blueprint of life 2.3

Question 1

outline the roles of Sutton and Boveri in identifying the importance of chromosomes

Answer 1

• Boveri worked on sea urchins and showed that their chromosomes were not all the same and that a full complement was required for the normal development of an organism.
  
  • Sutton worked on grasshoppers and showed that their chromosomes were distinct entities. He said even though they duplicate and divide they remain as a distinct structure. He associated the behaviour of chromosomes with Mendel’s work on the inheritance of factors and concluded that chromosomes were the carriers of hereditary units.

Question 2

describe the chemical nature of chromosomes and gene

Answer 2

Chromosomes consist of 40% DNA and 60% protein (histone). Short lengths of DNA make up genes so genes have the same chemical composition as DNA.

Question 3

identify that DNA is a double-stranded molecule twisted into a helix with each strand, comprised of a sugar-phosphate backbone and attached bases, adenine (A), thymine (T), cytosine (C) and guanine (G), connected to a complementary strand by pairing the bases, A-T and G-C

Answer 3

NA is a nucleic acid in the shape of a double helix. Each strand of the helix consists of four different nucleotides made up of deoxyribose sugar, a phosphate molecule and a nitrogen base. The helix is like a twisted ladder. The backbones of the structure, or the sides of the ladder, consist of the deoxyribose sugar and phosphate molecules. The bases form the rungs between the sides of deoxyribose sugar and phosphate molecules and are complementary (only pair with their matching base). Adenine pairs with thymine and guanine pairs with cytosine.

Question 4

xplain the relationship between the structure and behaviour of chromosomes during meiosis and the inheritance of genes

Answer 4

-Chromosomes are made of DNA. Genes are coded within the DNA on the chromosomes. During division each chromosome (which therefore includes the genes) makes a complete copy of itself. The new chromosome is attached to the original chromosome by a centromere.

In the initial division of meiosis the homologous chromosomes line up in matching pairs and one of each pair of homologous chromosomes moves into a new cell. Next the duplicated chromosomes separate to single strands resulting in four sex cells that are haploid,

Question 5

explain the role of gamete formation and sexual reproduction in variability of offspring

Answer 5

Gamete formation results in the halving of the chromosome number (n) (diploid to haploid) and sexual reproduction results in combining gametes (haploid to diploid) to produce a new diploid organism (2n). The processes involved in forming this new organism result in variability of the offspring.

Question 6

what are the two stages of meiosis.

Answer 6

• random segregation of individual chromosomes with their associated genes ie, different new combinations of the original maternal and paternal chromosomes and
  
  • the process of crossing over where the maternal and paternal chromosomes of each pairmay exchange segments of genes making new combinations of genes on the chromosomes.

Question 7

explain the relationship between homozygous and heterozygous genotypes and the resulting phenotypes in examples of co-dominance

Answer 7

in some cases, both alleles are expressed in the phenotype and the two alleles are said to be co-dominant. In this case both alleles are labelled with upper case letters.

example: These animals have an allele for both red and white hair. As neither is dominant, cattle with both alleles have a mixture of red and white hairs scattered over their bodies and are called roan

Question 8

describe the inheritance of sex-linked genes, and genes that exhibit co-dominance and explain why these do not produce simple Mendelian ratios

Answer 8

ex-linked genes and genes that are co-dominant do not display the phenotype ratios predicted by Mendel’s laws.
example:
The gene is carried on the X chromosome and there is no corresponding gene on the Y chromosome. Therefore males need only one allele for colour blindness on the X chromosome while females require two.

Question 9

outline ways in which the environment may affect the expression of a gene in an individual

Answer 9

Hydrangeas are plants that have different flower colour (pink or blue) depending on the pH of the soil they are grown in. In acid soils (less than pH 5) Hydrangeas are blue. In soils that have a pH greater than 7 Hydrangeas are pink. The pH has an effect on the availability of other ions in the soil and it is these ions that are responsible for the colour change.