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Summary of the Chapter-8-Heredity with Key-Points:
- Variations that occur during reproduction can be passed down to offspring.
- These variations may enhance the chances of survival for individuals.
- In sexually reproducing organisms, each trait is represented by two copies of a gene. If these gene copies differ, the dominant trait is the one that is expressed, while the other is considered recessive.
- Traits in an individual may be inherited independently, leading to new combinations of traits in the offspring during sexual reproduction.
- Sex determination varies across species. In humans, the sex of the child is decided by the father's chromosome: an X chromosome results in a girl, while a Y chromosome results in a boy.
1. Which of the following processes maximizes the number of successful variations in a species?
a) Asexual reproduction
b) Sexual reproduction
c) Binary fission
d) Budding
Explanation: Sexual reproduction combines genetic material from two parents, resulting in greater diversity in the offspring, which can increase the chances of survival under varying environmental conditions.
2. In Mendel’s experiments, what trait was dominant in the first-generation (F1) pea plants?
a) Shortness
b) Medium height
c) Tallness
d) Wrinkled seeds
Explanation: Mendel's experiments demonstrated that tallness is the dominant trait, which appeared in the F1 generation when tall and short pea plants were crossed.
3. What determines the sex of a child in humans?
a) Mother's X chromosome
b) Father's Y chromosome
c) Mother's mitochondria
d) Environmental factors
Explanation: The sex of a child is determined by the father’s contribution. If the father provides an X chromosome, the child will be female (XX); if he provides a Y chromosome, the child will be male (XY).
4. What is a gene?
a) A section of RNA
b) A type of protein
c) A section of DNA that codes for a protein
d) A section of DNA that makes a hormone
Explanation: A gene is a segment of DNA that contains instructions for synthesizing proteins, which in turn control traits.
5. In Mendel's dihybrid cross, which combination of traits appeared in the F2 generation that were not present in the parent generation?
a) Short plants with wrinkled seeds
b) Tall plants with round seeds
c) Short plants with round seeds
d) All progeny were identical to the parents
Explanation: Mendel’s dihybrid cross showed that traits such as plant height and seed shape are independently inherited. New combinations like short plants with round seeds were observed in the F2 generation.
6. Which of the following best explains why variation is important for the survival of species?
a) Variation leads to identical individuals
b) Variation ensures that all organisms are perfectly adapted to their environment
c) Variation allows some individuals to survive and reproduce in changing environments
d) Variation reduces the chances of reproduction
Explanation: Variations provide differences among individuals that may offer survival advantages in different environmental conditions, promoting natural selection.
7. What type of trait is expressed when only one copy of the gene is enough to show the characteristic?
a) Recessive trait
b) Dominant trait
c) Co-dominant trait
d) Incomplete dominant trait
Explanation: A dominant trait is expressed even when only one copy of the gene (allele) is present. For example, in Mendel’s experiments, tallness was dominant over shortness.
8. What do we inherit from both parents that help determine our traits?
a) Genes
b) Hormones
c) Organelles
d) Proteins
Explanation: Genes, which are made of DNA, are inherited from both the father and the mother. These genes determine various traits of the offspring.
9. Which of the following is NOT true regarding asexual reproduction?
a) Offspring are genetically identical to the parent
b) There is very little variation in the population
c) Two parents are involved
d) It occurs in organisms like bacteria
Explanation: Asexual reproduction involves only one parent, and the offspring are typically genetically identical to the parent.
10. If a parent with blood group A and another parent with blood group O have a child with blood group O, what can be inferred?
a) Blood group A is recessive
b) Blood group O is dominant
c) Blood group A is dominant
d) Both blood groups A and O are co-dominant
Explanation: Blood group O is recessive, and blood group A is dominant. If the child has blood group O, both parents must carry the O gene, and the A gene from one parent is not expressed in the child.
11. What type of reproduction results in the greatest genetic diversity?
a) Asexual reproduction
b) Budding
c) Sexual reproduction
d) Binary fission
Explanation: Sexual reproduction leads to genetic diversity because it involves the combination of genetic material from two different parents.
12. What is the term used to describe the passing on of traits from parents to offspring?
a) Variation
b) Mutation
c) Heredity
d) Adaptation
Explanation: Heredity refers to the process by which traits are passed from parents to their offspring through genes.
13. What do you call a gene that is not expressed when a dominant gene is present?
a) Dominant gene
b) Recessive gene
c) Co-dominant gene
d) Carrier gene
Explanation: A recessive gene is only expressed when both alleles for a trait are recessive.
14. In a monohybrid cross, if a homozygous tall pea plant (TT) is crossed with a homozygous short pea plant (tt), what will the F1 generation look like?
a) All short
b) All tall
c) Half tall, half short
d) Medium height
Explanation: Since the tall allele (T) is dominant, all the offspring will display the tall phenotype.
15. Which of the following refers to a physical characteristic that is inherited?
a) Chromosome
b) Protein
c) Trait
d) DNA
Explanation: A trait is a physical characteristic such as eye color, height, or skin color that can be passed from parents to offspring.
16. Which of these traits is controlled by a dominant gene?
a) Free earlobes
b) Attached earlobes
c) Color blindness
d) Hemophilia
Explanation: Free earlobes are controlled by a dominant allele, while attached earlobes are controlled by a recessive allele.
17. Mendel used pea plants for his experiments because:
a) They take a long time to grow
b) They have distinct traits and are easy to pollinate
c) They are only available in one variety
d) They do not undergo genetic variations
Explanation: Mendel chose pea plants because they grow quickly, have distinct traits, and can be easily manipulated for cross-pollination.
18. In a dihybrid cross, how many different types of gametes are produced by a plant with the genotype RrYy?
a) 2
b) 4
c) 8
d) 16
Explanation: A plant with the genotype RrYy can produce four types of gametes: RY, Ry, rY, and ry.
19. The 3:1 ratio observed by Mendel in his monohybrid cross experiment was observed in which generation?
a) F1 generation
b) Parental generation
c) F2 generation
d) None of the above
Explanation: The 3:1 ratio of dominant to recessive traits appeared in the F2 generation when Mendel allowed F1 hybrid plants to self-pollinate.
20. What is the role of DNA in heredity?
a) It produces energy for cells
b) It carries genetic information from one generation to the next
c) It transports nutrients to cells
d) It forms the structure of proteins
Explanation: DNA stores and transmits genetic information, allowing heredity to occur.
21. Which of the following combinations will always produce an organism with a dominant phenotype?
a) TT and Tt
b) tt and Tt
c) tt and tt
d) Tt and Tt
22. Which scientist is considered the father of genetics?
a) Charles Darwin
b) Gregor Mendel
c) James Watson
d) Francis Crick
23. What is the phenotypic ratio of the F2 generation in a dihybrid cross?
a) 1:2:1
b) 3:1
c) 9:3:3:1
d) 1:1:1:1
24. Which of the following is true about a recessive allele?
a) It is always expressed
b) It is expressed only when both copies are recessive
c) It never influences phenotype
d) It only affects plants
25. Which of the following combinations of chromosomes determine a male in humans?
a) XX
b) XY
c) YY
d) XO
26. Which of the following is a possible genotype for an individual that is homozygous recessive for a trait?
a) AA
b) Aa
c) aa
d) A
27. How many pairs of chromosomes are present in human beings?
a) 20
b) 22
c) 23
d) 24
28. In Mendel’s experiments, what ratio did he observe for tall to short plants in the F2 generation?
a) 1:2
b) 3:1
c) 9:3
d) 2:2
29. What does a Punnett square predict?
a) The age of an organism
b) The genetic outcomes of a cross
c) The lifespan of an organism
d) The mutations in genes
30. Which type of inheritance pattern involves multiple genes controlling a single trait?
a) Polygenic inheritance
b) Incomplete dominance
c) Co-dominance
d) Simple dominance
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