(a) (i) State Mendel’s Law of Segregation - Leaving Cert Biology - Question 10 - 2009
Question 10
(a) (i) State Mendel’s Law of Segregation.
(ii) Name two cell organelles, other than the nucleus, that contain DNA.
(b) In guinea pigs the allele for black hair (... show full transcript
Worked Solution & Example Answer:(a) (i) State Mendel’s Law of Segregation - Leaving Cert Biology - Question 10 - 2009
Step 1
State Mendel’s Law of Segregation.
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Answer
Mendel’s Law of Segregation states that during the formation of gametes, the two alleles for a trait segregate from each other, meaning that each gamete receives only one allele for each gene.
Step 2
Name two cell organelles, other than the nucleus, that contain DNA.
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Answer
Two organelles other than the nucleus that contain DNA are mitochondria and chloroplasts.
Step 3
Explain the terms alleles and dominant.
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Alleles are different forms of a gene that arise by mutation and are found at a specific position on a chromosome. A dominant allele is one that masks the effect of its paired (recessive) allele in the phenotype, meaning if at least one dominant allele is present, it will manifest in the organism's traits.
Step 4
What term is used to describe alleles that lie on the same chromosome?
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The term used to describe alleles that lie on the same chromosome is 'linked'.
Step 5
Why is it significant that the two pairs of alleles, mentioned above in relation to guinea pigs, are located on different chromosome pairs?
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It is significant because linked alleles tend to be inherited together, while alleles located on different chromosome pairs can assort independently during gamete formation, allowing for greater genetic variation in the offspring.
Step 6
Determine all the possible genotypes and phenotypes of the offspring of a cross between the following guinea pigs: Brown hair, heterozygous short hair X Heterozygous black hair, long hair.
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The possible genotypes resulting from the cross are:
BbSs (Black hair, Short hair)
BbsS (Black hair, Short hair)
Bbss (Black hair, Long hair)
bbSs (Brown hair, Short hair)
bbsS (Brown hair, Short hair)
bbss (Brown hair, Long hair)
The corresponding phenotypes are:
Black hair + Short hair (from BbSs and BbsS)
Black hair + Long hair (from Bbss)
Brown hair + Short hair (from bbSs)
Brown hair + Long hair (from bbss).
Step 7
Explain the term species.
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A species is defined as a group of organisms that can interbreed and produce fertile offspring in natural conditions. Members of a species share common characteristics and genetic similarities.
Step 8
What is meant by variation?
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Variation refers to the differences among individuals within a species, which can be observed in physical traits, behaviors, and genetic makeup.
Step 9
State two causes of variation.
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Genetic Factors: Differences in genes and mutations can lead to variability.
Environmental Factors: External conditions such as climate, food supply, and habitat can cause variations among individuals.
Step 10
What is the significance of inherited variation in the evolution of species?
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Inherited variation is crucial for evolution as it provides the raw material for natural selection. Variants that confer advantages increase the likelihood of survival and reproduction, leading to their prevalence in future generations.
Step 11
State two types of evidence used to support the theory of evolution.
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Fossils: The fossil record shows the progression of life forms and the adaptations over time.
Comparative Anatomy: Similarities in structure among different species indicate common ancestry.
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