Genetics+LSci

Reproduction

Sexual reproduction involves the meeting of two gametes. Each gamete contains half the genetic information to make one whole cell (they are called haploid cells). When the gametes fuse, the cell is then called a zygote, this will replicate many times to make an embryo (these cells are all called diploid cells). The time it takes from fertilisation to birth is called the gestation period. In humans, the gestation period is 9 months.
 * In animals the gametes are eggs and sperm.
 * In plants the gametes are pollen and ova.

If the cell divides into two separate cells, then identical twins are formed. Non-identical twins occur when two eggs are fertilised by two separate sperm at the same time.

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The menstrual cycle

Genetic Traits Complete the genetic traits handout with all of your recessive and dominant traits identified and those of the three "family" members you selected. Read page 105 of Science For Life 10 and then use your completed genetic traits handout to answer the questions in the following document:

Each genetic trait is determined by one or more genes. Each version of that trait is known as an allele. The alleles a person has are determined by their DNA code. Each person carries two alleles per trait, this is called the genotype. A genotype is represented by two letters.

FOR EXAMPLE: Hair colour has four main alleles - red, blonde, brown and black. Blood type has four main alleles - O, A, B and AB Hitch-hikers thumb has two alleles - present and not present

The phenotype of a trait is represented as a word, it is controlled by the genotype and the environment.

Dominant traits are always expressed in the phenotype, a person showing the traits can have one or two dominant alleles. In a genotype, a dominant allele is represented by a capital letter. Recessive traits can be carried but not shown, a person requires two recessive alleles in order to show that trait. In the genotype, a recessive allele is represented by a lower case letter. 

Transcription/Translation

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