smc-3648-50-Meiosis

BIOLOGY, M5 2024 HSC 33

Female Jack Jumper ants (Myrmecia pilosula) have a single pair of chromosomes. During meiosis, crossing over occurs. The diagram shows the crossing over and the position of three genes on the chromosomes.

Outline the significance of crossing over for the Jack Jumper ants. (2 marks)

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Draw the chromosomes of the four possible gametes after crossing over for the Jack Jumper ants occurs. Include the alleles for each gene. (2 marks)

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a. Significance of crossing over:

→ Genetic variation increases in the Jack Jumper ant population through recombination.

→ This enhanced genetic diversity improves the species’ chances of survival when faced with environmental changes, as some ants may carry beneficial adaptations.

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a. Significance of crossing over:

→ Genetic variation increases in the Jack Jumper ant population through recombination.

→ This enhanced genetic diversity improves the species’ chances of survival when faced with environmental changes, as some ants may carry beneficial adaptations.

♦ Mean mark (b) 54%.

BIOLOGY, M5 2024 HSC 6 MC

The diagram shows the karyotypes of a body cell for a male and a female fruit fly.

How many chromosomes will the egg of a female fruit fly have?

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→ In the diagram, the female fruit fly has 8 chromosomes in body cells (2 sex chromosomes + 6 autosomes across pairs I, II, and III)

→ During gamete formation, the female fruit fly’s cells undergo meiosis which halves the total chromosome number.

→ Therefore her eggs will contain half that number, resulting in 4 chromosomes total.

♦ Mean mark 50%.

BIOLOGY, M5 EQ-Bank 26

The diagram shows a model developed in the early 20th century of crossing over of homologous chromosomes.

Explain how the difference between this model and our current model of crossing over reflects an increased understanding of the way in which new combinations of genotypes are produced. Support your answer with a diagram. (4 marks)

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→ The model shows that crossing over occurs between homologous chromosomes before DNA replication. This means that when sister chromatids are formed, they will contain the post-crossing over sequence.

→ In the new model, DNA replication occurs prior to crossing over, where crossing over only occurs when replicated homologous chromosomes line up in tetrads, and only 2 homologous pairs exchange information.

→ In this way, the new model will produce 4 unique chromatids while the old model will produce only 2. Therefore new model produces a wider range of genetic variability in offspring.

→ Possible unique chromatids:

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→ In this way, the new model will produce 4 unique chromatids while the old model will produce only 2. Therefore new model produces a wider range of genetic variability in offspring.

→ Possible unique chromatids:

BIOLOGY, M5 EQ-Bank 7 MC

In which of the following do both processes result in genetic variation of offspring?

DNA mutation and polypeptide production
Cell differentiation and gamete formation
DNA mutation and gamete formation
Cell differentiation and polypeptide production

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By Elimination

→ Cell differentiation is the specialisation of cells into a specific type, e.g. the differentiation of specific plasma B cells. This does not impact the individual’s genome or their offspring (Eliminate B and D).

→ Polypeptide production is a result of the individuals DNA and does not effect their genotype and thus has no effect on offspring (Eliminate A).

BIOLOGY, M5 2017 HSC 24

Three genes are arranged along a homologous pair of chromosomes as shown.

1. What is the individual's genotype before crossing over occurs? (1 mark)
  
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2. Label, on the diagram below, the alleles after crossing over has occurred. (1 mark)

Explain the effect of independent assortment of chromosomes on the genotype of the offspring. (2 marks)

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a.i

a.ii

b. Independent Assortment

→ A random alignment of homologous chromosomes takes place during meiosis.

→ The possible number of chromosome combinations is consequently increased.

→ Therefore, the genetic variation of offspring increases.

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a.i

a.ii

♦♦♦ Mean mark (a)(i) 11%
♦♦ Mean mark (a)(ii) 35%.

b. Independent Assortment

→ A random alignment of homologous chromosomes takes place during meiosis.

→ The possible number of chromosome combinations is consequently increased.

→ Therefore, the genetic variation of offspring increases.

♦ Mean mark (b) 48%.

BIOLOGY, M5 2019 HSC 28

Huntington's disease is an autosomal dominant condition caused by a mutation of a gene on chromosome 4. It causes nerve cells to break down.

Stargardt disease is an autosomal recessive condition caused by a mutation of a different gene on chromosome 4 . It causes damage to the retina.

A patient is heterozygous for both Huntington's (Hh) and Stargardt disease (Rr). His father's extended family has numerous cases of both of these diseases. His mother does not have either disease and is homozygous for both genes.

Complete the tables, showing the TWO alleles the patient inherited from each parent. (2 marks)
The diagram shows the patient's homologous pair of chromosome 4 at various stages of meiosis.
Add the relevant alleles to the diagram to model the production of possible gamete combinations. Include a key and an example of crossing over. (4 marks)

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♦ Mean mark (a) 47%.

♦♦♦ Mean mark (b) 25%.

BIOLOGY, M5 2020 HSC 28

A student drew a diagram to model part of the process of meiosis.

Explain the misunderstanding of meiosis shown in this model. (3 marks)

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Explain the effect of meiosis on genetic variation. (3 marks)

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→ In the diagram above, the paired homologous chromosomes are incorrectly drawn.

→ Prior to crossing over, each chromosome duplicates forming the sister chromatids with one being maternal and one being paternal.

→ In the model above, they are shown as a mix of both, when in actuality the sister chromatids should be identical.

b. The Effect of Meiosis on Genetic Variation

Independent Assortment

→ when chromosomes are lined up along the cells equator in independent order and orientation to all other chromosomes.

Random Segregation

→ different combinations of maternal and paternal chromosomes end up in resulting gametes, increasing variability amongst them.

Crossing Over

→ the process of exchanging genetic material between chromatids of homologous chromosomes during Meiosis I, leading to unique combinations of alleles on each chromatid.

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→ In the diagram above, the paired homologous chromosomes are incorrectly drawn.

→ Prior to crossing over, each chromosome duplicates forming the sister chromatids with one being maternal and one being paternal.

→ In the model above, they are shown as a mix of both, when in actuality the sister chromatids should be identical.

♦♦♦ Mean mark (a) 25%.

b. The Effect of Meiosis on Genetic Variation

Independent Assortment

→ when chromosomes are lined up along the cells equator in independent order and orientation to all other chromosomes.

Random Segregation

→ different combinations of maternal and paternal chromosomes end up in resulting gametes, increasing variability amongst them.

Crossing Over

→ the process of exchanging genetic material between chromatids of homologous chromosomes during Meiosis I, leading to unique combinations of alleles on each chromatid.

♦ Mean mark (b) 43%.

BIOLOGY, M5 2020 HSC 19 MC

Which diagram correctly models one phase of meiosis in an organism that has six chromosomes in its somatic cells?

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By Elimination:

→ Option D would end up with 12 chromosomes in its somatic cells (Eliminate D).

→ Option B and C show meiosis 1, as they are arranged in tetrads. Option C will end up with 12 chromosomes in its somatic cells, while option B is an incorrect model as it does not correctly display homologous pairs arranging in tetrads. (Eliminate B and C).

→ The diagram in option shows metaphase II of meiosis in a cell with 6 chromosomes.

♦ Mean mark 19%.