* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Exam practice answers 8
Survey
Document related concepts
Gene expression programming wikipedia , lookup
Sexual dimorphism wikipedia , lookup
Y chromosome wikipedia , lookup
Group selection wikipedia , lookup
Inbreeding avoidance wikipedia , lookup
Neocentromere wikipedia , lookup
Genetic drift wikipedia , lookup
Heritability of IQ wikipedia , lookup
Human genetic variation wikipedia , lookup
X-inactivation wikipedia , lookup
Population genetics wikipedia , lookup
Designer baby wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Transcript
OCR A2 Biology 8 Meiosis and variation 1 (a) A locus is the position of a gene on a chromosome. Alleles of the same gene are found at the same position on homologous chromosomes. (b) (i) Chiasma/chiasmata (or crossover). (ii) Prophase of division 1. (iii) If the chiasma forms between non-sister chromatids, the alleles on homologous chromosomes can be exchanged. This produces new combinations of alleles in the gametes. New combinations of alleles mean that there is genetic variation. Selection can occur and the species can evolve to meet the needs presented by changes in the environment. 2 (a) QqRr. (b) (i) Qr and qR. (ii) Qr, QR, qR and qr. (iii) Qr and qR. 3 (a) (i) meiosis = A (ii) mitosis = C (iii) fertilisation = B (b) Gametes are sex cells produced for sexual reproduction. During fertilisation, two gametes fuse and restore the diploid number of chromosomes (2n). 4 (a) When a selective force places pressure on the species and the frequency of alleles changes as a result. This changes the phenotype, making the species better adapted to the environment. (b) Without variation there would be no differences between the individuals and none would possess characteristics making them slightly better adapted. Therefore, selection could not occur. (c) In the selection of dairy cows, a breeder may want to achieve a higher milk yield per cow. The breeder will select females by their ability to produce a high yield. He or she will select a bull by looking at the bulls’ female offspring to see whether they produce a good yield. This bull and the high-yield cows will be bred together. The female offspring will be assessed for their ability to produce a high yield and the best will be bred again. This continues for many generations. The bull’s sperm may be collected and frozen so that it can be used later during artificial insemination. Hodder Education © 2013 1