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?
- 2
- 4
- 6
- 8
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)
Show Answers Only
→ 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:
Show Worked Solution
→ 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:
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
BIOLOGY, M5 2017 HSC 24
- Three genes are arranged along a homologous pair of chromosomes as shown.
-
- What is the individual's genotype before crossing over occurs? (1 mark)
--- 1 WORK AREA LINES (style=lined) ---
- Label, on the diagram below, the alleles after crossing over has occurred. (1 mark)
- What is the individual's genotype before crossing over occurs? (1 mark)
- Explain the effect of independent assortment of chromosomes on the genotype of the offspring. (2 marks)
--- 5 WORK AREA LINES (style=lined) ---
Show Answers Only
a.i `text{Aa Bb Gg}`
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.
Show Worked Solution
a.i `text{Aa Bb Gg}`
a.ii
♦♦♦ Mean mark (a)(i) 11%
♦♦ Mean mark (a)(ii) 35%.
♦♦ 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)
--- 0 WORK AREA LINES (style=lined) ---
Show Answers Only
a.
\begin{array} {|c|c|}\hline \text{Alleles from father} & \text{Alleles from mother} \\
\hline \text{H, r} & \text{h, R} \\ \hline \end{array}
b.
Show Worked Solution
a.
\begin{array} {|c|c|}\hline \text{Alleles from father} & \text{Alleles from mother} \\
\hline \text{H, r} & \text{h, R} \\ \hline \end{array}
♦ Mean mark (a) 47%.
b.
♦♦♦ Mean mark (b) 25%.
BIOLOGY, M5 2020 HSC 28
- Explain the misunderstanding of meiosis shown in this model. (3 marks)
--- 6 WORK AREA LINES (style=lined) ---
- Explain the effect of meiosis on genetic variation. (3 marks)
--- 6 WORK AREA LINES (style=lined) ---
Show Answers Only
a.
→ 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.
Show Worked Solution
a.
→ 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?
