monohybrid cross

1. What percentage of individuals of roan suit can be obtained by crossing cattle of red (AA) and white (aa) suit with incomplete dominance

Task 6 No. 2301

Explanation.

R: AA x aa

G: A a

F: Aa – 100%

With incomplete dominance, heterozygotes have an intermediate trait.

Correct answer – 100%

Answer: 100|100%

100|100%

Source: RESHU USE

2. What percentage of night beauty plants with pink flowers can be expected from crossing plants with red (A) and white (a) flowers (incomplete dominance)

Task 6 No. 2302

Explanation.

R: AA x aa

G: A a

F: Aa – 100%

With incomplete dominance, heterozygotes have an intermediate trait.

In this case, it does not matter at all which of the signs is dominant white or red. The main thing is that when they are crossed with each other in the offspring, we will get 100% of plants with an intermediate trait Aa – pink.

Answer: 100|100%

100|100%

Source: RESHU USE

3. Determine the ratio of genotypes in the offspring when crossing heterozygous plants of the night beauty

Task 6 No. 2303

Explanation.

R: Aa x Aa

G: A A

a a

F: AA 2Aa aa

According to Mendel’s second law, when heterozygous plants are crossed, the offspring split according to the genotype 1:2:1

Answer: 1:2:1|1 : 2 : 1|121|211|2:1:1

1:2:1|1 : 2 : 1|121|211|2:1:1

Source: RESHU USE

4. Homozygous dominant gray sheep die when switching to roughage, while heterozygous ones survive. Determine the genotype of a gray viable individual

Task 6 No. 2316

Explanation.

The task describes one trait, heterozygotes survive, which means the Aa genotype

Answer: Aa

Aa|Aa

Source: RESHU USE

5. During self-pollination of a heterozygous tall pea plant (high stem – A), the proportion of dwarf forms is (%)

Task 6 No. 2319

Explanation.

R: Aa x Aa

G: A A

a a

F 2: AA 2Aa aa

According to Mendel’s second law, when heterozygous organisms are crossed, the offspring split according to the genotype 1:2:1, according to the phenotype 1:3, i.e., 25% of recessive individuals appear in the offspring.

Answer: 25|25%

25|25%

Source: RESHU USE

6. What is the probability (%) of having tall children in heterozygous parents with short stature (short stature dominates tall stature)

Task 6 No. 2324

Explanation.

R: Aa x Aa

G: A A

a a

F: AA 2Aa aa

According to Mendel’s second law, when heterozygous organisms are crossed, the offspring split according to the genotype 1:2:1, according to the phenotype 1:3, i.e., 25% of recessive individuals appear in the offspring.

Answer: 25|25%

25|25%

Source: RESHU USE

7. When a plant heterozygous for one pair of traits is crossed with a homozygous one, the proportion of homozygotes in the offspring will be

Task 6 No. 2332

Explanation.

R: aa x aa

G: a A

a a

F: Aa aa

50% 50%

With such a crossing, 50% heterozygotes and 50% homozygous recessive individuals are obtained.

OR

R: AA x Aa

G: A A a

F: AA Aa

50% 50%

With such a crossing, 50% heterozygotes and 50% homozygous dominant individuals are obtained.

Answer: 50|50%

50|50%

Source: RESHU USE

8. What number of phenotypes is formed in the offspring when crossing Aa x Aa in case of complete dominance?

Write down a number for your answer.

Task 6 No. 2333

Explanation.

R: Aa x Aa

G: A a A a

F: AA 2Aa aa

According to the second law of Mendel (the law of splitting), when heterozygous organisms are crossed in the offspring, splitting occurs according to the genotype 1:2:1, according to the phenotype 1:3, which means that 2 varieties of phenotypes are formed.

Answer: 2

Source: RESHU USE

9. What is the probability (in %) of dark-haired parents (Aa) having children with blond hair (dark color dominates over light)?

Task 6 No. 2334

Explanation.

R: Aa x Aa

G: A A

a a

F: AA 2Aa aa

According to Mendel’s second law, when heterozygous organisms are crossed, the offspring splits according to the genotype 1:2:1, according to the phenotype 1:3, i.e. 25% of recessive individuals (fair-haired) appear in the offspring

Answer: 25|25%

25|25%

Source: RESHU USE

10. Determine the ratio of phenotypes in offspring in a monohybrid crossing of two heterozygous organisms with complete dominance. Write down the answer in the form of a sequence of numbers showing the ratio of the resulting phenotypes, in descending order.

Task 6 No. 20468

Explanation.

When monohybrid crossing of two heterozygous organisms with complete dominance, the ratio of phenotypes is 3: 1 (Mendel’s splitting rule)

Answer: 31

Answer: 31

Source: Demo version of the USE-2017 in biology.

11. How many alleles of one gene does the egg of a flowering plant contain?

Write down only the appropriate number in your answer.

Task 6 No. 20781

Explanation.

each gamete contains only one allele of each gene.

Answer: 1

Source: RESHU USE

12. How many different phenotypes are obtained by self-pollination of plants with pink corolla petals (heterozygote) in case of incomplete dominance?

Task 6 No. 20956

Explanation.

When self-pollinating plants with pink corolla petals in case of incomplete dominance

Aa x Aa we get 3 phenotypes: AA red; Aa pink; aa white

Note.

The manifestation of the trait (color) is not important, you need to know that when heterozygotes self-pollinate with incomplete dominance, 3 phenotypes are obtained

Answer: 3

Source: Typical test tasks in biology, edited by G. S. Kalinov, T. V. Mazyarkin. 10 options for tasks. 2017

13. The round shape of the fruit of the tomato dominates over the pear-shaped, the red color of the fruit – over the yellow. Determine the genotype of a tomato with pear-shaped yellow fruits.

Task 6 No. 21127

Explanation.

pear-shaped and yellow fruits are recessive traits, so the genotype is aabb

Answer: aabb

aabb|aabb

Source: RESHU USE

14. What is the probability of birth (in%) of healthy boys in a family where the mother is healthy and the father is sick with hypertrichosis, a disease caused by the presence of a gene linked to the Y chromosome?

Task 6 No. 21264

Explanation.

because this gene is linked to the Y chromosome, then all sons will be sick with hypertrichosis. This means that the probability of the birth of healthy boys in this family is 0%

Answer: 0

Source: RESHU USE

15. In humans, protruding ears (B) dominate over the gene for normally closed ears (b). What is the father’s genotype if the mother’s genotype is bb, and among their children there were 50% lop-eared and 50% with normally flattened ears?

Task 6 No. 21273

Explanation.

In order to establish the “purity” of the organism, an analyzing cross is carried out, in which the studied individual with dominant traits is crossed with a recessive homozygote (bb). If the offspring from such a crossing turns out to be homogeneous, then the individual is homozygous (its genotype is BB). If in the offspring there are 50% of individuals with dominant traits, and 50% with recessive ones, then the individual is heterozygous (its Bb genotype).

Genotype of parents, for example, mother ♀ bb; father ♂ Bb

Answer: Вв|Bb

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