Sex Determination 8


Published on

A2 biology edexcel

Published in: Technology, Education
  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Sex Determination 8

  1. 1. Sex determination <ul><li>Starter activity: </li></ul><ul><li>Complete the following information from these parents </li></ul>
  2. 2. Parents Red rose White rose SSrr ssRR Gametes Sr sR F1 X F1 Red White SsRr SsRr Gametes SR Sr sR sr SR Sr sR sr F 2 F 2
  3. 3. Learning objectives <ul><li>Describe how the sex of the baby can be determined </li></ul><ul><li>Recall the significance of meiosis, random fertilisation, genetic variation, recombinant chromosomes </li></ul><ul><li>Understand the significance of mutations and the effects by chemical and radiation </li></ul>
  4. 4. Sex determination <ul><li>Sex determination is caused by the male and female of the species </li></ul><ul><li>What is the ratio between the sexes in the off spring? </li></ul><ul><li>List the name of the 2 sex chromosomes </li></ul><ul><li>The rest of the chromosomes are known as autosomal chromosomes </li></ul><ul><li>Explain what is an autosomal chromosome? </li></ul><ul><li>The ‘X’ chromosome is usually larger than the ‘Y’ chromosome. But when it comes to pairing there are regions that are similar, but there are also regions which are not i.e. there are regions found on the ‘X’ chromosome that are not present on the ‘Y’ chromosome. This is due to there being genetically dormant regions. Even though the sex chromosomes determine the ‘sex’ of the baby, they do not have all the genes which are responsible for the sexual characteristics </li></ul>
  5. 5. Cont…. <ul><li>Explain why the female/male sex chromosomes are known as the ‘homogametic/heterogametic’ chromosomes. </li></ul><ul><li>They pair during ‘prophase I’ of meiosis and separate at ‘anaphase I’ and the chromatid separation will occur at ‘anaphase II’ </li></ul><ul><li>Explain why females can only have ‘X’ chromosomes </li></ul><ul><li>During the stage of meiosis the sperm will carry 50%/50% of the ‘XY’. Because at fertilisation there is an equal chance of the ‘egg’ fusing with ‘sperm’ carrying the ‘X’ and ‘Y’. This is the reason why the male determines the ‘sex’ of the child </li></ul><ul><li>In the early stages of embryo development there are no ‘physical feature to determine the sex of the child. A method used in the first few months is the detection of the ‘SRY’ gene which is the male hormone producing gene. The presence of male hormone is the deciding factor </li></ul>
  6. 6. Recall……… <ul><li>Recall the significance of </li></ul><ul><li>Meiosis </li></ul><ul><li>Random fertilisation </li></ul><ul><li>Genetic variation </li></ul><ul><li>Recombinant chromosomes </li></ul>
  7. 7. Mutation <ul><li>Explain the term ‘genetically mutated’ </li></ul><ul><li>During the process of DNA replication, there is an exact copy made of the gene, therefore the features are the same from generation to generation. Mutation is when there is a change in the information from the original version or the amount present in the new organism. This can occur in ‘body’ cells </li></ul><ul><li>List 3 causes and effects of mutations </li></ul><ul><li>If mutation occurs in the formation of the gametes, the mutation will be carried to the next generation they are referred to as ‘germ-line mutation. This is an important way for genetic variation to occur within a population </li></ul>
  8. 8. Cont…. <ul><li>Mutation can occur spontaneously due to there being a mistake during the DNA replication stage. ‘Mutation rate’ is referred to as the amount 1 allele will mutate. For example in the ‘purple maize grains’ mutate at the rate of 1 X 10 -5 , which means only 1 mutation will occur in 100 000 (1 purple : 100 000 white). An altered DNA molecule replicates the changed nucleotide bases, so the mutant gene is passed onto the next generation. This is the essence for the process of evolution </li></ul><ul><li>Explain the benefits of spontaneous mutation? </li></ul><ul><li>Mutagens are external environmental sources that can rapidly increase the mutation rate </li></ul><ul><li>List chemicals and sources of radiation that cause mutation </li></ul>
  9. 9. Mutagens <ul><li>Mutagens will operate by altering the DNA by ‘adding’ or ‘deleting’ one or more bases in the sequence </li></ul><ul><li>E.g. the chemicals ‘Nitrous acid’ and ‘5-bromouracil’ can directly change the nucleic acids and alters the genetic code by converting 1 base into another e.g. ‘C’ to ‘U’ which will bond to ‘A’ rather than ‘G’. This is referred to as the ‘point mutation’. Point mutation can refer to the (deletion, insertion, and substitution of the bases </li></ul><ul><li>Explain the significance of the effects of mutations occurring </li></ul><ul><li>‘ Base deletion’ can result in a shift in the ‘reading frame’ </li></ul>
  10. 10. Cont…. <ul><li>See effects of ‘substitution’ on the haemoglobin to give rise to ‘sickle-cell anaemia’ </li></ul>