated?: It was formulated
by studying the inheritance of two characters simultaneously through dihybrid crosses, resulting in a 9:3:3:1 phenotypic
ratio.
6. What would happen if independent assortment did not occur?: The alleles for two
traits would be inherited together, resulting in only two types of gametes and no recombinants in the F2 generation.
7. How does segregation of alleles account for the outcome of a monohybrid
cross?: Each organism has two alleles that segregate during gamete formation, leading to four different combina-
tions in the offspring, three of which contain the dominant allele.
8. What is a testcross and how is it used?: A testcross determines the genotype of an individual with
a dominant phenotype by crossing it with a homozygous recessive individual.
9. What are the expected outcomes of a testcross if the dominant phenotype
individual is heterozygous?: The F1 progeny would show a 50-50 outcome of two phenotypes.
10. What are the expected outcomes of a testcross if the dominant phenotype
individual is homozygous?: The F1 progeny would be 100% the dominant phenotype.
11. How do you combine probabilities to solve complex genetic problems?: Mul-
tiply the individual probabilities for each trait.
12. What are the key events of interphase in meiosis?: Chromosomes replicate into homolo-
gous pairs to form a diploid cell.
13. What happens during Meiosis I?: Homologous chromosomes separate to form two haploid cells
with replicated chromosomes.
14. What happens during Meiosis II?: Sister chromatids separate into haploid cells with unreplicated
chromosomes.
, BIOL 113
Study online at https://quizlet.com/_htkstb
15. What are the main differences between meiosis and mitosis?: Mitosis occurs in
somatic cells with one division, producing two identical diploid cells; meiosis occurs in germ line cells with two divisions,
producing four non-identical haploid gametes.
16. What is unique to meiosis that is not found in mitosis?: Synapsis, the pairing of
homologous chromosomes.
17. What is the chromosomal theory of inheritance?: Mendel's heritable factors (genes) are
located at specific positions (loci) on chromosomes, which undergo segregation and independent assortment.
18. How do Mendel's Laws relate to the behavior of chromosomes during meio-
sis?: Sutton linked chromosome behavior during meiosis to Mendel's laws, observing that chromosome pairs
segregate equally into gametes and assort independently.
19. What explains Mendel's Law of Segregation in terms of chromosome behav-
ior?: Each allele is on a different member of a homologous pair of chromosomes and moves to opposite poles during
anaphase I.
20. What explains Mendel's Law of Independent Assortment in terms of chro-
mosome behavior?: Homologous pairs line up randomly on the metaphase plate during meiosis I, leading
to equal probabilities of genotype combinations in gametes.
21. What are the main sources of genetic variability in sexually reproducing
organisms?: Mutation, independent assortment, crossing-over, random fertilization.
22. What is crossing over and when does it occur during meiosis?: Crossing over is
the process of genetic recombination that occurs during the pachytene phase of prophase I, where homologous
chromosomes exchange genetic information at the chiasma.
23. How does linkage interfere with independent assortment?: Linked genes are located
on the same chromosome and tend to be inherited together, violating the principle of independent assortment during
gamete formation.
24. What are some reasons for deviations from Mendelian ratios?: Sex-linkage, incom-
plete dominance, co-dominance, pleiotropy, polygenic inheritance, and epistasis.
25. What is the difference between incomplete dominance and co-dominance?-
: Incomplete dominance occurs when a dominant allele does not completely mask a recessive allele, resulting in
an intermediate phenotype (e.g., snapdragon flower color). Co-dominance occurs when both alleles are expressed
distinctly in the phenotype (e.g., ABO blood group system).
26. What is pleiotropy?: Pleiotropy is when a single gene has multiple effects on the phenotype, such as a
pea gene affecting both flower and seed color.
, BIOL 113
Study online at https://quizlet.com/_htkstb
27. What is polygenic inheritance?: Polygenic inheritance is when a single trait is determined by
multiple genes, resulting in continuous variation in the population.
28. Give examples of polygenic inheritance in humans.: Height, weight, skin pigmentation,
hair color, eye color.
29. What is epistasis and how does it affect Mendelian ratios in a dihybrid
cross?: Epistasis occurs when one gene masks or modifies the expression of another gene, leading to modified
ratios, such as a 9:3:4 ratio in mice coat color.
30. Why is a recessive sex-linked gene always expressed in male Drosophila or
humans?: Males have only one X chromosome, so a recessive allele on the X is expressed, while females need two
copies of the allele for expression.
31. What are the steps to make a karyotype?: 1. Draw blood and culture in growth medium. 2. Add
phytohemagglutinin to stimulate mitosis. 3. Treat with colcemid to stop mitosis. 4. Centrifuge and lyse cells. 5. Stain
and examine chromosomes under a microscope.
32. Distinguish between aneuploidy and polyploidy.: Polyploidy involves extra whole sets of
chromosomes, while aneuploidy involves missing or extra individual chromosomes.
33. What causes aneuploidy?: Aneuploidy is caused by non-disjunction of homologous chromosomes
during meiosis I or sister chromatids during meiosis II.
34. What are some features associated with Down's syndrome?: Characteristic facial
features, short stature, learning disabilities, heart defects, susceptibility to leukemia and Alzheimer's, and growth failure.
35. What is Turner's syndrome and how does it demonstrate the role of the
Y chromosome in sex determination?: Turner's syndrome (XO) occurs when there is a missing X
chromosome in females, demonstrating the necessity of at least one X for female development.
36. What is Klinefelter's syndrome and its relation to the Y chromosome?: Kline-
felter's syndrome (XXY) occurs in males with an extra X chromosome, showing that the presence of a Y chromosome
determines male sex characteristics.
37. What is the modified phenotypic ratio resulting from incomplete domi-
nance?: The modified phenotypic ratio is 1:2:1.
38. How does epistasis modify the expected Mendelian ratio?: Epistasis can lead to
modified ratios such as 9:3:4 instead of the expected 9:3:3:1 in a dihybrid cross.
39. What is the significance of the synaptonemal complex during crossing over?-
: The synaptonemal complex is a protein structure that holds homologous chromosomes together during synapsis,
facilitating crossing over.
