Inheritance, Genes & Cell Division

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Chromosomes, Genes & Proteins

Inheritance is the transmission of genetic information from generation to generation.
Chromosomes are thread-like structures of DNA in the nucleus, carrying genes.
A gene is a short length of DNA on a chromosome that codes for a specific protein.
Alleles are different versions of the same gene; individuals inherit two alleles (one from each parent).
The sequence of bases in a gene determines the sequence of amino acids in a protein.

Zooming from cell to gene

The Inheritance of Sex

Sex is determined by the sex chromosomes: XX = female, XY = male.
The father determines the sex of offspring because he can pass on either an X or a Y chromosome.
Half of sperm carry X, half carry Y; if an X sperm fertilises the egg, the baby is female (XX); if a Y sperm, male (XY).
A Punnett square with X and Y chromosomes shows a 1:1 ratio of male:female offspring.

Karyotypes and inheritance of sex

Protein Synthesis (Extended)

Transcription: DNA base code is copied onto mRNA in the nucleus.
Translation: mRNA attaches to a ribosome; the ribosome reads codons (triplets) and assembles amino acids.
tRNA brings specific amino acids to the ribosome, matching anticodons to mRNA codons.
The amino acid chain folds to form a functional protein (e.g., enzyme, antibody).

Protein synthesis

Which Proteins are Synthesised? (Extended)

Gene expression controls whether a gene is transcribed/translated in a cell.
Most genes are 'switched off' to save energy; only essential genes are expressed.
All body cells contain the same genes, but different cells express different genes.
DNA controls cell function by directing protein production.

Mitosis

Mitosis is nuclear division producing two genetically identical daughter cells.
Chromosomes duplicate before division, then line up and are pulled apart.
Used for growth, repair, replacement of cells, and asexual reproduction.
Daughter cells are diploid (same chromosome number as parent).

Mitosis

Meiosis (Extended)

Meiosis is a reduction division producing four haploid gametes (genetically different).
Chromosomes duplicate, then the cell divides twice; homologous chromosomes separate in the first division.
Produces genetic variation via recombination and independent assortment.
Gametes (sperm, egg) have half the chromosome number of body cells.

Meiosis

Monohybrid Inheritance

Monohybrid inheritance involves a single gene with two alleles (dominant/recessive).
Genotype = allele combination; phenotype = observable characteristic.
Homozygous = two identical alleles; heterozygous = two different alleles.
A Punnett square predicts offspring genotypes and phenotypes; e.g., Tt × tt gives 1:1 tall:short.
Test cross (cross with recessive homozygote) reveals if a dominant phenotype is homozygous or heterozygous.

Homozygous and heterozygous chromosome pairs

Codominance & Sex-Linked Characteristics (Extended)

Codominance: both alleles contribute to phenotype (e.g., ABO blood groups: I^A and I^B are codominant).
Sex-linked genes are on the X chromosome; males (XY) are more likely to show recessive conditions (e.g., colour blindness).
Females can be carriers (heterozygous) and pass the allele to sons.
Punnett squares for sex-linked traits use X and Y chromosomes with alleles as superscripts.

Punnett square for a sex-linked condition

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Câu hỏi luyện tập

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1.What does the term haploid mean?
Easy
- AA nucleus containing two sets of chromosomes.
- BA nucleus containing a single set of chromosomes.
- CA person with only one X chromosome.
- DA person with XXY chromosomes.
2.When a somatic (body) cell undergoes cell division, two daughter cells are produced with the same chromosome number as the parent cell. Which type of division has taken place?
Easy
- AMeiosis producing genetically different cells.
- BMitosis producing genetically identical cells.
- CMeiosis producing genetically identical cells.
- DMitosis producing genetically different cells.
3.Which shows the correct size order of structures, starting with the smallest?
Easy
- Agene → DNA strand → chromosomes → nucleus
- BDNA strand → chromosomes → gene → nucleus
- Cchromosomes → gene → DNA strand → nucleus
- Dnucleus → chromosomes → DNA strand → gene
4.Males and females have a unique set of chromosomes. What is the correct combination of male and female chromosomes?
Easy
- AMale XY, Female YY
- BMale YX, Female XY
- CMale XY, Female XX
- DMale XX, Female XY
5.Albinism is a condition caused by a recessive allele. If both parents have albinism, what are the chances of the offspring being an albino child?
Easy
- A0%
- B25%
- C75%
- D100%
6.Which of the following structures in plant cells carry out protein synthesis under the control of the nucleus?
Easy
- ARibosomes
- BChloroplasts
- CMitochondria
- DCell walls
7.A woman who is a carrier for a recessive sex-linked condition has a child with a man who is unaffected. What is the percentage chance that their daughter will show the condition?
Medium
- A0%
- B25%
- C50%
- D75%
8.Which row in the table shows a comparison between meiosis and mitosis?
Medium
- Amitosis produces 4 daughter cells; meiosis produces 2 daughter cells
- Bmitosis produces genetically identical cells; meiosis produces cloned cells
- Cmitosis daughter cells are diploid; meiosis daughter cells are haploid
- Dmitosis involves two cell divisions; meiosis involves four cell divisions

Thêm câu hỏi

9.What is the transmission of genetic information from generation to generation called?
Easy
- Afertilisation
- Binheritance
- Cmeiosis
- Dreproduction
10.What carries a copy of the gene to the cytoplasm to make a protein?
Easy
- Aalleles
- BDNA molecules
- Cribosomes
- DmRNA molecules
11.In a monohybrid cross between two heterozygous individuals (Tt x Tt), what is the probability of obtaining a homozygous recessive offspring?
Medium
- A0%
- B25%
- C50%
- D75%
12.In a species of bird, the allele for long beak (L) is dominant over the allele for short beak (l). A heterozygous long-beaked bird is crossed with a short-beaked bird. What percentage of the offspring are expected to have long beaks?
Medium
- A0%
- B25%
- C50%
- D75%
13.A farmer crosses two heterozygous tall pea plants (Tt × Tt). The offspring are all tall. What is the probability that a randomly selected tall offspring is homozygous dominant?
Hard
- A1/4
- B1/3
- C1/2
- D2/3
14.The table shows the number of chromosomes in the body cells of four organisms. | Organism | Body cell chromosome number | |---|---| | A | 38 | | B | 46 | | C | 20 | | D | 76 | Which organism produces gametes with 19 chromosomes?
Easy
- AOrganism A: 38
- BOrganism B: 46
- COrganism C: 20
- DOrganism D: 76
15.Which statement about the genetic code is correct?
Medium
- AEach triplet of bases codes for one amino acid.
- BEach amino acid is coded for by exactly one triplet of bases.
- CThe genetic code is read in pairs of bases.
- DDNA directly assembles amino acids at the ribosome.
16.Colour blindness is a sex-linked recessive condition. A woman who is a carrier for colour blindness marries a man with normal vision. What is the probability that their first child will be a colour-blind boy?
Medium
- A0%
- B25%
- C50%
- D100%
17.In a genetic cross, one parent is homozygous dominant and the other is homozygous recessive. What is the genotype ratio of the offspring?
Easy
- A1:1
- B3:1
- C1:2:1
- DAll identical
18.Which process is used to produce gametes in humans?
Easy
- AMitosis
- BMeiosis
- CBinary fission
- DFertilisation
19.A cell has 12 chromosomes. After mitosis, each daughter cell has how many chromosomes?
Easy
- A6
- B12
- C24
- D48
20.In fruit flies, eye colour is sex-linked. The allele for red eyes (R) is dominant over white eyes (r). A white-eyed male is crossed with a homozygous red-eyed female. What percentage of the male offspring will have white eyes?
Medium
- A0%
- B25%
- C50%
- D100%
21.Which statement about meiosis is correct?
Easy
- AIt produces four genetically identical daughter cells.
- BIt reduces the chromosome number from diploid to haploid.
- CIt is used for growth and repair.
- DIt occurs only in body cells.
22.A cell has 4 chromosomes before it undergoes meiosis. How many chromosomes will each gamete have?
Easy
- A1
- B2
- C4
- D8
23.The diagram shows a Punnett square for a monohybrid cross. The trait is flower colour, where R = red (dominant) and r = white (recessive). Both parents are heterozygous (Rr). What is the probability that an offspring will have white flowers?
Easy
- A0%
- B25%
- C50%
- D75%
24.In a species of butterfly, wing colour is controlled by a single gene with two codominant alleles: C^B (blue) and C^Y (yellow). Heterozygous individuals have green wings. A blue butterfly is crossed with a green butterfly. What is the probability that an offspring will have yellow wings?
Hard
- A0%
- B25%
- C50%
- D100%
25.Haemophilia is a sex-linked recessive condition. A woman who is a carrier for haemophilia (X^H X^h) has children with a man who has haemophilia (X^h Y). What is the probability that a son will have haemophilia?
Hard
- A0%
- B25%
- C50%
- D100%
26.A cell from a fruit fly has 8 chromosomes. How many chromosomes will be present in each daughter cell after meiosis?
Easy
- A4
- B8
- C16
- D2
27.Which process produces genetically identical daughter cells?
Easy
- AMeiosis
- BMitosis
- CBoth mitosis and meiosis
- DNeither
28.In a test cross to determine the genotype of a tall pea plant (T = tall, t = short), the plant is crossed with a short plant. Which result would indicate that the tall plant is heterozygous?
Medium
- AAll offspring are tall
- BHalf the offspring are tall and half are short
- CAll offspring are short
- DThree-quarters of the offspring are tall
29.ABO blood group is controlled by three alleles: I^A, I^B and i. I^A and I^B are codominant, and both are dominant to i. A man with blood group A (genotype I^A i) and a woman with blood group B (genotype I^B i) have a child. What is the probability that the child has blood group O?
Medium
- A0%
- B25%
- C50%
- D75%
30.What is the function of messenger RNA (mRNA) in protein synthesis?
Easy
- AIt carries amino acids to the ribosome
- BIt carries a copy of the gene from the nucleus to the cytoplasm
- CIt forms part of the ribosome
- DIt catalyses the formation of peptide bonds
31.A scientist observes that a cell undergoing division produces four daughter cells, each with half the number of chromosomes of the parent cell. Which type of cell division is occurring, and what is the genetic relationship between the daughter cells?
Medium
- AMitosis; genetically identical
- BMeiosis; genetically identical
- CMitosis; genetically different
- DMeiosis; genetically different
32.In humans, which parent determines the sex of the child?
Easy
- AMother, because she provides the egg
- BFather, because he can contribute either an X or a Y chromosome
- CBoth parents equally
- DNeither; sex is determined by environmental factors
33.Which of the following is the correct definition of a gene?
Easy
- AA long strand of DNA that makes up a chromosome
- BA short length of DNA that codes for a specific protein
- CA section of a protein that determines a characteristic
- DA molecule that carries amino acids to the ribosome
34.What is the role of messenger RNA (mRNA) in protein synthesis?
Easy
- AAssembles amino acids into protein molecules
- BMoves a copy of the gene from the nucleus to the cytoplasm
- CDuplicates chromosomes before mitosis
- DControls cell function directly
35.Which of the following best describes a diploid nucleus?
Easy
- AA nucleus containing a single set of chromosomes
- BA nucleus containing two sets of chromosomes
- CA nucleus with half the normal number of chromosomes
- DA nucleus that has undergone meiosis
36.A cell from a fruit fly has 8 chromosomes. How many chromosomes will be present in each daughter cell after mitosis?
Easy
- A4
- B8
- C16
- D2
37.Which of the following is a difference between mitosis and meiosis?
Medium
- AMitosis produces genetically identical cells, meiosis produces genetically different cells
- BMitosis produces haploid cells, meiosis produces diploid cells
- CMitosis occurs in gametes, meiosis occurs in body cells
- DMitosis involves two divisions, meiosis involves one division
38.Colour blindness is a sex-linked recessive condition. A woman who is a carrier (X^C X^c) marries a man with normal vision (X^C Y). What is the probability that their son will be colour blind?
Hard
- A0%
- B25%
- C50%
- D100%
39.What is the name of the structure in the nucleus that carries genetic information in the form of genes?
Easy
- AChromosome
- BRibosome
- CMitochondrion
- DChloroplast
40.A gene is a short length of DNA that codes for a specific protein.
Easy
True or false?
41.Which type of cell division produces genetically identical daughter cells?
Easy
- AMitosis
- BMeiosis
- CFertilisation
- DBinary fission
42.What is the term for the combination of alleles that control a characteristic?
Easy
- AGenotype
- BPhenotype
- CGene
- DChromosome
43.In a monohybrid cross between two heterozygous individuals (Tt × Tt), what is the ratio of genotypes in the offspring?
Medium
- A1:2:1
- B3:1
- C1:1
- D2:1
44.Meiosis produces four genetically identical haploid cells.
Medium
True or false?
45.Which process involves the transfer of genetic information from DNA to mRNA?
Medium
- ATranscription
- BTranslation
- CReplication
- DMutation
46.In codominance, the ABO blood group system has three alleles: I^A, I^B, and i. Which genotype results in blood group AB?
Easy
- AI^A I^B
- BI^A i
- CI^B i
- Di i
47.Match each term with its correct description.
Medium
- Haploid
- Diploid
- Homozygous
- Heterozygous
- One set of chromosomes
- Two sets of chromosomes
- Two identical alleles
- Two different alleles
48.Arrange the following events of meiosis in the correct order.
Medium
- Chromosomes pair up and crossing over occurs
- Chromosomes line up at the centre of the cell
- First division: pairs are pulled apart
- Second division: chromosomes are pulled apart
- Four haploid daughter cells are produced
49.Complete the sentence about sex chromosomes.
Easy
Females have the sex chromosomes ____, and males have the sex chromosomes ____.
50.Human body cells have 46 chromosomes. How many chromosomes are present in a human sperm cell?
Easy
51.State the purpose of a test cross in genetics.
Medium
52.Human body cells have 46 chromosomes. How many chromosomes are present in a human sperm cell?
Easy
- A23
- B27
- C25
- D21

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